tA: » n . . d . r . b . . a u c t i o n in ^ . i n
th e rock c o r a t l t u r r t : .
slilEEillF
(m. V lljo e n v e r b a l c o m m u n i c a t io n ^ se e a i s u
(d)
lg .
•
Hffit«BDrpMals
mWfpn# co n s itH ra b le r e d u c tio n .
■ iiis iP m l# .
(S ec F ig . 2 7 ) .
The B asal C onglom erate o f th e E ureka S y n c lin e shows l i t t l e o r
, evidence o f m e ta m rp h lc a l t e r a t i o n a lth o u g h a t Sheba S id in g th e underlying "lev a o r tu ff e c a c u s grayw acke" h as been s l i g h t l y m etarorphosed and
„ a y * ta lli* # d .
f.
^MTRIBIVE ROCKS
(1 )
In tro d u c tio n
Some o f th e b a s ic ro c k s In th e a re a a re th o u g h t to be o f
Igaaeia o r ig in and p ro b a b ly b elo n g to th e Jamestown Igneous Complex.
Iflcladed w ith in t h i s group a r e :
1.
2.
3.
4.
m assive g re e n s e r p e n t i n i t e s .
i s o l a t e d u l t r a b a s i c zones w ith m a g n esite o c c u rre n c e s .
n le k e li f e r o u s m agnetic s e r p e n t i n i t e s .
t a l c zones in m assive s e r p e n t i n i t e s .
The a s s o c ia tio n o f b a s ic and u l t r a b a s i c ro c k s may be c l a s s i f i e d
is being o f th e " a l p in e ty p e " o c c u rr in g in fo ld e d geo s y n c lin a l sedim ents
ef am erogenic b e l t (T u rn er and V erhoogen, 1960).
The s e r p e n t in it c b o d ie s a re c o n fin e d p r im a r ily to twc a r e a s .
R*M# o ccurrence i s n e a r Sugden S id in g in th e c e n t r a l p o r ti o n o f th e
R*#* while th e o th e r main body o c c u rs in th e w e s te rn p o r ti o n o f th e a re a
(isrthwest o f S heba S id in g .
In a d d itio n a few m inor o c c u rre n c e s a re
k be found to th e so u th o f th e L ily ran g e on th e farm C r y s ta l S trea m .
Included in th e s e s e r p e n t l n i t e m asses a re zones o f m a g n e tite ,
md R lek el-bear.’ ng t r e v o r i t e .
The m assive body to th e n o rth and r o rth w e s t o f th e S c o tia T a lc
W e a rs to have in tru d e d in to th e sed im en ta ry sequences o f th e L ily
J ff llfte causing th e lo rm a tlo n to s p l i t in to th r e e d i s t i n c t bands th a t
**** f i r s t to to e e a s t o f E ureka S id in g .
They c o n tin u e tow ards th e
y ^bere tS e d iv e rg e n c e r e a c h e s i t s maximum.
Long narrow q u a r t z it e
a re severed by th e b a.,ic I n tr u s iv e # .
I n te rc a la tio n s of
^ y i h i t e and th e numerous a l t e r a t i o n p ro d u c ts o f s e r p e n t i n i t e s o ccur
^ ^ W t t e Kaodiss r o c k s .
m
a
t
H
-S t r l f » " t r l c . l
iS IIIiS s s s n . t.i.
« '
, 8*11 narrow b o d ie s .
T hese b o d ie s appear to be s te e p ly in c lin e d
Isnaef o r sh e e ts ly in g co n c o rd a n t ly w ith th e s u rro u n d in g q u a rtz l i e s o f
th# Lily S y n c lin e .
The o ip o f th e f o l i a t i o n i s d i f f i c u l t to m easure
hit a s n e rilly conform s to th e r e g io n a l s tr u c t u r e p ro b a b ly in d i c a t in g
that i t unA rw ent d e fc rm a tio n a l e v e n ts s im i la r to o r synchronous w ith
y s s e o f the a d ja c e n t rock ty p e s .
(w ) Btwmrahl#
A d i f f i c u l t y a r i s e s in tr y in g to e s t a b l i s h v# e th e r o r n o t th e
tcfBefiUnite b o d ies w ere in tru d e d a t h itfi te n d e r at u re o r w hether th e y
sire e n la c e d as " c o ld in t r u s i o n s '’ .
T h is d i f f i c u l t y is duu to th e f a c t
tfcst the In tr u s iv e s e r p u n t l n l t e s a l l o c c u r i n c lo s e p ro x im ity to th e
h lip rtiit G ra n ite c o n t a c t.
The g rad e o f m etarorphism along t h i s c o n ta c t
U seaettoes ex trem ely h i ^ i as is seen by th e o c c u rre n c e o f s i l l i m a n i t e
ad pyroxene-bearing h o r n f e l s e s .
The f a c t t h a t a h i # grade a u re o le
g ee ,, dn th e g r a n i te s id e o f th e s e r o e n t i n i t e mass n ea r Bar 5 beacon
md i» t on th e south s id e s u g g e s ts th a t metamorphism was p r im a r ily uue
ts the in tru s io n o f th e igneous g r a n i t i c r o c k s .
The m etanorphic in f lu e n c e s o t th e u l t r a b a s i c b o d ie s a re s l i g h t
ad the su ccessio n s a d ja c e n t to them have a l t e r e d assemblage?: t h a t may be
ti m if l e d as b elo n g in g to th e g r e e n s c h is t f a c i e s o r to th e lower g rad e
m b p s e f th e a l M te - e p id o te - a m p h ib o llte f a c i e s .
Bowen and T u t t l e have
hwd •rp e rim e n ta llv t h a t t h e r e i s no lik e lih o o d o f a s e r p e n tin e magma
milting below KOCrC (T u rn er and V erhoogen. 1960).
On t h i s e x p e rim en tal
data, however, H e s s 's (1938) id u a t h a t an u lt r a b a s ic magma c o u ld be
lafcrwhd a t low te m p e ra tu re w ith 5 to 15 p e r c e n t H2O p r e s e n t , must be
fsjectetf.
Bowan pro p o sed a th e o ry o f mechanism o f u l t r a b a s i c in t r u s i o n
dam pen he s ta te d the* th e "magma” a t th e tim e o f i n t r u s i o n c o n s is te d
logs^r e f o li v in e c r y s t a l s kep t m obile by sm all q u a n t i t i e s o f i n t e r # m # a r magmat i c l i q u i d o r even w a te r vapour.
G r a v it a ti o n a l s e t t l i n g
®f ttw e liv in e would be a mechanism c a p a o le o f p ro d u cin g "magmas" o f t h i s
%#, I t was argued t h a t th e s e b a s a l t i c magmas sh o u ld be e x p e c te d to b i
•ttNpeeied by o th e r and m r e s i l i c e o u s ro c k s r e p r e s e n tin g th e coraple•■Aepy liq u id d i f f e r e n t i a t e (T u rn e r and V erhoogen; 1 % 0 ),
B earing t h i s l a s t m entioned f a c t in mind an! th e ap p a re n t h i #
^### o f s l l i f ic a ti o n and e h e r t i f i c a t i o n o f p r a c t i c a l l y a l l th e
^•Wsatens in th e a re a th e w r i t e r su g g e s ts t h a t m ight t h i s n e t be some
■WMSfcm o f th e p ro c e s s e s o u tl in e d above?
Th# ultT& b##ic bodi#m have bean t e r p e n t i r i z e d and o n ly in
lagt***# w r e o l i v i n e rem nant# ob # ery # d .
Tne #e7T»r* l ^ i z a t l o n 1* mc-e
gf less evenly d i s t r i b u t e d th ro u g h o u t th e u lt r a b a s ic ma sse s. Hess (1933}
th a t l i * u llrm b e e lc b id !* * he examined ahowed a la c k n f volume
ehtfige when a l te r e d to s e rp e n t in i t e .
He a lso s ta t e d t h a t th e s e ^ e n t i n i isttofi r e s u lte d d u rin g th e l a s t s ta g e s o f th e same c y c le o f igneous
activity es th e intrusio™ , o f th e u l t r a b a s i c .
Bowen and T u t t l e have shewn,
jflv tv t, th a t s e r p e n t i.ii z a ti o n ap p ro x im ates to an e q u a l-volum e replacem en t
,?d occurs at te « p e Ta t u rs s c f %X) to 400°C .
W a ter, s i l i c a and carbon
dioxide n ecessary m r th e a l t e r a t i o n fcould hdve boon d e riv e d from th e hy d ro theflBl s o l u t ie u s em anating from nearby g r a n i te I n t r u s i v d s , o r from magraatic
ester* o r efeVer charged geo s y n c li n a l sed im en ts ( f u rn e r and V e-hoogen, 1960),
These w r i t e r s a ls o g iv e a r e a c tio n in which o l i v i n e i s re p la c e d
ay the came volume o f s e r p e n t in e .
The ex c ess M^) and S 10^ b eing removed
in sel it ion.
SMg^S 104 ♦ 4H20
S i^O^ ♦ 4MgO ♦ S 10,
( O liv in e )
(in tr o d u c e d ) ( S e r p e n t in :)
( Removeo in s o lu tio n )
itie »eta«urp*iic m in e ra l assem blage o f th e s e r p e n t i n i t e o c c u rre n c e s
in the re p o rt area g e n e ra lly show a la - k o f m in e ra ls o th e r th a n s e m e n tin e
(aetlflD fite), m a g n e tite , m a g n e s ite , q u a rtz and r a r e l y o l i v i n e and c n m m ite .
The serp en t in J M te s near Sugden S id in g show s ig n s o f a c t i n o l i t e
•ad d tl o r ite in d i c a t in g t h a t a h ig h te m p e ra tu ru was p r e s e n t to cau se th e
tlm H lo n o f the u l t r a b a s i c r o c k s .
e re i s abundant m agnesite
im lap ed due p ro b ab ly to th e in t r o o u c ti o r o i CCL to th e s e r p e n t i n i t e .
T urner and Verhoogen (1960) show t h i s r e a c tio n as follow s*
*4 S
"h
( s e r p e n ti n e )
*
"2
S
sh
(ta lc )
h :
* ^
3
(m a g n e site )
O i l i e s t io n o f th e s e rp e n t i n i te - b e a r in g ro ck s p ro b ab ly was th e la s t
W to * to have ta k e n p la c e .
Hess ( 1933) s ta t e d e m p h a tic a lly th a t
*GP#m&WL*#tion prece d ed s t e a t i t i z a t i o n and T urner and Verhoogen (i9 6 0 )
r o t as adamant a s H ess n e v e r th e le s s ap p e ar to s u p p o rt t h i s view .
^ lllMHPatlon o f th e s e r p e n t i n i t e s to t a l c may be due to tn e e f f e c t o f
^ •prow s h y drotherm al s o lu ti o n s p ro b a b ly d e riv e d from th e .ear by
k*N§ive H e ls p ru it G r a n it e s .
The f a c t t h a t b la ck n e e d le s o f to u rm a lin e
* * * * * tc it h e r w ith th e t a l c would te n d to s u p p o rt t h i s c o n te n tio n .
Other e% ancles o f t a l c d e p o s its o f th e s t e a t i t l z e d ty p e
****ttng of concordant le n tic u la r b o d ie s o f a lte re d u l t r a b a s i c s a re
by Hess (1 9 3 3 ).
(v )
O rigin
n * pr—gnce o f ollvlTW, —g n e tlt e , chromlt* »nM nlciiel together
d # m#»eeita end te le tcurrence, ewggeet th et the r ic k , o r ig in a lly wore
# e W f w " me*te,l»n rich parent rock o f u ltreb ,« lc conpultlm n pd:My e p erld etlte or du nlte.
Berth (1*52) e t e t i d " th e home o f the
W W 1«, gomerolly p e e k in g , the folded mountain chain,".
T h a w .re
fMgmm*ly ecoo^anled by w r p e n tln lte , but , , me, .ta te d e a r lie r tht
,mM"* *# to he* the ultrebealc bod le. Intrude , t l l l remain, although
bam, and T u ttle (1949) th in k t h a t there i s no e s cap e from th e c o n c lu s io n
bat #m#tao a an be Intruded o
in th e w ild a ta te.
(b)
H g im y U ( k m l t e
(1 )
I n tr o d u c tio n
The term " M e la p ru lt G ra n ite " ma, w e d by H a ll (191P ) to d o a c rlb e
tkcfo&aoan g r a n lte - g n e is s th a t c o n s t i t u t e , a la rg e a r e , o f th e E a s te rn
Tiamamaml Waaymld.
t h l l k o th e d a rk h o m b le n d a -b e a rin g K adi V a lle y
n ft^ ta j tb # M ela p ru lt G r a n ite i s e s s e n t i a l l y , l e u c n c r a tI c v a r i e ty but
baabmaa mmmioua d a rk eonea r i c h In b l o t l * e .
in )
E i« M O c c u rra n c a . Descr l o t i o n and S tr u c t u r e
Th# M e ls p ru it G r a n ite o c c u rs alo n g th e e n t i r e n o r th e r n f r in g e
»f 9 » B e tte rto n M ountain Land where i t b u i l d , v.oU -rounded h i l l s t h a t
fell|& rt o t th e K ro k x illp o o rt R ng«.
T h is range forms th e w atershed
*****
C ro c o d ile R iv e r In th e n o rth and th e Kaap R iv e r in tno s o u th .
^ th e eliol® o u tc ro p s a r e p o o r ex c ep t whero th e Kaap R iv e r has
, ** p
gatanit-9s,
L a rfe a re a s c o n s i s t o f f l a t - l y i n g e x te n s iv e ly
awwoawd rock and n e a r Louw'e C reek S t a t i o n th e g r a n i te s a r e o v e r l a in
^ *®ft s tr e tc h e s o f a r a b l e farm 1and.
The g r a n i te s exposed in th e aro a may ro u g h ly be d iv id e d in to
s ite e o r ie e i1.
2»
3o
i n t r u s i v e c o n ta c t g r a n i t e s .
homogeneus g r a n i t e s .
m assive g n e i s s ic g r a n i t e .
I.
I n tr u s iv e C o n ta c t G ianit& a
The g r a n i te along th e C o n ta c t B o lt i s an in t r u s i v e g r a n i te th a t
been in je c te d in to th e d a rk c o n ta c t a m p h ib o lite s .
The in t r u s i v e
0 f th e se ro c k s ap p e ars lim ite d to th e fr in g e o f th e j r o n l t e m a ssif
extends northw ards fo r o n ly a few hundred y a rd s b e fo re grad a t lo n a lly
diinging in to a more compact f in e r - g r a in e d homogeneous g r a n i t e .
*
T y p ic a lly , th e g r a n i t e seen in th e area i s medium- to c o a rs e srsinsd and l i # i t i n c o l o u r .
Hand spocim one c o n s is t o f q u a r t z , f e ls p a r
^ Is ie a .
In t h i n s e c t io n th e ro ck i s p r i n c i p a l l y conposed o f q u a r t z ,
tScxociina, tw inned and untw inned p la q io c l a s e f e l s p a r ( u s u a ll y o li g o c la s e
at i l b ite ) , m u sco v ite, b io t it© and m ngnotlt© .
In a d d itio n m inor amounts
si grs#n hornblende and epidot© wore n o te d .
The c o n ta c t zone i s c h a r a c te r iz e d by numerous in t r u s i v e
M&gstite bodies and v e in s as w e ll as g r a n i t i c and a p l i t i c o c c u rre n c e s .
[ * 11* , o f w p h ib o li t* r e la r g e ly r d s t r i c f e d to t h i s son© end a r e fd ld e d
lefrther with th e g r a n i t e s .
The f o ld in g h as deform ed th e I n tr u s iv e
iitiim and in th e Kaap R iv e r c u t t i n g n e a r H oneyoird S id in g a w e ll exposed
tsitcrop *cw s eonceoporaneous f o ld in g 01 g r a n i te v e in s and a m p h lb o lite .
I)udinaged s tr u c t u r e s o c c u r on th e f la n k s o f th e fo ld s w hile in th e
h_ags some# m inute p a r a s i t i c fo ld in g h a s ta k e n p la c e ( s e e P la t e s 16 and
II). A ll along tn e c o n ta c t th e g r a n i te s appear deform ed and have
ebdeualy undergone e x te n s iv e f o ld i n g .
L ine art io n s c o n s id e re d to be
:# # ie tW w ith th e fo ld in g a re w e ll d e v e lo p e d , e s p e c i a ll y i n th e Kaap
Urn e v ttin g and in th e a re a to th e n o rth o f th e bea co n , Bar 5 . The
ttlitienehip o f th e l i n e a t io n s to th e fo ld in g i s e x p la in e d mere f u ll y
Wsr S tru c tu ra l G eology l a t e r in t h i s r e p o r t .
The g r a n i te s a re w e ll f o l i a t e d alo n g th e im m ediate c o n ta c t
W ale# fla k e s ( e s s e n t i a l l y m u sc o v ite ) show a p a r a l l e l o r i e n t a t i o n ,
iatfcir s e c tio n t h e l i n e a t ed g r a n i te s i i s p la y b u ck led and tw is te d
trystali o f mica ( s e e P la te # 18 and 1 9 ).
Thn quart.- in th e deform ed
fMtite.* shows s t r a i n e x t i n c t i o n a/v* th e p .a g i o c la s e f e l s p a r
w ig s c lis e ^ a lb ite ) i s f r e q u e n tly seen undergoing in c i p i e n t a l t e r a t i o n
^ w ic ite .
M tw rous p e g m a tite and s p l i t s v e in s p e n e tr a te th e e a r l i e r
M M## and x e n o lith s and th o r o f o r e p o s t- d a t e them .
The p e g m a tite
*tos anaetoalze th ro u g W u t th e c o n ta c t a re a and e ty g m a tic vein# are
^RW Aly seen in th e c o n ta c t a m p h ib o lite s and x e n o l ith s .
^
&# made I n th e mapping o f th e g z a n it* # m d t h - p eg m ati.e#
W th e ir o b e c ire y a d e tlo n m l n a tu r e in p e o n y exposed c r c * .
arg e:
3nd c o a ts a
SfsSMMSik:.,
2.
*'
U M M m m * (k m o U * # .
« U i l M C iw lM tc a r . n , t r ,
m m
S lie& E g iS
- 60 North n f Eur*»:» S ld in y and on th e f a r t P e r l , m lp a a tlt# # ,
ea m iatin g o f I n ti a w ta l y mlaed g r a r i ltl c M d a m p h lb o litlc co u n try r o c k ,
g* #%po##d.
F lo # f o ld ln q and I r r e g u la r banding # a : a le c noted
(*, Plmt. ao).
A few merehy a rea # o c c ir a t th o fo o t o f th e alo p e# le a d in g i f
to the g r a e l te h i l l # and ao rin g * a re to be found In eome o f th e ahear
W t h . a r m l f In tru m lcn
(in :
H##t TMm tA* I n t r w l v # body #pr##dln^ In to th * m urm undlng
w & m crti re e u lte d In a m lneT m loglcal and t e x t u r a l r e c o n a tr u c tlo n o f th e
met f a h n c e n t orodweed a th e rm al au * e o le o f c o n ta c t metamorphlma.
#y m m alntag th e m in e ra l aeeem blage# In euccem elve eta g e e e w y from th e
gmeite# I t w w p e a e lh la In tf i la a re a to d e fin e =**1 I d e n t if y th r e e fa c ie #
of aetamerphlma.
Theme a r e , e t a r t l n g a t The c o n ta c t *xl p ro g re e e lv e ly
1.
2.
3.
th e h o rn b le n d e -h o rn fe is f a c ie s
a i b l t e - e p l d o t e a e f h l b o l l t e t a c le a
a t f a c i e # . (Sae F lq . Z7)
be# been d e a l t w ith wore f u l l y e a r l i e r In t h i s r e ^ r t .
I t 1#
mfTloilani h a re to w r i t lew th e wide v a r i e t y o f met amor ph ic m i.ie ra ls
from aill& m am ce end g a rn e t# n e a r tlte i n t r u e lv e g r a n i te c o n ta c t#
m # e ^ a pT ogre##ive dw creaee in metemcrp*,ic g rad e to th e eouth sAere
"ek am# a c t b m l i t e f i n a l l y g iv e may to e n t i r e l y u n a lte r e d # ed lm eit# .
The d e f i c i e n t o f m etam orphic phenomena in th e eedlm ent# o f
mid he# been n oted mid comme n t ed 'p o n by mmerou#
i n th e pmmt.
One o f t h e mo#t p le u a lb l e ex p lan atio n * to
i l a t a * advmmed w Read ( : 9 5 l ) who c o n a id e re d t h a t th e b a e ic rock#
m m d b # th e f b 'm ta in Lm*d # cted a# b u ffe r# t h a t d i# # ip e te d th # i* a t
mlmnam e d th th e y e n i r # i n t r u a lo n e .
The r e l a t i v e abaenc* o f r e g io n a l m etam orphic e f f e c t # would aieo
V .a g e a t t h a t th e # u cc # eaie n a r e v e a le d to d a y could n o t have be n
md kamaath any g r e a t * t r m t l y * h i c cover ir. th e p a # t.
iv )
O rig in
The r e l a t i o n e h i p o f
g r a n i te s t< th e rock# o f th # K arbezton
Lmd ha# poeed nim m ro^ problea*# foi which many v l e * a i i d * r %v#
“ 61
“
bieit extended in an atte m p t to c l a r i f y o r e x p la in c e r t a i n phenomena. One
P* the forem ost d i f f i c u l t i e s h as been to account fo r th e o r ig i n o f th e
f i j x p V alley G r a n it e , th e N els p r u i t G ra n ite and th e c o rre so o n d in g 'G'
Series g r a n i te s In S w a zilan d and t h e i r r e l a ti o n s h i p s in tim e end p la c e ,
b ie f ly summed up below are s e v e r a l o f th e su g g est io n s , fin d in g s and
theories p re s e n te d in t h e p a s t .
»
Age d e te rm in a tio n s done on b i o t i t e s from th e a re a between
h'elsprult and Kaaomuiden have g iv e n an age o f 2*600 m illio n y e a rs
(W oeleysen, 1 9 62).
The nearby Kaap V a lle y G r a n ite h as been d ated as
being 3,200 2 100 m .y ., (Sam ple from th e farm S o m erset in th e B arb e rto n
V alley
K ic o lsy s e n , v e rb a l com m unication).
On th e B arberton-A gnee
*## road th e i n t r u s i v e r e l a t i o n s h i p s betw een th e Kaap V a lle y G ra n ite a« i
the S w « lla n d S ystem can be s e e n .
On th e o th e r s id e o f th e B arb e rto n
teuntain Land i n S w a z ila n d , th e G4 g r a n i te s have been g iv e n a mean age o f
J/ffO 6C a , y , . o b ta in e d by 't o t a l - r o c k ' a n a ly s is (A ll# o p p , R o b e rts and
S chreiner, 19 6 2 ).
Ne«- F o rb es Reef in Swaz 11 and th e G4 g r a n i te i s
itto rw lw in to th e SwaailarW System and a p U t i c - g r a n i t e d y k e le ts invade
the Jew atow n s c h is t* (H u n te r, 1961).
van Eeden (1941) r e p o rte d t h a t
the N ela p ru lt (G ranite was i n t r u s i v e in to both th e S w e tla n d and Moodies
Systems i n a d d itio n to th e Jam estown Igneous Complex.
In th e r e p o r t
# # g r a n i te s a r e o n ly i n t r u s i v e in to th e a c id and b a s ic rock s o f th e
OwHPWaeht S e r i e s on th e n o r th e r n lim b o f th e L ily S y n c lin e ( fo rm erly
rsgerdsd a s th e Jam estow n Com plex).
