四川省九龙县黑牛洞韧性剪切带型浸染状铜矿石的特征及其矿床学意义

Characteristics of ductile shear-type disseminated ores in Heiniudong copper deposit,Jiulong County,Sichuan Province

四川省黑牛洞铜矿赋存于中元古代变质火山-沉积岩中,含矿变质火山-沉积岩可能形成于扬子地台西缘大陆被动边缘裂谷带,经历了至少2次韧性变形,变质达到角闪岩相〔泥质原岩:十字石+铁铝榴石(蓝晶石),变基性火山岩:斜长石+普通角闪石+铁铝榴石〕。一方面,经构造动力作用(韧性剪切变形),原矿石经过改造形成韧性剪切带型浸染状矿石或矿化岩(简称剪切型矿石);另一方面,活化、迁移形成的含矿热液在合适的构造部位淀积成块状、准块状、角砾状和浸染状等矿石,形成以块状、准块状和角砾状硫化物为主的铜矿床。剪切型矿石的特征为:①矿石矿物和脉石矿物与围岩片理的产状基本一致,发育大量剪切条带、石英不对称透镜体和石香肠、不协调褶皱;②矿物晶体或集合体一般呈他形、透镜状;在平行片理的面(∥AB面,⊥C)上,矿石矿物集合体呈浸染状、斑点状和薄片状;在垂直片理走向的面(∥AC面,⊥B)上,则呈细条状、透镜状,甚至无根钩状,发育S∧C组构,与围岩变形特征相同;③石英动态重结晶颗粒、对称透镜体、布丁、条带和S∧C组构发育,矿石矿物集合体条带、对称透镜体、无根褶皱,以及与活化、迁移有关的溶蚀结构十分发育。研究结果表明,黑牛洞矿区发育的剪切型矿石和非剪切型矿石是同一构造过程的不同变形阶段,在不同的成矿作用和不同的地球物理化学条件下的产物。

Based on field mapping and drilling as well as indoor studies,the authors reveal that the Heiniudong copper deposit located in the extensional ductile shear zone is hosted by volcanic-sedimentary rocks in the Mesoproterozoic Liwu Group which experienced metamorphism of the staurolite-kyanite grade and was formed at the rifting valley in the passive continental margin of Yangtze platform,suffering from at least two times of ductile deformation. On the one hand original ores were changed into ductile shear-type disseminated ores by ductile deformation and on the other hand copper-rich fluids were formed by ductile deformation and precipitated in brittle fractures or shattered rocks,mainly forming massive and brecciated sulfide ores. Shear-type disseminated ores have the following characteristics：① Ore minerals and gangues are consistent with the deformation of host rocks. The mineral crystals are anhedral. Within the ductile shear zone,there are a lot of quartz lenses,shear-type bands,sausages and harmonious folds. ② The aggregates of ore minerals are in the forms of disseminations and spots on the side parallel to the schist （∥AB,⊥C）,and in the form of fine bands,lens,sausages and crooks on the other side （∥AC,⊥B）. There are S∧C fabrics and ＇δ＇ quartz porphyroblasts on the side （∥AC,⊥B）. The S∧C fabrics with ductile deformation features in the ductile shear-type disseminated ores show that ductile shear zone is extensional. ③ Ductile shear-type disseminated ores must have resulted from two phases of ductile shear deformation,whose ore and vein mineral deformation is consistent with features of hosted rocks,whereas non-shear type disseminated ores （disseminated ores） might have resulted from heat fluid,whose ore and vein mineral deformation is inconsistent with features of hosted rocks.