摘要:
龙玛拉铅锌矿床是位于冈底斯成矿带之念青唐古拉铅锌成矿亚带东段的一个典型矽卡岩型矿床。前人对矿床成矿物质来源及演化、成岩-成矿时代、矿床形成动力学背景等方面进行过一定的研究,但对矽卡岩矿物学及分带模式还缺乏系统的研究。为此,本文通过详细的野外地质编录、系统的镜下鉴定和电子探针分析,开展矽卡岩矿物组合、矿物成分及其分带特征研究。矿床矽卡岩矿物主要包括石榴子石、辉石、硅灰石、绿泥石和绿帘石等。矽卡岩矿物组合和化学成分在空间上具有明显的分带性。矽卡岩主要发育在角岩与大理岩接触带,或沿裂隙充填在围岩中,横向上显示了从褪色角岩→石榴子石矽卡岩→深色角岩→透辉石矽卡岩(矿体)→大理岩→角岩的分带特征。垂向上由顶板至底板表现出从角岩→石榴子石矽卡岩→透辉石矽卡岩→大理岩→石榴子石矽卡岩→透辉石矽卡岩→角岩的岩性分带特征。矿床石榴子石为钙铁-钙铝榴石类质同象系列(And7.92～88.63Gro5.92～86.46Pyr+Spe1.04～5.11),端员组分变化范围较大,表明矽卡岩的形成环境并不是完全封闭的体系。通过对铅锌主矿体的赋矿矽卡岩中石榴子石进行研究,表明成矿流体是从矿区南西方向向北东方向运移就位形成主矿体,为矿区寻找成矿岩体及深部找矿提供指导。
Abstract:
The Longmala lead-zinc deposit is a typical skarn-type deposit located in the eastern section of Gangdese–Nyainqengtanglha lead-zinc metallogenic belt. Although the source and evolution of its ore-forming materials, diagenetic and metallogenic ages, and the dynamic background of its formation have been well studied,systematic research on its skarn mineralogy and zonation model is lacking. In this study, detailed field geological cataloging, systematic microscopic identification, and electron probe analysis were used to investigate the mineral association and composition as well as zonation characteristics of this skarn deposit in Tibet. Skarn minerals in the deposit mainly consist of garnet, pyroxene, wollastonite, chlorite, and epidote. The mineral association and chemical composition of the skarn have an obvious zonation in space. The skarn develops mainly in the contact zone between hornstone and marble or fills in the wall rock along cracks, showing transversal characteristics from faded hornstone→garnet skarn→dark hornstone→diopside skarn(ore body)→marble→hornstone. In the vertical direction from the roof to the floor, the lithological zonation is from hornstone→garnet skarn →diopside skarn→marble→garnet skarn→diopside skarn→hornstone. The garnet in the deposit belongs to the homomorphic series(And7.92～88.63Gro5.92～86.46Pyr+Spe1.04～5.11), with a wide range of end-member components,indicating that the environment in which the skarn formed is not a completely closed system. The garnet in the ore-bearing skarn of the main Pb-Zn ore body shows that the ore-forming fluid migrated from the southwest to the northeast to form the main ore body. These findings provide guidance for future searches for ore-forming rock masses and deep prospecting.
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