东秦岭银家沟斑岩-热液脉型矿床黄铁矿流体包裹体红外显微分析及He-Ar同位素研究

The Yinjiagou Mo, Cu, pyrite polymetallic deposit located at the middle of East Qinling metallogenic belt, forms the typical mineralizing zones from inward to outward. Porphyry Mo mineralization occur in the K-spar granite porphyry, whereas vein Cu and pyrite mineralization distribute in the K-spar granite porphyry and quartz diorite porphyry as well as the contact belts with wall-rock. Pyite is extensive in above mentioned stages. This project is designed to research the infrared physical and chemical characteristics and the He-Ar isotope compositions of fluid inclusion in pyrite from above-metioned mineralizing zones vein using the frontier infrared microthermometric and He-Ar isotopic analysis, aiming to announce the ore-forming fluid evolution, find out the key causes that affect the infrared transmittance of pyrites and fluid inclusions, checkout the "antifact" that the light intensity influences the microthermometric results,proclaim the true ore-forming informations of each zones and mineralizing mechanism based on the fluid comparision of pyrite and quartz, and quantitative analyse the content of mantle substance involving into the ore-forming fluid. Based on these researches and combining the time-space distributions of the late Jurassic to early Cretaceous large-scale metallogenesis of the East Qinling, we would build the mode of fluid evolution for the Yinjiagou deposit and then discuss the metallogenetic relationship with lithosphere thinning.

银家沟斑岩-热液脉型钼铜硫铁多金属矿床位于东秦岭成矿带中段，矿化分带明显，斑岩型钼矿化主要发育于钾长花岗斑岩内，热液脉状铜、硫铁矿化分布于钾长花岗斑岩和石英闪长斑岩内及其与围岩接触带，黄铁矿在各矿化带均有出现。本项目拟利用红外显微技术和He-Ar同位素分析等先进方法，分别对各矿化脉体中黄铁矿进行流体包裹体红外显微观察、红外显微测温及He-Ar同位素分析，获得各矿化阶段物理化学参数并据此反演成矿流体演化；查明影响黄铁矿及其流体包裹体红外透光性的主要原因，就红外光强对测温结果的影响进行检验和校正，对比及探讨石英流体包裹体的代表性，揭示成矿流体的本质特征及各矿化元素的成矿机制；利用黄铁矿流体包裹体He-Ar同位素组成定量分析幔源物质对成矿的贡献；在综合分析基础上建立该多金属矿床的流体演化模式，并结合东秦岭地区晚侏罗世到早白垩世大规模成岩成矿事件的时空分布规律，探讨该期成矿事件与岩石圈减薄的关系。

银家沟矿床是以硫铁矿为主的钼多金属矿床，黄铁矿体主要以脉状产出于钾长花岗斑岩及石英闪长玢岩断裂带中，局部穿插入钼矿体中，黄铁矿Re-Os显示其形成于142 Ma。斑岩钼矿化石英中成矿流体同时发育高盐度和低盐度流体，指示流体沸腾是钼矿化的主要成因机制；在红外下观察发现脉状黄铁矿化黄铁矿中发育大量流体包裹体，其成矿流体的盐度随温度的降低而降低，表明流体混合作用导致了黄铁矿的大规模沉淀。钼矿化黄铁矿He-Ar同位素比较集中，表明钼矿化成矿流体来自于岩浆热液；脉状黄铁矿化的黄铁矿He-Ar变化非常大，暗示混合作用的存在，地幔He高达65%，表明有大量地幔成分参与到了黄铁矿的成矿过程中。以上证据表明斑岩和脉状矿化具有不同时，不同源的重大区别，虽然他们产出位置相近，但可能来自于不同的成矿系统。钼属于典型的斑岩型矿化，与中生代岩体存在着必然的成因联系；而硫铁矿极可能形成于另一期含有大量地幔组分的热液活动，可能与晚侏罗到早白垩世岩石圈减薄、地幔流体上涌有关。区域上强烈的伸展背景，为地幔流体的上涌提供了可能，斑岩中的构造裂隙系统为黄铁矿脉的侵位提供了有利的成矿空间，从而使黄铁矿化叠加复合在了斑岩钼矿化之上。