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2001 wednesday 15 august 12 areas distal from

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Unformatted text preview: . Recently used in Australian SEDEX and VMS deposits. • • • 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 and 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) W...
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