Chile
| Articulo
Upper jurassic au-zn mineralization in el faldeo district, chilean patagonia
Fecha
1997Registro en:
0016-7835
D91I1093
WOS:A1997XB30200010
WOS:A1997XB30200010
0
Institución
Resumen
The Jurassic Au-Zn mineralization at El Faldeo district is hosted mainly in felsic volcanic and subvolcanic rocks. Early epithermal gold mineralization is related to silicic alteration and deposition of pyrite, arsenopyrite, and minor sphalerite, galena, gold, and chalcopyrite, in veinlets and dissemination. The ore bodies are stratiform horizons (10-30 m thick and 150-240 m long) hosted in dacitic to rhyolitic lapilli to ash tuffs and lavas. Grades vary between 0.2 and 3.5 ppm Au. Fluid inclusion data indicate homogenization temperatures varying between 140 and 171 degrees C, salinities ranging from 0.2 to 3.4 wt.% NaCl equivalent, and gold deposition during boiling events. Late Zn mineralization consists of stockwork and dissemination of quartz, sericite, calcite, barite, pyrite, arsenopyrite, sphalerite, Ag-bearing galena, and minor gold. The ore bodies are irregular or stratiform horizons hosted in felsic volcanic and subvolcanic rocks. Ore grades vary from 2 to 8% Zn, 0.4 to 3% Pb, 20 to 110 ppm Cd, 10 to 100 ppm Ag, and 40 to 1100 ppb Au. Fluid inclusion data indicate ore deposition during boiling at homogenization temperatures varying between 250 and 330 degrees C, and salinities ranging between 4 and 23 wt.% NaCl equivalent. S, Pb, C, and O isotopic data support a magmatic and meteoric source for hydrothermal fluids with a significant role played by leaching of Paleozoic basement rocks. Field observations, radiometric dating, and structural interpretations support that mineralization occurred synchronously with magmatic and tectonic activity in an upper Jurassic intra-arc pull-apart basin environment. Finally, it is proposed that the Au-Zn mineralization at Fl Faldeo district corresponds to a hydrothermal system peripheral to porphyry copper.