山西五台山东腰庄金矿绿泥石成因矿物学研究

Genetic Mineralogy of Chlorite from the Dongyaozhuang Gold Deposit, Wutai Mountain, Shanxi Province, China

绿泥石作为常见的变质和热液蚀变矿物,其成分特征能够反映流体的物理化学条件,为其成因和有关的成矿条件提供重要信息。山西五台山东腰庄金矿位于新太古代五台山绿岩带,具有不同成因的多期绿泥石化现象,分别有前寒武纪区域变质作用有关的绿泥石（简称C1）、变质作用晚期热液矿化蚀变的绿泥石（变形的硫化物-（电气石）石英脉中;C2）和主成矿（矿体热液脉中;C3）等3期绿泥石。对不同期次绿泥石的成因矿物学研究显示,C1为镁质绿泥石,C2和C3为铁质绿泥石。相对C2而言,C3的Al含量相对升高。从早到晚,绿泥石形成温度分别为348～464℃（平均398℃）,288～490℃（平均380℃）和145～259℃（平均215℃）。C2和C3的lgf（O2）分别为-32.28～-24.76（平均-28.91）,-50.37～-35.71（平均-42.07）,对应的lgf（S2）为-10.24～-6.28（平均-8.49）和-19.26～-11.98（平均-15.23）。总体而言,东腰庄金矿围岩中的变质成因绿泥石（C1）相对富镁,而与早期矿化有关的热液绿泥石（C2）则相对富铁,形成于中温、高氧逸度（HM-NNO之间）的较氧化环境之中,而晚期与主成矿有关的热液绿泥石（C3）虽然也属于铁质绿泥石,但是其形成的温度和氧逸度（NNO-FMQ之间）等均有降低趋势。绿泥石的成分及物理化学性质在空间上表现出明显的差异性,其Fe/（Fe+Mg）从围岩至矿体呈升高趋势,而f（O2）及f（S2）值则呈现降低趋势,可以很好地指示成矿流体演化趋势和找矿。

Chlorite is a common mineral of metamorphism and hydrothermal alteration. Its compositional characteristics can reflect the physicochemical conditions of the fluid and provide insightful clues to the mineral genesis and related metallogenic conditions. The Dongyaozhuang gold deposit occurs in the Neoarchean Wutai greenstone belt, with various genetic multi-stage chloritization. In the deposit, at least three stages of chlorite have been identified. They include the chlorite formed in the Precambrian regional metamorphism（C1）, the chlorite, occurred in the deformed sulfide-（tourmaline）-quartz veins, formed by the hydrothermal alteration in the late stage of metamorphism（C2）, and the chlorite, occurred in hydrothermal veins of orebodies, formed in the main stage of gold mineralization（C3）, respectively. The genetic mineralogy of various stages of chlorite indicates that the C1 belongs to magnesian chlorite, while the C2 and C3 belong to iron chlorite. Comparing to the C2, the C3 is relatively rich in Al. From early to late stages, the C1, C2 and C3 have calculated formation temperatures varying from 348 to 464 ℃（average of 398 ℃）, from 288 to 490 ℃（average of 380 ℃）, and from 145 to 259 ℃（average of 215 ℃）, respectively. Especially, the calculated lgf（O2）values vary from-32.28 to-24.76（average of-28.91） for the C2, and from-50.37 to-35.71（average of-42.07） for the C3), and the lgf（S2） values vary from-10.24 to-6.28（average of-8.49） for the C2 and from-19.26 to-11.98（average of-15.23） for the C3. Generally, the metamorphic chlorite（C1） in the Dongyaozhuang gold deposit was relatively rich in MgO. The C2 which is a hydrothermal chlorite in association with the early gold mineralization is relatively rich in FeO, with the formation conditions of intermediate temperature and relatively high oxidized environment with oxygen fugacity in the HM-NNO buffer zone. The C3 which is a late hydrothermal chlorite in association with the main gold mineralization also belongs to the iron chlorite, but it was formed at relatively low temperature and in a relatively low oxidized environment with oxygen fugacity in the NNO-FMQ buffer zone. The significant spatial differences in chemical compositions and physicochemical properties of various stages of chlorites, such as the Fe/（Fe+Mg） ratios are gradually increased but the oxygen and sulfur fugacity values are decreased, for chlorites from the country rock to gold orebody, can be taken as indicators for tracking the evolution and flowing path of ore-forming fluids and for prospecting gold mineralization.