The Geo lo g i c a l S urvey ( V l s s e r , 1956) h as shown t h a t s e v e ra l
phases o f to e Mel s p r u i t G r a n ite w ere exposed in th e D i s t r i c t and th e y
Mggest th a t th e g r a n i te represents a s e r i e s o f products d e riv e d from
the pro cesses o f g r a n i t i z a t l o n .
S eed (19 5 1 ) i n t e r p r e t e d th e g r a n i te s as being th e p ro d u c ts o f
the ■ d g m etiiatio n o f s e e i - p e l i t i c and more s i l i c e o u s r o c k s .
He
c lssslfid s them as au to ch th o n o u s g r a n i te s i . e . granites produced by
W w ltlia tle r i t h a t a re surro%m4ed by great a u re o le s o f m ig a a tite s and
■eUeorphie r e c k s .
A utochthonous g r a n i t e s , Read e x p la in e d , formed in
Flsee a t to e b a se o f th e m ig m s tite com plex.
The g r a n i t i t e d m a t e r i a l , re n d e re d m obile by s o a k in g , w ill ten d
te m e as s w hole to w ard s In to a low er p r e s s u r e e n v iro n m en t. M obilized
■ • M a i , u s u a lly o n ly a f r a c t i o n o f the o rig in a l g r a n i tiz e d mass may
in co m p o sitio n ami c h a r a c te r from the parent m a te r ia l as i t moves
**■ • d i f t o r e n t en v iro n m en t.
The Of M ite s and g n eisses in the report arse are dominantly
N m rish with bbvndent o llg o c la s e and a lb ite felsp a r.
The 'ntru sive
*
62
-
mgp g r a n ite s and p e g m a tite s have an in c re a s e d p o ta sh c o n te n t and
^ggjellne becomes abundant. Read (1957) q u o te s se v e ra l examples i_f
y ^ fh thonous granites w ith s im i la r c h a r a c t e r i s t i c s to th o s e found xn
m #*#"
Kaaway (1963) was o f the o p in io n th a t th e granites represent
g* o riginal basem ent on which the sed im en ts were l a t e r d e p o s ite d . He
smeidere the whole to nave been deform ed and in tru d e d by la ter g r a n i te s .
The age o f 2 ,600 m .y. given f o r th e H e ls p ru it G ra n ite i s not
Mdltely in k ee p in g w ith th e id e a t h a t th e s e g r a n i te s r e p r e s e n t th e
beseeent.
The d if f ic u lty m ight be e x p la in e d by th e fa c t t h a t
iM age was determined using b i o t i t # o n ly and not th e ’ t o t a l - r o c k '
athod. The age o b ta in e d m itp t re p r e s e n t a superim posed p e rio d o f
* a # fp h l# s co in cid en t w ith the la s t i n t r u s i v e p hase o f g r a n i t e s .
B w llfw ro , v e r b a l c o w m m ic a tio n ).
Another problem o f prim e im portance i s th e ju x t a p o s iti o n o f
l i |t level and low lev el lo c k ty p e s and th e a s s o c ia te d metamorphlc
0WMWB m o o w te r e d throughout th e D i s t r i c t .
By high lev el rock
typei Is mesnt the etretlgraphlc s u c c e s s io n s co m p risin g the ro ck s o f th e
lebsrto n Mountain Land th a t were d e p o s ite d on th e low le v e l ro ck s made
g r a itite s , a ig m a tite s and g n e is s e s o f v ary in g c o m p o sitio n s .
With
W# $ W # (tevelopm ent o f g r a n i te s e n tir e ly s u rro u n d in g the M ountain
W It Wm generally been re g a rd e d as e x tr a o r d in a r y th a v th e metamorphic
elHNrrved i n th e a re a are p r a c tic a lly n e g l ig ib l e and are la r g e ly
te th e marginal o r c o n ta c t t o n e s .
In some p la c e s lo s s th a n
• *41* t i t * amd seldom exceeding 3 r e lie s firm the g r a n i te s th e fo rm a tio n s
#t e n tire ly u n a l te r e d .
I t would app#*r th a t th e P recam brian ro c k s in
Ms area w ire n e v e r c o v e re d by any great thickness o f younger fo rm a tio n s .
9*
th erefo re, la p rin cip a lly o f the contact metamorphlc
%MM4# # eemtect aureole o f varYimg grades and e x ten t.
Dynamic
# # $ # , # d a h a v e lo c a lly Influenced the rocks e sp ec ia lly along
W # add in strongly deforoad area# but wide scale regional oetsoor# # I s y o r l y d e v e lo p e d .
A oo# mentioned e a r lie r that the grmnlte 1# followed by a very
B # l# su eceselo n o f strata dipping outw ard from th e m a s s if.
Both th e
and the adjmeant sedimentary and volcanic rock sequences are well
* * # * . Centasperaneoue with tlx# m obility and in jectio n o f the granites
& * # 0#W llty emlata th at transport o f cer te in constitu en ts ( b lo t lt e ,
W aill# * * hornblende) along paths o f d iffe r e n tia l shear could have
*##fsd* thereby producing the conformable fo lia tio n s .
P erh ap s th e B est e f f i c i e n t e x p la n a tio n a p p lic a b le to th e area
ssy be found In * e g » a n n 'e I n f r a and s u p e r s tr u c t u re ! c o n c e p t.
Read (1957)
eeatlng Wepamnn shows how he d is tin g u is h e d between th e n o n -m lg m atttlc
lu p e rstru ctu re and a ig m a tlte I n f r a s t r u c t u r e .
The l a t t e r c o n d itio n s
advewlRg from below in v o lv e th e basem ent ro c k s and th e geo s y n c lin a l f i l l
g d s ria i w h ile th e t r a n s i t i o n a l to n e betw een th e m ig m atite s and th e s e d iggiitgry co v e r i s th e sp h ere o f a c t i v i t y o f r e g io n a l metamorphism.
W ith in th e m obile b e l t th e i n f r a s t r u c t u r e p e n e tr a te s th e su p e rliru e tu re .
The i n j e c t i o n i s accom panied by in te n s e metamorphism and
u te e o e e t iw and tongue* o f is a g a a tic g r a n i te u ltim a te ly appear a t h l ^ e r
1m ls.
F i n a l l y , and p u r e ly a s u g g e s tio n n o t based on any e x te n s iv e
iw ls tig n tio n i s an id e a proposed by D. A. P r e to r i u s ( v e r b a l con m unlcatlon)
c o n sid e rs th e p o s s i b i l i t y t h a t th e o l d e s t g r a n i te s en c o u n tered in
leStiNarr A f r ic a v i s . t h e Kaap V a lle y G r a n it e , th e G1 g r a n i t e s o f S w aziland
sod th e Old G ra n ite n o r th o f Jo h an n esb u rg amon% o t h e r s , m ight r e p r e s e n t
##
o f th e g r a n i t e m a s s ifs t h a t have been e le v a te d to t h e i r p r e s e n t
I lf p e titio n s .
The g r a n i te s enc i r e l i n g th e s e g e n e ra lly dome shaped b o d ies
o tfB M nger and may r e p r e s e n t some e x p re s s io n o f a " c r u s t o f g r a n ite " th a t
las le e a lly been made m o b ile , e s p e c i a ll y i n a re a s f r in g i n g th e u p li f te d
■W es.
M
Mm*
(i) IntadiKitefl
S e v e r a l v a r i e t i e s o f h y p ab y ssal dyke ro ck s o c c u r in th e a r e a ,
are seldom seen i n o u tc r o p , save where th e y a r e exposed in r i v e r b ed s,
le tba g r a n i te s th e dykes a r e more co n sp icu o u s due to t h e i r d a rk e r
eslew m tlen.
Good ex p o su re s a re t l s o afforded by th e road and r a i l
#% l8gs b etw w n E ureka arxi Honeybird S id in g s .
O fte n a c l o s e v is u a l s i m i l a r i t y e x i s t s between th e dykes and th e
W * re e k s o f th e O nverw acht S e r i e s e s p e c i a l l y where th e y a re w eath ered .
F o u r v e r i e t * e s o f dyke w ere d is tin g u is h e d in th e f i e l d .
WM
1.
d o l e r i t e d y k es.
2.
d iab ase dyke*.
3.
4.
p o r p h y r it ic d ia b a s e dykes.
a e p h l b o l i t i c d v k es.
T hese
—64 —
The dykes o c c u r In tru d e d *nto a l l th e fo rm a tio n s t h r o l l o u t th e
A few o c c u r a s low mounds
nding o u t above th e su rro u n d in g
fe re a 'lo n s, w h ile o th e r s In th e g r a n i te f o r e x a i^ l e , form n o ta b le
depressions.
I n most c a s e s o u tc ro p # a re poor and c o n t in u it y i s b r i e f .
The dykes t o th e so u th o f th e g r a n i te s s t r i k e ro u g h ly a t r i g h t
angles to th e tr e n d o f th e sed im en ta ry fo rm a tio n s in to which th e y in t r u d e .
Jsimting was n o te d ir. w e ll exposed o u tc ro p s o f a m p h ib o lite and q u a r t z i t e .
These j o i n t s a r e a ls o ro u g h ly o r ie n te d a t r i ^ i t a n g les to th e re g io n a l
trends.
The in t r u s i o n o f th e dykes t h e r e f o r e , may have been p a r t l y
controlled by th e r e g i o n a l j o i n t p a t t e r n .
A few dykes do d e v ia te from
tiM gen eral t r e n d | th e s e o c c u r me t l y in th e g r a n i te s where th e y s t r i k e ,
la a d d itio n to e n o rth -s o u th d i r e c t i o n , ro u g h ly n o r th e a s t.
A v e ry p e r s i s t e n t p o r p h y r it ic d ia b e ia dyke a ls o s t r i k e s n o r th east end can b e tr a c e d f o r s e v e r a l m ile s b e fo re i t d is a p p e a rs in to th e
granites.
The dykes w ith few e x c e p tio n s a n narrow , sometimes o n ly a few
fast In w id th .
The p r i n c i p a l e x c e p t ion i s th e dyke t h a t o c c u rs in th e
fteaiyMrd C re e k a r e a .
T h is dyke i s in p l a c e s , up to 100 f e e t wide b u t
pSMftSs and s w e lls i r r e g u l a r l y and in a d d itio n p o s s e s s e s o f f - s h o o ts t h a t
give th e im p ress io n t h a t th e dyke i s s t i l l w id e r.
Ifast o f th e dykes are
ebeearsd In t h e 3 rd dim en sio n b u t appear to be v e r t i c a l .
The p o r p h y r itic
exposed in th e r a i l - c u t t i n g n o rth o f E ureka S id in g d ip s s te e p ly tu
the w est.
(ill)
D e f i l e d D . « r i B t l a n o f th e PukM
l.
D s l . i l l * D xke:
O nly • few d o l e r i t e d y k e , w ere n o te d and th e s e p eased a t t i e * .
I * t i * M » d y k e s.
I n th e 6 i a n l t e s d o l e r i t e d y k . o c c u rs n o rth e a s t o f
WwyMxd S id in g w h ile n e a r L o w 's C reek on th e f a r * l l l y d a l e and
N p t i . th e dyke tr e n d in g n o rth I s f r e q u e n tly o f c o a rs e -g r a in e d d o l e r i t e
W p s ltle n .
A p o r p h y r it ic d o l e r i t e dyke o c c u rs on th e farm K llp b o k re n t.
In t h i n s e c t io n th e ro c k s a re f i n e - g r a in e d , h o lo cry a ta llln .
f . l ^ a . and p yrow n ..
Ophltlc Intergrsisth. o f p l.g lo c ls s .
W a r e
comieon.
A l t e r a t i o n o f th e c o n s ti tu e n t s u s u a lly
W e e * v a r i a b le am ounts o f c h lo r ite .
The f e ls p a r is g e n e ra lly
bytawmlte while th . pyroxenes ere euglte and p ig M n lte.
^ I l t U i BMgnetite and b l o t i t e was also n o te d .
a
#
A te . 1"
tS K
S i t a i* b e ,l t
B
iS S iS ir
_
OefT-l • * •
.
.
SSBWK
#
*
^
^
T 'r
f B
^
5555S
a # #
rnev*—
P I k l 2 3 ) c - a l io y c n t h e
T a r n A v c c a s r .o w l n f * . r e e
l a y e r s cT L o - .l d e r b a n d
rA h h lo m m e -'"* rated by e o l l
(e e q h e c e n t Z e p c a lte j
naa#
ebseure iA rge t r a c t s c f th* a re a im m ediately south o f th e L ily r i d g e .
$ ew ril re c e n t ro ck f a l . ; have ta k en p la c e on th e s h eer c l i f f y on th e
fsrs C r y s ta l S tre a m .
I.
pC5S 131S. PK-DEFORMk:IGN HISTORY OF TliE AFEA
E e r l l e r in t h i s r e p o r t s e v e ra l re a s o n s w ere g iven c o n te s tin g
tm p rev alen ce o f th e assem blage o f ro c k s fo rm erly c )a s s i f l e d by th e
Geological S urvey a s b elo n g in g to th e Jamestown Complex.
The evidence
was p resen ted in s ta g e s and th e f u l l im petus o f th e id e a , t h a t many o f
rocks b elo n g in g t o t h i s s u c c e s s io n do not appear to be a l te r e d b a s ic
igneous r o c k s , may n o t have been made s u f f i c i e n t l y te n a b le .
The rem arks t h a t fo llo w in t h i s s e c tio n a re based n o t on one
p articu lar f a c e t o f ev id en ce b u t were fo rm u lated from th e c o n s id e ra b le
count o f in fo rm a tio n o b ta in # i from s t r u c t u r a l and met am orphic
phenomena In th e a r e a .
An alm o st id e n t i c a l arrangem ent o f ro ck ty p e s to th o s e found
in the r e p o r t m reu, e x i s t in th e A s p h ib c le -S c h is t S e r i e s o f Pahang,
liilaya, and t h * i r o r i g i n h a s , d u rin g th e p a s t , been c o n s id e re d from
i%'.irsl view p i i i t s .
(R ic h a rd s o n , 1 9 47).
G e n e ra lly i t was conceded
k* i l l th e in v e s t ig a t o r s t h a t th e o r i g i n a l ro c k s m u s t have been r ic h
ie i f t a , m agnesia and lim e o r th a t a l t e r n a t i v e l y q u a n t i t i e s o f th e se
radicle#, to g e th e r w ith a l k a l i s , were in tro d u c e d d u rin g met m o rphism .
R e v e rtin g to th e ro c k s found in t h i s r e p o r t a r e a , a p re c is e ly
dmllar o r i g i n m ust k# e n v isa g e d .
The p a re n t ro c k s m ight p o s s ib ly have
bm one o f th e f o i l jw in g r1.
2.
3.
d o lo m itic lim e s to n e s , c a lc a re o u s and megneelan
xAale# and t u #f s .
b a s ic igneous ro ck s ( p o s s i b ly both i n t r u s i v e and
e x tru siv e )
sed im en ta ry ro c k s in f lu e n c e d by ir o n , megnesian
and lim e - r ic h e f f l u e n t s d e riv e d from u l t r a basic
igneous r o c k s .
With th e s e a l t e r n a t i v e s in v ie w , an a tt, spt was mide tc
Nwe^tnet the p o ssib le s t r a i i g r a p h i c co lu e n o f th e o r i g i n a l o r p r e *Smwtlenal s u c c e s s io n s .
T h is t a s k , a lth o u y ., v i r t u a l l y im p o ssib le
te •ceoapllsh s u c c e s s f u ll y w ith o u t c o n s id e ra b ly more d e t a i l e d study ^
Mag widkirtfljten, ( e . g . on t r a c e element a n a ly s is o f th e b a s ic s u i t e s ,
* " * * * ! # # # , c o u ld be a t t e s t e d using o th e r in fo rm a tio n .
The method u n d ertak en was to work backwards re ly in g e s s e n t i a l l y
on s knowledge o f s t r u c t u r e , sedim entology and raetemorphism to g e th e r w ith
the charges t h i s l e s t m entioned phenomena invokes in ro c k s o f v a rio u s
eheeical c o m p o sitio n s .
The ro ck s in th e f-rea, and fo r t h a t m a tte r in th e whole d i s t r i c t ,
i n trem endously v a r i a b le in ty p e , t e x t u r e and c o m p o sitio n , but many o f
##a may o f t e n be grouped in th e same g e n e tic c a te g o ry .
I t i s a lso th e
w riter's o p in io n t h a t th e r e a re no r e a l l y complex s tr u c t u r e s in th e
Barberton M ountain Land co m p arab le, fo r s x a s p le , w ith th o s e o c c u rrin g
in the European A lp s .
A d m itted ly some a r e a s a re lo c a ll y f a r from sim ple
stru ctu rally o r o th e r w is e but th e b ro ad er a s p e c ts o f th e M ountain Land
m seen to co m prise a system o f f a i r l y r e g u l a r s y n c lin a l b a s in s se p a ra te d
by narrower a n t i c l i n a l divio*'*1.
The p a t t e r n p re s e n te d in th e f i e l d ,
sltheugh b ad ly de face d by th e p a s s a g e o f tim e , orogeny and igneous
ictiv ity sh o u ld n o t be made more complex th a n i t r e a l l y i s by invoking
n numerous t h e o r i e s to d e s c rib e lo c a l v a r i a t i r n s .
I t was s e in e a r l i e r how, in th e s t r a t i g r a p h i e s ! colum n, th e
rocks were g ro u p e d .
(i)
(li)
(ill)
8 i th o s e o c c u rr in g on th e o rU .e rn lim b o f th e L ily
j y n e lln e
th o s e o c c u rrin g i n th e a n t i c l i n a l d iv id e south o f th e
M pin"S outhern f a u l t , and
th o s e o c c u rrin g on th e n o rth e rn lim b o f th e E ureka
S y n c lin e r e s p e c t iv e l y .
Tin su p p o sitio n was made, t n e ^ e 'o r e , t h a t th e ro ck s from th e g r a n i te
eestaet to th e L ily F a u lt a t th e b ase o f th e F ig - tr e e S e r ie s formed
H it e f on# d e p o s it io n a l " c e l l " , and t h a t th e ro ck s from th e f a u l t
wethmrda and I n c o r p o ra tin g th e E ureka S y n c lin e , formed p a r t o r th e
*@ie e f a second " c e l l " .
The L ily S y n c li n e , com prised o f c o n g lo m e ra te s , q u a r t * ite s
w i i v a r i e ty o f b a s ic s c h i s t s , l i e s o v e r fo ld e d to th e n o r th .
A
w tle n drawn th r o u ^ t th e c e n tr a l p o r ti o n o f th e a rea w v ld show th e
H tw renee e f s e v e r a l a c id o r s i l i c e o u s h o riz o n s on both th e no rth
«* the s o u th s id e o f th e main q u a r t z ite -c o n g lo m e ra te r id g e . Fw
# l * a t i o n s co u ld be advanced to e x p la in th e re c u rr e n c e o f th e se
W#w*e.
U ) The W r iz o n s on th e n o rth e rn lim b o f th e s y n c lin e may
eo u n o a t d ep th to re a p p e a r on th e *
^rr, si<hi.
T h is would
* the same tim e p ro b a b ly mean th a t th e b a s ic ro ck s w ere s im ila r ly
around in sympathy w ith th e s ili c e o u s h o riz o n s .
70
-
(2 )
T aking In to account th e p re s e n c e o f th e Main S o u th ern F a u lt
tost tr u n c a te s th e q u a rtz i t * block o f th e L ily S y n c lin e in th e NbordkaapJe s '- Luck S id in g a re a i t may be p o s s ib le to extend th e f a u l t e a stw a rd ? »
else along th e s o u th e rn p o r tio n o f th e L ily ridge
p a s t Eureka S id in g
ta l a w 's C re e k .
T h is h ig h an g le t h r u s t f a u l t can th e n be c a lle d upon
to explain th e r e p e t i t i o n o f be ,1c ro c k s and th e acid h o riz o n s im m ediately
tenth e f th e q u a r tz I t o r i d g e .
F ig u re 7 shows d ie g r em etic s e c tio n s o f
both p o s s i b i l i t i e s .
The problem Im m ediately in v o lv ed h in g e s around th e d i s s i m i l a r i t y
of the ro ck ty p e s on e ith e z s id e o f th e L ily conglomerate-quartzite r id g e .
k ee ly tlo n to t h i s p ro b ls * m ight p o s s ib ly be found i r th e fa c ie s p r in c ip a l
ef d is p e rs a l in a geo synclinal tro u g h .
The rocks may have had a common
scarce thus b elo n g in g to th e same p ro v in c e , b u t th e y co u ld d i f f e r in
d u ra e te r from p la c e to p la c e ( P e t t t j o h n , 1947).
P u tti n g t h i s in to o th e r
e l d s , th e ro c k s e ig h t have a markedly d i f f e r e n t l i t h o l o g i c a l ap p earan ce
hS e te e n o lo g ic a lly th e y may nave been o f one and th e same age.
At t h i s s ta g e # b r i e f g e n e r a l i l t e d p a la e o h is to ry o f th e
krlWPt»r« M bir.tain Land a s a whole might be c o n s id e re d b e fo re discussing
to# mere lo c a li z e d h i s t o r y o f th e L ily S y n c lin e ( see F ig . 8 ) .
B r ie f ly i t i s assumed t h a t th e O nverwacht r o c k s , c o n s is tin g o f
SlttaStle iimastorMts, l a v a s , a te . ware i n i t i a l l y la id down on a basement
sf grat&tee and g n e isse s.
F o llo w in g th e Onverwacht period o f d e p o s itio n
toast mat subsidence in th e c e n tr e o f the basin to g e th e r w ith u p l i f t in
plaaaa ammmd the edges.
b e e le m took place involving rocks fro# surrounding formations
togdhaf m itt seme granite and Onverwacht m aterial.
D eposition took
kkee 1m the nemiy formed deeper portions o f the geo syncline and the
Mg trae S e r ie s mes culminated by the outpourings o f lave and the
fcpesStion
f tu f f a c e o u s greyw ackee.
%t must be mentioned here that contorted pebbles o f banded
# # $ heee been Beund in the Baeal Conglomerate o f the Ibodles Byatam
I W e # e e l Servey, V lseer 1996), *Alch seems to indicate that the
make e f th e Bmwlland System had been folded to some extent bsfore
WWe tk e e
The fin a l stages Involved the deposition o f the Abodles
H its e f r e e k s i n th e central section o f th e basin and in other lo c a liz e d
* * # * # trm egreealon .
Sidwequsntly the Jarnestosm intru sive recks
" ft lejeeted into the various successions producing lo ca lized structural
W ialieoa.
- 71 F in a l ly th e N e ls p ru lt G ra n ite in t r u s i o n o c c u rre d in a s e r ie s
e f p u ls e s co n tin u o u s on one a n o th e r.
These p u l s e s ar e r e f l e c te d in
to e d e fo rm a tio n h i s t o r y o f th e sedim entary sequences o f t h e geo s y n c lin e .
The L ily S y n c lin e " c e l l " i s p ic tu r e d a s h aving been a
eiogeo syne lin e on the frin g e o f the g r e a t e r b a s in o r b a s in s to th e s o u th .
This sh allo w w a te r d e p o s itio n a l environm ent would be conducive to th e
development o f d o lo m ite s , lim e s to n e s and o rth o q u a rtz i t e s .
The a c id o r
siliceo u s horizons might a lso have been represented by e x tr u s iv e a c id
lava o u tp o u rin g s, fo 1lowed by f u r th e r deposition o f d o lo m ite fo rm a tio n s.
T here was no developm ent o f F ig - tr e e ro c k s in th e miogeo sync lin e
except in the w est between Bar 5 beacon and th e New C o n so rt Mine where a
narrow zone o f a r g i lla c e o u s sediments and c h e r t s were deposited.
T h is
lack o f F i g - t r e e d e p o sitio n was p o s s ib ly due to e le v a tio n o f th e a rea by
gRtdual updoming from below ( s e e F ig . 8 ) .
