西范坪铜矿成矿作用初步研究——兼论还原硫对斑岩铜矿成矿的制约

对西范坪斑岩铜矿的蚀变作用、流体包裹体特征等进行了研究,指出该矿床是由两期岩浆流体叠加作用所形成的.第一期热液作用形成了磁铁矿化和黑云母化,并形成了无矿石英脉;第二期热液形成了阳起石化;早晚两期热液的混合引起了钾长石化及强烈的矿化.由于第二期流体的叠加,将还原硫(H2S)带到浅部,并与第一期富铜的高盐度流体相混合,从而形成铜硫化物的沉淀.第二期富含还原硫流体的加入,是西范坪斑岩铜矿床形成的重要控制因素之一.

A Study on Mineralization of the Xifanping Deposit--The Role of Reduced-Sulfur in the Formation of Porphyry Copper Deposit

It has been proved that a large amount of reduced sulfur is necessary for the formation of porphyry copper deposit. At shallow crustal depths, the magma fluid will be partitioning into two phases: liquid and vapor(eg. Hedenquist and Lowenstern,1994 ).Sulfur tend to get into vapor,while copper tend to get into liquid along with chlorine(eg. Heinrich et al,1999). So it is very important to understand how the two fluids mix and make the copper to precipitate as sulfides ,which have been seen in all of the porphyry copper deposits.The ore body of the Xifanping porphyry copper deposit is centered in two porphyry intrusions. One is exposed, another is covered about 300 meters under the surface. The former intruded earlier than the later. Each of them secreted fluid during their ascent and cooling. The vapor from the earlier fluid escaped from intrusion into air. But the liquid from the earlier fluid did not leave the site of intrusion. When the later fluid superimposed on the earlier one, it provide reduced sulfur. As a result, a intensive mineralization occurred. And actinolite alteration superimposed on the potassium silicate alteration. Some fluid inclusion evidences were provided in the paper,which proved the role of the later fluid in the mineralization.