钦杭带南段庞西垌-金山银金矿田控矿构造分析及找矿指示

钦杭成矿带南段的庞西垌-金山银金矿田位于粤东与桂西交界处,包括庞西垌、金山、中苏、竹根坡、高村等银金矿床及一系列银金矿点,是20世纪80年代规划的十大银矿基地之一。庞西垌地区经历了多期的构造-岩浆活动,韧性剪切带和断裂构造尤其发育。印支期以来,可识别出3期主要构造:第一期为右行韧性剪切,前人利用糜棱岩中白云母测得时代为221 Ma;第二期为左行韧脆性剪切,北东向的庞西垌-金山断裂带反映最为突出,切过燕山晚期花岗岩;第三期为脆性走滑。银金矿体及矿石结构、构造主要受第二期左行韧脆性剪切带控制。应用里德尔剪切体系对控矿构造的分布特征分析显示,银金矿脉主要赋存于里德尔体系的D、R和T裂隙中;D裂隙是最重要的赋矿构造,热液蚀变岩型和石英脉型矿体呈透镜状左行斜列于主断裂面中,沿走向往南西侧伏;R和T裂隙主要发育梳状含金石英脉。R裂隙呈密集剪破裂产出,与主断裂面夹角15°~35°;T裂隙呈雁列状等距分布,与主断裂面夹角约为45°。这些矿脉就位体系,可以为该区进一步找矿作参考。

Ore-controlling structure analysis of Pangxidong-Jinshan silver-gold orefield, southern Qin-Hang belt:Implications for furthern exploration

The Pangxidong-Jinshan silver-gold ore-field is located in Guangdong-Guangxi border area, belonging to the southern part of the Southern Qin-Hang belt. It consists of Pangxidong, Jinshan, Zhongsu, Zhugenpo, Gaocun silver-gold deposits and some other ore spots and was among the top ten planning silver ore concentration areas of China in the 1980s. The Pangxidong area has well developed ductile shearing zone and fractures due to multiphase tectonic-magmatic evolution. At least three stages of deformation can be identified since Indosinian. The first stage is dextral ductile shearing at 221 Ma dated by phengite in mylonite. The second stage is the sinistral ductile-brittle shearing that cut the late Yenshanian granites, characterized by NE-trending Pangxidong-Jinshan fault. The last stage is brittle fault. Recent studies suggest that the Pangxidong-Jinshan fault zone, a regional NE-SW-trending structure formed during the second stage, played an essential role in the formation and localization of the fault-hosted silver-gold veins systems. Regional sinistral ductile-brittle shearing of the Pangxidong-Jinshan fault zone controlled the general occurrences and orientations of lodes and veins, and constrained the development of the internal structures, geometric details and final localization of lodes and veins. Therefore, the development and final localization of the silver-gold system can be comprehensively recognized in terms of both the Riedel shear system theory and the effects of the regional progressive deformation of sinistral ductile-brittle shearing, which may guide the further ore prospecting work in future. The D fracture is the most important ore-bearing structure. The lodes and veins belong to D fracture range lenticular sinistral en echelon in the main fracture. The R fracture and T fracture with en echelon arrangement mainly contain auriferous quartz veins. The R fracture shows intensive shear fractures output, with an angle of 15°~35° to the main fracture. T fracture shows nearly equidistant distribution, with an angle of 45° to the main fracture.