桂西隆林地区隆或金矿构造控矿模型及成矿预测

Structural Ore-controlling Model and Metallogenic Target of Longhuo Gold Deposit in Longlin Area, the Western Guangxi, China

滇黔桂“金三角”是世界著名的卡林型金矿矿集区之一。该区现有成矿研究多集中在孤立碳酸盐岩台地边缘,很少涉及孤立碳酸盐岩台地内部,导致台地内部的矿体就位因素与控矿模型还不清楚。详细研究了桂西隆林地区隆或金矿这一典型的台地内部金矿床,深入解析矿体控矿构造,构建控矿模型。结果表明隆或金矿区构造运动主要分为3期:第一期为海西期,形成NE向F0同生断层,并形成台沟相隔的古地理格局,其中在台沟相区沉积了薄层硅质岩-泥岩-粉砂岩组合,为矿床的形成提供了地层条件;第二期为印支期,形成了隆或穹隆及其NW向的磨毫次级背斜,为成矿提供了构造准备;第三期为燕山期,表现为F0断层的重新活动,成为矿区主要的热液流体通道(导矿构造),其西侧发育大量的平行次级正断层及伴生的牵引褶皱,并逐渐向西减弱为节理带和劈理带,这些次级断层-节理-劈理带共同组成了矿区的配矿构造系统,引导成矿流体在磨毫次级背斜核部的下石炭统英塘组硅质岩-碳质泥岩-凝灰岩中交代、充填形成层状矿体。因此,隆或金矿主要受岩性和构造联合控制。根据控矿模型并结合地球物理-地球化学-遥感资料,可以预测:NE向F0断层西侧附近,隆或金矿深部的次级背斜核部是有利的深部找矿靶区,含矿层位为下石炭统英塘组;F0断层与隆或穹隆核部的交汇部位是外围有利找矿靶区,含矿层位为下泥盆统郁江组,特别是与寒武系接触的不整合面附近。

The adjacent area of Yunnan, Guizhou, and Guangxi provinces, termed the “Golden Triangle”, is one of the world-famous Carlin-type gold ore concentration areas. Previous metallogenic research in this area mainly focuses on the mineralization at the edge of the carbonate platform. However, it rarely involves the interior of the carbonate platform, so the ore body emplacement factors and ore-controlling models are still unclear within the platform. The Longhuo gold deposit, a typical gold deposit located at the platform’s interior in the western Guangxi, was analyzed in detail;the ore-controlling structure and model were fundamentally constructed. The results show that the structures of Longhuo gold deposit can be divided into three periods.(1)The first period is Hercynian sedimentary, which forms the NE-trending F0syngenetic fault and the platform-trench paleogeographic pattern with the thin-layer siliceous rock-mudstone-siltstone components;the lithology provides the stratigraphic conditions for the formation of the deposit.(2)The second period is Indosinian orogenic, which forms the Longhuo dome and NW-trending Mohao secondary anticline;the anticline provides favorable tectonic conditions for the mineralization.(3)The third period is Yanshan metallogenic characterized by the reactivation of fault F0, which is the main hydrothermal fluid migration channel in the mine area. A large number of parallel secondary normal faults and associated traction folds develop on its western side, and gradually weaken into joints and cleavage zones to the west. These secondary fault-joint-cleavage zones together form the ore-allocating tectonic system of the mine area, guiding the ore-forming fluids to replace and filling the siliciclastic-carbonaceous mudstones and tuffs of Lower Carboniferous Yingtang Formation in Mohao secondary anticline core to form bedded ore bodies. Therefore, the Longhuo gold ore body is jointly controlled by lithology and tectonics. According to the metallogenic model, combined with geophysics-geochemistry-remote sensing data, it is predicted that near the western side of the NE-trending fault F0, the secondary anticline core of the deep part of Longhuo gold deposit is the favorable prospecting target. The ore-bearing stratum is Lower Carboniferous Yingtang Formation. The intersection of fault F0and the core of Longhuo dome is the favorable prospecting target for mineralization in the periphery of Lower Devonian Yujiang Formation, especially near the unconformity in contact with Cambrian.