云南普朗超大型斑岩Cu–Au矿床异常蚀变与矿化成因

Porphyry Cu deposits worldwide generally show typical alteration zonations from inner potassic outward through phyllic to peripheral propylitic zones, and copper mineralization is mainly associated with potassic, but rare with propylitic alteration. However, currently our detailed geologic investigation at the giant Pulang porphyry Cu–Au district (446.8 million tonnes at 0.52% Cu and 0.18 g/tonne Au) in Yunnan, SW China, showed that propylitic alteration occurs both on the periphery and in the core of the deposit, and copper mineralization is mainly (~90%) associated with propylitic rather than potassic alteration. This indicates that Pulang has an atypical alteration-mineralization zonation model distinct from other typical porphyry Cu systems globally. Therefore, based on detailed petrography, particularly the cathodoluminescence (CL) study, and advanced in situ analysis methods (e.g., LA–ICP–MS, SHRIMP/SIMS), we decide to conduct research on elemental, in situ Sr and O–D isotopic geochemistry of epidote in different occurrences (core and periphery, selectively pervasive replacements and vein-forming minerals), and geochemical characteristics (e.g., composition, formation temperature, Cu content) of quartz and fluid inclusions in different alteration and paragenesis. The aims of our study are in an effort to clarify the causes of atypical propylitic alteration and related copper mineralization at Pulang, thereby updating the classic porphyry-style alteration-mineralization model.

世界范围内的斑岩铜矿床通常呈同心环状蚀变分带，中心为钾硅酸盐化，向外过渡为绢英岩化，最外围为青磐岩化；Cu矿化主要与钾硅酸盐化蚀变有关，而青磐岩化阶段一般无矿化。然而，前期针对云南普朗超大型斑岩Cu–Au矿床的详细研究发现，青磐岩化在矿床外围和中心均有发育，且矿区Cu矿化主要（~90%）与青磐岩化而非钾硅酸盐化有关，表现出异常的蚀变与矿化特征。为此，项目拟在详细的岩相学、特别是阴极发光岩相学基础之上，采用激光消融等离子质谱、离子探针等原位分析技术，系统开展普朗矿区青磐岩化阶段不同产状（外围和中心，选择性交代和脉体矿物）绿帘石的主微量、原位Sr和O–D同位素，以及不同阶段脉体中石英/流体包裹体的微量元素和O同位素研究，揭示普朗铜矿床青磐岩化广泛发育且具有矿化的成因机制，进而完善斑岩铜矿床成矿模型。

世界范围内的斑岩铜矿床通常呈同心环状蚀变分带，中心为钾硅酸盐化，向外过渡为绢英岩化，最外围为青磐岩化；Cu矿化主要与钾硅酸盐化蚀变有关，而青磐岩化阶段一般无矿化。然而，前期针对云南普朗超大型斑岩Cu–Au矿床的详细研究发现，青磐岩化在矿床外围和中心均有发育，且矿区Cu矿化主要（~90%）与青磐岩化而非钾硅酸盐化有关，表现出异常的蚀变与矿化特征。为查明原因，项目对普朗斑岩铜矿中青磐岩化阶段矿物开展了相关研究。初期结果显示，青磐岩化阶段石英中原生包裹体的均一温度为277°–390°C（平均值332°C），不同产状绿帘石（外围和中心，选择性交代和脉体矿物）的δ18O值变化范围有限，在4.9‰–10.1‰之间，δD值在−70‰到−44‰之间，计算的青磐岩化阶段流体的δ18O值为4.5‰–9.7‰，δD值在−33‰到−8‰之间，指示普朗青磐岩化阶段流体主要为岩浆水而非前人认为的天水。.同时，我们通过详细的显微矿物学观察和分析有效示踪并恢复了普朗斑岩铜矿系统深部岩浆储库的演化过程，揭示镁铁质岩浆的反复注入可能为斑岩系统提供了大量S和部分Cl，同时活化了斑岩系统，有利于形成大的生命周期长的岩浆储库，最终促进普朗超大型斑岩铜矿床的形成。此外，通过对普朗铜矿所在义敦弧内成矿斑岩与无矿岩体中副矿物锆石和磷灰石的对比研究，我们发现，义敦弧成矿斑岩为一套富水和硫的氧化性岩体，而无矿岩体为一套富水但贫硫酸盐的还原性岩体，义敦弧南北岩浆氧化还原状态的不同导致了斑岩铜矿成矿的差异性。我们的结果也揭示前人提出的预测岩浆成矿潜力的全岩地球化学和部分锆石组分指标在义敦弧也适用，但部分锆石组分指标不适用，磷灰石组分可成为有效的成矿潜力评价指标。.项目在国际矿床学权威期刊Economic Geology和Society of Economic Geologists Special Publications上发表论文2篇，项目成果受到国内外关注和认可，产生了重要影响。