斑岩成矿系统中次浅成低温热液型矿床成矿机制研究：以新疆加曼特和小于赞金矿床为例

The different types of deposits in the porphyry ore system are the products of the different stages of hydrothermal events. Taking into account that the hydrothermal evolution is a continuous process, the transitional/subepithermal mineralization can occur between porphyry and epithermal mineralization. However, the studies before have primarily focused on the end members of porphyry ore system, little attention has been paid on the subepithermal mineralization. As a consequence, the source and mechanism of gold mineralization of the subepitehrmal deposit is still unclear. The Jiamante and Xiaoyuzan Au deposits in the western Tianshan, Xinjiang, are closely similar to the subepithermal mineralization on the mineral association, ore textures and hydrothermal alteration. This offers an important opportunity to constrain the ore-forming mechanism. Furthermore, the bismuthinite and bismuth in the Jiamante are first found in the Au deposits in the western Tianshan, Xinjiang. Microscopic observation, fluid inclusions, stable isotopes and in-situ trace elements of sulfides and single inclusion will be carried out in this study. Therefore, the objectives of this work are to trace the characteristics and evolution of fluids, source of ore-forming materials and occurrence of gold and its relationship with Cu and Bi. Based on these applications, it is aim to understand the ore-forming mechanism of the Jiamante and Xiaoyuzan deposits, and to reveal the materials and time-space linkage between these different styles of mineralization. Furthermore, it cannot only improve our understanding of the porphyry ore system, but also is very significant to further mine exploration in Xinjiang western Tianshan.

斑岩成矿系统中各端元矿床是热液不同演化阶段的产物。但热液演化是一个连续过程，势必会在深部斑岩型与浅表浅成低温热液矿化之间形成过渡的次浅成低温热液型矿化。过去研究主要集中于各端元矿床，而对次浅成低温热液矿化未给予足够重视，导致其物质来源和成矿机制尚不清楚。新疆西天山的加曼特和小于赞金矿床在矿物组合、矿石组构、热液蚀变等方面与次浅成低温热液矿床十分相似，为解决该类矿床成矿机制问题提供了良好机遇。另外，加曼特中辉铋矿和自然铋的发现为西天山金矿床中的首例，极具特殊性。本项目拟通过对不同类型和阶段的矿石-脉石矿物开展岩矿相学鉴定、流体包裹体、稳定同位素及硫化物-单个包裹体微区成分分析，查明Au赋存状态及与Cu、Bi耦合关系、物质来源、流体性质和演化，解决金成矿机制问题，揭示次浅成低温热液矿化在斑岩成矿系统中的纽带作用。此项研究有助于深化对斑岩成矿系统认识，为新疆西天山找矿勘查提供理论依据。

新疆西天山也里莫顿盆地中产出的加曼特和小于赞金矿床在矿物组合、矿石组构、热液蚀变等方面与典型的低硫型和高硫型浅成低温热液金矿床存在显著差异。本研究对两个金矿床进行了系统解剖，查明了赋矿火山岩的时空演化序列、岩石成因和构造背景，厘定了矿床成因，建立了也里莫顿-吐拉苏火山岩带晚古生代成矿系统，恢复了矿床的形成和保存变化，指明了找矿勘查方向。研究表明，也里莫顿盆地大哈拉军山组火山岩LA-ICP-MS锆石U-Pb年龄为357~366 Ma，与毗邻的吐拉苏盆地同套火山岩地层的喷发时代一致，均为晚泥盆世-早石炭世，而不是过去普遍认为的早石炭世。火山岩富集大离子亲石元素、亏损高场强元素，是在北天山洋向伊犁-中天山板块俯冲过程中、由俯冲带沉积物熔体交代地幔楔部分熔融所形成。加曼特和小于赞金矿床的成矿流体均具有中低温、低盐度的特征。H-O同位素和黄铁矿Co/Ni比值显示成矿流体具有岩浆热液-大气降水的混合性质。成矿金属和S、C组分主要来源于赋矿火山岩及隐伏次火山岩。水-岩反应或硫化作用可能是金等成矿元素沉淀富集的重要机制。加曼特矿床中载金硫化物的Rb-Sr等时线年龄为323.8±1.7 Ma，与吐拉苏地区浅成低温热液金矿床的形成时代基本一致，暗示两个盆地中的金矿床为同一构造-岩浆-热液活动的产物。综合矿床地质特征、成矿流体性质和成矿物质/流体来源，认为加曼特和小于赞分别属于次浅成低温热液型和中硫型浅成低温热液型矿床，与区域上同时代的不同类型热液矿床构建成了一个完整的浅成低温热液-斑岩-矽卡岩型金多金属系统。受益于上覆沉积地层的保护，也里莫顿盆地中金矿床剥蚀程度较低，盆地内部剥蚀程度相对较高的加曼特地区深边部可能存在隐伏的斑岩型铜金矿化。