Proyecto Navidad. Análisis de la alteración y mineralización en el depósito Loma Galena, Chubut, Argentina

VERÓNICA BOUHIER; MARCELO PAOLINI; MARCOS JIMENEZ; MARTA FRANCHINI; GRACIELA MAS; AGNES IMPICCINI,

San Juan

Congreso; X Congreso Argentino de Geología Económica; 2013

Navidad Project, Chubut, Argentina. Alteration and mineralization analysis of Galena Hill deposit.The Navidad Project is located in the region of Gastre (42.4 ° S - 68.81 ° W), Chubut, southwest of the North Patagonian Massif geological province. It is a Ag-Pb world class deposit with epithermal characteristics. The project consists of 8 deposits arranged along three parallel NW-SE structures called, from north to south, Navidad, Esperanza and Argenta Trends.Galena Hill, one of the 8 deposits, is located in the Navidad Trend and contains resources over 100 Moz Ag and about 650000 t of Pb, with an average grade of 124 g/t Ag and 1,89 % Pb. It is the richest in sulfides. The mineralization is hosted in a volcano-sedimentary sequence of the Cañadón Asfalto Formation (Middle-Upper Jurassic). Mineralization (argentiferous pyrite, marcasite, galena, sphalerite, chalcopyrite, bornite, tennantite, covellite-digenite) has a stratiform and structural control. Three different zones are recognized: a) subvertical multiepisodic veins and hydrothermal breccias present in fragile lava flows; b ) semi-massive sulfides hosted in chaotic levels and autobrecciated roof of the volcanic flows in the upper sedimentary-volcanics contact, and c) disseminated sulfides in the upper sedimentary sequence. The host rocks show moderate to strong alteration to calcite, chalcedony, kaolinite, smectite, illite-smectite, yugawaralite, and chlorite. The ore, gangue, and alteration minerals indicate that the pH of the hydrothermal fluids fluctuated between alkaline, neutral, and acidic, with temperatures below 230 °C, except locally in zones near hydrothermal fluid conduits. Boiling, fluid mixing, and brecciation were processesassociated with the genesis of the mineralization at Galena Hill.