Paragenesis of the Intermediate Sulphidation veins of Minas Nuevas zone, “O Nivel”, located at auriferous-polymetallic mining district Zaruma-Portovelo Paragenesis of the Intermediate Sulphidation veins of Minas Nuevas zone, "O Nivel", located at auriferous-polymetallic mining district Zaruma-Portovelo

Abstract

The mining district Zaruma-Portovelo (MDZP) is an intermediate sulfidation epithermal ore deposit related to N-S striking veins with sub-vertical dips to the east. Despite it has been exploited since incas to current time, the studies about hydrothermal processes involved in the auriferous-polymetallic veins formation at Minas Nuevas have been scarce. The goal of this study is to interpretate the mineralization stages and their relationship with Au at O Nivel mine using macroscopic and microscopic techniques of the veins, geological mapping and grade assays were performed. Three mineralization stages were identified: the first one quartz (Qz)- chalcedony (Chc)- magnetite (Mt)-pyrite (Py)± chalcopyrite (Ccp)- gold (Au), the second one Qz-Chc-Ccp-marmatite (Mar) ± galena (Gn)-tetraedrite (Ttr)- tennantite (Tnt)- electrum (El), the third one Ccp-Sphalerite (Sph)-Gn-Ttr-Tnt and the last one of oxidation supergene event related to azurite (Az)- malachite (Mch)- hematite (Hm)- specularite (Spec). The Au is related with stages one and two, in veins with colloform-crustiform textures. The veins at O Nivel present epi-mesothermal features of intermediate sulfidation and they are located at adularia-boiling zone in the precious metals (Au-Ag) and base (Cu-Pb-Zn) transition.