黔西南莲花山萤石矿床多期构造叠加及成矿意义

    • 摘要: 右江盆地位于特提斯构造域和太平洋构造域的结合部位,不仅发育了多期构造活动,同时形成了大量低温热液矿床。近期,在右江盆地西北缘的黔西南莲花山地区新发现了一处热液型萤石矿床,其矿体主要赋存在断层内,矿石品位高,初步储量可达中型规模。该区构造复杂多样,但控矿规律不明,严重制约了下一步的找矿勘查工作。本文详细的野外地质勘查和构造解析表明:(1) 区内叠加构造明显,发育有典型的反“S”形褶皱和复杂的断裂构造;(2) 矿床主要受控于莲花山背斜核部和南东翼的NE向断层和张节理;(3) F19、F21、F22是主要的含矿断层,表现出多期的构造活动。莲花山地区至少经历3期明显的构造活动,D1为S–N向缩短形成了莲花山近E–W向褶皱及一系列左行逆冲断层;D2表现为NWW–SEE向的缩短变形,使得莲花山背斜呈现为反“S”形褶皱,同时形成了NE向和NW向断层并发生强烈的右行逆冲活动;D3主要为NW–SE的伸展作用,其中先存断层活动明显,同时在褶皱和断层附近发育大量不同规模的张节理。莲花山萤石矿体主要赋存在NE向断层内,表现为同轴脉体向内生长,暗示了NE向断层晚期伸展活动为含矿热液沉淀提供了张性空间。结合区域研究成果,本文认为印支期和燕山早期不同方向挤压缩短形成了莲花山地区的构造格架,而燕山晚期的伸展作用导致的先存断层伸展活化为成矿提供了有利空间。多期次构造叠加在右江盆地内低温热液矿床中表现明显,可能是大规模成矿的重要机制之一。

       

      Abstract: The Youjiang Basin is situated at the junction of the Tethys and the Pacific tectonic domains. It has not only witnessed poly-phase structural activities but also developed abundant low-temperature hydrothermal deposits. Recently, a new hydrothermal fluorite deposit has been found from the Lianhuashan area in the northwestern margin of the Youjiang Basin, southwestern Guizhou. The fluorite deposit is characterized by fault-controlled mineralization and shows high ore grades. However, it is difficult to prospect the fluorite orebodies in the Lianhuashan area, largely due to the complex structural styles and fault systems. Detailed field geological survey and structural analysis reveal the following: (1) The mining area exhibits significant superimposed structures, with typical reverse "S"-shaped folds and complex fault systems; (2) The deposit is mainly controlled by NE-trending faults and tension joints in the hinge zone and southeastern limb of the Lianhuashan anticline; (3) The F19, F21, and F22 are the main ore-bearing faults and show the features of multiple-period activities. In general, the study area had undergone at least three-stage tectonic activities. The first stage (D1) was driven by nearly north-south compression, which led to the development of nearly EW-trending folds in the Lianhuashan and a series of sinistral thrust faults. The second stage (D2) involved the NWW–SEE compression, which resulted in the development of the Lianhuashan anticline with a reverse S-shaped fold, and NE and NW-trending faults accompanied by intense dextral thrust activities. During the third stage (D3), the nearly NW-SE extension caused the reactivation of pre-existing faults and formed a large number of tension joints within the fault zones and folds. The fluorite ore bodies hosted in NE-trending faults show the feature of coaxial veins growing inward, suggesting that the tensile spaces controlled by NE-trending faults play a key role in the ore-bearing fluid transport and precipitation. Combined with regional research results, we consider that the tectonic framework of the Lianhuashan area is controlled by the shortening deformation in different directions, and the reactivation of pre-existing faults caused by the extension in the Late Yanshanian period provides the favorable space for mineralization. Superposition structures are the key ore-controlling factors in low-temperature hydrothermal deposits within the Youjiang Basin, which may be one of the most important mechanisms of large-scale mineralization.

       

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