AUTHORS: Stuart Simmons, Kevin Brown
Gold, silver and associated trace metals are found in hot springs, geothermal wells, and volcanic emissions within Taupo Volcanic Zone, making it a natural laboratory for studying precious metal transport and deposition. Deep hydrothermal solutions (near neutral pH) with the highest concentrations of aqueous H2S contain the highest concentrations of gold, consistent with gold solubility experiments. These solutions, however, are significantly undersaturated in gold, meaning that the ultimate control on gold concentration is the deep supply of metal rather than availability of aqueous H2S. Gold subsequently deposits in three distinct shallow hydrothermal environments: 1) geothermal wells; 2) hot springs; and 3) disseminated in altered volcanic rocks. The efficient precipitation of gold in geothermal wells due to boiling provides the best analogy to understanding the conditions of ore formation in many epithermal veins. Comparison with the giant Ladolam gold deposit indicates that compositions of gold transporting solutions are diverse. Optimal epithermal ore forming conditions depend on the hydrothermal metal flux coupled with an efficient mechanism of metal deposition.
KEYWORDS: Gold, Silver, Metal Transport-Deposition, Epithermal
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