西藏雄村矿集区侏罗纪斑岩磷灰石矿物化学特征对新特提斯洋俯冲成矿作用的指示

摘要

雄村矿集区位于西藏冈底斯成矿带南缘,区内成矿作用与新特提斯洋俯冲作用有关,现已勘查评价了一个大型还原性斑岩铜金矿床(I号矿体)和一个大型氧化性斑岩型铜金矿床(II号矿体).为了查明引起I、II号矿体成矿特征差异的原因和含矿斑岩的区别标志,本文选取I、II号矿体含矿斑岩和非含矿斑岩中磷灰石为研究对象,通过对三套斑岩磷灰石单矿物的挑选、阴极发光照相(CL)和电子探针分析(EMPA),提出了磷灰石中Cl含量受控于共存硅酸盐熔体组分,I、II号矿体含矿斑岩比非含矿斑岩具有更高的Cl/F(分别为0.76、0.26、0.07),高的Cl含量对促进Cu、Au的溶解和迁移具有重要作用的新认识;含矿斑岩磷灰石高Cl低S指示金属元素Cu、Au可能以Cl的络合物为主进行迁移([CuCl2]–、[CuCl]0、[AuCl2]–);I、II号矿体含矿斑岩氧逸度低于非含矿斑岩,含矿斑岩较低的氧逸度可能指示成矿过程可能发生了结晶硫化物相的预富集;雄村矿集区I、II号矿体含矿斑岩磷灰石与非含矿斑岩相比具有更高的Mn、Ca、Cl含量,更低的Si、S、F含量,可以作为含矿斑岩的判别标志,对指导区域与新特提斯洋俯冲有关的斑岩型铜金矿床找矿突破有重要义.%The Xiongcun ore concentration area is located on the southern margin of the Gangdise metallogenic belt, Tibet. The mineralization in the Xiongcun ore concentration area where a large reduction porphyry copper gold deposit (No. I orebody) and a large oxidized porphyry copper gold deposit (No. II orebody) were explored and evaluated related to the subduction of the Neo-Tethys. In order to find out the difference of ore-forming characteristics of No. Ⅰand No. Ⅱ orebody and the difference between fertile porphyry and barren porphyry, the authors selected apatite from No. Ⅰ and No. Ⅱ fertile porphyries and barren porphyry as the research object. Through the selection of apatite from three porphyries, cathodoluminescence (CL) and electron microprobe analysis (EMPA) were conducted, and the authors found that the content of Cl in apatite is controlled by the composition of coexisting silicate melt, and No.Ⅰ and No.Ⅱ fertile porphyries have higher Cl/F than barren porphyry (0.76, 0.26, 0.07, respectively), which indicates that high Cl content played an important role in accelerating the dissolution and migration of Cu and Au. The high Cl and low S in apatite of fertile porphyries indicate that the Cu and Au probably migrated mainly in the form of Cl complexes such as [CuCl2]–, [CuCl]0, and [AuCl2]–. The oxygen fugacity of fertile porphyries is lower than that of barren porphyry, and the low oxygen rnfugacity of fertile porphyries may indicate that saturation of the magma with sulfide might have occurred in the mineralization process. Compared with apatite of barren porphyry, the apatite of fertile porphyries has higher content of Mn, Ca, Cl and lower content of Si, S, F, and thus apatite can be used as an indicator mineral for mineral exploration related to the subduction of the Neo-Tethys on the southern margin of the Gangdise metallogenic belt.