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Gold and metal enrichment in natural granitic melts during fractional crystallization
journal contributionposted on 2023-05-16, 18:54 authored by Mustard, R, Ulrich, T, Vadim Kamenetsky, Mernagh, T
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. Â© 2006 Geological Society of America.
Department/SchoolSchool of Natural Sciences
PublisherGeological Soc America, Inc
Place of publicationBoulder, CO, USA