Towards th e so u th and away
from t o e m argins o f th e b a s in th e deep w ate r fly s e h o r a r g illa c e o u s
facies a t ta i n e d i t s g r e a t e s t developm ent. T h is zone i s alm ost e n t i r e l y
elastic and th e d e p o s itio n must have been n e a rly c o n tin u o u s w ith o n ly a
tHr interruptions d u rin g which tim e bedded c h e r t s w ere deposited. As
# # Besin f i l l e d with thousands o f fe e t o f shales and greywackea,
•vbeidenee must h ave ta k e n p la c e probably c a u sin g t u r b i d i t y flow s o f
material around the margin# o f the a re a th u s c a u sin g considerable
w a ie tlo n s in th e c o m p o sitio n .
Subsequently th e en tire sequence was tr a n s g r e s s e d by a group
e l reeks th a t may be designated m o lts e e .
T h is group c o n s is te d o f th i c k
c la s tic la y e r s com prised m ainly o f sandstone# and s h a le s much c o a rs e r
##& to# Hyech end containing notable conglomerate#. Continued
#to#Menm# probably took place and toe geo syncline was deformed and in
pi We# int ruded by basic and u ltra-b asic magma.
Subsequent to the major de format lane the intrusion o f the
%l#prult Granites took place into toe margins o f the deformed area.
metamerphle e ffe c ts from the intru sion s produced a contact
WAauoz^hlc aureole t h a t decreased in in ten sity sway from t h e g r a n i t e s .
I t 1# therefore p o e e ltle , that the greet variation s o f heeic
W a llie e eu e recks on e ith e r side o f the L ily Syncline can be
•*|fJai»ed as having been due to t
( l ) o r ig in a l fa c ie s variation o f ozposltiun coqpled with
( l i ) d if fe r e n tia l metamorphism o f the contact metemorphic
typ e.
No g r e e t ?*et» s v a r i a ti o n s need be c a lle d fo r to e x p la in th e
A f f e r e n t ro ck ty p e s en c o u n tered a c ro s s th e L ily S y n c lin e .
I n v e s tig a ­
to r s such a s R ic h ard eo n (1 9 4 7 ), T i l l e y (1948) and T u rn e r and Verhoogen
(I9u0) h av e Whosm t h a t ro c k s ra n g in g in co m p o sitio n from hornblende
a q p h ib o iite s , t r e a o l i t e - e c t l n o l l t e a m ^ iib o lite s and ta lc o s e s c h is ts may
fee d e riv e d by d i f f e r e n t g rad es o f c o n ta c t metam orphla# from e ith e r
dolom itic H a e s to n e s o r b a s ic igneous r o c k s ,
In te rm s o f s t r a t i g r a p h i c c l a s s i f i c a t i o n t h e r e f o r e , th e
e a r l i e s t ro c k s to be la y ed down on th e basem ent o f . rc h a e a n g r a n i te g naleses» a s sed im en ts o r la v e flow s w ere th o s e b elo n g in g to th e
dftverwmeht S e r i e s .
In th e b a s in th e r e w ere f a c i e s v a r i a ti o n s away
fro* th e s h o r e li n e and o n ly in th e d ee p er p o rtio n s w are F i g - t r e e
S erie s r o c k s d e p o s it e d .
The e n t i r e sequence was th e n tra n s g r e s s e d by
Noodles S ystem co n g lo m erates and q u a rtz i t e s and s u b se q u e n tly fo ld e d .
At th# same tim e a s th e fo ld in g lo n g itu d in a l s t r i k e f a u l t s w ere developed
ifld b a s ic and u l t r a b a s ic ro c k s w ere In tru d e d .
(•)
I n tr o d u c tio n
f««tur«* found in th . Ymrlou. rook tYP*. Iwv. kwn
T i l * in t h l . r * o r t
i t 1. Irfn d M h * . to dloeuo* th .
o tM O t* . . f t h . o r * mopp«l.
hn ^ t r t #111 bo T o ta
th# tw to n lo hlMOTY o f th . w
«id to p l w . i t into th .
*^ #"#1 # t m # t * # l M t t * n .
Th. .tr u e tu m l t w M n o l r uwd ln,th*_
(1999,
####% 1# th at doflna# ^ d* S l t t w (1998), h o i * (195$), ho
IS # # * 8 h , 1983) mid C loo, ( 1 * 7 ) .
(h)
M ieiu n
hliMlnij mid fo lio tla n M tltu d o . In th . w o . mr. w ry * * 1 * S # M ck n o l ^ r lk o 1 . o * # o .i# # t .ly ...t-m o o t mid d w io tlo n # fro# t h l .
m * 0 tl li * o M tlralY duo 9 . th . foroK ul In lK tlo n o f b .,lc I n tn m lw .
# d I n n .llw d fo ld in g .
P o llo tlo n In th* g r m t lf . 1 .
d w l * m l In
# 8 oantnot mon* Wiar. th* mllgonont o f n lo . f l ^ w In th# plmm of
M W lt n Id » . t o^ dm it.
Northaord. m»* fio # th , oontoct th . y m i l t .
Ihidhdd * r # Uom ogon*.. mid l o w . I t . M ld tW ch .^ w to r.
Tho f o l i a t i o n I n w r lo b ly d i p . w u th n w y fro # t h . y m t l t ,
#Mdl* m ^ 1 . follom od by mi * p m t l y o o n fO im .b l, w d ln o n to rY w o k
m u ,1 1 1 * .
T h . w m d t . h .» p o w lb ly u n d,rgon# m, ipm ard A w ing
x m a t l n g In r .m l l* w w i t o f t h . w i w t l t u o n t , . I o n , p W h . o f d l f f o m n t l . i
No g r e e t f a c i e s v a r i a ti o n s need be r e l i e d fo r to e x p la in th e
d if f e r e n t ro ck ty p e s en c o u n tered a c ro s s th e L ily S y n e lln e .
I n v e s tig a ­
to r s such as R ic h ard so n (1 9 4 7 ), T i l l e y (1948) and T u rn e r and Verhoogen
(i960) have shown t h a t ro c k s ra n g in g in co m position from hornblende
M p M b e lite s , tr e m llte -m c tln o lite a m p h ib o lite s and ta le o s e s c h is ts may
be tlerlv e d by d i f f e r e n t g rad es o f contact m etenorphism from e i th e r
d e lc B ltic li n e s to n e s o r b a s ic igneous ro c k s .
In term s o f s t r a t i g r a p h i c c l a s s i f i c a t i o n th e r e f o r e , th e
e ir lle s t ro c k s to be layed dbwn on th e basem ent o f A rchaean g r a n i te y w ls s e s , a s sedimentm or la v a flow s w ere th o s e b elo n g in g to th e
Owmwcht S e r i e s .
In th e b a s in th e r e w ere f a c ie s v a r i a ti o n s ms-ay
le sa th e s h o r e lin e and o n ly in th e d ee p er p o r tio n s w ere F i g - t r e e
Series rooks d e p o s ite d .
The e n t i r e sequence was th e n tr a n s g r e s s e d by
iie d ie s S ystem c o n g lo m erates and q u a r t z i t e s end s u b se q u e n tly folded.
At th e same tim e a s th e f o ld in g lo n g itu d in a l s t r i k e f a u l t s were d eveloped
m i b a s is and u l t r a b a s i c ro c k s w ere in tr u d e d .
(#)
Btm ctiam l f.m tur.# found in th .
rook t?p w haiv* h##n
# w l l « In
r«port
It 1«
h.r* to dieeuw tho
o f th* w
m^ipod.
An « t t ^ t w ill b . mod. to
th# toctomio h lito r y o f th . « r * «nd to p l w . I t Into th*
*tru«ti*ml p t t « m .
Th* «tn ictu r*l t*r»lnolo#f uwd In th*
,*011 1* th *t d*fln*d by d* S it te r (1 9 3 6 ), W *l*
R«m**Y (1*9#,
A * Md b , 1#M) *nd C lo o , (1*47).
(k )
w g im # m # T i i i e i n n
m**lm* *nd foll«tlom mttltud** In th . *r«» *r* v*TY r* g # li* .
A*
itr lk * 1* *ppm%lm«t*lY .* * t-* * # t *%d d*vl*tlon* h o " thl»
####%i*m # # * n tlr* lv du* to th . for«*ful In jK tlo n o f b**lc Intru#)**#
W WwllmW h ld ln * .
f o ll« tlo n In th . y m n lt ., 1, k**t d*v*lop*d In
# * * w t* » t mom* Wi*r* th* »ll*nm*nt o f mlc* f
In th* pl*m* of
tW aU a* 1*
*vld*nt.
Ibrth**rd« «**y from th . oontK t th* y n l t .
mif* h*w**n*ow mod lo w * It# f o l i a t e ch#T**t*r.
Th* M i n t lam i r ^ r l . b l y d ip * «owth «»*Y f i t " th * y * n l t *
m w i* W 1* N llm m d by «n # p * r * n t l y o o n k w b l * w d l —mt*ry
N * l * l*«.
Th* y m l t * h«* p o w lb ly m d*r»»n* «n ipw m d d»»ln*
In T * * ll# m * n t * f th * « o n « tltu * n t* .lo n g p ath * o f d l f f * r « i t l « l
- 73 The M -dlm entsry s u c c e s s io n s fo llo w in g on th e g r a n i te s d ip
stee p ly to th e so u th o r a r e alm ost v e r t i c a l a t tim e s .
The F ig - tr e e
sequence p r o v id e s th e g r e a t e s t v a r i a ti o n s in th e d ip d ir e c ti o n s o f
NdMing due to t h e Innum erable t i g h t i s o c l i n a l fo ld s t h a t occur in
#e@e in co m p eten t banded a r g i lla c e o u s s t r a t a .
Measurements ta k e n in
the fo ld h in g e s have a v a r i a b le sp read ( s e e F ig . 1C).
T h e re i s in th e a r e a , a marked c o in c id e n c e o f s c h is to s it y
# # {fl-iisar/ s t r u c t u r e s such a s bedding and th e v e r t i c a l a t t i t u d e o f
ewtSBGrphlc r o c k s o v e r a c o n s id e ra b le a r e a .
The o v e r - a l l symmetry
e f # e f t i i r i c and th e p a r a l l e l alignm ent o f b i o t i t e and q u a rtz le n so id
agg reg ates s u g g e s ts t h a t th e s c h i s t o s i t y h a s been achieved by com pression
agff&l t o th e f o l i a t i o n .
A l t e r n a t i v e l y , the fin e -g ra in e d lam inated
sedim ents may h av e been fo ld e d w ith th e development o f a s la t y cleav ag e
p a r a lle l to th e a x i a l p la n e s o f th e f o ld s .
The a x ia l p la n e cleav ag e
e f s c h i s t o s i t y pro duced i s due to p la n a r flow o f material normal to
M S W etaio n .
U)
F o ld s
(i)
G e n e ra l F o ld in g o f th e Masks i n tarn A re#
A long th e g r a n i te c o n ta c t b e l t f o ld in g car be seen both in
# # e m i t e s th e m s e lv e s and in th e adjacent contact a a p h ib o lite zo n e .
l a t e p h ase g r a n i t i c , a p l i t i c end p e g m a tite I n tr u s iv e * were
t*$W ted In to th e a ^ h i h o l l t e s end i t th e same tim e th e y w ere fo ld e d
to g e th er p ro d u cin g s im i la r f o ld s and a tte n d a n t li n e a t io n * .
The d is tu r b a n c e s lu n g th e c o n ta c t b e l t h a s r e s u lt e d In
tk e a x i a l p la n e s o f which dip a t a n g le s v a ry in g bwtw#en 15
a g r e e s t o th e s o u th r t i l l e th e fo ld axes tre n d ro u g h ly e a i t - w s t .
###WMKS o f tiie s e f o ld s a r e seldom c l e a r l y
soon and in a d d itio n
t» # # e e e e lle w t Kaap R iv e r ex posure th e r e a re a few f o ld s d is p la y e d
la an I r r i g a t t o n furrow c u t t i n g on th e firm L ovedale.
mi #
The b a s ic ro c k s u c c e s s io n s a re c o m p a ra tiv e ly f r e e o f fo ld e d
sW oetures and th e m ajor re a d ju s tm e n t in th e s e ro ck s h as ta k e n th e form
• f n t 1 1|.J 11 am end re a lig n m e n t o f m in eral c o n s ti tu e n t s 4n th e p i m e o f
fo w t s t r e s s .
H it,
The H oodies System ro c k s have acted as a more r i g i d competent
The o c c u rre n c e w ith in th e s u c c e s s io n o f f l a t t e n e d , boudlnaged
th at p la s tic flow d is to r tio n , due princip ally to
SH H eee in t m p e r e t u r e and a h ig h c o n f in in g p r e s s u r e , was p ro b ab ly
(fig 9 )
Poles to axial planes of
Isoclinal folds
Plunges of isoclinal folds
Poles to bedding p lanes of
the banded Fig-tree su ccession
i n th * U l y M in #
operative* In th e a r e a .
Only lo c a ll y do le s s c o s ^ c te n t bands occur
but th e s e weaker ro c k s h iv e not been a p p re c ia b ly a f f e c te d due to th e
protect io n affort.'*d them by t h e i r s t u r d ie r n eig h b o u rs.
The F ig -tr* e S e r ie s * c o n s is ti n g o f a l te r n a t in g narrow
irgillaceous bedded u n it s h a s behaved e n t i r e l y as an incom petent mass.
Stiong compression h a s r e s u lt e d in c o n s id e r a b le s h o rte n in g and fla tte n in g
ef the succew lo n and the fo rm a tio n o f t l # t is o c l i n a l f o ld s .
These
feMe plunge s te e p ly to th e e a s t in th e L ily Mine a rea and p lo t s ( F ig . 9)
ffcm a d is tin c t ^>read a long a g r e a t c i r c l e .
T h is f e a tu r e e i th e r
la d ie ste s d i f f e r e n t ia l com pression and a co rre s p o n d in g v a r i a ti o n o f
■ r~ a » rt in th e ' a 1 d ire c tio n , o r i t co u ld pro b ab ly r e p r e s e n t a superIspesed f o ld in g on an o r ig in a lly uneven s u r f a c e .
The Onverweeht S e rie s o f b r i t t l e q u a r t z - s e r i c i t e s c h is ts has
recorded th e m ost rouaerous m inor s t r u c t u r a l fe a tu re s .
These incItxle
eoaji^ate fo ld s , c re n u la tio n f o ld s and ac co rd io n f o ld s and w ill be d e a lt
etth sh o rt ly .
The L ily S y n e lln e i s th e m ajor s t r u c t u r a l f e a tu r e o f th e area
Sid c o n sis ts o f a m assive i e o c l l n a l l y fo ld e d s y n e lln e th e so u th e rn !imh
af ahieh i e o v e rf o ld e d to th e n o r th .
The syne li n e i s b e s t seen n ear
I##*# C*w* (s e e P la te 1) w hile in th e c e n tr a l p o r tio n o f the area th e
• te w tw e i e th a t o f a c lo s e d * o ld .
To the w est th e s tr u c t u r e i s most
by th e i n t r u s i o n o f s e r p e n tin ite s and th e q u a r t z i t e s n ea r th e
I k 5 beecon d ip e t shallow a n g le s to th e s o u th e a s t form ing a g e n tly
mt&A e r beein-eheped s tru c tu re w ith an a x ia l tra c e d i r e c t i o n routftly
pw aliel to th e fo ld a x ia l p la n e o f th e great Eureka S y n c lin a l in fle c tio n .
The a p p ro x im ately e a s t-w e s t tr e n d in g L ily Sync lin e bends to the
i w t t w s t near Eureka S id in g and then o n ly r e v e r t s back to th e re g u la r
timdi o f th e fo rm a tio n in th e J o e ’ s Luck S id in g a re a.
(11)
Fold.
I.
F nlH .
T y p ls .l conjugal, fo ld , occur In th . b r lttl* l«*ln«t«d rock.
W
QmwMwM * M i.»
I . WditWn U U i.w .
MM —Wd 1«
. H l . i f l W #im l. h o rlten . o f th . Lily S y n clln . north o f
w i h a w m , «nd In th . co n tK t mpl l b o l l t . w h l . t . n . = Howyblrd
P l# t# 25 I n d i c t . , t h . approxlm rt. « U . of a c o n ju g a l fold
l a k M t i , haiWad f m g l n o u a c h w t« o f t h . F l* - tr w S . r l . « foimd to
# # # # * e f t h . L ily M n ..
Th. com pat** 1 ^ * « o f c h .r t hava baokan
{Plate 24 / Tight IsoclInal
f o l d s h e w in g p a r a a l t l c
f o l d i n g I n t h e h lr i g e z o n e
a n d quart.% f i l l e d t e r B l c n
crac k e.
M oodlee e h a le e
L ily b y n c l l n e
--E u re k a .
(P iu te 25) Con ' 'i f a t e f ol d in
b&nded fe rr u g ln o u m c h e r t s of
th# F i f - t r e e S e r i e s wemt o f t h e
L ily K in * . The c h e r t y r o n p e t e i .t
w i t # b r e a k a n g u l a r l y w h ile th e
In c o m p e te n t m h tle 1# m oulded
betw een t h e h a r d e r l a y e r p.
( #] I p h t l y ] e # e t h a n
*.ual
# l:e ;.
>!apression
• - of
2
.
S n m i l A 'i "
W
t/tB l
M W U m llY —
nw eU —1 « » .
u m ii «r r « Um
^
B p iS ilS :
s^ ^ ^ S f® 5,555,
», # K t * * d I p r "
^
h)
mmm-
) 8SSQG ia te d with
inV tinw ^ate p re s su re i conjugate folds
M ax im u m | e e s s u r e t
s EE55r-'-sr tfom :*
beacon
*1,
KWP M V . V M M "
( H o n .iy b lr l)
i c, i
D iagram ih o w ln g :-
* 1 ) ., p .hbW
Siding
-
' e
s
s
r
- —
••> ■ s s s s m
"
s r ' -
The a x ia l p la n e s o f th e i s o c l in a l fo ld s in th e a rea are a l l
,t##ply dipping c r v e r tic a l #ugge#tlng th a t a s tro n g h o r iz o n ta l
seflpt-tftive s t r e s s f i e l d was r e s p o n s ib le fo r th e f o ld fo r R ation.
Large
g p litu d e * and narrow wave le n g th s a re en c o u n tered in th e L ily Mine but
folding on a la r g e r s c a l e i s re s p o n s ib le fo r lo c a liz e d d is tu rb a n c e in
the railw ay c u t t i n g to th e so u th v est o f th e S c o ti a T a lc M ine.
H ere V'.*
Onv*?wacht and F i g - t r e e s u c c e s s io n s are tl< # itly fo ld e d w ith th e a x ia l
pisras d ip p in g a t approximately 80 d eg ree s to th e n o r th e a s t.
The fo ld s
pl#gm to th e s o u th e a s t a t a p p ro x im ately 30 d e g re e s .
The fo ld a x ia l
trace tg a ln tr e n d s n o rth w e st - s o u th e a s t i . e . s im ila r to th e Eureka
Synclinal a x ia l t r a c e .
A'.so in c lu d e d w ith in t h i s broad fo ld are
nawrous m inor f o ld s o f th e c r e n u la tio n and c o n ju g a te ty p e .
(a)
L lm A le n :
In th e a re a mapped th e r e are two main type# o f l i n e a t i o n .
The
first are th o s e lin e a t io n # produced by f o ld in g on a m icro sco p ic s c a l e .
M l v a r i e ty i s m a n ife s t in th e b r i t t l e q u a r t z - s e r i c i t e s .h is t# o f the
Onverwacht S e r i e s .
As has p r e v io u s ly been mentioned th e c re n u la tio n
folds have alm ost h o r iz o n ta l ly in c lin e d a x i a l plan#*.
These fo ld s
pwdwee m llnem tlon t h f t plung* to the w*at aA. angle# aeldom g re a te r
%0 d#gr#e# (### F ig . 13).
The second type o f lin e a tio n 1* caueed
'of the e lo n g a tio n o f f: agments such as in d iv id u a l g r a i n s , groups of
pains and ■mall in c lu s io n s .
On a s l i g h t l y la r g e r s c a le elo n g ated
***le* almo rem ult In m linemr eymmetry.
Lii^ationm o f th i* eecond
are th e more f r e q u e n tly en c o u n tered v a r i e ty and o cc u r in
$recticallY a l l th e rock s u c c e s Io n s .
To th# rerth#a*t o f .'ur#km Siding *#11 developed lineation#
«%« in th# *h*#r*d m*rt% -##riclt# mchiet horizon# (### P lete ^6).
Slsmsiaratl a r i a n t a t ; o n o f e lo n g a te d f a b r i c elem ents, in t h i s I n s ta n c e ,
fragments and quartz ’ nests* produce an alignment o f d if f e r e n -
tWly ###th#r#d con stitu en t* .
On weathered face# the clear linear
fAM# 1# mean to plumg# to th# w##t at angla# varying hetmean 30 and
(# i# F_g. 15).
Th##a lineation# #ho« an lntere#tin g
*l#tlon#hip with th# ir truaive granltaa.
Plate 27 Indicate# that th"
#W#ta po#t-date# th# fi remtion of ^ e lineation# a# no linear fabric
b#
trmnamittcd to Ji# intruaive v#in.
In th # S b rb a S id in g a r a e outcrop# o f +h# Ba^al Connlomerate
** taa Ruraka Synclln# d lap lay elongated n#bbl*a th a t al#o produce a
l*##tion.
The reh b le# hav# b##n M attered in the bedding plane and
** #&OMgat#d In the ' a ’ d l- e c tlm and plunge a lm a t v e rtic a lly (#ee
o f a l i n e a t l o n except in is o la te d i n s ta n c e s , fo r e x s n p le ,
® rth o f th e S c o ti a T a lc Mine wher# th e y plunoe to th e s o u th e a s t.
frv e lo p w n t
In th e L ily Mine in d iv id u a l sraphlbole and c h lr T it# c r y s t a l s are
jiig r^ d w ith t h e i r long ax as e t r i ^ i t a n g le s to th e g r e a t e s t d efo rm ativ e
forces.
They a re e lo n g a te d in th e p la n e o f th e bedding but a re not
always a lig n e d in th e t h i r d dim ension and, th e r e f o r e , can o n ly be
regarded as p ro d u c in g a p la n a r f a b r i c and n o t a l i n e a t l o n .
The l in e a ti o n s n o rth e a a t o f E ureka
S id in g
and th e f la tte n e d
pebbles a t Sheba S id in g a r e p ro b a b ly r e l a t e d to th e same p ro c e s s th a t
produced th e fo ld in g in th e L ily M ine.
In F ig u re 15, i t can be seen
that p l o t s o f a l l th r e e p a ra m e te rs l i e on a g r e a t c i r c l e and have a
f lir ly w ide sp re a d p ro b a b ly in d i c a t iv e o f s ^ r p o s i t i o n on ar r r e g u la r
surface.
The g r e a t c i r c l e th a t th e s e p o in ts f a l l on i s co l
ie n t w ith
* * a x i a l p la n e c le a v a g e , s c h i s t o s l t y and bedding t h r o u ^ c u t ...» a re a .
F u r th e r H r > atiuns o cc u r alo n g th e C o n ta c t B e lt (s e e P la t e s 28
Md 2 9 ) .
On th e farm s P e r l , Lovedale and M aude's R ust th e y a re m an!fast
la th e g re n ltfc s b u t a re c o n fin e d to th e im m ediate c o n t a c t.
They are
en tirely a b se n t le s s th a n a q u a r t e r o f a m ile to th e n o r th . The 1 in e a tio n s
l i l t o c c u r in th e above-m entioned a re a a re b e s t s e e n , how ever, in th e
ta f tr u e tiv e c u t t i n g in th e Kaap
v e r a t H oneyhird.
