Abstract

The high-grade Chañarcillo vein silver deposit in northern Chile has been repeatedly cited as an exemplar for supergene silver sulfide enrichment beneath a rich oxidized zone. By analogy with the supergene upgrading of copper deposits, it is claimed that silver released during oxidative weathering migrated progressively downward in acidic solutions to the upper parts of the underlying sulfide zone where it was reprecipitated under more reduced conditions as replacive sulfides, sulfosalts, alloys, and the native metal. Evidence is presented to show that the putative silver sulfide enrichment zone is more likely to have been a product of hypogene vertical zoning in a deposit of native Ag-Co-Ni-As type.

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