滇西北羊拉铜矿床深部石英斑岩脉的发现及其成岩成矿年代学研究

The Yangla copper deposit is a typical large scale ore deposit in Jinshajiang tectonic belt. Recently, quartz porphyry veins was newly discovered in the deep deposit, with chalcopyrite and pyrite mineralization, and the age of petrogenic and metallogenic of quartz porphyry veins has become a key problem to study the genesis and mineralization of Yangla copper deposit. In this proposal, the newly discovered quartz porphyry veins will be as the research object. Spatial distribution, shape attitude and mineral composition will be studied, through lithology-tectonic-altered mapping and detailed observations of quartz porphyry. The diagenesis age, material source and diagenesis of quartz porphyry will be studied by using LA-ICP-MS zircon U-Pb dating, combining with element geochemical and Sr-Nd-Pb isotopic geochemistry. Re-Os dating of chalcopyrite and pyrite will be used to research the minerlization age of quartz porphyry, association with C-H-O-S-Pb isotopic and fluid inclusions geochemistry, we try to discuss the minerlization and the source of ore-forming material and fluid of quartz porphyry. On this basis, tectonic setting of quartz porphyry will be further revealed, and the mineralization model of Yangla copper deposit will be constructed, which can provide more evidence for genesis and prospecting prediction of Yangla copper deposit.

羊拉大型铜矿床为金沙江成矿带内的典型矿床。近期在其深部新发现石英斑岩脉，并发育黄铜矿化、黄铁矿化，其成岩成矿年代已成为制约羊拉铜矿床成矿作用和矿床成因研究的关键问题。本申请拟以羊拉铜矿床深部新发现的石英斑岩脉为研究对象，通过“岩性-构造-蚀变”填图和石英斑岩的精细解剖，研究羊拉铜矿床深部石英斑岩脉的空间分布、形态产状和矿物组成；利用LA-ICP-MS锆石U-Pb同位素测年获得石英斑岩的成岩年龄，结合元素地球化学和Sr-Nd-Pb同位素组成，研究其物质来源和成岩作用；采用黄铁矿、黄铜矿Re-Os同位素测年确定斑岩型矿化的成矿年龄，结合电子探针、C-H-O-S-Pb同位素组成和流体地球化学资料，探讨石英斑岩的成矿物质和成矿流体来源及成矿作用。在此基础上，进一步揭示石英斑岩成岩成矿作用的构造背景，建立矿床成矿模型，为完善羊拉铜矿床成矿理论和找矿预测提供依据。

深部矿化花岗斑岩（项目申请时岩性定为石英斑岩，经岩矿鉴定修改为花岗斑岩）为羊拉铜矿床的找矿新发现，其成岩成矿年代已成为制约羊拉铜矿床研究的关键科学问题。本项目通过对羊拉铜矿床的矿化花岗斑岩研究，得到如下认识和结论：①“岩性-构造-蚀变”填图和矿化花岗斑岩精细解剖显示，花岗斑岩呈脉状产出，受NE向断裂控制；其内外接触带具硅化、绢云母化、绿泥石化、碳酸盐化等蚀变，可细分为11个矿化-蚀变带；花岗斑岩的斑晶主要为石英、斜长石及褪色黑云母，基质由石英、长石和少量黑云母组成；矿石矿物主要为黄铜矿、黄铁矿及少量辉钼矿、闪锌矿，脉石矿物主要为石英、方解石，矿物生成顺序为黄铁矿→黄铜矿+黄铁矿+辉钼矿+石英→闪锌矿+方解石。②花岗斑岩成岩年龄为206.6±2.8Ma~218.6±2.9Ma，其形成稍晚于花岗闪长岩（228Ma-239Ma）；花岗斑岩属准铝-强过铝质、钙碱性-高钾钙碱性系列S型花岗岩，形成于碰撞晚期-碰撞后的构造环境，可能为形成花岗闪长岩的残余岩浆在浅成就位的产物。③本项目获得花岗斑岩旁侧石英脉中辉钼矿的Re-Os同位素年龄为229±2.7Ma，该数值为矽卡岩成矿期的成矿年龄，并不能代表矿化花岗斑岩的成矿年龄。花岗斑岩中存在中温-中盐度与低温-低盐度成矿流体体系，流体混合作用是矿质沉淀的主要机制。H-O同位素组成表明成矿流体来源于岩浆水与大气水的混合，S、Pb同位素组成表明硫来源于深部地壳-地幔岩浆、铅源于地壳-地幔岩浆混合铅。④羊拉铜矿的成矿模式为“热水沉积-岩浆热液成矿-构造热液改造”，构造控矿模式为印支期“岩浆侵入接触构造＋层间断裂”和燕山-喜山期“入字型构造＋阶梯状构造”。⑤项目提出了3个找矿预测方向及相应的勘探设计方案，其中，里农西侧深部斑岩型铜矿是找矿勘探的重点。同时，羊拉矿床的通吉格、加仁等矿段和西侧的跟古矿区亦是斑岩型铜矿的重点勘探区段。一旦证实深部存在规模型斑岩铜矿，势必带动整个金沙江成矿带的找矿勘探工作，亦将获得巨大的经济效益。