广西大厂长坡-铜坑锡多金属矿床中两种黄铁矿的元素地球化学特征

Elements geochemistry of two types of pyrite in Dachang Changpo-Tongkeng Sn-polymetallic deposit,Guangxi,China

广西大厂长坡-铜坑锡多金属矿床中的黄铁矿明显有两种类型:条带状黄铁矿和脉状黄铁矿。矿相特征表明,部分黄铁矿可能由胶黄铁矿重结晶而成。黄铁矿的微量元素测试结果表明,样品以沉积成因特征为主,其中具脉状黄铁矿样品的部分参数较接近热液沉积岩特征值。黄铁矿的稀土元素测试结果表明,成矿流体并非完全来自深源物质,还有浅源物质的参与,并在相对还原的环境中发生过较强的分馏作用;黄铁矿的稀土特征介于富矿围岩硅质岩和酸性侵入岩花岗岩之间,表明既有与泥盆纪硅质岩相同成因的黄铁矿,又有经后期花岗岩浆活动改造而成的黄铁矿。结合矿床地质特征,认为大厂长坡-铜坑锡多金属矿床的成矿作用至少存在两期,泥盆纪以沉积作用为主,燕山晚期经历了花岗岩浆的热液叠加改造作用,锡矿的形成主要受燕山晚期花岗岩浆活动的影响。

There occur two significant geological mineralizations in the Changpo-Tongkeng tin- polymetallic deposit of Dachang. Two types of pyrite are mainly layer （or similar to layer） and vein. The banded ore has not only original band structures and pyrite, but also vertical pyrite veins along the cracks. The mineralogical characteristics indicate that some pyrite had suffered re-crystallization. The test results of the trace elements in the pyrite show that the pyrite mainly formed in sedimentary environments, but some parameters of the sample with vein pyrite are close to hydrothermal characteristic scales. REE testing results show that the pyrite does not entirely come from the deep source, as well as has the participation of the shallow source. It has been suffered strong fraetionation process in deeper and anoxic environments. The rare-earth characteristics of the pyrite are between siliceous rocks and intrusive rocks （granite）, indicating that the pyrite has two origins. The origin of some pyrite is like that of the Devonian siliceous rocks, and some pyrite has been reformed by granitic magma activities. Combined with the geological characteristics, this paper indicates that there are at least two mineralization phases in the Changpo-Tongkeng tin-polymetallic deposit, that is, the dominate sedimentation in Devonian and the granitic magma hydrothermal transformation in late Yanshan. The formation of the tin ore is mainly affected by the late Yanshan granite magma activities.