A ll th e s e lin e a tlo n #
plitfge t o th e so u th w est ( F ig . 14J .
ow ards th e w est n ea r th e B ar 5
beacon s tr o n g ly d eveloped lin e a t lo n # o c c u r in th e sh eared in t r u s i v e
g r* tite s and in th e n eig h b o u rin g q u a r t * - s e r i c i t e s c h is t h o r iz o n s . These
plunge to th e s o u th e a s t as do th e o c c u rre n c e s in th e a d ja c e n t J o e 's Luck
Siding g r a n i te s and h o r n f e l s e s ( F ig . 1 4 ).
In th e s e b o d ie s alo n g th e g r a n i te m argins th e p a r a l l e l s u rfa c e s
ire determ in ed by alig n m e n t o f in d iv id u a l c r y s t a l s o f m ica, hornblende
ifid o th e r e lo n g a te d In c lu sio n * o r a g g re g a te s .
P l o t s o f th e U n e a t io n s from th e two s e p a ra te l o c a l i t i e s along
$be c o n ta c t i l f f e r c o n s id e r a b ly In plu n g e d i r e c t i o n but n e v e rth e le s s ,
fern two maxima * T hese c o n c e n tr a tio n s a re seen to l i e on th e a x ia l
plsne o f th e l a t e p h ase c o n ta c t g r a n i te fo ld in g (s e e F ig , 1 4 ). I t tm jld ,
there f e r e , appear lo g i c a l t h a t th e fo rm a tio n o f th e li n e a r f a b r ic and th e
fsMing alo n g th e c o n t a c t w ere conterpor% neeus.
(e )
Deformed C onqlO M tratf P e w i t s
T m l o c a l i t i e s e x i s t w here b a s a l co nglom erates o f th e doodles
Sfstee a re f l a t t e n e d and defo.m ed.
The f i r s t o f th e s e i s th e L ily
^
'
i-
S ynelinr where a g r e e t th ic k n e s s o f
th e fo rm a tio n i s couposed o f
mer a t e s and q u a r t z i t e s .
The
second l o c a l i t y o c c o rs to th e south
of th e L ily S y n c iln e and com prises th e b a s a l conglom eiate o f the Eureka
Sync l i n e .
The b a s a l conglom erate forms th e lowermost in i t o f the
Moodies S y ste m .
The co n g lo m erates in th e L ily S y n c iln e have a c q u ire d , in
ad d itio n to th e f l a t t e n i n g , a f o l i a t i o n , due to th e "d rag g in g o u t" o f
the p eb b les i n t o e lo n g a te d , as w nll as boudinaged form s.
The com ponents a r e t i g h t l y cem ented to g e th e r anc, few
in d iv id u al p e b b le s can be e x tr a c te d w ith o u t them b re a k in g .
I t was
thus Im p o ssib le to a c q u ire any specim ens f o r th e purpose o f stu d y in g
the e x te n t o f d e fo rm a tio n .
The second o c c u rre n c e i s e n t i r e l y d i f f e r e n t , in th a t th e
pebbles a re c o n ta in e d In a le s s com pact, more f r i a b l e m a trix o f impure
shale and q u a rtz i t # , w ith th e r e s u l t t h a t on w eathered s u rfa c e # pebble#
My be f a i r l y e a s i l y f r c e f.
However, owing to t h e i r extrem ely
fractu red n a t u r e , o n ly a few a re unbroken on rem oval.
The p e b b le s exposed in th e ro ad c u t tin g s n ea r Sheba 3 i *<ng
v*ry c o n s id e ra b ly in s iz e and shape ( see P la t e s 30 and 3 1 ) .
They
co n sist o f a g r e e t / a r i e t y o f rock ty p e s ( see Moodies S y ste m ). Jto«st
eeeem ere p e b b le s o f c h e r t .
I t was n o te d t h a t d i f f e r e n t rock ty p e s
«xhibited d i f f e r e n t m o u n ts o f d e fo rm a tio n .
The
* t l e gr i t l c
txpestare* e r e
y w e lly
c h e rt p e b b le s a r e most e x te n s iv e ly e lo n g a te d and f la tte n e d
and q u e r tm ltic p e b b le s r e t a i n a more rounded s h # e .
The
e x tre m e ly w eath ered and th e g r a n i t i c p e b b le s w°re
decom poted to e x t r a c t from th e co n g lo m erate.
The p e b b le s a r e a lig n e d w ith t h e i r long exes (A
mlm#img nearly v e r t ic a l.
The 'ah' planes o f the pebb . ,
a
F W l e l to t h e p la n e o f th e bed d in g .
28 r e p r e s e n t a ti v e
formed
chart pebble* w ere o b ta in e d from th e c u t t i n g and th e meas fere^ ta
#f their aw .r (A ), .n te ^ e d ia te (B) and minor (O axes were not
Unde formed b a s a l conglomerates o f th e Iteodies Systeffl o cc u r
* A a marherton @hla-lo-WgWiu Dm road and nusarous pebbles fro#
M s horlaon **re obtained by M. J . V iljoen and the w riter, for *na
M#a$e e f comparing them sdth the dafarmad pebbles.
The pebbles
oonalsted o f c h e rts, bended c h erts, greywackes, quartzites
W y a m te a .
r
i
—
a.
C r .t,.,
(l)
(11)
c h e rt #rd bended chert
q u a r t : i t * , qray#ackes and g ra n ite .
" " ' " " 'tr u c tK l .n d the * , B ,n d A , c r . ' l o ,
,,
m herlcal mince no n -d l# to rted peb b le, ire Invariably t r l a x la l
ellip ao id * .
The value# fo r A, B and C ware c a lcu la te d u#iM the
formula fu r * u n it e l I ip so id {/Glume o f *] iip so id - 4 W h . B J Z . )
# u b # tltu tln g th e r a tio for the defcrmed and then the
a & k rm e d c h e rt pebb!*#.
^ The a c tu a l form ula f o r c a lc u la tin g th e w i x m e o f m
e llipsoid i s
3
, where a , c mnd a -© present th e holf-.nxes o f
th# un it e llip e o ld .
By using the values A, B and C obtained from the
****** th* problem Is In no way ^ fee ltd a , ra tio s a re i nvn 1ved. The
e & kui^iA n . u#img th e formula
&» halving o f the values for A, B and C.
Mreemt#*## r#*#jn u n sffe c ted .
E x m ^ le i
A, , B; , C ,
"
^ r e l y n e ce ssitate
The u ltim ate answers In
5 : 3 : 1.2
(deforsm d)
( T ift. 1 o v G ra p h s h o v i n g
t h e z e i a t i o z i e h i p e b e tw e e n
t h e A ,B , an d C a x e s o f
u n d efo rm ed c o n g lo m e ra te
p e b b le # .
r
4 ^ " /^
IOC
% 3
^
g
_
24
A^
125
**&
5.4 9
s im i la r l y f o r B| and Cj
R : C
h r th # m d e fo rw d p#bbl## <
"
5
3 *
4 :3
'A
4
3
4 K A
3
x ...4_A £— 2 - i
5
5
%
&<
3^6
#nd mimiimrlY
m.
B and C .
* k n w t l . » in A, ' " " C d l r « t , . r . « '
c .lc u l^
wiag th e r e l i t i o n t i i l p s t
A
x
100
e.
X 100
c,
.
- C *
C
A
:r w ,
h , ih . r M r t .
.
* 9 .2
M p T ..e n t i n , M . x t . n . l w
ln c r,n M o f 4 9 . « .
MY " i u . . 10T B w d C w r . w l t u l . W .
T h, v .lw w
- . b . SW Ing -mr. th u .,i
3.
f. r ^
incr#A&# o f 44 .2 p e r c a n t.
f o r B *f &ncr#a#» o f 12.25 p e r c o n t.
ff y C #
o f 40 .0 3 p e r c * n t.
,.
v
, , , . , : ; ; : : . ™
W t.« * n J n # '* Luck S id in g *nd t w r l k a * .
;
-
-
:
-
sis
iS S iiiig :'
W W lng
1" * 1 " " "
^
it i..
A,
*
.
.
I o n , M l . o ( d e k r m o d p . W » l « »nd
I o n , M l , o ' u n d .fo r « P d p « h W . . ,
— —
UW t o ^ x , . c .
«1 .
th . p .b b l« .
^
F a u ltin g is not w r y e v id e n t in thu ir e a ind only minor
d is lo c a tio n s o ccur t h a t are rxssocistod w ith th e f o ld in g o r tho
in tr u s io n s .
M ention has boen made, both In th e s e c tio n s on th - L’ ly
Mins and th e Economic G eology, o f th e proposed a d d itio n to th e ax 1s tin g
geo lo g ical map o f th e a r e a , o f s f u r th e r lo n g itu d in a l t h r u s t f a u l t , v iz .
thy L ily F a u l t .
Reasons fo r assum ing the p resen ce o f t h i s f a u l t arv
eleo g iv e n and I t w^s m entioned how such a f a u l t wouH f i t in to the
«xi$tim> p a t t e r n o f
.tin .^ in th e B a rb e rto n M ountiln Land.
There i s some f i e l d ev id en ce to support th e idea o f a f a u lt
Immediately w i t h o f th e q u a rtz i t s -tonglom er a te h o riz o n o f th e L ily
Syncline,
Mi>ch o f th e a rea 5 s , how ever, o b scured due to masking by
scree f a l l i n g berk and co v e rin g th e c r i t i c a l zo n e .
The q u a rtz i t i c
toefcs o f th e L ily S y n c lin a a re f r e q u e n tly m y io n itic along th e c o n ta c t
with tho b a s ic r o c k s .
M ention ho# been made by de S i t t e r (1956) of
thick m y io n itic zunes n ear o r a d ja c e n t to t h r u s t f a u l t s .
The proposed
fs u lt in th e a re a mapped would be conform able w ith th e so u th e rn lim b o f
the s y n c iln e .
Th© arcjisneut in fav o u r o f th e p re cnce o f th e f a u l t h a s been
•tren g th en ed by th e w r k done in th e adjacem : s e c tio n o f tho L ily
Syncilne betw een Noordk imp and J o e 's Luck S id in g .
Here V iljo e n
(w Tbal com niunication) mapped a s tro n g f a u l t fth o Main S o u th ern F a u lt)
B a t tr u n c a te s th e q u a r t z i t e block o f th e w e^torn e x tre m ity o f th e L ily
S fftclin*.
The f a u l t t r a c e was found to be f i l l e d w ith v e in q u a r t z .
In a d d itio n th e sequences to th e south e f th e fsul*: were fu and to be a
et* p lete r e p e t i t i o n o f th e s tr a t ig r a p h y a s i t o c c u rs to th e ix?rth o f th e
q u a r t* ite s .
The f a u l t i s co n s id e re d to be a h i # anqlt lo n g itu d in a l
tte u s t f s u l t w ith th e u n d e rly in g su c c e s s io n s up throw n to th e s o u th .
The p re s e n c e o f th e f a u l t p ro v id e s tho most s u ita b le
explanation o f th e s t r a t i graph le a l p ic tu r e p re s e n te d In th e f i e l d .
The o c c u rre n c e o f in t r u s i v e s e r p e n t ln it o in th e a re a s to th e
nertiieaet and n o rth w est o f Eureka S id in g may re p r e s e n t I n tr u s iv e
M ie s e e p le c e d *]ong th e zone o f f a u l t i n g .
O radod bedding In th e s h a le # ind graywacke# o f th e F lg - tr a e
Sarla# ### o f uw In d * te ,a ln i n n th e d i r e c t i o n o f y o u rg in g from th e
bwiie s c h i s t s but i t could not be used als^ w h c re .
F lo u r# T in d i c a t e # , dlng.-ammm tlcall/, s e c tio n # th ro u ^ i th e
The r o la tlo n W ilp o f th e f a u l t s to th e sy n clln * * and a n t i c l i n a l
divid# a r e a ls o I l l u s t r a t e d .
A d d itio n a l s tr u c t u r e s in tho i r e a nre e s s e n t i a l l y o f p. lo c a liz e d
nature and to r e produced c o n te u p o ra n e o jsiy to g e th e r w ith tho major
stru c tu re s Tho fo ld in g i s p r a c t i c a l l y a l l o f a claav ag e o r s im ila r
type v#tere compress Ion has been th e maximum defo rm ativ e f o r c e .
O ften
rts o e ia te d w ith th e s e fo ld s are boudinaged s tr u c t u r e s on th e fla n k s th a t
are produced by th e e x te n s io n and b reak in g up o f th e more co m .sten t u n it
layer#.
Minor p a r a s i t i c f o ld in g i s c o n c e n tra te d in tho c r e s t s o f th e
larger f o l d s .
T y p ic a lly th e se sm all s c a le s tr u c t u r e s a re W 01 M shaped
In the h in g e i t s e l f w n iie on th e fo ld lim bs they a re Z o r S shaped.
S tru ctu res o f t h i s ty p e w ere noted both in th e L ily Mine and in th e
Kssp R iv e r c u t t i n g .
From both f i e l d o b s e r v a tio n s and th in s e c tio n study i t i s
e ir ts ln t h a t th e r e h a s been a c o n s id e r a b le amount o* f l a t t e n i n g and
shearing w ith th e r e s u l t a n t fo rm ation o f a stro n g s ' h i s t o s i t y th a t has
i f a i r ly uniform r e g io n a l t r e n d .
R e c r y s tF llU a tlo r i in the form of
ties# ta k e s p la c e In th e cle a v a g e p la n e s .
Advanced s c h i s t o s i t y i
'sm ifv s t when f in e bedding i s t o t a l l y o b l i t e r a t e d by r e c r y s t u l l i t e t l o n
of q uart* i>» m . l a s m ica.
The s tro n g r e c r y s t a l l i z a t i o n in th e
asp h ib o lite zones i s m ostly iue to therm al a c tio n r e s u l t a n t from
s a g ^ tte a c t i v i t y .
The te x tu r e o f th e rock how ever, i s pro b ab ly due
to dynamic f o r c e s .
The deform ed f a b r i c s are dom inated by a s c h in to s ity
Aieh i s ID r e r e a d i l y c o r r e l a te d w ith com pression normal t o , r a t h e r than
•Mi s h e a r p a r a l l e l to th e s c h i s t o s i t y p lu iie.
P la t e s 6 and 7 show co m p o sitio n a l b in d in g o f th e s c h is U in
&# contact s n ^ h ib o l ite zone and the d e v e lo p ra n t o f b o udins.
J o in tin g # m entioned elsew h ere in t h i s r e p o r t , i s fre q u e n tly
wtn and h as a c o n s ta n t d i r e c t i o n o v e r most o f th e a r e a .
I t was shown
th # j o i n t # fa v o u r a tr e n d a t r l f i t a n g les to th e g r a n i t e c o n ta c t
wd are e s p e c i a ll y m a n ife s t in most o f th e r i g i d ro c k s .
The j o i n t s
%Of be re g a rd e d a s * a - c ' te n s io n jw in'.e in d i c a t in g th a t th e g e n e ra l
ib ie s -te ceasary f o r t h e i r fo rm ation p ro b ab ly came from th e d ir e c ti o n
sf the g r a n i t e s .
The s t r e s s pro d u cin g many o f th e j o i n t s was r e t th e
m s a# t h a t r e s p o n s ib le f o r th,. f o l i a t i o n a# j o i n t p ia n e s c u t th e
M is tio n and even a c t as sm all f r a c t u r e s alone which th e r e h a s been
<te¥ssBnt ( s e e P l a t e 4 ) .
The j o i n t i n g , o r at le a s t some o f i t , was p ro b ab ly one o f th e
#v*nt* *n th # a re a a s i t i s seen in a l l form ation# and In th e
b b # l v # dyk##.
Two o r even t ^ r e t d ir e c tio n # o f j o i n t i n g may #omet#**# be seen in th e same o u tc ro p ( sea P la t e 5 ) .
A long th e in t r u s i v e c o n ta c t th e r e is a p re v a le n c e o f
ptygm atlc s t r u c t u r e s and c o n to rte d g r a n i t i c and p e g m a titlc v e in s . They
ire g e n e ra lly seen m eandering about th e dark c o n ta c t am p h ib o litic
ic M -'is .
"Hie ptygm as appear to be independent o f th e te x tu r e o f th e
h a st-ro c k and a lth o u g h th e v e in s appear to be fo ld e d about a x ia l p la n es
that a re c o n s is te n t and r e g u l a r ly a lig n e d , th e araphibole s c h is to s it y
s?ees u n a f f e c te d exr© pt around th e m argins o f th e pty$pa i t s e l f (see
M ates 34 and 3 5 ) ,
de S i t t e r (1996) a t t r i b u t e s th e uause n f th i s
p e c u lia r ity to to e d i f f e r e n t r e a c tio n in th e s t r e s s f i e l d o f v ein and
best ro c k m a te r ia l i
each p o s s e s s in g d i f f e r i n g p h y s ic a l p r o p e r t ie s .
ih )
R e g io n a l S tr u c t u r e E f f e c ts on th e M ineral l o c a l l r a t i c n
Between Shehe S id in g and Louw's C reek i t i s b e lie v e d th a t th e
gBld m i n e r a l is a tio n was in tro d u c e d along th e l i l y F a u lt zone by
hydrotherm al s o lu ti o n s a s s o c ia te d w ith th e N e )s p ru it G ra n ite in t r u s i o n .
k look a t th e re g io n a l map in d ic a te s t h a t th e g e o lo g ic a l
- t r s i o n s in
a re a a re f a i r l y r e g u la r and tha% no ap p a re n t c o n t r o lli n g ‘ a c to rs are
evident to e x p la in th e l o c a l i z a t i o n o f th e gold in to w orkable o re
fc p o sits such as th o s e o f th e L ily and Rose*; F o rtu n e M ines.
P ro s p e c tin g hmy ta k en p] ace In a w e s te rly d ir e c ti o n from th e
Lily Mine and two o th e r sm all b u t very e r r a t i c o c c u rre n c e s have in th e
p u t bef-n mined on tn e farm s Avoca and C r y s ta l S tre # # e a s t o f Eureka
*##*.
T hese d e p o s its a ls o o c c u r in a p p a re n tly r e g u la r form ations
Wl #m e x p la n a tio n o f t h e i r w hereabouts i s not ea sy to d x p la ia .
A
farth er d i f f i c u l t y in v o lv ed i s t h a t th e m in e ra liz e d f a u l t zone o ccu rs
la a v a l le y where o u tc ro p s a re f a r from id e a l f o r th e a tta in m e n t o f
# t a r e l a t i n g to th e d e p o s it s .
A ll t h a t can be attem p ted in an e x p la n a tio n i s to p o in t out
* r t n n * lo c a li z e d d is tu r b a n c e s '1 t h a t may escape a t t e n t i o n on th*
i if c g te a l and s t r u c t u r a l maps accompanying t h i s r e p o r t .
The la r g e s t
9f t;.eee #o c a lle d " d is tu r b a n c e s " o c c u rs im m ediately n o rth o f th e *-ily
4tiw where th e q u a r t z it e - c o i^ lo m e r a te h o riz o n h as a s l i g h t i n f l e c t i o n .
W e i s a marked d if f e r e n c e in bedding o r i e n t a t i o n o v er a s h o rt
Hit a n te w ith in th e i n f l e c t e d zone and th e s t r i k e a l t e r s from E.N .B.
■» n s M .
4%%
*4 In eg
te
'v, U n a
is
I t i s n o t u n lik e ly t h a t th e e f f e c t o f th e g e n tle w arpina
boen tr a n s m itt e d t h r o u ^ th e a d ja c e n t ro c k s to th e south
th e F i g - t r e e ro c k s in th e mine a r e a .
The b r i t t l e q u a rtz s c h is t h o r iz o n n o rth o f th e mine a lso d is p la y s u in n r o b liq u e
t h a t may be r o ta te d to th e d is tu r b a n c e .
The sm all f a u lt
q Uar t t f i l l e d b u t th e r e i s no evidence o f any displacem ent of
the fo im a tio n s.
The e x a c t a i fe e t such a small d is tu rb a n c e as o u tlin e d
above would have on th e p r o v is io n o f s u ita b le lo c i fo r m ineral concen­
tr a tio n is d i f f i c u l t to im ag in e, but i t i s li k e ly to have c o n trib u te d
te o r a s s is te d in th e rearra n g em e n t and d is lo c a ti o n o f th e fo rm a tio n s,
tfcye ask in g them more a c c e p ta b le to subse . if d e p o t' ti o n and c o n c e n tra ­
tion o f o re form ing f l u i d s .
I t may sim ply be c o in c id e n c e out th e fa c t re m a irs t h a t each
of th e e x p lo ite d d e p o s its to d a te a re lo c s te d im m ediately icuth of
f a s tu rs s (how '- ; r s l i g h t th e y msy b e) seen in th e ro c k s n o rth o f tiie
F ig -tre e s u c c e s s io n .
North o f th e R o s e 's F o rtu n e .Mine th e Onverwacht sequence o f
< p * r tt- s s r lc l te s e M s t s b rc rK \e s in to tw3 s e p a ra te u n it s w ith b a s ic s c h i s t s
flU in g th* wedge betw een th e two lim b s .
No evidence to e x p la in t h i s
s p lit could be fo u n d , b u t th e s t r u c t u r e may r e p re s e n t th e a n t i c l i n a l
divide between th e L ily S y n c iln e nnd th e fvrr,.atlons to th e s o u th ,
A f u r t h e r example o f g e ld d e p o s its accompanied by a
corresponding i r r e g u l a r i t y in th e n o r th e r ly fo rm atio n s can be -.sen
M ft e f Eureka S id in g .
H ere th e L ily S y n c iln e i s g e n tly buckled in
I g reat a rc u a te shape convex to th e su c c e s s io n s in th e south ( see
3 ).
The L ily S y n c iln e and th e E ureka S y n c iln e a re n e a re s t
t# one an o th er In t h i s a :ea and th e in te rv e n in g Onverwacht and F ig - tr e e
rocks a re n a rro w e st alo n g t h i s com pressed zo n e .
The o ld w orkings o f
the Mexican and C le o p a tr a Mines o cc u r in t h i s l o c a l i t y .
I t i s c l e a r from e a r l i e r m entioned s tr u c t u r e s t h a t th e r e d ie
several v a r i e t i e s and s t y l e s o f d e fo rm a tio n e x i s t e n t in th e a r e a .
.in
the Ne# C o n so rt Mine - J o e 's Luck S id in g a re a th e se s tr u c t u r e s are w ell
foeiooed and w ere f i r s t In v e s tig a te d by Ramsay (1963) who was a b le to
heeg n ix e th r e e p h a se s o f d e fo rm a tio n .
L a te r M. S M ljo en 's In v e s tig a ­
t e # le d hi® t o b e lie v e th a t fo u r p e iio d s o f d efo rm atio n in f a c t ,
• tilte d In t h i s a r e a .
AlthvU^h o ccu rrin g adjacent to th i s e x ce p tio n ally tecto n lzed
m w th e Sheba S id in g - Louw's C reek a re a Is com paratively devoid of
f t m t a r a l p aram eters.
The w rite r who w rk e d in c lo se co lla b o ra tio n
sttti M. V iljo e n was able to recognize c e r ta in s ty le s lw ila r itle s n
sA ro t s tru c tu re s th a t were comron to both regions mapped. It is
H t h th # # # s i m i l a r i t i e s in mind t h a t an atte m p t * aa mad, to
t t v ttl a te th e s tru c tu r a l ev en ts.
I t i s g e n e ra lly a c cep te d by most g e o lo g is ts who have examined
y$e s tr u c tu r e o f th e B a rb e rto n Mountain Land, th a t th e r e g io n a l tre n d
sf tii# P recam brian fo rm a tio n s in th e a re a was I n i t i a t e d by th e f i r .i t
disstrophle e v e n t.
