Geochemical whole rock XRF analyses of representative lithologies within the Wakamarina Goldfield, Marlborough Schist Belt, New Zealand

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SR_1998-020-pdf
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Skinner, D.N.B.; Brathwaite, R.L. 1998 Geochemical whole rock XRF analyses of representative lithologies within the Wakamarina Goldfield, Marlborough Schist Belt, New Zealand. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 98/20 41 p.


Abstract: Geochemical analyses of very low grade psammitic Marlborough Schist, Wakamarina Quartzite, and associated metabasites and metagabbros from adjacent to the quartz lodes of the Wakamarina Goldfield show distinctive patterns of hydrothermal alteration when compared with average analyses of samples uninfluenced by hydrothermal fluids related to lode formation. The unaltered schists are geochemically synonymous with the volcanogenic Pelorus Group of the Caples Terrane, and have a calc-alkaline volcanic detrital origin, perhaps from mixed oceanic and continental arc sources that included a significant andesite-dacite component. Wakamarina Quartzite is not a metachert but a partly pelagic, sedimentary quartzite with a component of similar calc-alkaline arc volcanic detritus to that of the enclosing schists. On the other hand, metabasites interlayered with the schists, and metabasites and metagabbros associated with Wakamarina Quartzite are clearly tholeiitic with predominantly MORB elemental abundances. Hydrothermal alteration by the lode-forming fluids has significantly altered the geochemistry of the host schist envelopes, by causing depletion in actinolitic amphibole, stilpnomelane, pumpellyite and ankerite, depletion of Ca and Sr, and variable enhancement of K, Ba, Rb, Sb, As, Pb, Cu, P, U and Th. Alteration of metabasite and metagabbro hosts is similar except that hangingwall metabasite has enhanced Sr, and hangingwall metagabbro is depleted in Sb, Ni and Cr adjacent to lode quartz with very high levels of Cr. (auth)