四川盐源西范坪斑岩铜矿的钾长环斑结构及其意义

K-FELDSPAR RAPAKIVI TEXTURE AND ITS IMPLICATIONS, XIFANPING PORPHYRY COPPER DEPOSIT, SICHUAN

四川盐源西范坪斑岩铜矿床中存在大量钾长环斑结构。研究表明这一结构是由正在冷凝的岩浆分泌出的成矿流体与刚结晶的斜长石相互作用形成的。在流体 -矿物相互作用过程中 ,流体从已经结晶的矿物尤其是黑云母中萃取出大量铜等成矿物质 ,从而进一步提高了体系的成矿能力。钾长环斑结构的出现不仅为矿床的岩浆热液成因提供了佐证 ,而且是一种良好的找矿标志。

The Xifanping porphyry copper deposit is located in the southwestern Sichuan Province. The host rock is quartz monzonite. There are a lot of K feldspar rapakivi texture in this deposit. The characters of this texture are: (1) The width of the K feldspar rim is an inverse measure of the size of plagioclase porphyritic crystal; (2) The composition of orthoclase in K feldspar varies from 35.88% to 63.28%; (3) Some of the K feldspar replaces plagioclase porphyritic crystal from the edge of the core of the deposit. All these demonstrate that this kind of texture is developed by interaction between ore forming fluids secreted from magma and plagioclase phanerocryst. And the authors find many mafic minerals, such as hornblende and biotite, react with the fluids too during the interaction. The analyses of igneous and hydrothermal biotite suggest that a large amount of copper are leached from these minerals and added into the fluids. So this process promote the mineralization opportunity of porphyry system.