云南羊拉铜矿床成矿流体特征及成矿过程

摘要

The Yangla copper deposit is located in the middle part of the Jinshajiang belt. It was formed by the westward subduction of the Jinshajiang oceanic basin and collisional orogeny during the Mid-Late Triassic. Ore bodies are typically layered or bedded and controlled by interlayer fracture zones in the wall rocks. Based on the study of fluid inclusions, the present paper is to discuss characteristics and evolution of ore-forming fluids and to evaluate the relationship between fluid immiscibility and mineralization. According to the petrographic study, various types of fluid inclusions including predominant vapor or liquid-rich aqueous inclusions and daughter minerals-bearing multiphase inclusions, and subordinately mono-pha.se liquid and organic vapor inclu-sions, are present in anhydrous skarn stage ( Ⅰ ), hydrous skarn-magnetite stage (Ⅱ), quartz-sulfide stage (Ⅲ) and calcite-sulfide stage (Ⅳ). Daughter minerals-bearing multiphase inclusions are abundant in garnet ( Ⅰ ), epidote (Ⅱ) and especially in quartz ( Ⅲ). Ore-forming fluids of stage I and Ⅱ have high homogeniza-tion temperatures (413 - 593℃ and 336 - 498 ℃,respectively) and high salinities (19. 1 %- 49. 7% NaCleq, and 15.7%-53. 3% NaCleq, respectively). Stage Ⅲ ore-forming fluid has a wide homogemzation temperature range (148 - 398℃) and is characterized by existence of both high-salinity (35. 5%- 65. 3% NaCleq) and low-salinity (2. l%- 9. 6% NaCleq) end members. Stage Ⅳ ore-forming fluid is characterized by low temperature (132-179 ℃) and low salinity (3. A%- 10. 4% NaCleq). Based on the characteristics of fluid inclusions to-gether with geological features, fluid immiscibility (boiling) is suggested to be the main mechanism for metal precipitations in this deposit.%云南羊拉铜矿床位于金沙江构造带中部,是中—晚三叠世金沙江洋盆向西俯冲闭合-碰撞造山过程中形成的一个大型铜矿床.矿体多呈层状、似层状顺层产出,但明显受层间破碎带和滑脱带控制.从流体包裹体研究入手,讨论了该矿床成矿流体的特征、演化以及流体不混溶(沸腾)作用与成矿的关系.流体包裹体研究表明,干夕卡岩阶段(Ⅰ)、湿夕卡岩-磁铁矿阶段(Ⅱ)、石英-硫化物阶段(Ⅲ)以及方解石-硫化物阶段(Ⅳ)中发育多种类型的包裹体,主要为气液水两相包裹体和含子矿物多相包裹体,纯液相水包裹体次之,少见纯气相有机质包裹体.其中,含子矿物多相包裹体发育于Ⅰ阶段石榴石、Ⅱ阶段绿帘石,尤其是Ⅲ阶段石英中.Ⅰ、Ⅱ阶段成矿流体具有高温、高盐度特征,均一温度分别为413～593℃和336～498℃,盐度分别为19.1％～49.7％ NaCleq和15.7％～53.3％ NaCleq；Ⅲ阶段成矿流体均一温度为148～398℃,并具有低盐度(2.1％～9.6％NaCleq)与高盐度(35.5％～65.3％ NaCleq)共存的特征；Ⅳ阶段成矿流体具有低温(132～179℃)、低盐度(3.4％～10.4％ NaCleq)特征.根据流体包裹体的微观特征并结合矿区的宏观地质特征,认为流体不混溶(沸腾)是导致本矿区金属沉淀成矿的主要机制.