东天山古生代浅成低温热液金矿床的形成及保存：以马庄山金矿为例

The preservation and change of epithermal deposits is a hot research issue of the mineral deposit geology. It not only helps improving the hypabyssal/super hypabyssal magmatic-hydrothermal fluid metallogenesis theory, but also affects the international mineral exploration direction. The Mazhuangshan large gold deposit is hosted in Lower Carboniferous volcanic subvolcanic rocks in the East Tianshan Orogen. The present comprehensive studies show that it possesses some typical geological-geochemical characteristics of epithermal gold deposit, and was formed in late Carboniferous. In this project, we choose the Mazhuangshan deposit as a research object, take the metallogenic system theory as guiding ideology and integrate the studies on diagenesis chronology, metallogenic chronology and geochemistry, in order to investigate the ore deposit geology, geochemical characteristics, find out the source of ore-forming fluid and its spatial and temporal evolution, then construct the geochronological framework in the deposit area, confirm the preservation and change process of the deposit after its formation, and finally establish a formation-change-preservation model for the Mazhuangshan gold deposit. The expected achievement can improve the research level on Paleozoic epithermal metallogenesis system, and help us to further understand the distribution regularity of epithermal-porphyry deposits in East Tianshan Orogen; finally which is expected to provide a theoretical guidance for the further ore exploration work.

浅成低温热液型矿床形成后的保存和变化是目前矿床学的研究热点之一，不仅影响浅成低温-斑岩型成矿系统理论的完善，而且影响国际矿产勘查的方向。东天山马庄山大型金矿床赋存在下石炭统的火山-次火山岩中，显示浅成低温热液型矿化的特点，已有年代学结果表明其形成于晚石炭世。本项目选择该矿床为研究对象，以成矿系统理论为指导思想，结合成岩、成矿年代学和地球化学研究，解剖矿床地质、地球化学特征，查明成矿流体的性质、来源及时空演化规律，厘定矿区年代学格架，确定矿床形成后的保存和变化过程，从而构建马庄山金矿床的成矿-变化-保存模型。本项目预期成果不仅可以提高古生代浅成低温热液成矿系统研究的整体水平，而且有助于深入认识东天山浅成低温-斑岩型矿床的分布规律，有望为东天山找矿勘探工作提供理论指导。

浅成低温热液型矿床形成后的保存和变化是目前矿床学研究热点问题之一。本项目选择东天山下石炭统火山-次火山岩中的马庄山金矿床为研究对象，在常规研究的基础上，借助金属矿物原位成分/同位素测试、流体包裹体金刚石压腔测温、多种热年代学等测试技术，查明了成矿物质和流体的来源及时空演化规律，约束了成矿深度和成矿过程，构建了年代学格架，确定了矿床形成后的保存和变化情况，初步构建了东天山古生代浅成低温金矿床的成矿-变化-保存模型。取得的主要新进展与认识如下：. 马庄山金矿以蚀变岩型矿石占主导，含金矿物以银金矿和金银矿为主，围岩蚀变主要为硅化、绢云母化、绿泥石化、碳酸盐化和黄钾铁矾化。黄铁矿、毒砂等原位δ34S值为3.01‰–6.52‰，成矿物质主要来自新生的壳源岩浆。成矿流体以低盐度、中低温的盐水溶液为特征，主成矿阶段流体氢氧同位素集中在-0.3‰–4.0‰和-109‰–-85‰，反映其主要源自大气降水，水岩反应导致流体氧同位素出现一定漂移。. 首次获得马庄山地区石英斑岩的锆石U–Pb加权平均年龄为321.1±2.2Ma，闪长岩和英云闪长岩的黑云母40Ar/39Ar坪年龄分别为296.5±1.1Ma和246.5±1.1Ma，石英斑岩、英云闪长岩和绿泥绢英片岩的锆石(U–Th)/He年龄分别为210±52Ma、188±10Ma和212±47Ma，英云闪长岩磷灰石(U–Th)/He年龄为123±33Ma，含矿黄铁矿Re-Os年龄为~312Ma。上述高—中—低温热年龄限制了成岩、成矿和抬升冷却事件，结合区内浅成低温矿床的成矿深度0.1–2.2km，造山型金矿形成深度11.3–14.4km，利用热力学模拟，反演了研究区沉降-抬升变化过程，初步构建了东天山古生代浅成低温金矿床的成矿-变化-保存模型，即：马庄山金矿形成（312Ma）后，研究区发生7–10km的沉降；在三叠纪末—白垩纪早期发生快速抬升剥蚀，剥蚀厚度至少5km；~130Ma起，研究区进一步抬升到地壳浅表，深度小于2km，并且以较低剥蚀速率持续至今，使得矿床得以保存。. 所获得的成果不仅有助于深入认识东天山浅成低温-斑岩型矿床的分布规律，而且为东天山找矿勘探工作提供理论借鉴。