长江中下游成矿带沙溪斑岩铜金矿床多期次岩浆活动与成矿作用的关系研究

Fertile porphyries of intracontinental porphyry copper-gold deposits are commonly featured by their adakitic affinities, which are attributed to have formed by mixing mantle-derived and crustal-derived magmas. However, the actual magma mixing mechanism and the relative contribution of the mantle-derived and crustal-derived components are still controversial. The porphyry copper-gold deposits in the Middle-Lower Yangtze River Valley Metallogenic Belt are typical of the Mesozoic regional intracontinental mineralization in Eastern China. The Shaxi deposit is a representative porphyry copper-gold deposit in the belt, and the numerous mafic enclaves in the ore-forming magmatic rocks can shed light on these research questions. By means of the EPMA and LA-ICP-MS analyses of the rock-forming and accessory minerals from the pre-/syn-mineralization porphyries and the mafic enclaves, we aim to constrain the compositions and physicochemical conditions of the magmas in the various intrusive stages, and unravel the relative mantle-/crustal-derived contributions to the ore-forming materials at Shaxi. The study will also provide unique insights on the ore-forming material source and metallogenic model reconstruction, and hence strengthen our understanding in the intracontinental porphyry copper-gold metallogeny and the capacity to refine the current porphyry ore deposit model.

大陆环境斑岩型铜金矿床的含矿斑岩常具有埃达克岩亲和性，很多学者认为它们来自壳幔混源的含矿埃达克质岩浆，但壳源和幔源岩浆在形成含矿岩浆过程中的作用尚存在很大争议。长江中下游成矿带斑岩型铜金矿床是中国东部中生代大规模陆内成矿作用的典型代表，沙溪矿床是成矿带内最典型的斑岩型铜金矿床之一，矿床内成矿期岩浆岩中发育大量的镁铁质暗色包体，为研究壳源和幔源岩浆与成矿的关系提供了理想的研究对象。本申请拟以矿床中镁铁质暗色包体为突破口，重点对镁铁质包体、成矿前和成矿期岩浆岩中造岩矿物（角闪石和长石）、副矿物（锆石和磷灰石）和熔融包裹体开展电子探针、LA-ICP MS微区微量元素和同位素分析研究，厘定不同期次岩浆的物理化学条件和成分变化特征，确定壳源和幔源岩浆在形成含矿岩浆过程中的贡献，阐明沙溪矿床成矿物质的来源，构筑成矿模式。研究成果将进一步深化对大陆环境斑岩型铜金矿床成因的认识，丰富斑岩型矿床的成矿理论。

大陆环境斑岩型铜金矿床的含矿斑岩常具有埃达克岩亲和性，很多学者认为它们来自壳幔混源的含矿埃达克质岩浆，但壳源和幔源岩浆在形成含矿岩浆过程中的作用尚存在很大争议。长江中下游成矿带斑岩型铜金矿床是中国东部中生代大规模陆内成矿作用的典型代表，沙溪矿床是成矿带内最典型的斑岩型铜金矿床之一。本文系统搜集和整理沙溪矿床、长江中下游成矿带及邻区地质背景等方面的已有资料基础上，对沙溪矿床进行了代表性勘探剖面钻孔的矿化蚀变及相关岩体进行细致观察、对所采样品开展岩相学、矿物学和岩石地球化学等手段。结果显示沙溪矿床发育钾硅酸盐化、青盘岩化、绢英岩化和泥化蚀变分带，矿床内黄铁矿具有多阶段的特点，天水等其他流体的混入导致成矿流体氧化还原条件的改变是矿床成矿物质沉淀的主要机制；矿床的成矿岩浆为壳源岩浆和幔源混合的产物，矿床内成矿岩体中大量发育的新元古代继承锆石可能来自古华南洋俯冲作用形成的玄武质岩浆岩，这些玄武质岩浆岩扣留大量的铜金等金属物质堆积在地壳深部，为沙溪矿床的形成提供了所需的铜金等金属物质，底侵的基性岩浆则提供成矿所需的水和硫等成矿物质。同时，分离结晶作用对于长江中下游成矿带内斑岩型矿床成矿岩浆的形成具有重要作用。.本次研究进展与成果不仅深化了长江中下游成矿带斑岩型矿床的成因认识，也进一步完善了陆内斑岩型矿床的成矿理论。