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

拉拉铜钴块状硫化物存款矿床位于四川南部，距会理县中心不远，采用露天开采。透镜状矿体属于元古宙火山沉积岩中序，常与强烈蚀变辉长岩共生。探讨了两种成矿模式：（1）海底热液循环引起的火山同沉积成矿;（2）变质流体引起的后生热液沉淀成矿。在拉拉存款的更广泛的附近是许多类似的层状层状矿床（往往作为透镜体）;只有两个矿床目前被开采。一些大型矿石透镜体沿西北-东南方向排列。这种沿走向沿着排列的现象的原因尚不清楚。我们的研究项目的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的调查，（2）矿石沉积时的地质情况的重建，以及（3）与现代海底块状硫化物矿点的数据和结果的比较。拉拉存款的围岩包含两个非常有趣的和不同的蚀变岩类型，这些是石英，钠长石，这往往是矿石的直接寄主岩石，和蚀变辉长岩;“辉长岩”样品也含有硫化物矿物，矿物普通辉石大多被角闪石取代。很明显，这些蚀变类型岩石的形成将对理解矿石成因的不同步骤起关键作用。我们的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独特微量元素;例如，这些数据可以表明原始板块构造情况。研究结果也有助于拉拉厂地区其他块状硫化物矿体的分类和找矿。

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.