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Gold and metal enrichment in natural granitic melts during fractional crystallization

Mustard, R, Ulrich, T, Kamenetsky, VS and Mernagh, TP 2006 , 'Gold and metal enrichment in natural granitic melts during fractional crystallization' , Geology, vol. 34, no. 2 , pp. 85-88 , doi:

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Metal evolution in a composite granitic pluton was tracked by analyzing melt inclusions in 11 quartz samples from 7 zones at the Timbarra gold deposit, Australia. We present the first quantitative microanalyses of gold (Au) in granitic silicate melt inclusions using laser ablation inductively coupled plasma mass-spectrometry and show how Au and other metals become enriched during fractional crystallization in a granite intrusion. Au was enriched during fractionation from a monzogranite to a highly fractionated alkali-feldspar granite. Similar enrichment behavior for other metals implies that no gold-enriched precursor melt is required and fractional crystallization can enrich the Au concentration to economic levels. The low content of accessory oxides and sulfides, the absence of early Cl-bearing fluids, the volatile content in the melt, and a prolonged crystallization constitute important factors for extensive metal enrichment during crystal fractionation. These characteristics play a crucial role in felsic, highly fractionated plutons and their associated deposits such as intrusion-related Au deposits. The gold enrichment during fractionation also implies that Au is directly sourced from the granites.

Item Type: Article
Authors/Creators:Mustard, R and Ulrich, T and Kamenetsky, VS and Mernagh, TP
Keywords: gold; metal enrichment; LA-ICPMS; melt inclusions; fractional crystallization; intrusion-related Au deposit
Journal or Publication Title: Geology
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