(i)
iiia L iM M
The f i r s t s ta g e o f d efo rm atio n was re s p o n s ib le fo r th e
development o f th e ra a jrr synel?.nes t h a t tre n d in a n o rth e a s t-s o u th w e st
directio n , th e com pression b ein g d ir e c te d from th e n orthw est and s o u th lis t.
The m ajor higfi angle lo n g itu d in a l t h r u s t f a u l t s are th ought by
IIBSiy (1963) to be c o in c id e n t w ith th e f i r s t p e rio d o f f o ld in g .
The
Lily S y n ciln e i s c o n s id e re d to have o r ig i n a te d d u rin g t h i s p e rio d .
IgMiy (1 9 6 3 ) mentioned th e d i f f i c u l t y o f re c o g n iz in g th e s tr u c tu r e s
M the n o rth e rn s id e o f th e E ureka S y n c iln e .
He b e lie v e d ho'"ever, th a t
tw larg e f i r s t fo ld s e x is te d t h e r e .
These are the Woodstock A n tic lin e
tad ■ sync l i n e which he th o u g h t might p o s s ib ly be th e c o n tin u a tio n o f
tiw Lily S y n c iln e .
As th e p r in c ip a l s t r e s s d i r e c t i o n was o p e r a tiv e a t r i g h t
•Sglte to th e r e g io n a l tr e n d , th e g e o lo g ic a l su ccessio n s in th e area
a a h n u n t c o n s id e ra b le f o ld in g , s h o rte n in g and f la t t e n i n g .
The f i r s t phase cannot d i r e c t l y be s*en in th e area
im estig eted b ut i t nay be assumed o r deduced from th e sp read on a g re a t
elfsle o f p a ra m e te ru b elo n g in g t o th e second p h a s s .
T h is sp read
iMtteates t h a t i r r e g u l a r s u r f a c e s e x i s t e d b e fo re th e st r o n g development
•f • c le a v a g e , s c h is to s it y , f l a t t e n i n g and metamo-yhlsm.
The L ily
?wlt rod th e Main S o u th e rn F a u lt among o th e r s %n pro b ab ly be
*#»ei#t#d w ith th o f i r s t fo ld in g .
I t i s a lso c o n sid e re d l i k e ly th a t
% basic and u it r a b a * i c ro ck s 1.) uhe a re a were e^ > ia -d e a rl y in th e
fWsyncllnel te c to n i c h i s t o r y c «' t h e Mpur' a i n la n d .
Many la rg e b a s ic
o f te n o cc u r as mast** n r s h t e t s c'-.nc'rdsnt w.in t h e s tr u c t u r e
•f tfee e n c lo s in g s tr o n g ly fu id ed r e c k . .
In '■> few In s ta n c e s th e b as ic
**&# are kmwn to i n t r w * lr* u t r
- ' ' " j Cystnm r o c k s , out cro& se* t i n | ^ t l a t l o n i h i p s f t z - o - r e r a l l y
- .v.
The u l t r a b a s t c rocks
been aqueazed up iJ s n g n ajo v c l s l r . - r l .
devej m ed In th e
W W nelinal baaement d u rin g th e o n s e t o f f o l d i n g as p ic ^
by
a^u
]quo te d i n T urner a%%d Ver+wogen, 1% 0)
(iU
Second Ph
ip p to x if lw te NNW - bSF. d i r e c t i o n .
The tig h ,' fo lc .rig o f th e L ily Sync lin e
Mid F i g - t r e e S e r i e s , I n l t l a 1e d in th e f i r s t s ta g e , v is in t e n s i f i e d .
Ti.e
o eepussion was p ro b ib l> re s p o n s ib le t o - : d i f f e r e n t i a l v a r ia tio n o f
movement i n t h e N 1 dii-e.-.t.ion o f th e is o r l j n«-.l fold# In th e l i l y Mine and
i d j ie e f i t F ig - tr e e ro c k s
L ine a t io n s w r e produced ee r'.y on in th e q u e r t z - s e r i c i t e s c h is ts
asftii u f E ureka S ld in r and a stro n g f r l i f d o n and s c h i s t o s i t y in th e
fom stions was i n i t i a t e d by th e dynamic in flu e n c e s .
Ramsay (1063) a t t r i b u t e d th e numerous fa b ric s '.lev#loped o ver th e
*ele ares a s la r g e ly r e s u l t i n g from s t r a i n s u ffe r e d by th e n cks du rin g
the second ph«.se o f de form at io n .
He showed r e g io n a lly th a t th is second
phase produced a « la ty c le a v a g e t h a t c ^ o s s -c u t th e f i r s t formed fo 'd s and
sss best seen In th e E ureka and Ulundx Syncllnes,
W ith in th e a re a d ia v u sse d in t h i s r e p o r t in d ic a tio n s o f th i s
phase a re seen in th e e lo n g a tio n and o r i e n t a t i o n o f th e long axes o f th e
oengloaerete p e b b le s a t Sheba S id in g ,
The p eb b les a r e f la tte n e d in the
pline o f th e bedding and produce a li n e a t io n th a t p lunges s te e p ly (s e e
Fig. 1 5 ).
Ramsay n o te d s im ila r deform ed and li n e a r o r ie n ta t e d p eb b les
Kmih o f t h e Keep R iv e r, w est o f J o e 's Luck S id in g .
A lthough c le a v a g e i s a p p a re n tly a b sen t i t i s li k e ly to be
e&Stelned v i t h l n th e bedding p la n e s .
The d i f f e r e n t i a l sh e a rin g o f th e
i b l U i n th e I l l y Min# i s c o in c id e n t w ith bedding p la n e cle a v a g e (se e
Piste U ) .
I t h as a lso been shown e a r l i e r ( F ig . 15) how I t is
m s id a re d t h a t th e fo ld in g in th e L ily M ine, th e li n e a t io n s no rth o f
le a k s S id in g and th e p eb b le l i n e a t io n s ft Sheba S id in g a re I n t e r Ramsay a ls o p o s tu la te s th e in tro d u - t i o n a t t h i s s ta g e o f th e
S r e i i t e i n t r u s i o n and th e main p e rio d o f m in e r a liz a tio n . He
fardi stro n g s t r u c t u r a l co n fo rm ity between th= s la t y cle a v a g e in th e
W W Uwrphosed se d im e n ts , th e s c h i s t o s l t y o f th e p h y l l i t i c ro ck s and
W® w ith in tile g r a n i te s th e m s e lv e s.
W ell developed te c to n i c
•tmtures p ro b ab ly developed w h ile th e g r a n i te was c r y s t a l l i z i n g .
I f n ts s r e th o u ^ it to have been b ro ad ly synchronous d u rin g th e second
d e fc ra w tie n b ec au se th e r e i s ev id en ce n o rth o f E ureka S id in g of
« fnw iite o r o p l i t i c v e in c r o s s - c it in g and, th e r e f o r e , p o s t- d a tin g
%e iin e e tio n s in th e q u a r t z - s e r i c i t e s c h i s t h o riz o n . The lin e a tio n s
WW&iy fu m e d e a r l y on in th e h i s t o r y o f th e g r a n i te emplacement
W the v e in seen in th e q u a r t * - s e r i c i t e s c h is t v ery li k e ly r e p re s e n ts
* W # p h ase i n t r u s i v e .
A f u r th e r l a t e p hase e v e n t is p robably
in the folding o f th e granites along the con test.
Mtprult
T h is f o ld in g , c l e a r l y seen in th e Kaap R iv e / c u t tin g was
responsible t"sr th e p ro d u c tio n o f li n e a t io n s th a t appear to be confined
lo ltiy ^ th f c o iit,je t zo n e .
The f o ld in g , o f a s im ila r ty p e , is thought
t@ havf been produced in th e g r a n i te s ana <Mflphibo 1 it.es v*iile th e
lf*rv*ives w r e in a s e m i- p la s tic s t a t e .
The in tru s io n o f th e N e ls p ru it G r a n ite was re s p o n s ib le fo r th e
p.oduri la n o f th e metaflior^riic f a h r i c s in th e a d ja c e n t fo rm a tio n s . The
intensity o f the therm al aureole d e c re a s e s away from th e g r a n i te co n tact.
In th e L ily Mine the alignm ent o f in d iv id u a l araphibole c r y s ta ls
*as p a rtly developed by dynamic metamorphism and f l a tte n in g duo to
M h^m ssion and p a r t l y due to th e rm al metamorphism a s s o c ia te d w ith the
in tro d u ctio n o f th e hydro therm al m in e r a liz in g s o lu tio n s .
( iii)
T h ird Phase
Th# * # jo r event in the Mountain Lend d u rin g th i# #t#oe *m* the
gieet in f l e c t i o n o f th e E ureka and U lundi S y n c lln e s .
Ramsay ( l% 3 )
( a m i s le ty cleavage and s c h i s t o s l t y folded b / la rg e and small se a l a
Saids.
The co m p ressiv e s t r e s s e s were found to be i t right arm ies to
the e a r l i e r deform ations v iz . from th e n o rth e a s t i i so u th w e st.
The
Lily Sync l i n e was p ro b a b ly in v o lv ed in a swing from ME - SW to an
H « o x isate east-w est d i r e c t i o n .
In ad d itio n to th e m ajor f o ld i n g i t i s li k e ly t h a t th e fo ld in g
#f A# #r#m mrthweat o f Sootia Talc Mine can be related to th* same
parted o f distu rb a n c e although i t should a lso be borne in mind th a t the
WWwct&on e a r lie r o f the b##lc intru sive mew probably had the
ft tite fi in flu e n c e in th e lo c a l d efo rm atio n o f th e region.
( iv )
F o u rth Phase
Aweey (1963) coneidered that the development o f conjugate
Wd*
eYndmomv* with the format ion o f the arcuate atrvcture o f tne
Iwefc* and U lundi S y n c lln e s .
He was how ever, not em phatic «fc°ut th U
W #e#n0 , l 0 ,| th et they mey po at-date the 3rd Phaae and be related to a
I n t Qi period o f d e fo rm a tio n .
S ubsequent to Ramsay's wor^ s e v e ra l
&*#0 &l#etor# have awntloned the occurrence o f conjugate folds prrducing
tid ia r s tre s s d ire c tio n s .
The c o n ju g a te f o ld s were noted -rom w idely
I n th e r e p o r t a re a nu m ro u s c r e n u la v k n f o ld s , o fte n
t66Mp«!iied by a few c o n ju g a te f o ld s , were n o te d .
I t r.ae been showr,
• e t i e r how t h f ,e m iner s tr u c t u r e s I n d ic a te th a t a v e r t i c a l o r near
wrtieal wrea# f ie ld e x iste d in th e a re # .
A lth o u ^ i th e maximum
itresa ap p e ars to have baen o p e r a tiv e in the i.inge zone o f th e Eureka
Syaeline and a re a s to th e n o r th , i t i s n e v e rth e le s s m a n ifest to a
d e g ree In ad jacen t re g io n s .
F in a lly a t a much l a t e r .tag * jo in tin g a ff e c te d th e form ations
ini la te in tru siv e # .
I t is l i k e ly t h a t a l l th e p h ases o f d eform ation
ire r e l a te d to one c o n tin u o u s d ia s t r o p h lc event p o s s ib ly connected w ith
A# updoaifly o f th e g r a n i t e s .
The Sw aziland G eo lo g ical Survey
(M#*er, 1961) re c o g n iz e s th e f a c t t h a t the G% gran ite# a re th i youngest
intrusive g r a n i te s s o u th e a s t o f th e B arb e rto n M ountain Land
They
i?e dated a t between 2.200 - 50 m .y ., and 2,680 - 340 m .y ., W A lls o p p ,
bhlAs #«d S c h rein er ( l% 2 ) .
The i n t iu s io n o f th e s e g r a n i te s
tiwreteTe, may h a w been re s p o n s ib le fo r th e v e rtic a l p re s s u re s th at
podved th e h o riz o n ta l a x i a l p la n e s in th e minor fo ld s t r u c t .-'en.
la* sucoeeeive event e ith .e r re ju v e n a te d p re v io u s s tr u c t u r e s such as
invite and fra c tu re s o r o b l i t e r a t e d e a r l i e r formed phenomena.
Seatlnuoua re -o rie r^ .a t^ m o f s tre s s f i e l d s produced by d i f f e r e n t i a l
■mwiit o f th* u^w elling *a#s m ight e x p la in th e v a rie d s tr u c tu r e s
tWR In the f ie J d ,o d a y .
S u b d iv is io n o f th e d i a s t r o p h i w in to
#eeeaaive p u lc * i o r p h ases serves th e u s e fu l p-irpose o f em phasising
‘M main events t h a t to o k p la « e and r e l a t e s th*m c h ro n o lo g ic a lly to
m w e tiie r.
(•)
in to to U a n
A p art from th e gold occurrences in th e a re a th e r e a re se v e ra l
W$1 t i e s where th e non-m etallic m in e ra ls megnesite ami t a l c have been
* •4 In the p a s t.
The S c o ti a Talc Mine near Sheba Siding i s i t
RHer.fc being worked on a small s c a le .
I n t e r e s t was again showr, in th e n ic k e l o c c u rre n c e northw est
on th * farm Bon A ccord, d e s c rib e d by P a r tr id g e ( 1942).
^%*ba S id in g
I t 1# p ro p o sed in t h i s aectlo n to b rl* fly mention th*
**ime ere
d e p o s its and t h e i r economic i .p l i c a t i o n s .
- 90 -
(b)
Maaneslte
Magnesite o c c u rs n ear Sugden S id in g on th e farm Annex
Riverbank.
I t i s found as a compact o r amorphous v a r i e ty in vein s
ramifying th e a l t e r e d b a s ic s e r p e n t i n i t e .
Two m agnesite b ea rin g
i s m s w ere n oted w i t h i n th e s e r p e n t i n i t e body.
These zones h a d an
approximate e a s t- w e s t s t r i k e d ir e c ti o n and d is p la y e d o n ly ir r e g u la r
stowings o f m a g n e s ite .
Numerous tre n c h e s a n d p ro sp o o t w inzes c cur
la LUe a re a o ut t h e m in eral was o n ly rained from two sm all q u a r r i e s ,
one in t h e e a s t and t h e o t h e r , a n d la r g e r o f th e tw o, in th e west near
to Sugden S id in g ,
The d e p o s its were d e s c rib e d by van Z yl e t . a l(l9 4 2 )
tfd sin c e t h a t tim e l i t t l e o r no f u r th e r mining has ta k en p la c e .
The e a s t e r l y quan-y d id not appear to bw o f any s ig n ific a n c e
#md wore a t t e n t i o n was devoted to th e w e s te rly o c c u rre n c e . The quarry
W tre n c h e s d is p la y “ ze b ra o r e " , I .e . a l te r n a t in g narrow seams of
ssskhered s e r p e n t i n i t e and m agnesite (s e e P la t e 2 2 ).
The m a g n esite seams vary from a ^-Inch t o 2 in ch es in width
md *r*: In c lin e d a t shallow angles to th e n o r th .
The seams ir e
Mpareted by d ir ty brok’i a! a ad s e r p e n tin ite y 3 to 4 inches in w idth.
ThWasr v e rtic a l o r n ea r v ? t i c a l , seams o f magnesite i n t e r s e c t th e
atrrott seams a t rig h ^ ang.e j .
A lthough a s h a f t e x i s t s in th e c entre
sf tile quarry ther** ' i no ev id en ce o f th e depth o f th e body. Abundant
magmaslte s t i l l r « r • 3Xposed in the q u a rr y .
Much o f i t i s pure
* l t e festt the g r e a t e r par*, i s di s co lo u re d due to im p u ritie s.
The
pe# m ag n esite has a poi^nllaneous te x tu r e while- the re r s iin d tr is
# ath y .
I n t h i n s e c t io n th e w eathered s e r p e n t i n i t e shows ab undw t
M tig s r ite , m a g n e tite and c a rb o n a te m a t e r i a l .
In a d d i t i o n se v e ra l
iliarad d i v i n e c r y s t a l s w ere n o te d .
The m agnesite has a p p a re n tly formeJ from an o r ig i n a l u Itr a NdUs In tru siv e by p ro c e s s e s in v o lv in g chem ical w e ath erin g and th e
in filtra tio n o f carbonate w aters which have r e a c te d with th e magnesium
s e ip e n tin ite s .
In a d d itio n to th e occurrences n ea r Sugden S id in g f u r th e r
W &eatlona o f m agnesite were found to th e n orthw est of th e S c o tia
ftk %ne.
Magnesite bearing s e r p e n tin ite is exposed on the west
h * of th e r iv e r c u ttin g .
Much o f th e s e rp e n tin ite has bean
t o # yallowlah brown earthy colour and Lha megnesite on
Wrf*e outcrop appears impure.
Large s e r p e n t i n i t e i n t r u s i v e bodies occur In th e w es ter n
portions o f th e a r e a .
Not in f r e q u e n tly a s s o c i a t e d w ith th e s e serp en ttn ite s a re to n e s o f t a l c .
P ro sp e c t tre n c h e s are f re q u e n tly encountered
are c e n tr e d around th e S c o ti a T alc Min< .
The d e p o s it a t S c o ti a T alc i s s itu a te d between twD q u a i t z i t e 6»agloserate bands o f th e L ily Sync li n e in a zone o f in t r u s i v e , a lte r e d
s e rp e n tin ite .
The mine was developed e a rly t h i s c e n tu ry and was worked
p v m tly by Union C o r p o ra tio n .
I t is a t p re s e n t being worked p r iv a te l y .
The t a l c o c c u rs as l e n t i c u l a r b o d ie s th a t pinch and sw e ll from
iiitfece o u tc ro p s to an unknown d e p th .
These b o d ie s, of which th e r e are
t # kmwn o c c u rr e n c e s , c o n s is t o f t a l e i " a v a r i e ty o f g reen and gr*y
e ileers.
The l e n t i c u l a r b o d ie s ir e seldom w ider th a n 30 f e e t and an
M M## width o f 15 f e e t i s e s t i m a t e d .
In c o n tr a s t w ith th e w all lock#
sf sE F p en tin ite a,id c a lr a r e o u s s e r p e n t i n i t e t h e o re zone i s in te n s e ly
M ild and shows siic k en sld e d s u rf a c e s in d i c a t iv e o f stro n g sh e a rin g
te rs tw e .
The c o n ta c t between the com m ercially re c o v e ra b le t a l c and
IN * 1 1 rock i s sh arp in th e low er l e v e l s .
L a te r a l G rad atio n in to
Npwe ta ic o s e m a te r ia l u f uneconomic g rad e o c c u rs in th e upper reac h es
sf the d e p o sit.
The two l e n t i c u l a r b o d ie s knrw:, as th e N orth and 'o u th bodies
W p e e tiv e ly , a re s e p a ra te d from one a n o th e r by a narrow band o f ttfiitis h
6Vfc»st*t#-*lch s e r p e n t i n i t e .
G ra d a tio n in to ta lc - c a r b o n a te s c h is t was
ilse en c o u n tered .
The N orth body, th e l a r g e r o f th e tw o, widens o u t from
tarfiee with in c r e a s in g d epth and a t th e same tim e th e q u a l ity o f th e
W# increases s y m p a th e tic a lly .
Th# t a l c mined i* o f a f a i r l y h i # , q u a l i t y , th e only
te llte r ie u s i s p u r i t i e s being t h . b la ck s c h o r l i t e to u rm a lin e t h a t a t
M## I s w r y ab u n d a n t, e s p e c i a ll y in th e d ark g reen t a l c o ^ e .
The
* s t q u a lity t a l c I s g ray o r p a le g reen in c o lo u r .
. T a lc i s reg ard e d a s «#n a l t e r a t i o n p ro d u ct from m ild hydro * * * 1 m et#D rphl#m perhap# aid ed by dynuU c met vm rphlsm and not
^W lW S therir^i (B a t^ n a n , 1958).
I t i s ap p a re n t t h a t th e S c o tia d e p o s it has la r g e ly been
controlled by in te n s iv e s h e a rin g and hydrotherm al replacement from
lelutions th a t p ro b ab ly emanated from th e in tr u s iv e g r a n i te s .
(d )
H ickel
An o c c u rre n c e of t r e v o r i t e , s itu a te d app? .im ate ly 1^- m iles
airth w st o f Sheba 3 id in g on th e farm Bon Acer -j was f i r s t d e sc rib e d as
i tww s lr w r a i by A. F . C ro sse in 1921.
He showed i t to be an ox id e of
if## and n ic k e l.
P a r tr id g e (1943) on re -e x a m in a tio n o f th e d e p o s it,
®ted and d e s c rib e d a lso fo r th e f i r s t tiro s , th e m in eral n e p o u lte , a
tiek el-eag n esia n -h y d rated s i l i c a t e .
Some d e t a il e d r rin e ra lo g ic a l work
tti c a rr ie d o u t on t h i s o r e and P a r tr id g e d e s c rib e d t r e v o r i t e being
replaced by m a g n e tite .
He a lso noted a tr a n s p a re n t m ineral and th e
aiefcel s u lp h id e m i l l e r i t e .
Hn concluded th a t th e o re was a re p la c e
swt ^ A s i t fo rm d by th e in tr o d u c tio n of rick® l b e a rin g s o lu ti o n s .
M ille d p r o p e r t ie s o f th e new m in eral nepoi I t e were given and assays
indicated t h a t t h i s m in eral c o n ta in e d a high p e rc e n ta g e o f n ic k e l and
m th e r e f o r e d e s ir a b le as an o re o f n l c k t i .
Renewed I n t e r a c t in t h i s d e p o s it was shown In 19b2 by Rand
Rae# #1.0 undertook e x p lo ra to r y d r i l l i n g and have s u b se q u e n t!/
Wmdbnad work In th e l o c a l i t y .
B r ie f ly th e geology o f th e a re a
a* fo llo w * .
In tru d e d
into th # q u art* it# * o f th e L ily Sync li n e i s an u J tri. b a s ic body now
#W#& t o t a l l y a l t e r e d to a e r p e n t i n l t e .
Tne I n tr u s iv e m### prob#bly
t#w#d o # n # ld # r# b le ^ d o m in g o f th e a te e p ly d ip p in g r e g u la r #ucce##ion#
ed i## v lt# ft in th e s p l i t t i n g up and s e p a r a tio n o f th e q u a r t z it e
lotltofl* which now d ip a t sh allo w an g les to t Ke s o u th e a s t.
I t 1# c o n s id e re d l i k e l y t h a t th e n lc k a ll f e r o u s m a te r ia l waa
l&#W08#d In to th e a re a as an o r i g i n a l c o n s ti tu e n t o f th e u lt r a b a s ic
3ub#*qu#nt ah a a rln g to o k p la c e In th e are# p ro v id in g
"AtaW# ch m n e l# f o r th# in tr o d u c tio n # t # l # t # r atag e o f hydrotherm al
ml#tiww a # # o c la tw w ith th e N # l# p ru lt G ra n lt# ##%,l#c##ent.
The h o t
*#*w# s o lu tio n s a re th o u g h t to have been r e s p o n s ib le f o r t h e s o lu tio n
I m ita tio n o f th e n ic k e l b e a rin g c o n e tltu e n ta w ith in %heae #hear
%n th # neighbourhood u f th e t r e v o r i t e n ic k e l d e p c a lt n ea r th *
h##con th e # # r p # n tln lt# h## been #he#red and la ac h la to # # in
«bm##.
The t r e v o r i t e o c c u r. In th e *he#r zone u n d e rly in g th e
W tmltw k * r l:o n b-jt l a no more th a n a few f e e t w ide.
North o f th e S c o tl* T alc Mini in th e s e r p e n t in it e s th a t occur
b#tw##n th e c o n ta c t a n p h lb o llte s s-'-d th e q u artz i t e 3 anr c o n g lo m erates,
ftffther magnet‘c ro ck o u tc ro p s were en co u n tered in d ic a tin g t \ a t the
gccticrenc# d e s c rib e d e a r l i e r i s not an is o la te d one but th a t th e r e may
be several s m aller d e p o s its in the area.
