钦杭带北东段十字头斑岩钼矿的成矿流体、成矿岩体及成矿模式研究

Porphyry Mo deposits are the most important resources for Mo, and they can be divided into Climax (Granite) type and Endako (Quartz monzonite) type. Ore deposit models of these two types of deposits show obvious differences, including ore minerals, ore-forming element association, ore-related intrusions, mineralizing fluids, wallrock alterations, sources of mineralizing fluids and materials, and geologic setting, etc. In addition, there are evident differences in ore grade and metallogenetic potentiality. The former generally is high-grade large to super-large deposits, but merely a few of the latter can be up to large deposits commonly containing low-grade ore. Therefore, ore deposit genetic types and ore deposit models are crucial for evaluation of metallogenetic potentiality. In northeastern section of Qin-Hang ore zone, several middle to small porphyry Mo deposits have been found, and they form a porphyry Mo minerogenic prospect. However, no detailed researches on porphyry Mo deposit in this region have been done. Therefore, we select the Shizitou Mo deposit to carry out detailed wallrock zoning, fluid inclusion, H-O-S-Pb isotope and ore-formation pressure studies on ore deposit, and zircon U-Pb dating, whole rock elemental geochemistry and Sr-Nd isotope, and zircon Hf isotope studies on ore-related intrusion to obtain deposit genetic type and ore deposit model. In addition, we will compare it with typical porphyry Mo deposits to propose metallogenetic potentiality of this deposit and possible regional exploration guides.

斑岩钼矿是金属钼最重要的来源，其成因类型包括Climax型（花岗岩型）和Endako型（石英二长岩型）。两类斑岩钼矿的成矿模式存在较大差异，包括矿物组分、矿化元素、成矿流体、围岩蚀变、成矿岩体和成矿地质背景等。两者成矿潜力也明显不同，前者品位高，常形成大型、超大型矿床；后者品位较低，多为中小型矿床。因此，确定斑岩钼矿的成因类型和成矿模式是成矿潜力评价的关键。钦-杭成矿带北东段新发现一批斑岩钼矿形成一个斑岩型钼矿的远景区。目前尚无针对该区斑岩型钼矿的详细研究。本项目选择江西省十字头钼矿为研究对象，开展围岩蚀变、流体包裹体、氢氧硫铅同位素和成矿压力等矿床地球化学研究，以及锆石U-Pb定年、全岩元素和Sr-Nd同位素、锆石Hf同位素等成矿岩浆岩研究，在确定十字头钼矿成因类型和成矿模式基础上，与世界典型斑岩钼矿进行对比，探讨其成矿潜力，并提出可能的区域有利找矿标志。

我国是钼资源储量最大的国家，斑岩钼矿是钼最重要的来源，因此，开展我国典型斑岩钼矿的研究具有重要的科学意义和社会意义。本项目选择江西省十字头钼矿为核心研究对象，同时开展沙坪沟钼矿、德兴铜钼矿、治岭头钼矿与十字头钼矿的对比研究，取得如下重要结果：（1）江西十字头钼矿形成于160Ma，成矿流体为NaCl-H2O流体，贫CO2，低压条件下成矿流体沸腾作用导致金属沉淀。（2）浙江治岭头钼矿形成于110Ma，产于大陆弧环境，是典型的俯冲带环境产物。成矿流体为NaCl-H2O流体，贫CO2。成矿压力小，成矿机制为低压条件下成矿流体沸腾作用导致金属沉淀。十字头和治岭头钼矿均为典型的Endako型斑岩型钼矿。（3）选取亚洲最大的沙坪沟超大型斑岩钼矿为研究对象，开展系成矿流体和矿床地球化学的精细研究。主成矿期钾化带和黄铁绢英岩化带成矿流体曾发生过沸腾作用，成矿流体沸腾期间也发生了CO2的相分离作用。沙坪沟钼矿主成矿期的辉钼矿-石英脉形成的压力可以高达1.6 kbar，表明其成矿压力明显高于大多数的斑岩型矿床，沙坪沟钼矿为典型的Climax型斑岩钼矿。（4）德兴铜矿田发育大规模的斑岩型铜钼金矿化，选取最富钼的富家坞铜钼矿床开展研究，富家坞矿床的含子晶包裹体可以进一步划分为IIIa和IIIb，前者为气泡消失包裹体均一，后者为子晶消失包裹体均一。富家坞矿床沸腾包裹体的大量存在说明强烈的多期沸腾事件促进了大型Cu-Mo矿化。IIIb型包裹体不是沸腾包裹体组合的端元组分，因此不能用于计算捕获条件。本次研究通过详细的流体包裹体岩相学观察，排除了IIIb型包裹体的影响，获得真实的形成压力。.研究成果已经正式发表9篇国际SCI文章，其中第一标注4篇，第二标注2篇，第三标注3篇。本项目详细的流体研究识别出Endako型（十字头、治岭头）、Climax型（沙坪沟）斑岩钼矿的成矿机制和差异，也对比了斑岩型铜钼矿（富家坞）的成矿机制，大大深化了对我国优势矿种钼形成机制的认识。