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Veladero high-sulfidation epithermal Au-Ag deposit, Argentina: volcanic stratigraphy, alteration, mineralization, and quartz paragenesis, The
Holley, Elizabeth A.
Holley, Elizabeth A.
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2012
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2012
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2013-12-01
Abstract
The Veladero Au-Ag high-sulfidation epithermal deposit is located in the El Indio-Pasuca belt in Argentina. Veladero is an oxidized deposit that hosted reserves of 12.2 Moz of Au and 226.2 Moz of Ag at the end of 2008. Ore is primarily hosted in silicified breccias. The volcanic package at Veladero is a coalescing complex of domes, diatremes, and hydrothermal breccia bodies, mantled by a thick apron of volcaniclastic deposits. These units are inferred to be of Cerro de las Tortolas age (16.0 plus or minus 0.2 to 14.9 plus or minus 0.7 Ma) at Amable in the southern part of the Veladero area, and Vacas Heladas age (12.7 plus or minus 0.9 to 11.0 plus or minus 0.2 Ma) at Filo Federico in the northern part of Veladero. Emplacement of hydrothermal breccia units was accompanied or shortly followed by multiple pulses of magmatic-hydrothermal and alternating jarosite alteration from about 15.4 to 8.9 Ma. Alunite and jarosite40 Ar-39 Ar ages and U-Pb zircon ages of crosscutting dikes restrict mineralization at Amable to the period from 15.4 to 12.14 plus or minus 0.11 Ma, probably commencing closer to 12.7 Ma. At Filo Federico, Au mineralization commenced after the beginning of alunite alteration at 11.05 plus or minus 0.12 Ma. The new data suggest that the maximum age of mineralization in the belt is slightly higher than previously recognized The bulk of Veladero Ag is hosted in Ag-bearing jarosite in the jarosite-argentojarosite solid solution. Some silver occurs as less than 0.1 Mu m iodargyrite and aggregates of less than 0.1 Mu m particles with variable Ag, I, Br, Cl, Hg, Se, S, and Fe concentrations. Rare Ag-Fe sulfides were identified. Veladero Au exists as greater than 800 fineness grains of native Au. A phase of euhedral, fracture-controlled quartz with growth zone parallel iron oxide inclusions has been identified at Veladero, post-dating leaching of the host rock to vuggy quartz and pre-dating Au mineralization. The quartz is evidence that the fluids that transport the precious metals are distinct from the magmatic vapors that interact with meteoric water to produce alteration in high-sulfidation disseminated deposits, and that at least the first stage of metals are transported by a low-temperature fluid also capable of precipitating quartz
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