Mineralogy and geochemistry of El Dorado epithermal gold deposit, El Sauce district, central-northern Chile

Carrillo-Rosúa, J., Morales-Ruano, S., Morata, D., Boyce, A.J. , Belmar, M., Fallick, A.E. and Fenoll Hach-Alí, P. (2008) Mineralogy and geochemistry of El Dorado epithermal gold deposit, El Sauce district, central-northern Chile. Mineralogy and Petrology, 92(3-4), pp. 341-360. (doi: 10.1007/s00710-007-0203-7)

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Publisher's URL: http://dx.doi.org/10.1007/s00710-007-0203-7

Abstract

The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous andesites of the Los Elquinos Formation at La Serena (≈ 29°47′S Lat., 70°43′W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E fault structures associated with quartz-illite alteration (+supergene kaolinite). The main ore minerals in the deposit are pyrite, chalcopyrite ± fahlore (As/(As + Sb): 0.06−0.98), with electrum, sphalerite, galena, bournonite-seligmanite (As/(As + Sb): 0.21−0.31), marcasite, pyrrhotite being accessory phases. Electrum, with an Ag content between 32 and 37 at.%, occurs interstitial to pyrite aggregates or along pyrite fractures. Pyrite commonly exhibits chemical zonation with some zones up to 1.96 at.% As. Electron probe microanalyses of pyrite indicate that As-rich zones do not exhibit detectable Au values. Fluid inclusion microthermometry shows homogenization temperatures between 130 and 352 °C and salinities between 1.6 and 6.9 wt.% NaCl eq. Isotope data for quartz, ankerite and phyllosilicates and estimated temperatures show that δ18O and δD for the hydrothermal fluids were between 3 and 10‰ and between −95 and −75‰, respectively. These results suggest the mineralizing fluids were a mixture of meteoric and magmatic waters. An epithermal intermediate-sulfidation model is proposed for the formation of the El Dorado deposit.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Boyce, Professor Adrian and Fallick, Professor Anthony
Authors: Carrillo-Rosúa, J., Morales-Ruano, S., Morata, D., Boyce, A.J., Belmar, M., Fallick, A.E., and Fenoll Hach-Alí, P.
Subjects:G Geography. Anthropology. Recreation > GE Environmental Sciences
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Mineralogy and Petrology
ISSN:0930-0708

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