An experimental study of the morphological evolution of pyrite under hydrothermal conditions and its implications

Abstract A hydrothermal experiment study on the morphological evolution of pyrite has been conducted to simulate the pyrite behaviors during the gold precipitation conditions (180–220 °C, S/Fe molar ratio is 4/1 to 1/1). The experiment products mainly consist of pyrrhotite and pyrite through X-ray powder diffraction and transmission electron microscopy analysis. The scanning electron microscopy results show that the pyrite morphology is related to the temperature and S/Fe molar ratio. When S/Fe molar ratio drops from 4/1 to 1/1 at 200 °C, the pyrite morphologies change from a combination of {210} and {111} to a combination of {111} and {100} or a single form such as {100}. When S/Fe molar ratio is 3/1 and temperature drops from 220 °C to 180 °C, the pyrite morphologies vary from a combination of {210} and {111} to a combination of {111} and {100} or a single form such as {100}. The grain sizes of pyrite are positively correlated with the pyrite proportion in the products. The morphological evolution of pyrite under experimental conditions is similar to the hydrothermal gold deposits in the Jiaodong Peninsula, Shandong Province, China. The pyrite appears as {210} or a combination of two single forms under experimental conditions, consistent with the observations in gold-bearing hydrothermal mineralization. These results indicate that the pyrite morphologies could reflect the physicochemical conditions of the ore-bearing fluids, and provides a useful morphological typomorphism tool for gold exploration.