Mineral paragenesis of early biotite veins at the Kuh-E Janja Cu-Au porphyry deposit, Southeastern Iran: importance of microtextural observations in studies constraining the relative timing of hypogene Cu mineralization

Минеральный парагенезис ранних биотитовых жил на медно-золотом порфировом месторождении Кух-э-Джанджа (юго-восточный Иран): значение микротекстурных наблюдений для определения относительной последовательности формирования гипогенного медного оруденения

Veins consisting primarily of biotite are the earliest stockwork vein type recognized at the Kuh-e Janja Cu-Au porphyry deposit in southeastern Iran. These early biotite veins may contain quartz and minor amounts of sul-de minerals such as chalcopyrite and pyrite. Observations at the hand-specimen scale do not provide reliable constraints on the paragenetic relationships, as the early biotite veins have been repeatedly overprinted during the evolution of the magmatic-hydrothermal system. Microscopic investigations show that the sulde minerals in the early biotite veins are texturally late, providing evidence that sulde deposition did not occur at the high temperatures of biotite formation and potassic alteration of the host rocks. Chalcopyrite primarily occurs along hairline fractures that crosscut or refracture the earlier biotite veins. Biotite in contact with the chalcopyrite can be apparently unaltered or is replaced by chlorite, depending on the degree of wall-rock buffering of the magmatic-hydrothermal uids that caused hypogene Cu mineralization. The ndings add to the growing body of evidence that Cu mineralization in this deposit type occurs at temperatures close to the transition from ductile to brittle conditions (<450°C) following a drop in the pressure regime from lithostatic to hydrostatic conditions.