安徽青阳高家塝-狮金山钨钼多金属矿床成矿流体系统和成矿机制研究

Gaojiabang W-Mo deposit and Shijinshan Cu-Mo-Au polymetallic deposit are two typical deposits around Qingyang-Jiuhua intrusion in Anhui Province, which developed not only high temperature W-Mo, but also medium and low temperature Cu-Mo, Pb-Zn and Au-(As). The structural setting, ore-hosted formation and element associations of the two deposits represent the general features of Jiangnan transitional metallogenic zone which is clearly different from Tongling and Guichi ore district of the Middle and Lower Yangtze River metallogenic belt and the Southern Anhui metallogenic belt. In this natural science funding project, we intend to make the magma-fluid-ore forming as the main line, focus on the paragenesis and zoning of the metallogenic elements of high temperature and medium-low temperature, study the above two closely neighbouring deposits and their related magmatic rocks. We aim to ascertain the genetic relationship between the mineralization with the regional structure, magma origin as well as their evolution, determine the characteristics of the ore-forming fluid system of the W-Mo deposit and the Cu-Mo-Au polymetallic deposit, and discuss the metallogenic mechanism. Further, we will confirm the mineralization characteristics and ore-controlling factors of the deposits in Jiangnan transitional metallogenic zone as well as the difference and relationship of magmatism and mineralization between the study area with the adjacent regions, and then provide useful information and powerful evidence for the regional metallogenic theoretical study and prospecting exploration practice.

高家塝钨钼矿床和狮金山铜钼金多金属矿床是安徽青阳-九华岩体周边众多矿床中的典型，不仅发育高温的钨-钼元素，而且产出中-低温的铜-钼、铅-锌和金(砷)元素，构造背景、赋矿地层和元素组合等代表了江南过渡带成矿作用的总体特征，其与北侧沿江成矿带的铜陵矿集区和贵池矿集区以及南侧的皖南成矿带均有明显不同。本项目拟以岩浆-流体-成矿为主线，针对高温和中-低温两类元素的共生和分带，对上述两个紧密相邻矿床及其相关岩浆岩进行深入研究，分析成矿作用与区域构造和岩浆起源及其演化的成因联系，确定钨钼矿床与铜钼金多金属矿床成矿流体系统特征，探讨成矿作用机制，进而确定江南过渡带成矿特征和控矿因素及其与邻区成岩成矿作用的差异和联系，为区域成矿理论研究和找矿勘查实践提供有用信息和有力依据。

安徽青阳高家塝-狮金山钨钼多金属矿床是江南过渡带北端新发现的一个大型斑岩-矽卡岩-热液脉型矿床，成矿金属元素表现出钨钼在上、铜金在下的逆向分带特征。本项目深入研究了高家塝-狮金山钨钼多金属矿床相关花岗闪长质侵入岩的成岩年龄、岩浆起源和结晶条件、矿质来源和成矿机制，探讨了岩浆起源和演化与成矿的关系及成矿金属元素分带的控制因素。研究取得的重要成果和新认识如下：（1）高家塝-狮金山钨钼多金属矿床相关岩浆岩主要为花岗闪长岩和花岗闪长斑岩，锆石U-Pb定年显示其均形成于燕山晚期早白垩世，但赋矿花岗闪长斑岩侵位略早，岩石地球化学和Sr-Nd同位素组成特征显示两个花岗闪长质侵入岩具有相同的岩浆起源，相对于长江中下游成矿带铜陵矿集区，岩浆中同化混染了较多的上地壳物质。（2）高家塝钨钼矿床和狮金山铜钼金多金属矿床的成矿作用受统一的岩浆热液系统控制，两者在空间上紧密相邻，控矿岩体均为略早形成的花岗闪长斑岩体，成岩和成矿物质来源相同。（3）赋矿小型花岗闪长斑岩岩枝与成矿关系密切，而相邻的大型花岗闪长岩体反而不成矿，原因是，虽然它们的岩浆起源相同，但经历演化后至先后侵位结晶时的岩浆特征和结晶条件发生了显著变化，花岗闪长斑岩岩浆结晶时处在较还原的环境下，岩浆中富含F和Cl，有利于钨（钼）富集于岩浆期后热液流体中，进而形成大型钨（钼）矿床；深部岩浆房中的岩浆向着相对氧化的环境转化，因而有利于铜钼金多金属的出溶和富集成矿。（4）高家塝钨钼矿床的成矿流体富含CH4，成矿环境偏还原，流体不混溶和沸腾作用是矿质富集和沉淀的主导因素；随着区域构造应力向伸展的转化，岩浆-流体系统逐渐由还原向偏氧化环境演变，流体中CO2含量逐渐升高，有利于铜金多金属元素出溶；随着流体沸腾作用的持续进行和大气降水的混入，成矿温度降低，狮金山矿床铜、钼、金沉淀；成矿流体进一步演化，CO2和H2O成为流体主要成分，大气降水大量混入，成矿温度明显降低，铅、锌沉淀。