Genesis of the Lala Copper-Cobalt Sulfide Deposit, Sichuan-Province (China) and its comparison with modern marine sulfide occurrences

拉拉块状硫化物矿床位于四川南部，距会里县城不远，为露天开采。透镜状矿体属新元古代火山沉积岩中层序，常与强蚀变辉长岩伴生。讨论了两种成矿模式：(1)海底热液循环引起的火山同沉积成矿；(2)变质流体引起的表生热液矿沉淀。在拉拉矿床更广阔的附近地区，有许多类似的层状层状矿床（通常为透镜状）；目前只开采了两个矿床。一些大型矿石透镜体在西北-东南方向排列。这一引人注目的罢工路线的原因尚不清楚。我们的研究项目目标是解决拉拉矿化的成因，并基于(1)我们自己对岩石和矿石样品的矿物学和地球化学调查，(2)重建矿床沉积时的地质情况，(3)与现代海底块状硫化物赋存的数据和结果进行比较。拉拉矿床的围岩包含两种非常有趣和独特的蚀变岩石类型，即含石英的钠长岩（通常是矿石的直接寄主岩）和蚀变辉长岩；辉长岩样品中还含有硫化物矿物，其中辉长岩矿物大部分被角闪石所取代。很明显，这些蚀变类型岩石的形成将对了解矿石成因的不同步骤起关键作用。我们地球化学工作的另一部分将考虑岩石和矿石样品中可能在变质和变形地质过程中幸存下来的不同微量元素；例如，这些数据可以显示原始的板块构造情况。研究结果也将有助于对拉拉厂地区其他块状硫化物矿体进行分类和勘查。

The Cu-Co bearing Lala massive sulfid deposit is located in south Sichuan (China) not far away from the county center Huili, and is mined in an open-cast working. The lense-shaped ore bodies belong to the middle sequence of young Proterozoic volcano sedimentary rocks, often associated with strongly altered gabbro. Two models are discussed to explain the ore formation: (1) volcano synsedimentary ore formation caused by seafloor hydrothermal circulation; (2) epigenentic hydrothermal ore precipitation caused by metamorphic fluids. In the wider vicinity of the Lala deposit are many more similar layered stratiform ore deposits (often as lenses); only two ore deposits are mined at present. Some of the large ore lenses are aligned in a NW-SE direction. The reason for this remarkable alignment along a strike is unknown. Our research project objective is to solve the genesis of the Lala mineralizations and is based on (1) our own investigations of the mineralogy and geochemistry of rocks and ore samples, (2) the reconstruction of the geological situation at the time of ore deposition and (3) a comparison with data and results from modern seafloor massive sulfide occurrences. The surrounding rocks of the Lala deposit contain two very interesting and distinct altered rock types, these are the quartz-bearing, albitite, which often is the immediate host rock of the ore, and the altered gabbro; the “gabbro” samples also contain sulfide minerals, the mineral augite is mostly replaced by hornblende. It is clear that the formation of these altered types of rocks will play a key role to understand the different steps of the ore genesis. Another part of our geochemical work will consider distinct trace elements which might have survived the metamorphic and deformational geological processes in the rock and ore samples; such data could, for example, indicate the original plate tectonic situation. Our results will also help to classify and to explore more easily the other massive sulfide ore bodies in the Lalachang area.