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

• DOI: 10.1007/s00710-007-0203-7
• Publication Date: 2007-10-16T12:17:26Z
• Authors: J. Carrillo-Rosúa; S. Morales-Ruano; D. Morata; A. J. Boyce; M. Belmar; A. E. Fallick; P. Fenoll Hach-Alí
• Keywords: Epithermal; Epitermal; Cobre; Oro; Gold; STABLE-ISOTOPE GEOCHEMISTRY; Chile; 01 natural sciences; Copper; 0105 earth and related environmental sciences

The original publication is available at www.springerlink.com 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 (29º47´S Lat., 70º43’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 ºC and salinities between 1.6 and 6.9 wt. % NaCl eq. Isotope data in quartz, ankerite and phyllosilicates and estimated temperatures show that 18O and D 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 El Dorado deposit. Departamento de Mineralogía y Petrología. Departamento de Didáctica de las Ciencias Experimentales. Grupo de Investigación de la Junta de Andalucía RNM-0131. Proyecto BTE-2003-06265.