Hydrothermal Alteration in Dashuiqing Gold Ore Belt,Nei Mongol,China and Its Relation to Gold Minerlization
内蒙大水清金矿带交代作用及其与金矿化关系

The Dashuiqing gold ore belt is one of the reworked greenstone gold ore belts.It occurs in a shear zone near the contact between the Anjiavingzi Quartz monzonite they and Precambrian greenstone.There ane fwo stages of evolution of the shear zone:ductile shear in early stage and extention crush in the later.Hydrothermal alteration related to gold mineralization in the belt only occurs in the later stage, and no any gold mineralization occurred in the former stage. There are four stages of hydrothermal alteration in the Dashuiqing goldore belt: albitization in the first stage,chlorite replacement (with some pyrite) in the second stage, the main gold mineralization only in the third stage, which is composed of five substag6s: sericite-quartz-pyrite assemblage, massive quartz--pyrite, quartz-polymetal sulphides, veined pyrite-quartz and fine-grained pyrite,respectively, and quartz-carbonite assemblage in final stage.The main gold ore formation period is the early four substages of the third stage.Their physico-chemical conditions for the hydrothermal alteration are discussed in the paper.