The Cuajone copper porphyry-type deposit (Peru): characterization and correlation of solid inclusions in pyrite with types of hydrothermal alteration

The Cuajone mine (Moquegua, Peru) corresponds to a porphyry copper-type deposit formed in the Toquepala Group volcanic. Hydrothermal alteration and mineralization were developed in connection with the late emplacement of quartz monzonite, quartz latite, porphyritic micrograno-diorite, microtonalite and porphyries. Both the Toquepala Group and the intrusive rocks are affected by potassic, propylitic, and sericitic type of hydrothermal alteration. Pyrite, containing either micrometer-sized intergrowths of chalcopyrite and pyrrhotite, cubanite and mackinawite or pyrrhotite alone, as solid inclusions, were the subject of this study. The intergrowth types were classified according to their morphological properties. When considering frequency and relative abundance of the sulfide assemblages that constitute inclusions in pyrite, a correlation with the type of hydro-thermal alteration can be established. Pyrrhotite occurs in all types of hydrothermal alteration, but it is predominant in the potassic zone. Cubanite, even if far less abundant, is typically associated with the sericitic alteration but it also occurs in the potassic and propylitic zones. Mackinawite is most common in the propylitic zone. The observed sulfide mineral associations suggests that they evolved in a temperature range from 500 degrees C down to 180 degrees C.