I t I s a lso re p o r te d t h a t t r e v o r i t e h as been fo u n i within th e
rjgtia T alc Mine and i s m doubt r e l a t e d t < the same p e rio d 0 f
i.ir» railx atlo n es th o s e to th e n o rth w e s t.
(
9
)
Gold
The L ily G old Mir*, w as, u n t i l r e c e n tly , one 0 f th e few
remaining sm all s c a le gold mi.tes s * l l l In o p e ra tio n In th e B aro erto n
D istrict.
The mine occu r* about j m ile s south o f Louw* s C reek S ta t io n
end Is s itu a te d on ro c k s belo n g in g to th e low er p a r t o f th e F ig - tr e e
Series.
T h is S e r ie s ab u ts up a g a in s t ta ic o s e ro ck s to th e n o rth ,
ktong th e c o n ta c t i s th e zone known as th e Main Reef Z one.
The
{Mpesed L ily F a u lt o c c u rs w ith in th e Main Reef Zone, a zone marked by
A w e d , s l l l c i f l e d and b r e e d a t e d r o c k s .
The F i g - t r e e s u c c e s s io n c o n s is ts o f narrow a l t e r n a t i n g band*
sf d ia ls , banded I r o n s to n e , c h e r t s , grayw ackes and t h e i r me*amorphic
liter at Ion p r o d u c ts .
I n a d d itio n to th e Main Reef th e r e a re se v e ra l o th e r r e e f s
to th* so u th c o n s is ti n g o f v e in q u a r t z .
T hese v e in s f i l l s h ear zones
la W v e r t i c a l l y d ip p in g s t r a t a
In th e c e n tr a l p o r tio n o f th e mine
U 1 p lu nging p i p e - l i k e o r e sh o o t th a t p ii'c h e s o u t w ith d e p th .
The
ieo t s tr u c t u r e U c o * > le x , c o n s is ti n g o f b r e e d ated co u n try ro ck w ith
r# laam # n t v e in s o f q u a rtz t i l l i n g th e f r a c t u r e s and b r e c c ia c a v i t i e s .
The fo rm a tio n s in th e mine a re deform ed and a re fo ld e d In to
tight i s o c l in a l s t r u c t u r e s .
The bedding I s in a l l c a se s v e r t i c a l or
Assply d ip p in g end I s a f f e c te d by two s e ts o f f r a c t u r e sy stem s, th e
w i t l e a l and th e o th e r a c r o s s - c u t tin g f l a t f r a c t u r e ty p e .
In
"as in s ta n c e s th e i n t e r s e c t i o n o f th e t w f r a c t u r e system s wet
keW to h av e a d i r e c t b e i r in g or, th e o c c u rre n c e o f pay zones.
Although th e Mein R eef Zone h as pioved to be th e m - A
9s-. atemt lode in th e mine, s e v e r a l o th e i r e e f s o f te n c o n ta in in g fre e
were w orked.
T hese r e e f s n e a rly always proved to be e r r a t i c .
H s s s iiS ^
w M S§pm i
T h is
and exploits •
a iflO U iiv e
d ut in
e x ld ie e d
unts o i =*-
. 7 - r
r tw r s lo W = f th *
s ~
a m
z * a tS S S ~
g
# B E
(e )
A d d itio n a l S o ld Occur re n e w
Betywen J o e 's Luck S id in g and Luuw's G, aek numerous old
writings c o n sis tin g o f tr e n c h e s , a d i ts and s h a f ts define a zone of
iin e ra liz a tio n t h a t h as a s t r i k e le n g th o f o v er 12 m il**.
The m ireraliz e d zone occurs a t the base of th e F I g - tr e e
re c essio n and also corresponds to a la te ra l e x te n s io n o f the L ily
KN) R ose's Fortune o r e h o rizo n s.
Along t h i s zone aoout t.to m ile?
ts the e a s t o f Louw'n Creek i s the o ld Ki.nberley Imperial Mine,
while to th e west o f th e L ily Mine two sm aller o c c u rre n c e s » namely
the Mexican and th e C leo p atra are to be found on the farms Avoca and
Crystal Stream re s p e c tiv e ly .
Recent tren ch in g on th e e a s t e r n p o rtio n o f the farm C ry s ta l
Stream h a s proved th e o c c u rre n c e o f gold in th is a rea but v alu es are
e rratic.
Near J o e s Luck Siding in th e Kaap River V alley, f u rth e r
indications e x is t th a t th e a u rife ro u s h o riz o n is co nt inu ous in to t h i s
e#a
O u tcro p s a re v ery poor along th e v a lle y but 'b a r ' developm ent,
i.e. development o f a s l l l c i f l e d and m ineralized s h ear zo n e , is a t
ttims dlseM iyible.
A few o ld tre n c h e s and s h a f ts show the sequence
*ieh is very s im ila r to th a t exposed near th e L ily Mine.
I t Is considered lik e ly , th a t th e frequent occurrence of
geld m in e ra liz a tio n along the same recognizable s t r a t ig r a p h i c h o riz o n
ht§ la rg e ly been determined by s tru c tu ra l c o n tro l and in th is r ig a rd
it Is J u s tif ia b ly f e l t th a t th e In ferren ce of a lo n g itu d in al f a u lt,
the Lily F a u lt, i s not e n tire ly unw arranted.
The envisaged fa u lt
seuld have acted s a chafmelway fo r th e o r e -b e a r in g s o lu tio n s and in
tills manner would not be u n lik e the o th e r m ajor f a u l t s in th e B arberton
fcfti th a t are known fo r t h e ir c o n tro llin g influence on th e m in eralizatio n.
I t has been mentioned elsew here in t h is re p o rt t h a t th e L ily
R eef o re horizon i s b r e e d a te d .
The s e c e s s i o n in the Rose s
frrttm e Mine to o , i s d istu rb e d in th e form o f a narrow zone o f da# # 0 sed b re c c ia .
In a d d itio n the lower F i g - t r e e succession in th e s e
tines and elsew here on su rface outcrop d is p la y s evidence of s h e a rin g
•ft lo c a l mataacrphism.
A lso along th e en v isag ed f a u l t th e r e are
bsdlas o f ta le s c h is t and what may be in tru siv e s e r w n tln ite s .
him* may a lso be a rock type o f in tru s iv e o rig in th a t has
w bseqeently undergone a lte r a tio n due to p ro c e s s e s of heaL , p re s s u re
W m k w lc a l w e a th e rin g .
F in a l) , 'b a r ' developm ent along th a
eestaet may be in d i c a t i v e c f secc.idaiy replacem ent along • fa u lte d
Bee Main
fis H h a s b e e n c o n i t r j e d .
2
#s=sm%= #=
3
^ M p m rW
seqik'nce.
reg k w l
k, INTRODUCTION
A b r i e f s u w a ry o f th e l o c a l i t y , rod© o f o c c u rre n c e and
sineralogy o f th e v a r io u s gold d e p o s its in th e B arb erto n A rea i s given
together w ith a d e s c r i p tio n o f th e s t r u c t 'i r a l environm ent o f th e L ily
Nine, T h is i s follow ed by a d 't a i l e d stu d y o f th e mine i t s e l f and
finally an atte m p t i s maJe to jhow how th e depos' can be woven in to
the o v e r a ll m in e r a liz a tio n p a t t e r n o f th e D i s t r i c t .
I t i s w ell known, t h a t th ro u g h o u t th e B arb e rto n Mountain I.and
met o f th e go ld o c c u rre n c e s a re lo c a te d on 01 very n ear to re g io n a l
W t p la n e s .
A g la n c e a t th e diagram ( F ig . 1) shows th e d i s t r i b u t i o n
ef th# gore Im p o rtan t mines and t h e i r r e l a ti o n s h i p to th e m ajor f a u l ts
la the a r e a .
Two f a u l t s in p a r t i c u l a r a re prom inently studded w ith
lines, some o f which a re no lo n g e r worked due to th e d e p le tio n o f o x id ic
» » . T hese im p o rta n t f a u l t s a re th e 3heba and Barbrock lin e s of d istu rb an ce.
fm 9f th e la r g e s t adcee in th e D is tr ic t occur along th e Sheba F a u lt,
ftm, fa lr r im i mmd Sheba Gold Mine#.
These la r g e lo n g itu d in a l f a u l t s , re p re s e n te d in a d d itio n by th e
S w tw *! F a u lt n ea r T hree S i s t e r s , th e S ad d le b ack , Inyoka and Karahlafeane
W it* to th e so u th east o f th e M ountain Land, pro b ab ly serv ed as major
##R#W #y# f o r c i r c u l a t i n g hy d ro th erm al s o lu ti o n s .
S econdary channels
sr f r a c tu r e s branch from th e s e i a u l t li n e s ex ten d in g th e m in e ra liz a tio n
te ad jacen t a r e a s .
Much o f th e m i n e r a l iz a t io n , i t w ill be n o tic e d , i s e s s e n t i a l l y
M ltricted to th o s e r e g io n s n e a re r to th e g r a n i te s yet i t i s e q u a lly
s ip if l e a n t t h a t v e ry few d e p o s its o cc u r w ith in th e g r a n i t e s , th e m selv e s.
% few o c c u rre n c e s found in th e g r a n i te s a re e s s e n t i a l l y q ra rt* vein
M Uia* e f *em r to n es o r leoletmd w dlm entary x en o lith a containing gold
W e e p f e r m i n e r a l iz a t io n , e . q . th e O verton Mine on f o u n ta in View Farm
%#le# w r th o f Honeybird S id in g and an occurrence on th e farm
Gamete nnrthwest o f R evolver Creek.
The la rg e r mines, notably the Agnes Mine, Falrview , and New
Cammrt Mine# are disposed about the faap Valley G ranite plutun (Read,
1951).
The m in e r a liz a tio n appears to d e c e a s e in m o u n t away from th e
g ran ites - th a t i s , tow ards th e s o u th e a s t.
The mines away from th e
contact zones s re a lso c h a ra c te r iz e d fay low -grade su 'p h id e o re .
(b )
Tvm » a t a i m a H E i t U a n Q ttu n a n iia a l a tha. 8M.i2g ite fl
M o u italn liiiri
Q rlb n ltt (1961) d e s c rib e s th r e e ty p e s o f o re bo d ies In th e
Barberton A rea.
Ha f i r s t m entions Tw tasoraatic rep lacem en ts o f fo o t and
hanging w all ro c k s in f a u l te d a r e a s .
S u lp h id e s and n o n -m e ta llie gangue
l i t e r a l rep lacem en t h as ta k e n p la c e in b re e d ated and n ry lo n itiz ed zo n e s.
He q u o tes New C o n e c it, F a ir v ie w , Sheba and Agnes Mines as b eing examples
ef t h i s ty p e .
The second ty p e o f o c c u rre n c e a re th e g o . 4 / q u a rtz v e in d e p o s its .
The p l d i s d i s t r i b u t e d f in e ly in w hite o r b la ck q u a rtz w ith o c c a sio n a l
totting s u g g e s tiv e o f vug d e p o s it io n .
Mines f a l l i n g in to t h i s ca teg o ry
include th e F o rtu n a and P io n e e r.
The th i r d ty p e a re p ip e s formed by m ineral *to p in g . The famous
f i t h t d r a i shoot a t Sheba i s c i te d as an example to g e th e r w ith o th e r
N ailer examples from th e same m ine.
The l a t t e r a re s m a lle r and
breccia f i l l e d .
(c )
M ineralogy o f th * B a rb e rto n S a id a t n g U .il
S o * (to ta lle d work h as been done on m ineralogy o f th e o re
j ^ o s t t . In t h . D i s t r i c t .
In 1957, de V i l l i e r s attem pted « c l a e e i f i c a tl e . end d is c u s s e d th e m ineralogy o f th e more Im portant d e p o s it s .
He
e ta e lu M from p a r a g * w t i 6 ev id en ce t h a t th e gold o c c u rre n c e s were »U
femW d u rin g a s in g le s e ta llo g e n ic age.
Both he and van Eeden (1941)
m n I n egrM m ent w ith th e id e a t h a t th e m in e ra liz in g hydrotherm al
le lu tio n s were d e riv e d from th e N e ls p r u it G r a n ite .
H earn (1 9 4 3 ),
l e e m r , was o f th e o p in io n t h a t th e Kaap V alley G ra n ite wasla r g e ly
»N|»n%.lble fo r th e in tro d u c e d s o lu ti o n s .
V i l l i e r s su b -d iv id e d th e d e p o s its in to 4 main t / p e s o f
sulphide a re i
1.
2
.
o r e s c o n ta in in g a rs e n o p y rite and p y r r h o ti te In
which th e p ir a g e n e tic sequence appeared to be
a r s e n o p y r it e , p / r r h o t i t e and th e n c h a lc o p y r itc .
p y r i t i c o r e s w ith a rs e n o p y rite f i r s t to fo u r
foll owe d by p y r i t e , second g e n e r a t i o n a r s e n o p y r i t e ,
p y r r h o t i t e and c h a lc o p y r it e .
3.
le a d o re s w ith p y r i t e , s p h a l e r i t e , t e t r e h e d r i t e ,
c h a lc o p y r ite and g a le n a , form ing in th a t o rd e r
4,
an tlm o n ial o re s w ith p y r i t e o r a rs e n o p y rite
form ing e a r l y follow ed by b e r t h i e r l t e , m a rc a s ite ,
s t l b n l t e .md f i n a l l y m e ta llic antIm ony.
Gar^iue m in e ra ls w ere g e n e ra lly found to be e a rly in th a sequence
with go ld one o f th e l a s t m in eral# to be in tro d u c e d .
G r lb n ltz (1961) added a 5th ty p e - no* a s u lp h id e c l a s s i f i c a t i o n
tewever, b u t g p ld - q u a r ti o r e .
The r e g io n a l d i s t r i b u t i o n o f th e ty p e s has o n ly been mentioned
is an ex trem ely g e n e ra liz e d manner by G r ib n itz (1961) q u o tin g C.A . S tr a u s s .
He mentions th a t arse n o p y r."tic o re s become r a r e r In o c c u rre n c e s south end
wythwest o f New C o n s o rt M ine.
Next In th e zonal arrangem ent o f th e o re
types a re p y r i t i c d e p o s its w ith very sm all c r y s t a l s .
These are follow ed
coarsely c r y s t a l l i n e p y r i t e s form ing la rg e im pregnation zo n e s.
The
pl4/q u a r t z v ein s a re m entioned as o c c u rrin g n ear to th e Kaap V alley
Srsftite.
A nttm onlal o r e s o cc u r l a p o ck e ts in th e f i r s t th r e e zo n e s.
de V illie r s (1957) c o n s id e re d most d ep o sits to have formed at
■derate tem peratures and d e p th s and s t ate* th a t th e p y rrtio tl+ e and
e m e p y r ite o res o f New C o n so rt and L ily Mines were due to In tro d u c tio n
d h i # tem peratures and g re a t depth.
de V i l l i e r s fu rth e r c l a s s i f i e d
tN E a g le 's Nest Mine, New C o n so rt Mine and Lily Mine to g e th e r as a ll
kailmg o re of th e a r s e n B p - /rite - p y r r h o tite group.
The E a g le 's N est Mine worked m ainly o x id iz e d o r e s . S u lp h id e s
sirs en c o u n tered in b r e e d a te d zones along o r near th e c o n ta c t o f
heruginous banded c h e r t and s e r i c i t e s c h i s t .
The main s u lp h id e was
Ffrtte w ith a r s e n o p y r ite , p y r r h o ti te and c h a lc o p y r ite .
The New C o n s o rt m l i'e r a li z a t lc n o c c u rs along folded and
•U ielfled cof t a c t s o f a lte re d s h a le o v e rly in g b a s ic s c h i s t s . The gold
-$ a s s o c ia te d mainly w ith a r s e n o p y rite and le s s e r amounts o f p y r r h o ti te .
O tabopyrlt#, s t l b n l t e , te tr e h e d r ite , g alen a, tr e v o r i te , p e n tla n d lte ,
W em llte. maucherlte end n a tiv e blemuth al#o occur to a le ss e r degree.
The L ily Mine o c c u rs ap proxim ately th r e e m iles south o f the
n iire s t g r a n i te ex posure a t Louw*s C re e k .
I t is also n o rth c f both th e
Shebs and B erbrook F a u l t s .
Mapping w ith in th e mine I t s e l f to g e th e r w ith
rtg io n ai trapping h as b r o u ^ it to l i g h t c e r t a i n fe a tu r e s th a t suggest th e
presence o f an a d d i tio n a l f a u l t , th e " L ily F a u lt " .
T h is a s p e c t has be'.n
discnised under th e Economic Geology o f th e are# where i t i s shown the",
fiaserous o l d w orkings could p o s s ib ly d t f i n e a f v r th e r m in e ra liz e d l i r a i " L ily L in e” .
I t w ill b t n o tic e d on c o n s u ltin g th e e x i s t in g G eo lo g ical Survey
^ o f th e D i s t r i c t t h a t two f a u l t s (Sheba and Bar brook F a u lt s ) o ccur in
the a n tic lin a l d iv id e s between m ajor s y n c lln e s .
The Sheba F a u lt separm .ee
9* Eureka S y n c lirw from th e U lundi Sync li n e w hile th e B ar brook and th e
mabf Saddleback F a u lts sep arate th e U lundi S y n c lin e from th e Saddleback
Syncline.
A f u r th e r example o f m ajor f a u ltin g a s s o c ia te d w ith r /n c lin e s
stela's n e a r T hree S i s t e r * where th e Scotsm an F a u lt s tr ik e * *.n an e a it- w e it
directio n p a r a l l e l to th e n o rth e rn limb o f th e L ily S y n c lin e .
A
p recisely s im i la r arrangem ent appears to e x i s t between Sheba S id in g and
le a ^ s C r e e x w#iere th e L ureka S y n c lin e and th& L ily S y n c lin e are
# # r a t e d by th e L ily F a u lt .
The Kaap R iv e r has eroded much o f th e a rea immediately n o rth
gf the E u rek a S y n c lin e th u s d e s tr o y in g end o b l i t e r a t i n g the f a u l t tr a c e ,
Th# roefce in the r iv e r v a lley are m ainly composed o f so ft b a s ic s c h is ts
s£th occasional s h a le and c h e r t bandi p ro v id in g the o n ly re s ista n c e to
tN erosive c y cle.
The L ily F a u lt tone ru n s p a s t th e area south o f J o v ' s Luck
SMiiig and continues f o r a sh o rt d istan ce in th e n o rth e rn bank o f th e
K*p R iver.
I t th e n c r o s s e s th e r i v e r and appears to j o i n up with
fee m ineralized Woodstock F a u lt ,
A f u r t h e r f a u l t e x te n d in g from j u s t n o rth o f J o e 's Luck
tMlna to the a re a n o rth o f .toordkaap was mapped.
The f a u l t p la n e is
m il defined a /d i t u s u a lly occ*$ied by a la rg e q u a rtz v e in .
This
nsaed th e Main S o u th e rn F a u lt ru n s n o rth o f the Kaap R iver and
tf#B#tes th e q u a r t z i t e b lock o f th e w estern e x tre m ity o f th e L ily
H T tlite l i n e .
In th e area n ea r J o e 's Luck S id in g th e behaviour o f
% fa u lt U not c l e a r b u t i t i s considered li k e ly th a t i t c o n tin u e s
tie w th e s c u th e rn edge o f th e q u a rt* ite -c o n g lo m e i ate h o riz o n past th e
$«Ai« Tmic Mine and e a s t tow srds Louw's C reek (« • V U jo e n ,
a W
^ %
^ r %
%
\ f 'C u i y
$ y n c % % p ro L b ly
in d ic a tiv e o f s h e a rin g a s s o c ia te d w ith th e f a u l tin g whicn i s co n sid e red
to be o f th e high an g le t h r u s t f a u l t ty p e .
(» )
m a c U nraat
P i s t e 36 g iv e s a g e n e ra l view o f th e L ily Mine looking e a s t .
The mine I s s i t u a t e d on ro c k s b elo n g in g to th e lower p o r tio n o f th e F ig tree S e r i e s .
The banded ir o n s to n e s and s h a le s shut up a g a in s t ta ic o s e
rocks In th e n o r th .
A long th e c o n ta c t i s th e zo - known as the Main
ieef Zone.
The Main Reef was f i r s t worked from s u rfa c e where th e o re
was q u a r r i e d .
The mine I s s i t u a t e d on th e slo p e o f a h i l l and as th e
quarry became deeper i t was found n e c e ss a ry to d r iv e s e v e ra l c ro s s c u ttin g a d i t s n o rthw ards in to th e h i l l to in t e r s e c t th e o re zone a t a
tower le v e l.
The c r o s s - c u ts i n t e r s e c te d s e v e ra l o th e r r e e f s to th e south
ef th e Main R e e f.
In th e c e n tr a l p o r tio n o f th e mine on 1 L e v el, 4
iwh z e e fs w ere lo c a te d and developed l a t e r a l l y .
The M ill A d it in th e
l i f t was s t a r t e d a s a c r o s s c u t but then r e v e rte d to a d riv e p a r a l l e l to
fo rm a tio n s t h a t c o n tin u e d to th e area im m ediately below the d ev e lo p ­
ment o f 1 L e v e l.
The 2 Level w orkings are in o x id iz e d rock fo r sosie
distance b u t as th e tu n n e l proceeds w est 'n to th e h i l l s i d e , su lp h id e o r
&*sh ro c k ta k e s o v e r .
H i^ ie r up in th e Mine above th e 1 Level w orkings '.re s e v e ra l
ia te iw d ia te le v e ls th e more im p o rtan t o f which have proved +o be th e
70 F t. L ev sl and th e S u rfa c e L e v e l.
Both these le v e ls and th e i n t e r a r tia te le v e ls o c c u r in o x id iz e d rock and developm ent has been c u r t a il e d
in the west by th e p re s e n c e o f s u lp h id e ro c k .
The r e e f s c o n s is t o f v e in q u a rtz f i l l i n g shear zones in th e
it r a ta .
The Main R eef Zone i s p a r t l y b re e d ated as is a zone o r shoot
ia the c e n tra l p o rtio n o f the mine south o f th e Main R e e f.
The shoot
o u t near th e s u r fa c e and has also been q u a r r ie d , w h ile w ith depth
#e plunging s t r u c t u r e narrow s and f i n a l l y appears to pinch o u t below
lU w l.
The term "shoot" I s g en erally m ^ lo y e d to describe c o n c e n tra Hgn* o f o r e o f hypo gene o r i g i n r s d is tin g u is h e d from sypergenw
a w n tra tio n s .
However, p o c k e ts , n e s ts and bonanzas may r e f e r to
titte r supergene o r hypo gene c o n d itio n s and f a l l in to th e d e f i n iti o n
ef ere sh o o ts. (B atem an, 1958).
C e re j& l vmlw c f
o x rlc m lv n a ^ a fA Z lro ;
d ro
'o r :
c f 'f l c o , LI y A u l t %j
^.
Tcp : e T T :
% u & rry ; G m n tr o r l p h t ,
The Main Reef Zone hag proved to bt th e most c o n s is te n t lode
*ith a r av erag e grade in th e o x id iz e d o re o f between 3 and 5 dw ts,
fhe
% F t Level r e e f was more e r r a t i c but co n ta in e d abundant fre e gold,
fhe rem aining r e e f s in th e mine have a l l proved to be very e r r a t i c .
¥ tlu » s a re g e n e ra lly unpayable t u t ex trem ely ric h pods c o n ta in in g fre e
geld w ere e n c o u n te re d a t i n t e r v a l s along th e v e in s .
