Ore mineralization controls in Rosario porphyric Cu-Mo system: Collahuasi District, Chile

摘要

This work is focused on understanding the ore mineralization controls in Rosario porphyric Cu-Mo system through the study of molybdenite and bornite associations, its relationship with hydrothermal alteration events and veinlets occurrences. To achieve this objective, 9 drill holes distributed in three sections were mapped, corresponding to a total length of 3014 meters. A total of 56 representative samples were collected for thin polished preparation sections in order to determine textural characteristics of the veinlets, the opaque minerals association and the temporary relationship. Two main events of molybdenite and bornite were detected: The first was related to a potassic to phyllic alteration, called early-transitional with veinlets of quartz, chalcopyrite, bornite (‘A’ type) and quartz, orthoclase, molybdenite, chalcopyrite and bornite (‘B’ type) where the main textures are in intergrowth and simple contact. This pulse is closely related to porphyry Rosario, which crystallization age is around the 37-35 Ma, and which age of mineralization is approximately near 36 Ma. The second event detected is younger than the first one, having an approximately 33 Ma age it is called late high sulfidation event, include veinlets and disseminated occurrences of pyrite, bornite, enargite and quartz, it presents minor chalcosite, digenite, covellite, luzonite, and molybdenite (‘E’ type). This high sulfidation (HS) event also includes minerals of advanced argillic alteration, like quartz, sericite, alunite, dickite, zunyite and pyrophyllite (obtained with PIMA). According to the age difference between the two events mentioned, we might think that the epithermal veins seems to have been generated by younger intrusive and possibly superimposed to Rosario porphyry.