摘要:
帮布勒矿床是近年来在西藏冈底斯—念青唐古拉多金属成矿带西段新发现的大型矽卡岩型Pb-Zn矿床。闪锌矿作为该矿床的主要矿石矿物之一,其矿相学特征及化学组分对于揭示成矿物理化学条件和流体演化过程具有重要意义。本文选取帮布勒矿床近端及远端矽卡岩中不同世代闪锌矿开展详细的显微结构观察和电子探针成分研究。结果表明,帮布勒矿床闪锌矿可划分为2个世代:第Ⅰ世代闪锌矿主要产于近端矽卡岩,呈暗红色-棕红色,常与乳滴状黄铜矿共生,并交代他形磁铁矿、磁黄铁矿,Fe元素含量较高(部分闪锌矿Fe含量>10%),Zn/Fe值<10;第Ⅱ世代闪锌矿可进一步分为两类:第一类(Ⅱa)闪锌矿在近端及远端矽卡岩中均有发育,呈棕黄色,充填于辉石、石榴子石等矽卡岩矿物间及其裂隙中;第二类(Ⅱb)闪锌矿主要产于远端矽卡岩中,呈黄色-浅黄色,与方铅矿和石英共生,第Ⅱ世代闪锌矿相比于第Ⅰ世代闪锌矿Fe、Mn含量明显偏低,Zn含量较高。闪锌矿Fe元素温度计估算结果显示,从第Ⅰ世代至第Ⅱ世代成矿温度逐渐降低,分别为160～314℃、138～157℃,与闪锌矿Zn/Fe比值指示结果一致。综上证据,本文认为帮布勒矿床早期成矿流体温度高且富含Fe、Mn、Cu等元素,随着成矿流体温度逐渐降低,流体中Fe、Mn元素含量显著降低。同时,成矿流体自矿区北西向南东运移过程中温度逐渐降低,指示在矿床南东方向具有寻找远端Manto型高品位矿体的潜力。
Abstract:
The recently discovered Bangbule deposit is located in the western part of the Gangdise–Nyainqentangula Pb-Zn-Ag polymetallic metallogenic belt, Tibet. The chemical composition of sphalerite, one of the primary ore minerals in this deposit, is of great significance because it reveals the physicochemical conditions of mineralization and evolution of ore-forming fluids. This study investigated different generations of sphalerite from the proximal and distal skarns of the Bangbule deposit using microscopic observation and electron probe microanalysis. Two generations of sphalerite（Sph-I and Sph-II） were identified by their mineral associations,microscopic characteristics, and geochemical features. Sph-I was mostly found in the proximal skarn, which is dark red and coexists with chalcopyrite, replacing magnetite and pyrrhotite. The Fe contents of the first generation are high（Fe content of some sphalerite is greater than 10 %）, whereas the Zn/Fe value is typically less than 10. Sph-II can be subdivided into two types: Sph-IIa and Sph-IIb. Sph-IIa is brownish-yellow and is found in both proximal and distal skarns. This generation sphalerite is usually filled in the gap of skarn mineral grains（e g.,pyroxene and garnet） and their fractures, and the Fe contents are obviously lower than that of the Sph-I. Sph-IIb is mainly developed in the distal skarn, which is light-yellow and co-exist with galena and quartz, and Fe contents are distinctly lower than those of the Sph-I and Sph-IIa. The estimation of Fe-in-Sphalerite thermometers demonstrate that the mineralization temperatures from the Sph-I（160–314 ℃） to the Sph-II（138–157 ℃） are comparable with the results of sphalerite Zn/Fe ratios. Based on the above features, it is suggested that the early ore-forming fluids in the Bangbule deposit are of high temperature and rich in Fe, Mn, Cu, etc. As the temperature of ore-forming fluid decreases gradually, the content of Fe and Mn in the fluids decreases significantly. Spatially, the temperature and oxygen fugacity of the ore-forming fluid gradually decreased during the migration from the northwest to the southeast of the deposit, indicating that there is potential to find distal Manto-type ore-bodies in the southeast direction of the deposit.
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