The main shoot p ro v id e d th e lo c i fo r about s ix "bonanza" gold
p*d, w h ile th e b r e e d a te d m a te ria l gave o re w ith a <po6 average g rad e,
(aae T a b le I I ) .
The term "bonanza* i s commonly used to d e s ig n a te an
e x c e p tio n a lly r ic h sh o o t o r bunch o f o re and i s p a r t i c u l a r l y a p p lic a b le
* ith r e f e r e n c e to gold o r s i l v e r . (Batem an, 195%).
TM *
II.
TABlf Cf OUTMT MD CM TOWME
The fo llo w in g ta b l e r e p r e s e n ts th e annual tonnages o f o re
s i l l e d end th e <pld o u tp u t in f in e ounces fo r both th e L ily Mine and
the H ose’ s F o rtu n e Mine to g e th e r .
No s e p a r a te f ig u r e s were kept fo r
th# two m ines b u t ap p ro x im ately 90 p e r ce n t o f th e o re was o b ta in e d
fle e t h . L ily M ine.
Toni M l l i a
P e rio d
J u ly 1*9# J u ly
19*9 l * t J u ly 19*0 l i t J u ly
1961 1 s t J u ly 1962 -
3 0 th
3 0 th
3 0 th
3 0 th
31st
J w 1939
J u n . 19*0
J u n . 1961
J u n . 1962
ttareh 1963
17,288
10/A O
10,469
10,713
9,146
2 ,4 7 0 .1 0
6 ,7 2 9 .8 4
4 ,9 0 3 .5 2
2 ,7 4 0 .8 3
1.9 9 9 .1 9
TOTAL
53,276
1 8^843^ 4^
wm> t #yiV 1 HI* vw.m,w.
-rr
•
betw een 1 s t J u ly 19% and 3 1 s t March 1963,
(b )
Rock Tvn«.
■I
,
' P " P * " ^ 1-llY f a u lt o c cu r,
*d
lh . %,ln * „ f Zone
,.n .
e ^ llL C
T ! c h .rty M nd, Md * « w « , of vein q u .r t: In d l.tu r w d
j u i w o m , m d f r r u g ln n u ,
South o f th , Main R .,f th .
" M k n bKom#, mor, r»»ilm r ind 1, a p p m r.tly u t t l » d l.tu rb w l.
k^ ,^h :.% L T
m
«
rn
m
tln
g
l
l
^
t
V * '1 * % " * " " * " » * 4 .rl, .n a l.L .rx,
gT" ,
« to n ,lv .ly .
Th. , h „ . , . n . , p , .r , l l , ] to th^"
I w T L r " " form ation, , r . r , r i j g l n l : ^ by a :t.r * d Iron o ,W ..
g » « tn lt.) , and n . froquontly MplKPO by h y d m lh m w l
U c o n tain in g Km# gold m ln # r.l:l* « tlen .
Thp w in , vary In
ttie k n e ss from a few m i l l i m c ta r s up to s e v e r a l f e e t -;c io s s , p inc hin g and
g e l l i n g along th e e n t i r e le n g th o f th e sh ear p la n e s .
The q u i r t z Is of
#rw th a n one age and o c c u rs in s e v e r a l co l o u r s ind f o x t u r o s .
Some i s
essiiv® and v itr e o u s ran g in g from c l e a r to w h ite , gray and b lu e - g r a y ,
ih il* o th e r v«»ins ar e more c h a r t - l i k e with a f i n e g r a n u l a r t e x t u r e .
88*1 ro ck a l t e r a t i o n on e i t h e r side o f th* v e in s i s alm ost n o n -e x iste n t
in d icatin g th a t th e hydro th e rm al s o lu tio n s were low to moderate in
temperature.
No dim ensions o f th e ro o fs can be given as they p inch and
me11 e r r a t i c a l l y and sometimes d is a p p e a r completely on ly to reap p e ar
again w ith in a m atter c f a few f e a t .
(c )
attiK B g jlU M
P r a c t i c a l l y a ll tho ro ck s in th e mine have underg rne m etaaorphic
a lte r a tio n .
Those ro ck s le a s t a f f e c te d are th e s h a le s and graywackes
ytposed a t the entrance to t h o L ily A d it and the M ill A d it.
These g ray nekes a r e fin e -g rain ed and in th in s e c t i o n c o n sist o f p o o rly so rte d
f«rt* frag m en ts to g e th e r w ith v a ria b le amounts o f f e ls p a r ( o rth o c la s e
a l b l t e ) , s e r i c i t e , c h l o r i t e and m ica.
The rock shows l i t t l e o r no
ittifrnce o f bedding and adjacent s h a le s o f te n c o n ta in to u rm a lin e in d ic a tin g
Sgfe th e r e h as p ro b ab ly been some a lte ra tio n .
T hin s e c t io n stu d y o f s h a le s taken at random throu./hout the
» lite in d ic a te d a w ide v a r i e ty o f d iff e r e n t metamorphic and other
■bMMls* G e n e ra lly p r e s e n t was q u a r t z , s c r i c i t e , c h l o r i t e , and th e
i»fl o re S (h e m a tite , m a g n e tite , U m onite and g o e t h ite ) .
Much o f tn e
H tfln a l e e d le e n t hue been a lte re d to a b io tite -a m p h ib o le h o r n f e ls .
Dm e e h l b o i e e are o r i e n t a t e d w ith t h e i r long axes ro u ^x ly p a r a l l e l to
# f o lia tio n .
They a re in v a r ia b ly tr e m o lite o r a c t i n o l l t o in
M M O titlon b u t lo c a l l y g r u n e r i te may be developed where th e re la m abundance
f b m . (% m er11i o ry e ta le w r e eoes ra d ia tin g from a nnrro* m m #*tlte-4w m atlte
W la te r e a la te d between c h e rty q u a rts (see P la te 59).
Spotted s h a le j and s l a t e s a r . commonly developed in d ic a tin g a
f^rly low g rade o f m etm orphlm (M ark er» 19 5 6 ).
R e c o n s titu tio n of
triolfial m ate ria l in the sed im en ts has formed new m in e ra ls , one o f the
being b l o t l t e .
Tho b lo tlte Is g enerally reaponslble for
% spotted n a tu re o f th e s h a l e s .
There i s o f te n some s ig n o f th e
M M nel bedding in th o rock and th e a g g reg a tes o r 'n e s ts ' of < le a are
marmllel to th e fo lia tio n but w ithin the Individual
n ests
%t f la k e s d i t o l s y d e c u s s a te s t r u c t u r e s .
The rem aining p h y l l o s t l i c a t e s
'fiew1 arow td each o f th o l i t t l e mica c l u s t e r s .
The o r ig i n a l sedim ent*
* # k a v * montalned ju e t s u ff ic ie n t aluminous m aterial ^nd a lk a lis to
W #$k# mice# a s th e re i s very l i t t l e an d alu slte p re s e n t.
Where
* M * alte does occur th e c r y s ta ls are feebly developeo and can e a s ily
h* overlooked duo to th e ir diffu * e nntur# mnd zhv pre»#nc# w ithin th**
of obund ant unexpelled inclusion#.
W cally d#v*i*»ped garnet»be^riiig hornfelse# occur with a
marked c r y s ta l alignm ent.
Th# garnet* ar* #**11 and hav* po* cllo b la* tic
or " s ie v e " s tr u c t u r a .
Magnetlt* and g a rn e t p o rp n y ro b la » t$ have pushed
sslde th e m a trix o f s e r i c i t e , mica and q w r tz in to a m icroscopic
WWlwmge w.t r e m .
r#e pre##mc* o f tourm alin# in p r a c t i c a l l y a l l th e rocks
wamlmed mggemt* th a t boron pnatmatolyalm probmbly waa re la te d to th#
m tm irphim i o r the hydrothermal ao lu tlo n # .
There wa# a n oticably marked
aeecentretion of taw m alin e In d istu rb ed shear and breccia xon## aa well
# In o th e r lea* denee o r c o ^ a c r p#rmeabl# zones, e .g . in the 70 F t.
level stop*#.
S l l l c i f l e s t l o n , c h # rtlf Ic a tlo n and m ,lo n ltl* a tlo n is n oticeable
A * # #llcken#ldlm g and shearing is e v id e n t.
In th# shear zones th#
hsve been formed i n t o a shiny bla ck compact b r i t t l e c l a y .
* & # a ltl* # tia n Is evident In #om# of tho crush ion#s and succ###lvo
e#aye In the format ion o f a tru e mylonlt# can b# dl#tlngul#hed In th in
Som#
v t i vein* #r# sp o ra d ica lly chorty ano th# micro" i t a l l l n e te x tu re i i o fte n only in t# rn * )t# d hy ra d ia tin g tr#m ollte
(ee# P la te
A few diamorJ d r i l l holas yl#lded cor# from
nw m e t on 2 Le%»^ .
This cor# was p a rtly brecciated And o a rtly
f t * * well mln#rBli%ed e sp e c ia lly in th e Main Reef and in
ia te d d w r erea
The ro<-k# Wien examined in th in sectio n
o f qUKTK, c h lo r ite , carb n n aie, tre m o lite and m agnetite.
l l t e forme
zcnms around the ch erty quartz and is
*d by calc:;T@.
At tim es th e l ^ r o s s io n obtained Is th a t the
.
meedlea
jrowdng from the c a l c lle p a r tic le s .
Carbonates
t
v ^bwnd^rt i;- th e Tocka o f the breccia zone and shear planes
» - t . " lepleced a r f i l l e d by w ell formed rhombic e a lc lte veins. In the
2 ^*e oarhenate veins mrnre nor seen but ar# probably maakmd
a. ^m t:rn o f jd je c e n t m a te ria l.
Wear the 2300 f&dlt Tnere ara developed some (halcw dor lc #f*d
*&!./* ^mtcnes in a mck nc: unl'k# p o lic e In appearance and te x tm r
"'lom deny f i l l s creek * , xaint plane* and o th e r c a v itie s and hi#
b m * W the leeching o f s i l i c a from the g r o u n d in g a lte re d she)**
.nv
A, ' Jk
atrwmeljr aeroue.
- 106 I n t h i n s e c t io n th e leached rock c o n s is ts o f a d srk v itre o u s
ittbstance and
m a te r ia l newly formed in c a v i t i e s c o n s is ts c f q u artz
led f ib ro u s a g e - a t e * o f chalcedony ( s e e P la t e 5 8 ) , w ith prom inent
id w iru litic c r o s s e s .
In a d d itio n th e r e i s a l i t t l e o p al w ith th e
chalcedony.
The met am orphic assem blages in th e mine are o f a low grade
t e e o f r e g i o n a l metamorphism f a l l i n g in to th e c a te g o ry of th e g re e n ic b ist f a c i e s .
Metamorphism was pro b ab ly th e r e s u l t o f d ia stro p h is m
coupled w ith e f f e c t s o f h e a t p ro v id e d by th e in t r u s i v e rocks in th e urea.
ysA Beden (1 9 4 1 ) c o n s id e re d th a t th e Jamestown Complex was p a r t ly th e
csuse o f t h e metamorphism o f th e rocks in to trtiieh i t in tru d e d as w ell as
being r e s p o n s ib le f o r th e e i l i c i f ic a tlo n o r c h e r t i f i c a t i o n o f many o f th e
•w eeesio n s.
I t was m entioned e a r l i e r th a t th e t a l c s c h i s t s no rth o f th e
Uly F a u lt may have o r i g i n a l l y been b a s ic in t r u s i v e s o f th e Jamestown
&#pl#x*
The conform able s u c c e s s io n has been used as a f a c to r a g a in s t
in t r u s i v e o r i g i n o f th e se ro c k s h u t th e p o s s i b i l i t y should not be
Hjeottfited t h a t th e b a s ic rocks in tru d e d in to or along th e f a u l t p la n e .
L o c a lly , th e a e ta iw rp h ic m in e ra ls found a re in d i c a t iv e o f
•tig h tly h ig h e r g ra d e s o f m etam orphim but hydrotherm al s o lu tio n s
M o o n sib le f o r th e in tr o d u c tio n o f th e m in e r a liz a tio n may have
sM tH buted to w ard s t h e i r fo rm a tio n .
The n e a re s t j r e n i t o body i s
I te * two and a h a l f m ile s to th e n o rth and th e mine may be reg ard ed as
Id lin g in t o th e p e r i p h e r a l o u te r zone o f c o n ta c t metamorphism produced
hv the g r a n i te i n t r u s i o n .
S.
STRICTURE OP THE Mlffc
D u rin g th e c o u rs e of mapping th e m ire a d e t a il e d s tr u c t u r a l
was u n d e rta k e n end th e item s lis te d below were in v e s tig a te d
F o ld s .
F r a c tu r e s
Bedding.
S c h U to U ty and cleav ag e
B r e e d a t io n and rock fr a c tu r in g
3oudinage
P * w lh i,
t h . i t n K t u r . . In t h . mln.
- 107 (a )
F o ld s
Throughout th e mine th e fo ld s a r e of a t i g h t is o c l in a l n a tu re .
The f o ld in g i s a l l o f a s im ila r ty p e , i . e . th e d i s t a n c e s between th e
bedding u n i t s p a r a l l e l to th e a x i a l p la n e remain c o n s t a n t w hile th e
d is ta n c e s m easured a t rig f it a n g les to th e same u n i t s ar# v a r i a b le . Tho
fold axes a r e m ostly s te e p ly d ip p in g but show a spread in th e a x ia l
plane.
A pye diagram p lo t in d ic a te s a c o n c e n tra tio n o f p o le s th a t d ip
both n o rth and south and a ls o a g re a t c i r c l e with v e r t i c a l fo ld a x e s.
(See F ig . 9 ) .
The fo ld s p lunge s te e p ly to th e e a s t and a lso show a
spread o f p o le s p o s s ib ly in d i c a t in g e i t h e r d i f f e r e n t i a l com pression of
the f o ld s and a v a r i a t i o n o f movement in t h e ' a ' d i r e c t i o n , o r s u p e rUposed f o ld i n g .
The fo ld * a re c h a ra c te r iz e d by l a r a e am plitudes and
narrow wave le n g th s ( s e e P i s t e s 40 and 4 2 ) .
Ramsay 1 1962b) developed
a method to e s tim a te th e amount o f f l a t t e n i n g in f o ld s based e n t ir e l y
an th e th ic k n e s s o f a com petent bed measured a t any p o in t in th e f o ld ,
and the o b serv ed a n g le o f I n c l in a t io n between the bedding and th e a x ia l
plane o f the f o ld .
The photographs ( P la t e s 40 and 42) were en larg ed
several tim e s and used in an attem p t to determ ine th e approxim ate
•mount o f f l a t t e n i n g in th e F ig - tr e e s u c c e s s io n .
The v alu es o b ta in ed
sere p l o t t e d on a graph (s e e Fig. 18) and Lh* r e s u l t a n t cu rv es gave th e
percentages o f f l a t t e n i n g to be 37% and 46% resp ectively.
An average
value, 4 1 .9 * , r e p r e s e n t s t h e f l a t t e n i n g a d d itio n a l to th e o r ig i n a l 36%
shortening u f th o fle x u r e f o ld .
The e n t i r e s u c c e s s io n h as th e r e f o r e
undergone an approxim ate s h o rte n in g and f l a t t e n i n g combined o f about
62.55 p e r c e n t .
T h is f ig u re was d eriv ed as fo llo w s «- The o r ig i n a l
unit le n g th was assumed to have been 100.
S h o rte n in g o f 36% reduces
the u n it le n g th to 6 4 .
S u b se q u e n tly , th e a d d itio n a l f l a t t e n i n g of
41.5% re d u c e s th e u n it le n g th 64 to 26 . 5 6 .
The combined s h o rte n in g
and f l a t t e n i n g i s th e r e f o r e 36 ♦ 26.56 o r 62.56 per c e n t.
Around
the f o ld s and som etim es in c lu d ed in th e e a re q u artz v ein s o f both
primary and secondary o r i g i n .
The prim ary q u artz v e in s are g e n e ra lly
disturbed by te n s io n J o in ts in th e c r e s t s o f th e f o ld s .
Where no
gpiirtz accom panies th e folding th e altered or metamorphosed s h a le s
exhibit t e n s i o n c ra c k s t h a t have su b se q u en tly been f i l l e d by secondary
leathered m a te r i a l.
The e n t i r e formation is c l e a r ly fo ld e d but due
to the g r e a t am p litu d e o f in d iv id u a l folds i t was only l o c a l l y , and by
chance, t h a t c r o s s c u ts exposed th e h in g e zo n e s.
An attem p t was made
to c o r r e l a t e th e fo ld zones on th e v a rio u s lev els b u t t h i s was not
found p ossib le due to t i e com plete absence o f any fa v o u ra b le marker
horizons.
Folding expresses I t s e lf In a milder form diere It gently
h c t l .. » . w d lm n t,.
TTw M l 1 p i t " , o f t h . . . f o l d .
L
t * U o n t i l mnd c o l n c id . w ith t h . v . r t l c . 1 « t r w , f l . l d o f t h . fo u rth
phase o f de fo rm a tio n mentioned ea rlier under S tr u c t u r a l
*ology.
8
2S
( r i a t e 4 2 ) T ig h t I g o c lliia l
f o l d # s h o w in g r& rro w w&v#
l e n g t h e &nd Im rg #
a m p lltu d e B . F i g - t r e e # h a le n
2 L evel c ro s s c u t
u ll y Mine.
(M g 1 8 ) Graph ehowlng th #
p e rc e n ta g e f l a t t e n i n g
c:
th * F l g - t r * * euocemmlon
I n th e L ily Min#.
,
J - ' «
- loe tyejcling o r w arping a lso occount* fo r many o f th e I r r e g u l a r i t i e s In
bedding d ip and s t r i k e (s e e F ig . 10).
(b )
F r a c tu r e s
Two s e ts o f fra c tu re s e x is t In th e m ine.
(1 )
V e r ti c a l f r a c t u r e system .
( 1 1 ) Cross-c u ttin g f l a t fracture system
(1 )
V e rtic a l F r acture System
warn
Prom the point o f view o f reef development the most
to th e 70 F t Level end then on to the su rface.
^@ ###
rsck shaped l i k e a c a m - a e y e id le n s .
, .L. a
(Fig-
,n a « 4 T
*h—
the same p la n e as t h a t co n ta in e d by th e bedding and Ru.ster ..near.
also re p re s e n te d a s th e P In te rm e d ia te s t r e s s .
H is
The p o le s A o f th e c y ro id s tr u c t u r e and S
and E' o f
th e
i k f t ie a l s h e e r , l i e on a g re a t c i r c l e o r ’ a t ' p la n e .
The p o V t Io r
eselmisa com pressIv# fo rc e I s lo c a te d on t h i s p la n e , making an
«ngle o f
30 d eg ree s to t h s s h ear p l m n HG.
The minimum s tr e s s J l i e s 90
Aejpees s m y from P max. alsu on th e 'a c ' p la n e .
The p o le to th e c y ro id loop (p o in t A) and 2# th e p o le to th e
master s h e a r p la n e (FG) make an angle w ith one an o th er of 38 d e g re e s.
This i s 7 d e g re e s le s s th e n th e th e o r e t i c a l v a lu e o f 45 deg ree s as
ca lcu la ted fo r th e an g le (DCF) betw een th e second o rd e r sh ear and th e
sain f a u l t in f ig u r e 20.
The cymoid loop i s t h c u ^ t to be a second o rd er s tr u c tu r e
re s u lta n t on r e o r i e n ta t e d s t r e s s e s a d ja c e n t to che mein e a st-w e s t
it r i k e - s l i p s h e a r .
F u r th e r l a t e r a l movement a 1c.xj th e sh er^ p la n e in th e mine
ceuld e x p la in th e f l a t t e n i n g o u t o f th e s tr u c t u r e i-vtc 3 cyrsjid lo o p ,
tbs an g le o f which h as a le s s e r v a lu e th a n t h a t based on t h e o r e ti c a l
c a lc u la tio n .
The geom etry o f th e v e in s h as no do u t/ p la y ed some p a r t in
the l o c a l i s a t i o n o f th e "bonanza" g o ld p o c k e ts .
U n fo rtu n a te ly most
ef th e se " s t r i k e s * were made b e fo re t h i s study was undextaken and th e
mast n a tu re o f th e v ein s c o u ld o n ly be r o v ^ tly e s tim a te d .
In lA is
connect io n th e m in e r, W . R , Thomson, was o f h e lp in explaining the
edb e f o c c u rre n c e o f th e d e p o s it .
The m a jo rity o f the gold wa»
•atvontered to g e th e r with th e quarts in th e p lu n g in g v ein s and i t
tf p e ttt t h a t e l i c i t changes i n th e a t t i t u d e o f th e v ein s produced
hwewable s t r u c t u r a l lo c i fo r g o ld c o n c e n tra tio n .
Thv la r g e s t and
rlebeet o f h e p o c k e ts was e o c e u rte ro d in th e b r e e d s shoot j u s t above
1 le v e l ( s s i F ig . 6 ) .
A pproxim ately 3,0 0 0 ounces were e x tra c te d from
• s e m e r o u A ly 2 5 ’ x 12 ' x 2 ' .
Above t h i s s ev er a tm a lio r fin d s o f
hms th a n i f c m m ces were made.
Where th e shoot e n te re d th e quarry
Between I
Level and 2 Level a pocket o f t 800 ounces In the
far® o f a ta b u la r co re vias e x tr a c te d from an a rea o f 12* x V x 1 '. In
the s u lp h id e zone j u s t above 2 Level a sm all pocket ( & 250 ounces) was,
fgend to g e th e r w ith s m a lle r is o la te d p a tc h e s o f v i s i b l e g o ld .
The gold
extended to a ,o u t 10 f e e t below 2 Level and from t h i s p o in t down no
fu rth e r v i s i b l e gold was e n c o u n te re d .
The shoot a p p a re n tly pinched o ut
below 2 L e w i.
The zone o f b r e c c ia t io n was roughly d e lim ite d by d r i l l i n g on
1 Level and in p ’ act,* down th e shoot i t was found co n fin ed to a narrow
section between th e und’ s tu rb e d r e g u la r sedim entary la y e r s .
The rock
in the lower le v e ls i s w e ll m in e ra liz e d as a r e s u l t o f th e replacem ent
and e a s e o f e n t r y o f s o lu tio n s in to th e d is tu rb e d zo n e s.
D r i l l i n g a lso in d ic a te d t h a t th e Main Reef Zone on 2 Level
* * b re c c ia te d and re p la c e d by s u lp h id e m in e r a liz a tio n .
Narrow f r a c tu r e
planes in th e w inzes and in th e main c ro s s c u t cn 2 Level are f i l l e d by
e s io ite v e in s .
From th e in v e s t ig a t io n i t would appear th a t th e sh earin g was
pest f o ld in g in age and t h a t s u b se q u e n tly , q u a rtz v e in s were in tro d u ced
lato th e f r a c t u r e and s h e a r plane® .
(1 1 )
C rq y» -cu ttlD Q _ L lat F ra r tl ffi-,S x rt—
D i f f i c u l t y was o f te n experienced in o b ta in in g a th re e
dimensional p la n e o f f r a c t u r e s th a t c ro s s c u t th e sedim entary la y e r s ,
p a r e n t s t r i k e and d ip measurement* o f th e f r a c t u r e s had th e r e f o r e to
ke W e n by memauring two v ector, in the frecture plene.
Fro# these
readings t r u e d ip end strik e v a lu e s were derived u sin g a W ulff s
asree y sphlc net (see F ig . 11).
Poles o f the true dips »nd strikes
Us in the no rth w est q u ad ran t o f th e diagram in d ic a tin g a ^ ^ t l s h
u u th - e a s te r ly d ip and a n orth. , s t - southw est s t r i k e fo r th e majority
af the frectu res.
