西藏浦桑果铅锌多金属矿床矽卡岩矿物学特征及其地质意义

Mineralogical characteristics of skarn in the Pusangguo Pb-Zn polymetallic deposit of Tibet and their geological significance

西藏浦桑果铅锌多金属矿床位于南冈底斯成矿带火山岩浆弧内,矿区矽卡岩型铅锌矿体主要呈似层状和透镜状近东西向赋存于白垩系塔克那组第4岩性段矽卡岩化大理岩中,矽卡岩矿物较发育。为进一步查明矽卡岩矿物种属及矽卡岩类型,剖析矽卡岩的形成环境及其与成矿的关系,在对矽卡岩矿物系统的显微镜下鉴定基础上,利用电子探针对矿区内主要矽卡岩矿物化学成分进行了系统分析。结果表明,石榴子石主要为非连续的钙铁榴石钙铝榴石类质同像系列(And47.39~98.17Gro0.59~50.22Ura+Pyr+Spe0~3.53),且早期主要形成钙铁榴石,部分钙铁榴石含锰质较高;单斜辉石主要为钙铁辉石-锰钙辉石-透辉石类质同像系列(Hd37.91~74.16Jo0.91~61.66Di0.43~46.07);似辉石主要为硅灰石,端员组分为Wo99.09~99.26En0.50~0.56Fs0.13~0.24;角闪石主要为镁角闪石,具钙质角闪石属性;绿帘石贫铁、镁而富铝、钙;绿泥石属于密绿泥石类。矿床矽卡岩矿物组合特征表明,浦桑果矿床矽卡岩兼具钙质矽卡岩和锰质矽卡岩的特征。早期矽卡岩形成于高温、偏碱性、强氧化的开放体系中,成矿流体具有较高氧逸度。锰质矽卡岩矿物特征及独立银矿物的存在综合表明矿区具有银矿找矿潜力,为下步找矿工作提供了思路和方向。

The Pusangguo lead-zinc polymetallic deposit is located in the volcanic-magma arc of the southern Gang- disc metallogenic belt, Tibet. The skarn type orebodies mainly occur in nearly bedded and lenticular shapes in nearly east-west direction and are hosted in the skarnized marble of the Cretaceous Takena Formation, with lots of skarn minerals developed in this deposit. In order to further identify the species of skarn minerals and types of the skarn and analyze the formation environment of the skarn and its relationship with mineralization types, the authors analyzed the chemical composition of the skarn minerals by using the electron microprobe technology and on the basis of the systematic microscope observation. According to the results obtained, the garnet is mainly composed of dis- continuous isomorphism of andradite and grossular （ And47 39 - 98.17 Gro0. 59 - 50.22 Ura ＋ Pyr ＋ Spe0- 3. s3）, the clinopyrox- ene is mainly composed of hedenbergite-johannsinite-diopside （Hd37.91 -74. 16Jo0.91 -61.66Di0.43-46.07） , the pyroxenoid is mainly wollastonite, and the endmember compositions are Wo99.09-99.26Eno.50-o.56FSo. 13-0.24. In addition, the horn- blendes are mainly magnesium hornblendes and have the features of calcium hornblende, the epidote is relatively enriched in aluminum and calcium but poor in iron and magnesium, and the chlorite belongs to the type of pycno- chlorite. The skarn mineral assemblage characteristics indicate that the skarns in the Pusangguo deposit have the features of both calcium-skarn and manganese-skarn. At the early stage of skarn mineralization, the skarns were mainly formed under the conditions of high temperature, pH, oxygen fugacity, and the ore-forming fluid had high oxygen fugacity. Manganese skarn mineral characteristics and the single silver minerals show that this deposit has the silver ore prospecting potential, which can serve as the next step prospecting direction in the future exploration