滇西兰坪盆地金满—连城脉状铜矿床成因研究

【作者】 王光辉；

【导师】 侯增谦； 宋玉财； 薛传东；

【作者基本信息】 昆明理工大学 ， 矿产普查与勘探， 2010， 硕士

【摘要】 印度-亚洲大陆碰撞形成的青藏高原为研究大陆碰撞造山与成矿提供了天然的理想场所。兰坪盆地位于青藏高原东缘,夹持于澜沧江缝合线与金沙江-哀牢山缝合线之间,在盆地西部沿澜沧江缝合带发育一套热液脉型Cu矿床,其形成于碰撞造山带强烈变形的前陆盆地内,系后生矿床,矿床的分布受逆冲推覆构造系统的控制,矿体产状严格受陡倾的断裂控制,呈脉状产出。对于这套脉状Cu矿床而言,其形成机理、与碰撞造山作用的耦合关系、不同矿床之间的时空分布特征、成矿流体的运移和驱动机制、流体中金属组分和元素的来源以及金属的沉淀机制等问题,既无法用世界上已知的成矿理论加以解释,也没有被过去的工作深入阐明。鉴于此,本次工作选择这套脉状Cu矿床中目前规模最大的金满、连城矿床为研究对象,通过对其矿床地质特征的详细研究,并结合流体包裹体和同位素地球化学研究结果来揭示他们的发育特点,初步建立矿床成因模型。金满、连城矿床位于澜沧江断裂带东侧,矿区内主要的构造型式为金满-连城复式倒转背斜,背斜轴向NNE,出露的地层主要为中侏罗统花开佐组和上侏罗统坝注路组,赋矿围岩为中侏罗统花开佐组石英砂岩、粉砂岩、泥岩等碎屑岩和绢云母板岩、钙质板岩等弱变质岩,矿体产状受陡倾的断裂控制,呈脉状产出,典型矿石的矿物组合为石英+碳酸盐+含Cu硫化物、碳酸盐+含Cu硫化物和纯硫化物脉,矿石结构主要为半自形-他形粒状结构和交代结构,矿石构造则以脉状、浸染状和块状构造为主。对连城矿床采用辉钼矿Re-Os定年,结果显示矿床形成年龄为48-49Ma,处于青藏高原碰撞造山主碰撞期(65-41Ma)。流体包裹体研究结果显示,金满、连城矿床的成矿流体为一套富CO2、中-低温(170-350℃)、低盐度(<10-15 wt% NaCleq.)的流体系统。通过对主成矿期石英-碳酸盐-硫化物脉中的石英H-O同位素、方解石C-O-Sr同位素和硫化物矿物的S、Pb同位素组成进行测试,结果显示,流体中的δ18O水值和δD值分别为3.7-10.3‰和-111--89‰,表明流体来源于变质水和/或岩浆水,因盆地内无成矿期岩浆活动,据此可判断流体为变质水来源,C-O-Sr同位素组成分别为δ13CPDB值介于-7--4‰之间,δ18OPDB值变化于-18.0--13.0‰之间,87Sr/86Sr比值变化范围为0.709-0.714,反映变质碳酸盐岩和海相碳酸盐岩是热液方解石中碳的两个主要来源,δ34S值为-11--2‰,206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别变化于18.137-18.724、15.517-15.677、38.213-38.983之间,说明成矿流体中的S和金属组分来源于盆地基底变质岩系(深部地壳)和围岩地层(浅部地壳)的混合。综合金满、连城矿床地质特征、流体包裹体和同位素地球化学研究结果,我们认为金满-连城脉状Cu矿床是一种与变质流体活动有关的矿床,其形成源于印-亚大陆碰撞挤压所触发的澜沧江缝合带再活动,再活动引起盆地基底岩石发生变质作用并形成变质流体,流体运移和上升过程中萃取深部变质岩和浅部地层中的成矿元素,当浅表岩石在褶皱-逆冲作用下形成开放空间时,流体快速上升就位成矿。更多还原

【Abstract】 The Tibetan Plateau is an ideal area for understanding metallogenesis of continent-continent collision because it yields many mineral deposits with clear tectonic setting. Lanping basin is located in the east of the Tibetan Plateau, clamping between Lancang River suture and Jinshajiang-Ailaoshan suture. Along the Lancang River development a hydrothermal vein-type Cu deposits in the western basin. All of the deposits were formed in the intense deformation foreland basin of the collision belt, which were epigenetic deposits. The distribution of these deposits were controlled by the thrust-nappe structure system, and orebody occurrence strictly controlled by the steep dip of the fault. To the vein-type deposits, which formation mechanism and relationship with collision orogenesis are poorly understood. Meantime, how distribution of different mineral deposits in spatial and temporal? How is its transport and drive of the ore-forming fluid? Where were metal components and other elements in fluid from? How precipitation of metal component, and so on, these questions neither be explained by the known mineralization theory nor be futher clarified by the work of the past. So, this study aims to investigate their developed characteristics and establish the preliminary genetic models.Jinman and Liancheng copper deposits located at the eastern of the Lancang River suture, which major structural patterns was the double reverse anticline of the Jinman-Liancheng, and the anticline axial was NNE. The exposed stratus mainly are middle Jurassic Huakaizuo formation (J2h) and upper Jurassic Bazhulu formation (J3b). Among both of them, quartz sandstone, siltstone, mudstone and other clastic rocks, and sericite slate, calcareous slate and other weak metamorphic rocks of the Jurassic Huakaizuo formations are main host rocks for ores.Ores mainly consisted of quartz, carbonate minerals, and Cu-bearing sulfides. Main ore structure are subhedral-xenomorphic granular texture and replacement texture, vein-type, disseminated, and block structure. Molybdenite Re-Os dating showed that the Liancheng deposit formed at 48-49Ma. Fluid inclusion studies show that the ore-forming fluids of the Jinman and Liancheng ore deposits is a rich in CO2 with middle-low temperature (170-350℃) and low salinity (<10-15 wt% NaCl) fluid system. The results of isotope geochemistry show that the value ofδ18OH2O and 8D were 3.7%o to 10.3%o and-111‰to-89%o, which demonstrated the fluids come from metamorphic water and/or magmatic water. However, because it was no mineralization magmatic activity of the Lanping basin, so the ore-forming fluid was source of metamorphic fluid. The carbon-oxygen-strontium isotopic composition of calcite display that the value ofδ13CPDB were between-7‰and-4%o,δ18OPDB were between-18.0%o and-13.0%o, and the value of 87Sr/86Sr were changes between 0.709 and 0.714, all of these datas reflected that metamorphic carbonate and marine carbonate were the main source of carbon in hydrothermal calcite. The value ofδ34S were between-11‰and-2%o,206Pb/204Pb were changes between 18.137 and 18.724, 207Pb/204Pb were changes between 15-517 and 15.677,208Pb/204Pb were changes between 38.213 and 38.983, show that the sulfur and metal components of the ore-forming fluids drived from the basement metamorphic rocks and host rocks.According to the results of the geologic features with fluid inclusions and isotope geochemistry, we think that the metamorphic fluid which was formed by the Lancang River suture reactive again formed the Jinman and Liancheng ore deposits. In the process of the metamorphic fluid rised up and migration, it extracted metal and other components from deep metamorphic rocks and shallow stratus. When the superficial stratus formed faults in the fold-thrust events, the ore-forming fluid rapid rise up in place. If the suddenly changed in surrounding environmental pressure such as from static rock pressure to hydrostatic pressure, the ore-forming fluid taken place boiling and CO2-immiscibility, thus results metal sulfides precipitation.更多还原