THE COMPOSITION OF GOLD IN THE CERRO CASALE GOLD-RICH

The Cerro Casale gold-rich orebody, located in the Maricunga Belt, in northern Chile, is a Miocene deposit hosted in diorite and granodiorite porphyries. Two broad types of hypogene alteration are associated with gold mineralization: potassic and white mica. The geochemical study of gold crystals involved the electron-microprobe analysis of 176 gold grains from 29 samples. These samples were collected from diamond drill-cores at various depths. The gold crystals deposited during potassic alteration have high abundances of Ag (8 to 28 wt.%) and low concentrations of Cu (n.d. to 0.24 wt.%). However, gold crystals deposited during white mica alteration have low concentrations of Ag (1 to 9 wt.%) and higher abundances of Cu (0.06 to 0.34 wt.%). In addition, gold crystals recovered from fragments of both porphyries included in a white mica hydrothermal breccia apparently maintain their original Ag and Cu concentrations