The plot o f apparent poles to fractures l i e eround
at a ^ l e s v w r y i^ between 20 and 40 degree*.
iillSiill
P oint re p re se n tin g directio n
an d In c lin a tio n o l ap p aren t
fractu re tin eatio n
P o les to tru e (derived) d ip s
of fractu re p la n e s
D irection o l dip of fractu re
p la n e s (detW edi
P o l e s t o a p p a r e n t d ip
p l a n e s o f f r a c tu r e s
P o l e s to t r u e d i p s o f
f r a c tu r e p l a n e s
Hydro the m e 1 s o lu ti o n s end s h e a rin g .
A few other fracture# occur that dip eore ateeply but these
— ear to be connected with the v ertica l fracture system and are quart:
T ile d .
The fla t-ly in g fractures do not extend far throw# the
w d W t s but "jimqf strata and a tr e l# ta n o u t, re-appearlng again
lower down.
In certa in aactlona o f the Lily and Rose's Fortune Minas the
flat fractures were found to have a direct bearing on the occurrence of
r-mee.
In general values ware found to be greater at t » e Inter­
section o f a v e rtic a l "reef fractime" and a f la t fracture.
The Increased values mare esp ecia lly noticeable In the Rosa's
s u in ta in economic p a y a b ili ty .
(c )
Baddlrva
■KSt
me largely found In the F ig -tree a e r ie s .
(a )
.....
n r A l i t n a '" '
a s h
c ia « a g a
:!;:™
^ g a ec o p lc a lly coneplcuoua
f
d«finite
-
N eedles o f aaqphlbole a re commonly found w ith t h e i r long or
‘c1 axes r o u ^ tly p a r a l l e l to th e bedding p la n e s and In th i s re s p e c t may
be re g a rd e d a s a p la n a r f a b r i c .
The c r y s t a l s as seen In th e ‘ a c 1 plan e
are w e ll a lig n e d and th e p ris m a tic c r y s t a l o u tl in e i s c l e a r ly d efin ed
to g e th e r w ith some b a s a l s e c t io n s .
The 'a b ' p la n e , how ever, d is p la y s
randomly o r ie n ta t e d p ris m a tic s e c tio n s a lo n e .
The ta lo o s e
developed p a r a l l e l to
developed p a r a l l e l to
sh a le s t o th e s o u th .
co n g ress io n norm al to
s c h i s t to th e n o rth o f th e mine h as a s c h is to s it y
th e r e g io n a l tr e n d o f th e fo rm a tio n s.
I t i s a lso
th e a x ia l p la n e s o f th e f o ld s in th e F ig - tr e e
The f a b r ic was th u s probably developed by
th e p la n e o f s c h i s t o s i t y .
C le av ag e in th e sedim entary la y e rs is a p p a re n tly ab sen t but
is p o s s i b ly in th e bedding p la n e .
T here is t h i n s e c tio n evidence o f
m inute bedding p la n e s l i p (s e e P la t e 1 4 ).
B re c c ia tio n is la r g e ly c o n fin ed tv th e Main Reef Zone and th e
Blunging o re sh o o t b u t does o cc u r in a m ild er form in p r a c t i c a l l y a l l
th e f r a c t u r e tones and where fo ld in g o f b r i t t l e components has caused
th e h in g e ro n es to s h a t t e r .
The b r e c c ia tio n c o n s is ts o f fra g a e n ta ry
s h a le s end s l a t e s in a m a trix o f f in e red c l a y , q u a rtz p a r t i c l e s and
ir r e g u l a r q u artz v e i n s .
The b re c c ia in th e s u lp h id e zone is re p la c e d
by q u e r t * , s u lp h id e s and c a rb o n a te m a te r ia l d i l l * t h a t in th e oxide
lone i s la r g e ly decomposed to ru b b le .
M ylcniti* a t io n and s lic k e n s id in g o c c u rs in crush zones and
W lginal ml mere! constituent# are pulverised end have been yound into
» mwp&ct b la ck b r i t t l e c la y .
T h is clay appears to have ac ted as a
lu b r i c a n t in many f r a c t u r e p la n e s .
Th.
«
* . 1 . * * p r iy m c k . w l f " "
E.srsKi.rss.rssLKSt'm.s/ssx
movement.
(f)
but th e f a c t t h a t th e y e x i s t x>es in d ic a te th a t some o f th e q in r tz
vein* found in th e mine were p r e s e n t in th e sedim entary su ccessio n s
p rio r t o d e fo rm a tio n .
(g )
M a ja i
J o i n t i n g and rock f r a c t u r in g seem tc be c lo s e ly r e l a te d in
th a t b o th phenomena a re la r g e ly r e s t r i c t e d to th e massive sedim entary
u n its .
The t i ^ h t i s o c l i n a l f o ld in g d is p la y s shear jo i n tin g in th e
steep fla n k s o f th e f o ld where l a t e r a l s h o rte n in g has been e x te n s iv e
and te n s i o n j o i n t i n g in th e c r e s t s o f th e f o ld s .
The j o i n t s in both
the h in g e and fla n k s o f th e fo ld s d ip tow ards the fo ld ax e s.
(h )
P o s s ib le R . l irtlftnnM r
t h ‘ S t r u c t u r . . In t h . M1m
As h as been shown, th # fo rm a tio n o f t h i n ly bedded F i g - t i r e
seeks in th e mine is in te n s e ly fo ld e d , sh o rten , d and f l a t t e n e d . This
deformation was produced la rg e ly d u rin g th e fo rm ation o f th e major
ly n e lln e e o f th e Bar b e -to n M ountain Land, i . e . c o in c id e n t w ith Ramsay's
(MM) le t period o f fold ing.
Synchronous with the fold development
ass th e fau lting on a r e g io n a l s c a l e .
The L ily F a u lt - s to n e o f
d**lm g s t the contact between T lg-tree and underlying Onverssecht
faeke peovlded the enam el o f entry for ths hydrothermal mineralising
s o lu tio n s .
The I n itia l deformation produced t l f i t Iso clin a l folds that
elamme steep ly to the e a st.
The variable spread of the plunged can be
resribad eith er to d iffe r e n tia l movement in the 'a ' direction o f folding
produced by v a r i a b le compress 1ve s tr e s s e s , or th e s u p e r is p o s itio n o f
hid e em ms already deformed or folded succession.
There Is howyer,
» eemelueive evidence In the aree or In adjacent areas of an e = l l «
saeke In the y _ e n * r Moodies conglomerates.
This dnes Indicate the
p o s s i b ili ty o f some p re v io u s uneven surfaces.
The major or v ertica l fracture system wes developed after the
FlIlE lllE SSit
- 115
The s h e a rin g o r s t r i k e - s l i p movement produced c o in c id e n t
cleav ag e -b ed d in g r e l a t i o f ^ h i p e in th e F ig - tr e e sedim ents o f th e mine.
The in t r u s i o n o f th e N e ls p r u it G ra n ite s was found by Ramsay (1963) to
have ta k e n p la c e ducting th e 2nd phase o f d e fo rm atio n .
I f th e h y d ro th erm al s o lu tio n s from th e in tr u s io n are assumed
t@ h av e been th e so u rc e o f th e gold fou. i th ro u g h o u t th e D i s t r i c t then
th e m i n e r a liz a tio n o f th e L ily Mine ruist have ta k e n p la c e subsequent to
th e f r a c t u r e developm ent, i . e . e i t h e r l a t e d u rin g th e 2nd phase o r
d u rin g t h e 3rd p h a s e .
(a )
I n tro d u c tio n
In r e c e n t y e a rs th e opening up o f the mine has led to fu rth e r
development o f e x i s t i n g s e c tio n s in a d d itio n to work elsew here in th e
Due to th e lim ite d s c a le o f o p e ra tio n s i t was always found
necessary to c e a se m ining in th e s u lp h id e o r fre s h ro c k .
However, In
s in e .
c e r t a i n in s ta n c e s th e abundance o f p y r r h o tic e and q u artz w arranted
investigation and a n a ly s is end developm ent co n tin u ed fo r a w mile.
In
th is r e g a r d th e developm ent o f th e two w inzes below 2 Level was under-
W w , k lk M d n , W lM t lM . o f fo ld in g , * o c « io tlo n and
.in e r .llt .t lo n ,
T h . p o M l b l l i t y o xl.tod th a t v i . l b l . gold lo d w m lf t
b . e n c o u n tered In t h l . to n ..
T h . w intM r . p » « « n t . d p r o je c ti o n , of
th e o r . .hoot In h ig h e r l e v e l , b u t l i t t l e .ucceot we. encountered wl-h
I n c r e a tln g d epth and work was c u r t a i l e d .
A few d r i l l h o le s were desig n e d to probe th e s u l p h i d e b re c c ia
m tm m sm
The o r e s u i t e from th e L ily .41ne c o n ta in e d te n m in erals in
a d d itio n to th e gangue o r co u n try r o c k .
The n e s t abundant su lp h id e
noted was found to be p y r r h o t i t e and t h i s was follow ed In r e l a t i v e
abundance by a r s e n o p y r it e , m a g n e tite , p y r i t e , m l n l k a v i t e - p y r i t e ,
c h a lc o p y r itp , h e m a tite , iim o n ite , g o e th ite and g o ld .
A part from th e
p y r r h o ti te and a r s e n o p y r ite th e rem aining m in erals were o n ly p re s e n t
in sm all am ounts.
The g ar ju e v a r ie d c o n s id e ra b ly thro u g h o u t th e mine but
g e n e ra lly c o n s is te d o f q u a r t z , c a rb o n a te s , am phiboles, to u rm a lin e ,
q u a r t z - c h io r lte - e a r b o n s te m a te r ia l and th e c la y m in e r a ls .
The quarts
o ccu rred in s e v e r a l forms and v a rie d from W hite to b lu e -g ra y and was
e ith e r f r o s te d o r t r a n s l u c e n t .
M assive bo d ies o f c h e rty q u artz were
en co u n tered i n a l l s e c tio n s o f th e m ine.
(b) tta.Mlntiala
(i)
E x tr a c tio n T .» t
B efo re d i s c u n l n g th e m ineralogy o f th e mine I t I s o f I n te r e s t
te n o te th e r e s u l t , o f an e x t r a c ti o n t e s t done on two sam ples o f L ily
nine o r e I n order t o g a in some Idea o f th e v a rio u s elements p re s e n t fo r
m e ta llu r g ic a l p u rp o s e s .
The te s ts were c e r r l e d o u t In M arch, 1935, by
th e C o n s u ltin g I f e t a lli s rg l s t fo r E a ste rn T ra n sv aa l C o n s o lid a te d Mines
IM tm d.
N ef. » . Q.M 2.
2 bags each 2 ,000 l b s . w e l # t .
1.
S u lp h id e o re
2 ,1 6 d w tt, Au,
2.
Oxide o r e
4 .0 2 d irts . Au.
A n aly sis e f th e o x id is e d o r e gave t h . w e l# it p ercen tag es o f th e
C o n s titu e n ts .
From th e s e resu lts th e c a tio n p e rc e n ta g e s have been
c a lc u la te d ( s e e T a b le I I I ) .
W eight %
,H I .. W
i^ p
3
"0
85.00
1.12
0.10
8 .0 5
2.35
0 .3 0
W t . C W zI
(f e r tlc )
(* « "* ")
0,20
P y rite ( F * 2 '
0 .5 8
A re e n le * • •
tr a c e
tra c e
tra c e
AntleoiW s ^
Bism uth
B l.
Copper
Nickel
tra c e
C o b a lt
Zinc
CtCOj
U fO )
* . w b l . . l k . l l (M f -
3. 5)
7CTM.
—
"............. ""**~
,
__ .wiit s i l i c a makes
. . . . “P s ™ : " "
i* * f E
r
t
r
end 4 5 ) and gangue m a te ria l was In v a ria b ly found to precede th e
s u lp h io e s le a v in g r e l i c t c r y s t a l s o r ag g reg a tes tra p p e d w ith in th e
p y rrb u tite .
The rep 1a c c e n t o f c h e rt o f te n produced a mosaic w ith
th e sp aces between th e in d iv id u a l q u a rtz g r a in s p ro v id in g th e most
fa v o u ra b le r e p la c in g environm ent,
E uhedral c r y s t a l s and fragm ents o f a rs e n o p y rite are rep laced
e r e n t i r e l y surrounded by th e l a t e r p y r r h o t i t e .
E tching o f th e co rn e rs
e f a r s e n o p y r ite i s common but replacem ent i s seldom com plete (s e e P la te
4 7 ).
The p y r r h o t i t e i t s e l f , la c k s e x te rn a l c r y s ta l form and is u su a lly
moulded w ith in i t s s u rro u n d in g s . o r i s pseudoraorphous a f t e r e a r l i e r o re
m in e ra ls and gangue.
F re q u e n tly seen a s s o c ia te d w ith th e p y r r h o ti te ag g reg a tes are
sm all ir r e g u l a r p a r t i c l e s o f exsolved c h a lc o p y r ite .
P e n tl a n d it e , a
e - ' a s s o c ia te o f p y r r h o t i t e i s e n t i r e l y ab sen t from th e L ily o re
s u it .
In o n ly r a r e in s ta n c e s was p y r i t e seen to g e th e r w ith th e
p y r r h o v it e .
The form er m in eral g e n e ra lly o cc u rre d as “ isla n d s*
surro u n d ed and re p la c e d bv th e l a t t e r .
In th e p a r t i a l l y a l te r e d zones
on 1 Level and in some s e c tio n s on 2 Level both p y r it e and m e ln ik o v lte p v r i t e r e p la c e p y r r h o t i t e .
( iii)
X«Rav Bit5ractoaetax_InvestiaallQn of
N&M PVTitMUtl
The p o s s i b i l i t y o f ap p ly in g th e d (l0 2 ) v alu V c o m p o sltlo n
r e l a t i o n to n a t u r a l p y r r h o ti te was in v e s tig a te d by A rnold and Reichen
(1 9 6 2 ).
The X-Ray method was found to be a convenient and reaso n ab ly
a c c u r a te method o f m easuring t a m etal c o n te n t o f hexagonal r k tu r a l
W T d i o t l t e ,.
A rm ld and R e ic h e r (1962) found e x p e rim e n ta lly t h ^ th e
copper i n s o lid s o l u t i o n , o v er a co m p o sitio n range 4 6 .5 t , w 7 atomic
ir o n .
P y rrh o tlt.
tl<w« u w d to . b t . l n . ro w *
M M f r w o f v l w .1 l^ » U T lti« ..
of
The p y r r h o t i t e wee crushed «rW p re p -red f^r sp e ctro sco p ic
a n e ly e is .
T h is ame c a rrie d o u t to g e t an in d ic a tio n o f elem ents
oth e r th a n ir o n and su lp h u r t h a t »' jht be p r e s e n t.
The examination
in d ic a te d th a t c o b a lt, n ickel and copper were p re s e n t in tr a c e amounts
only.
The percentages were th e re fo re , too email to a ffe c t th e la ttic e
param eters as determined by Arnold and Reiman (1 962).
Specimens were also prepared for X-Ray analysis and equal
p ro portions o f a n a ly tic a lly pure p o ta ssiu m c h lr:id * w.=.-re stixcd with th e
sulfA idte f o r use as an in te rn a l s ta rx ia rd .
Measurements were made with
a P h il lip s X-Ray D iffractom eter equipped w ith an atitometic c h a rt
Each (IC S) r e f l e c t i o n was measured r e l a t i v e to th e (220) and
(2 2 ?) r e f l e c t i o n s o f th e a n a ly ti c a ll y pure IC 1, lo c a te d a t 36.6
2 and 6 4 .4 2
2 $ Ve Kee 1#
2P e # X e €
S can n in g and c h a r t speeds w ere £ degree p er m inute and 2
in c h es p e r d e g re e .
Peak p o s iti o n s were me?-.ured to 2 0 .1
2A .
S ta n d a rd d e v ia tio n s o f th e mean 2 <• (102) v a lu e s and th e corresponding
d ( 102) v a lu ta w ere ♦ 0.0004 A° r e s p e c t iv e l y .
The d( 102) v a lu e s o b ta in e o were 2.0638 , 2.0638 and 2.0672.
T hese v a lu e s c o rresp o n d to v a lu e s o f 4 7 .3 , 47 .3 and 47 .4 atum ic per
c e n t i r o n , ( s e e F ig . 2 2 ) , and th e s e in tu r n giv e approxim ate
te s p e r a tu r e s t f 2^0% and 320®C, ( s e e F ig . 2 3 ).
i h l s t ^ t s s in to s e io u n t a p r e a s o r . o f about 10 b a r s . The
e f f e c t o f p r o c u r e u a u a lly r e s u l t s In th e r a i s i n g o f th e t « | i e n t u r e
e f f o m e tlo n b u t t h i s seldom e x c eed . 10 to 2 0 % , even ' t p re e s u re s o f
s e v e r a l th ousand atm o sp h eres. (E dw ards, 1954).
The te s p e r a tu r e o f fo rm a tio n o f th e p y r r h o ti te m in e ra lis a tio n
HO*
(T u rn er and V erhoogen, I9 6 0 ,.
( F i g 2 2 ) G rap h a f t e r A rn o ld I S 62
showing t h e e x p e r i m e n ta lly
d e r i v e d X -rav d e t e r m i n a t i v e
curve fo r n a tu ra l hexagonal
p y r r h o t i t e # . s u p e r im p o s e d i n
r e d a r e d l 1 0 2 )A v a l u e # f o r
p y r r h o t i t e # fro m t h e i . i l y -.Ine
an d t h e d e r i v e d a t o m i c > Fe
( m e t a l # ;•
* w r» .i (« •» •» .-)
23 ) Oraoh a f t e r C l a r k C I S t - ' )
t h e e x p e r im e n ta lly
a r r iv e d c u r v e o f Atomic /*Fe
a g s ln e t rem p era tu re i n C fo r
n a t u r a lly o c c u r r in g p y r r h o t it e # .
S m arleip oeed In red on th e
a r m * a ** A tom ic c f * v a lu e * o f
m p r r b v tlte frcm t h e L ily f i n #
Bmmther w ith t h e t e v p e r a tu r e e
@f fo r m a tio n t h u s d e r iv e d .
{ n r
I t was m entioned by d# V H l le r s (1957) th a t he co n sid ered the
Lily o c c u rre n c e to be a h ig h te m p eratu re d e p o s it formed a t g r e a t d ep th .
Although g iv in g no a c tu a l te m p e ra tu re v alu e I t i s co n sid e red by th e
w rite r t h a t th e e x p e rim e n ta l work done on th e p y r r h o ti te # , to g e th e r w ith
m in e ra lo g lc a l and p e t r o lo g ic a l e v id e n c e , would tend to favour « lower
te m p eratu re th a n t h a t im p lie d by de Y i l l i e r s .
( iv )
ite n n ffB y tU ,
A r s e n o p y rite commonly accompanies p y r r h o ti te but never in any
g reat am ount.
The g r e a t e s t c o n c e n tr a tio n o f t h i s m ineral was found in
a r a i s e o f f th e w e s te r ly d r iv e along th e Main Reef Zone o f I L e v el. The
e re h as been p a r t l y a l t e r e d y e t i s d e le te r io u s to th e e x t r a c ti o n p ro cess
a t th e m i l l .
The a r s e n o p y r ite lik e th e p y r r h o ti te may form bands in
th e o r e b u t t h i s i s r a r e .
The m in e ra l o c c u rs e s s e n t i a l l y a s in d iv id u a l
e r a g g re g a te groups o f id lo n o rp h ic c r y s t a l s .
Movement w ith in th e o re
body d u r in g o r e d e p o s itio n h a s o f te n r e s u lt e d in t h i s m in eral being
f r a c tu r e d .
T here i s evidence o f in t e n t s sh e a rin g along bedding planes
with su b se q u en t d e p o s itio n o f l a t e r m in e ra ls .
The f r a c tu r e s in th e
su lp h id e g r a in s ,aay have been ch an n els used 'y o r e s o lu tio n s fo r th e
lo c a li z a ti o n o f th e g e ld .
The a r a e n p p y r ite i s e a s i l y d is tin g u is h e d f.tm o th e r s u lp h id e s
by i t s c o l o u r , a n iso tro p is m and h a rd n e s s .
S u rfa c e s u s u a lly ta k e ° n *
good p o li s h and th e r e l i e f o f ♦‘hr m in eral also a id s in i t s i v * * f ic a ti o n .
Xt i s f a i r l y r e s i s t a n t to rep lecesm n t but p y r r h o ti te was seen oorro d in g
e s s n srs o f c e r t a i n c r y s t a l s and p e n e tr a tin g f r a c t u r e , (s e e P la te 4 , ) .
I . M M tlo n W l« » o rp h lc c w n o p Y i I t . g r . i n . « n tlT .lY w rm im m d by
y y n t b t l t * w « r.
P y r l t . r r p l * w m tw m p Y T lt. In o r . o b t a i n ^ fro # t b . M "*p o r t k m of 2 I m ) M l t h . t n t w
ew , ^ 1 1 1 b .
? !r
M lwtropl# »*
# . l A t ^ # ln .ro l M . d l ^ ln c t lv ..
m .p w lm w , o b t . l m ^ f r o . " m ln .r.M » « l q u = V
BEIliiiir:
e ln r
re rlt.
The c r y s t a l 's unu su al c o lo u r a tio n may a lso p a r t ly be due to
th e p r e s e n c e o f h ig h ly r e f l e c t i v e gold (s e e P la te 5 1 ).
The gold veins
and I s o la t e d specks w ith in th e gudmundite probably in d ic a te a
conteraporanaous o r i g i n f o r p a r t o f t h e gold o re .
A few s a s p le s w ere o b ta in e d from dtsnp* a t th e o ld workings o f
th e M exican p r o s p e c t n ea r Eureka 5 1 l i n g .
These c o n s is te d e s s e n ti a ll y
o f w eath ered a r s e n o p y r ite c r y s t a l s h av in g good idiom crphic shapes. The
gangue c o n s is te d o f r a d i a ti n g la th s o f tr e m o ltte w ith f in e m icroc r y s t a l l i n e and is o la te d c o a re a g r a in s o f q u a rtz .
(v )
PluUngyilti
T h i . m in e r. 1 i s n e a rly .Iw ay s a s s o c ia te d w ith p y r r h o ti te h i t
never o c c u rs in g r e a t am ounts.
I t s p re se n c e was su sp e cte d p r io r to
m icro sco p ic e x a m in atio n due to th e m inute d is p la y , o f ir id e s c e n c e seen
on ta r n is h e d o r e s .
L aths o f i r r e g u l a r , in tim a te In te rg ro w th s o f th e
C h a lc o p y rite w ith p y r r h o t i t e se e n under th e m icroscope show mutual
boundary r e la tio n a l-.'p a and s u g g e s t, contem poraneous fo rm atio n e f th e
two m i n e r a l s .
C h a lc o p y rite was a lso se e n to g e th e r with p y r i t e and
a e l n l k o v l t e - p y r i t e where i t o c c u rre d r e p la c in g th e l a t t e r m ineral.
(v i)
E m its
In o n ly a few in s ta n c e s was p y r i t e noted in th e o r e s .
Its
aek< * and hardnaw mad. i t d is tin c tiv e .« « « * * « r e I t to eu rred with
aama a f t h . w a M m p y rlt..
S p K l - n . f r o . : lev el
iw le tle n sh lp between th e two m in e ra ls was not c l e a r .
replace w s e w p y r i t e to a l i r l t e d e x t e n t.
(v li)
ss.ln ia n « tte — r r l t e
(g e l o f
and
Author Anhaeusser C R (Carl Robert)
Name of thesis The Geology Of The Lily Syncline And Portion Of The Eureka Syncline Between Sheba Siding And Louw's
Creek Station, Barberton Mountain Land. 1963
PUBLISHER:
University of the Witwatersrand, Johannesburg
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