Authors / CoAuthors
Tanner, D. | Henley, R.W. | Mavrogenes, J.A. | Holden, P. | Mernagh, T.P.
Abstract
The accepted understanding of ore-forming fluids in hydrothermal ore deposits is underpinned by one major assumption: that quartz and included fluids faithfully record depositional conditions. Here, we present evidence of high-temperature deposition and evolution of silica hydrate that casts doubts on this assumption. Quartz microcrystals from the El Indio Au-Ag-Cu deposit (Chile) preserve a rare glimpse into the high-temperature evolution of silica. Aggregates of euhedral quartz microcrystals preserve cryptocrystalline cores bearing residual metastable silica hydrates (opal and moganite) - indicating that euhedral quartz progressively evolved from metastable silica hydrate. This sequential evolution (silica hydrate-opal-moganite-quartz) caused progressive dehydration, resultant in extreme '18O fractionation. We calculate that the precursor silica hydrate contained 27-54 wt% H2O, making it similar to viscous Si-rich fluids observed in magmatic-hydrothermal ore deposits. This cryptic silica hydrate is likely a common precursor in high-temperature hydrothermal ore-forming environments, but rarely preserved. The discovery of cryptic silica hydrate affects the paragenetic and geochemical interpretation of quartz and included fluids. Quartz matured from silica hydrate would record 'pseudo-primary' fluid inclusions and produce a bias in fluid provenance calculations within sub-volcanic systems.
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76497
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- External PublicationScientific Journal Paper
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2013-01-01T00:00:00
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