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

拉拉块状硫化物铜钴矿床位于四川南部(中国)，距会理县城不远，采用露天开采。透镜状矿体属于新元古代火山沉积岩的中层序，常与强烈蚀变辉长岩伴生。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作用；(2)变质流体引起的表生热液沉淀作用。在拉拉矿床更广阔的附近有许多更类似的层状矿床(通常是透镜体)；目前只有两个矿床被开采。一些大型矿石透镜呈NW-SE方向排列。这种沿着罢工的惊人排列的原因尚不清楚。我们的研究项目目标是解决拉拉矿化的成因，其基础是(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)矿床沉积时的地质情况的重建，(3)与现代海底块状硫化物产出的数据和结果的比较。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，这两种类型是含石英的钠长石，它通常是矿石的直接容矿岩石，以及蚀变辉长岩；辉长岩样品也含有硫化物矿物，矿物辉石大多被角闪石取代。显然，这些蚀变类型岩石的形成将对了解成矿的不同阶段起到关键作用。我们的另一部分地球化学工作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，这些数据可能表明原始板块构造情况。我们的研究成果也将有助于拉拉厂地区其他块状硫化物矿体的分类和勘查。

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.