Heavy mineral analysis

Heavy mineral analysis
What are heavy minerals?
→ minerals with a specific density ρ > 2.85 g/cm3
→ accessory minerals in clastic sediments with a proportion
of usually <1%
→ are smaller than the average grain size of the sediment
→ amphibole, pyroxene, zircon, tourmaline, rutile, apatite, ...
How to analyse them?
• fine to medium-grained sandstones, as fresh as possible (!)
• crushing and desaggregation (e.g., 10% acetic acid, ultrasonic, H2O2, etc.
• sieve fraction 63 – 125 µm (may be coarser, if necessary)
• separation of HM by specific density fluids such as Na-metatungstate
• counting of at least 200 grains under the microscope; embedded in special
resins or waxes with well defined optical properties (e.g., Meltmount 1.66)
• for details see Mange & Maurer (1991, 1992)
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Boenigk
1983
HvE
- Sedimentpetrologie
Grain-size dependence of HM assemblages
→ 63 – 125 µm
Boenigk 1983
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XYi = mineral X – mineral Y index
Hydraulic
behavior
= 100 * X / (X + Y)
ATi = Apatite – Tourmaline index
= 100 * apatite / (apatite + tourmaline)
Morton & Hallsworth 1994
HvE - Sedimentpetrologie
Modification of HM assemblages
source area
weathering
mixing
abrasion
sorting
authigenesis,
intrastratal solution
sedimentary basin
Morton & Hallsworth 1994
HvE - Sedimentpetrologie
Mange & Maurer 1991
weathering
3
Occurrence and stability of HM (weathering profiles)
- decreasing stability Morton & Hallsworth 1999
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Mange & Maurer 1991
4
Modification of HM assemblages
instrastratal
solution
Morton & Hallsworth 1999
HvE - Sedimentpetrologie
Tha-2
Sal-2
Fotos: HvE
Huy-1
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Weathering on transit
(alluvial storage)
example by Morton & Johnsson 1993
CMM
SMA / NMA
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Weathering
on transit
NMA
SMA
CM/MA
prox.
mid.
dist.
Llanos
CMM
Morton & Johnsson 1993
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Example:
Lower Rhine
Bay, Cologne
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Boenigk 1983
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Berger et al. 2005
Schwerminerale
→ Minerale mit spezifischer Dichte ρ > 2.89 (2,86) g/cm3
(engl.: heavy minerals oder dense minerals)
→ Charakteristische Merkmale:
- Habitus (Form, Spaltbarkeit, Oberflächenstruktur, ...)
- Farbe (Pleochroismus!)
- Lichtbrechung (unterschiedl. Einbettungsmittel!)
- Doppelbrechung (Mineraldicke und -orientierung beachten!)
- Auslöschung, opt. Charakter/Interferenzbild, Einschlüsse, ...
→ für die spezifische Merkmale der einzelnen Minerale siehe v.a.
Mange & Maurer 1991; im Skript sind nur einige Folien enthalten
mit Bezug zur Schwermineralchemie
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zircon
a: Eocene tuff horizon
b: Carboniferous sediments
100 µm
Meltmount 1,662
tetragonal,
ρ = 4.60 – 4.79
n = 1.92 – 2.02
Mange & Maurer 1991
Δ = -0.042
– 0.065
HvE
Sedimentpetrologie
tourmaline
trigonal, 1- , ρ = 3.00 – 3.25, n = 1.61 – 1.66, Δ = 0.017 – 0.036
Al(tot)
elbaite
Elbaite
1
4
Meltmount 1,582
Mange & Maurer 1991
100 µm
2
Schorl
schorl
7
5
3
Dravite
dravite
8
6
uvite
Uvite
Al50Mg 50
Al50Fe(tot)50
& Guidotti
1985, rocks
1,2: Henry
granitoid
host (source)
von
Eynatten & Gaupp
1999 rocks
4,5,6:
metasedimentary
host (source)
detrital
tourmaline grains
EY 6-1 (LOS)
H 1021-5 (BRA)
EY 9-34 (BRA)
tourmaline from
metasandstone
clasts
HvE - Sedimentpetrologie
EY 6-3/b (LOS)
EY 6-3/c (LOS)
EY 6-3/d (LOS)
Henry & Guidotti 1985,
von Eynatten & Gaupp 1999
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Mange & Maurer 1991
rutile – properties and occurrence
• beside sphene and ilmenite
the most important Ti - mineral
in the earth‘s crust
• chemistry:
TiO2 ( >99 wt.-%)
but ...
• main primary occurrence
in medium to high-grade
metamorphic rocks
• stable in sedimentary
environments
Nb
→
28000 ppm
tetragonal, 1 +
Cr
→
4400 ppm
n = 2.61 – 2.90
Fe
→
>30000 ppm
Zr
→
8400 ppm
V
→
7600 ppm
W
→
8100 ppm
U
→
84 ppm
Δ = 0.286 – 0.296
→ frequent occurrence as heavy mineral in (mature) clastic sediments
→ used for maturity (ZTR) and other indices reflecting source materials (RZi)
rutile
Cr in ppm (rutile)
HvE - Sedimentpetrologie
5000
metacumulates
4000
3000
rutile from
mafic rocks
2000
1000
rutile from
metapelitic rocks
28000
0
0
500
1000
1500
2000
2500
3000
Nb in ppm (rutile)
Zack et al. 2002, Chem Geol 184
Zack et al. 2004, CMP 184
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Mg/(Mg+Fe2+)
Cr/(Cr+Al)
1.0
chrome
spinel
0 1.0
0
1.0
A
chromitites
B
type-III
ophiolites
0.8
Kubisch
ρ = 5.09
0.6
n = 2.00
Δ = ./.
Meltmount 1,662
0.4
TiO2 wt.-%
harzburgites
cumulates
(dunites)
type-II
ophiolites
2.0
0.2
Diagramm nach Arai 1992,
Daten aus v. Eynatten 1996
lherzolites
IPB
1.5
type-I
ophiolites
0.0
Dick & Bullen
1984
MORB
1.0
Pober & Faupl
1988
IAB
0.5
0
0.05
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amphibole -
Fe3+/(Cr+Al+Fe3+)
0.15
?
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Fe2+/(Mg+Fe2++Mn)
blue sodic amphiboles
1.0
0.8
0.6
0.4
0.2
Mgriebeckite
von Eynatten et al.
1999, Sed. Geol.
0.0
0.0
0.2
0.4
0.6
0.8
1.0
Fe3+/(AlVI+Fe3++Ti)
HvE - Sedimentpetrologie
(G) Case Studies
1. Oligo-/Miozänes Vorland der Betischen Kordillere
2. Schweizer Molassebecken (Zentralalpen-Vorland)
3. Subherzynes Kreidebecken (Harz-Vorland)
4. ... ... ...
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