西藏冈底斯中新世邦铺斑岩成矿系统边缘铅锌富集机制

Research has shown that large porphyry deposits can also occur in collisional orogen environment in addition to the subduction background. The porphyry metallogenic system in collisional orogen in China is distinctive for the rich and diverse mineralization elements, whose outstanding performance is the large scale Pb-Zn enrichment in the edge of the porphyry metallogenic system. But for the already established collisional porphyry system, the Pb-Zn part is missing, and the origin, migration, enrichment of Pb-Zn are really controversial. For this purpose, we choose Miocene Bangpu porphyry-skarn Mo-Cu-Pb-Zn deposit which located in Gangdese porphyry copper belt, considering the origin and migration of Pb-Zn as an breach, using in situ Pb isotope and trace elements methods, combing the study of mine alteration-mineralization and ore-bearing fluid characters, in order to identify the skarn Pb-Zn enrichment mechanism on the porphyry metallogenic system edge. Through a comprehensive comparision, we define the control effect of the skarn process to the Pb-Zn mineralization, and finally answer the scientific question of the Pb-Zn enrichment mechanism on the porphyry metallogenic system edge in collisional orogen environment. The research will enrich the theory of continental collision porphyry metallogeny, and provide prospecting guidance in the Gangdese porphyry copper belt.

研究表明，大型的斑岩矿床亦可产于与俯冲无关的碰撞造山带。我国大陆碰撞斑岩成矿系统别具特色，成矿元素更为丰富且多样化，突出表现在斑岩成矿系统边缘富集大规模的铅锌。但就目前已建立的大陆碰撞斑岩成矿系统来看，唯独缺失了铅锌这一重要组成部分，对于铅锌的物质来源、迁移及富集机制更是存在较大争议。为此，项目拟选取青藏高原冈底斯斑岩成矿带中新世邦铺矿床-产于碰撞造山带的斑岩矽卡岩钼铜铅锌矿床为研究对象，尝试以铅锌物质来源及迁移机制为突破口，采用原位微区Pb同位素及原位微量元素分析等关键技术，结合矿区蚀变-矿化填图、富矿流体物化性质等研究，查明斑岩矿区边缘矽卡岩铅锌成矿机制。并通过综合对比，明确矽卡岩化过程对铅锌成矿的控制作用，最终回答大陆碰撞斑岩成矿系统边缘铅锌富集机制这一科学问题。研究结果对丰富完善大陆碰撞斑岩成矿理论具有重要科学价值，对冈底斯斑岩成矿带区域找矿指导具有重要科学作用。

项目在2018.1-2020.12期间执行，选取青藏高原冈底斯斑岩成矿带中新世邦铺矿床-产于碰撞造山带的斑岩-矽卡岩钼铜铅锌矿床为研究对象，以铅锌物质来源及迁移机制为突破口，采用阴极发光、石英及单个包裹体LA-ICP-MS成分分析等关键技术，查明斑岩矿区边缘矽卡岩铅锌成矿机制，并进一步探讨了深部岩浆房规模对斑岩成矿的控制。. 与斑岩成矿相关的流体演化大致可以分为三个阶段，分别形成A、B、D脉。A脉中金属含量（Cu=14.43~6700.97ppm，Pb=191.07~4595.76ppm，Zn=630.28~11749.95ppm）与B脉（Cu=36.63~9895.84ppm，Pb=29.31~5599.51ppm，Zn=64.91~9671.96ppm）相似，明显高于D脉（Cu=2.86~10588.41ppm，Pb=3.34~1835.18ppm，Zn=28.03~10194.38ppm），说明Mo-Cu-Pb-Zn具有一致的来源，均来自于深部的岩浆房而非围岩。冈底斯斑岩成矿带出露大面积的与斑岩铜钼矿化相关的中新世的埃达克质岩浆，这套岩浆在提供铜钼等金属来源的同时可以为成矿提供铅锌等金属物质。. 研究表明，矿床的规模和初始岩浆流体中金属的含量没有直接联系。Cu储量与Cumax/Cumin（初始出溶流体中Cu含量最大值和最小值的比值）具有明显的反比关系，这表明初始流体中金属的变化率是指示成矿规模更可靠的指标。而初始流体中金属的变化率受深部岩浆房控制，岩浆房规模大，足以形成稳定的流体系统，则出溶流体中金属含量变化小；相反，如果岩浆房规模小，则很难形成稳定的流体系统，导致出溶流体中的金属含量变化大。. 项目执行期间共发表论文6篇，其中国外SCI4篇，国内核心2篇。