9-6 Transport and deposition of nanoparticulate precious metals in hydrothermal fluids

Session: Early Career Investigators in Mineralogy and Crystallography

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The presence of metallic nanomaterials (i.e., nanoparticles, nanominerals, nanofluids, and nanomelts) in ore systems has been increasingly documented over the past decade. This challenges the traditional view that ligands (e.g., chloride- and bisulfide-bearing) are the only effective metal carriers in hydrothermal solutions. While metal-bearing ligands account for the metal content in ordinary ore deposits, they are incompatible with the significant precious metal enrichments (up to the wt.% scale) found in mm- to cm-sized bonanza-type ores due to their low solubilities (on the order of ppb). In this study, we report on nanomaterials enriched in Au-Ag-Cu from an epithermal bonanza-type ore in southern Mexico. These nanomaterials are paragenetic with liquid- and vapor-rich fluid inclusions indicative of boiling as the ore precipitation mechanism. Our data show that boiling metal-bearing brines can produce, aggregate, and accumulate metal nanomaterials, ultimately leading to concentrated gold, silver, and copper over-enrichments. These documented processes may explain the formation of bonanzas in metal-rich brines across various types of mineral deposits.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6272

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