In hydrothermal deposits there are many types of alteration, including potassic alteration (altered minerals are potassic feldspar and biotite), sericitization, silicification, argillazation, chloritization, carbonification and propylitization, but most of them belong to postor premineralization alteration except silicification formed during the mineralization period. Silicifation occurred in hydrothermal deposit formation from high, moderate temperature to low temperature and can be divided into early, middle and middle-late stages. The early stage is featured by formation under high temperature and accompanied by mineralization of Sn, W and Mo, while the middle stage was formed under moderate temperature and related to mineralization of Cu. The middle-late stage is characterized by moderate-low temperature and varied mineralization of Cu, Au, Zn, Ag, Pb and U.
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Boyle, R. W., The geochemistry of gold and its deposits, Canada, 1979.