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Unformatted text preview: . Recently used in Australian SEDEX and VMS
• Often disperse much larger haloes than base metals.
Often several hundreds of meters from the deposit.
Beware of analytical problems – volatile elements are very volatile
therefore hard to keep in solution. Wednesday, 15 August, 12 From Large et al. (2001)
Wednesday, 15 August, 12 Areas distal
from mineralization From Collins (1989) and Piercey (2009)
Wednesday, 15 August, 12 Duck Pond
Boundary Horizons Other Tools: Mineral Chemical Variations
• Use of mineral chemical vectors. •
• Micas – Ba-rich muscovites Possible to outline zones within deposits or within known camps –
not a really good regional exploration tool in grass roots exploration. Carbonates – Fe, Mn-rich carbonates
Chlorites – Fe,Mg,Mn,Zn-rich chlorites
Epidotes – Fe-Al relationships Wednesday, 15 August, 12 Alteration Indexes • Once we have established the gains/losses and spatial
association of elemental suites we can construct
elemental indexes. • In major elements we often use: • We can weight terms of the equation depending on
proximity to mineralization, elemental abundance, etc. • Since we often we mix ppm and wt% data we have to
normalize the data using Z-score, 2σ error on analytical
data, log transform and standardize, or some other
numerical factor (e.g., primitive mantle). • If we have good control on elements associated with
alteration we can apply factor analysis to datasets to help
us create indexes. Wednesday, 15 August, 12 Alteration Indexes: Examples •
• Spitz-Darling Index = Al2O3/Na2O ! [Spitz + Darling (1978)]
Based on premise that: • When feldspars of any kind alter to sericite or chlorite
they lose Na2O • Most alteration to clays results in residual Al2O3 gain in
altered rock relative to parent rock. • Greater intensity of alteration more Al2O3/Na2O gain. Wednesday, 15 August, 12 From Spitz
and Darling (1978)
Wednesday, 15 August, 12 From Spitz
and Darling (1978)
Wednesday, 15 August, 12 Alteration Indexes: Examples •
• Sericite Index = K2O/(K2O+Na2O) ! [Saeki and Date (1980)]
Based on: •
• Wednesday, 15 August, 12 Destruction of feldspar to sericite.
Destruction results in Na2O loss.
Sericite formation results in residual K2O gain. Alteration Indexes: Examples • Hashimoto Index = 100*(MgO+K2O)/(MgO+K2O+CaO+Na2O)
[Ishikawa et al. (1976)] •
• Good for felsic rocks.
Based on: • Feldspar and felsic glass destruction and losses of CaO
and Na2O. •
• K2O residual gains during sericite (muscovite) formation. Wednesday, 15 August, 12 MgO gains during chlorite alteration due to Mg-ﬁxation
from hydrothermal ﬂuids (e.g., Hajash and Chandler,
1981). Alteration Indexes: Examples • Chlorite-Carbonate-Pyrite-Index (CCPI) = 100*(MgO+FeO*)/
(MgO+FeO*+Na2O+K2O) [Large et al. (2001a)] • Builds on the Hashimoto Index: • Pyrite, chlorite, and carbonate formation in VMS result in
MgO and FeO* gains. • Destruction of rock feldspars result in Na2O and K2O
losses Wednesday, 15 August, 12 ALTERATION BOX
PLOT After Large et al. (2001a) AI = 100*(K2O+MgO)/(K2O+MgO+Na2O+CaO)
CCPI = 100*(FeO*+MgO)/(FeO*+MgO+Na2O+K2O)
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This document was uploaded on 03/06/2014 for the course ES 4502 at Memorial University.
- Fall '12