贵州锦丰(烂泥沟)超大型金矿床构造解析及构造成矿作用

Structure analysis and structural metallogenesis of Jinfeng (Lannigou) gold deposit in Guizhou Province

在矿区大比例尺填图的基础上,运用构造解析的理论和方法,对贵州锦丰(烂泥沟)金矿的构造特征、构造演化和构造控矿作用进行了系统的阐述。矿区构造线主要分为近NS向、NW向和NE向3组,其中NW向构造线控制了矿区的构造格架。构造变形主要经历了同生期裂陷、造山期挤压、后碰撞造山侧向挤压和岩石圈伸展等4个阶段。盆地裂陷期间(D2-T2)形成的同生断层为后续的构造活动提供了最初的构造薄弱面,并成为主要的热液通道;造山期挤压期间(T3)形成了矿区最为明显的近NS向和NW向大型倒转褶皱和逆冲断层以及配套的NE向右旋走滑断层;后碰撞造山侧向挤压期间(J1)形成走向NE的叠加褶皱,并在F2-F3"X"型断裂系上形成近EW向的拉张区,矿质沿着拉张的空间沉淀就位;燕山期(J2-K)岩石圈伸展,形成小规模的近水平逆断层。上述4个主要构造变形阶段与右江盆地的裂陷-闭合-坍塌的发展演化历史相吻合,成矿发生在由挤压向拉张过渡的构造体制转换阶段。造山期逆冲作用形成的构造闭圈和后碰撞造山期间挤压向伸展转变的过程中形成的局部张性构造环境是矿质得以大量聚集、沉淀的主要构造控制因素。构造成矿作用是锦丰(烂泥沟)金矿单一矿体垂向延深1000m以上的主要制约因素。构造成矿的观点将为在滇黔桂"金三角"卡林型金矿带的深部找矿提供重要的理论依据。

Jinfeng, previously known as Lannigou, is the largest known Carlin-type gold deposit in Yunnan-Guizhou- Guangxi triangle area of southwestern China. The structural eharaeteristies, evolution and metallogenesis of the Jinfeng gold deposit were detailed in this paper based on the large scale mine mapping and the theory and method of structural analysis. The structural lines of this deposit were classified into three groups, trending north-south, northwest and northeast respectively, in which, the NW trending structural line control the structural framework of the deposit. This deposit underwent four structural deformation stages, i.e., splitting in the contemporaneous stage, compressing in the collisional stage, lateral comperessing in the post-collisional stage and extending of lithosphere. A series of contemporaneous normal faults, such as F1, F7 which were northwest-southeast trend and dipped east in the deposit, were formed around the carbonate rock platform during the splitting stage of Youjiang basin. These faults provided a primary structural weakness plan for the late structure action. Because there existed Laizishan dome which was near north-south strike, compression direction in collisional stage changed gradually from east→west to northeast→southwest, and most obvious north-south and northwest strike structural lines were formed in the deposit. That is, a fold-fault structural association existed which was composed of strongly overturned folds and reverse faults. Accompanied northeast trend dextral shear belts, such as F2, were formed in this stage. The early contemporaneous faults, like F1, FT, correspondingly experienced dextral shear. The compression direction in the post-collision stage was northwest-southeast trend, and refolded the folds generated in the collisional stage into northeast strike superimposed folds whose hinge varied with the bedding of early stage folds. On the other hand, the compression area in north-south trend and the extension area in east-west trend were formed respectively due to the stress＇ distribution on the ＂X＂ type fault system formed in the orogenic stage. Because it was the firm rock of Laizi-shan dome in the west, the extension tended to happen in the east area and resulted in F2 ＇ s sinistral-normal slipping and F3＇ s dextral-normal slipping, with the orebearing fluid entering the extension area leading to gold precipitation. After this, lithosphere extended in the Yanshanian stage in which the small reverse fault slightly cut the former structure. The above four main structural deformation stages matched the evolution of Youjiang basin from splitting to closing and collapsing. Large scale gold metallogenesis occurred at the structural transition from collisional compression to extension tectonics. The structural trap formed by thrusting in the collisional orogeny stage and the splay setting in the transition process from compression to extension seem to have been the main controlling factors for large scale congregation and deposition of gold. Structural metallogenesis is the most restricted factor for the vertical extension of a single ore body for 1 000 m. The view of structural metallogeny would provide a significant theoretical basis for the deep exploration of Carlin-type gold deposits in Yunnan-Guizhou-Guangxi triangle area.