金川铜镍硫化物矿床矿石类型主要为浸染状矿石、海绵陨铁状矿石及块状矿石.采用矿相显微镜观察、磁性胶体浸润与电子探针分析等方法,对3种类型矿石中磁黄铁矿的结构状态、共生组合与成分特征作了研究,探讨了矿石成因及成矿过程.在浸染状矿石与海绵陨铁状矿石中,磁黄铁矿为单纯的六方(NC型)磁黄铁矿,或者六方与单斜(4C型)磁黄铁矿构成的不规则状交生体.这2类矿石中磁黄铁矿的成因很可能是岩(矿)浆中S含量低,且高温结晶后缓慢降温,后期又受到了富硫和/或高氧逸度流体的交代作用.在Ⅱ矿区块状矿石中,单斜与六方磁黄铁矿构成平行叶片状交生体,表明六方磁黄铁矿在高温下结晶后温度曾快速下降,这期间仅出溶了微量的黄铁矿,而当温度下降到254℃以下时,发生了六方磁黄铁矿中单斜磁黄铁矿出溶作用.磁黄铁矿的结晶类型、金属原子(Fe、Ni、Cu、Co)与硫原子比值M/S演化等佐证了块状矿石晚期贯入成因.依据Fe-S系统相图拟合曲线计算得到块状矿石中六方磁黄铁矿结晶温度为743～518℃,且在结晶过程中,硫逸度logf(S2)曾从0.427降至-3.767.%To determine the genesis of sulfide ores and mineralization process of the Jinchuan Ni-Cu deposit,the authors studied the mode of occurrence,intergrowth and composition of pyrrhotite in the sideronitic,disseminated and massive sulfide ores under microscope by using the magnetic colloid method and electron microprobe analysis.The pyrrhotite in sideronitic and disseminated ores occurs in the form of irregular intergrowth between hexagonal and monoclinic pyrrhotite,or exclusively as hexagonal pyrrhotite,which was formed in a S-poor slow cooling environment,and interacted with high oxygen fugacity fluids after hexagonal pyrrhotite crystallization.The pyrrhotite in massive sulfide ore of No.Ⅱ ore block exhibits lamellar intergrowth between hexagonal and monoclinic pyrrhotite,which was formed in a rapid cooling environment.When the temperature is lower than 254℃,the monoclinic (4C) pyrrhotite will be exsolved from hexagonal pyrrhotite matrix.The genesis,lower M/S ratio and different chemical composition of pyrrhotite indicate that massive sulfide ores were formed by the emplacement of the last stage sulfide liquids.According to the thermometer formula of Fe-S system,the authors obtained the crystallization temperature of hexagonal pyrrhotite in massive sulfide ore,which varies in the range of 743～ 518℃,with the sulfur fugacity (logf(S2)) varying from 0.427 to-3.767.
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