柴北缘锡铁山铅锌矿床控矿构造特征及找矿预测

锡铁山矿床是中国西部的超大型铅锌矿产地之一,产于柴北缘晚奥陶世滩间山群的大理岩和片岩之中,是与海相火山喷流-沉积有关的矿床。很多学者已经从地球化学、岩石学、同位素测年等对该矿床的成矿时代、成矿流体性质、矿床成因等开展了研究,但对于锡铁山矿区构造控矿特征一直存在争议,普遍认为褶皱构造对矿区的控矿作用明显。文章主要以详实的野外观测为基础,分析了矿区的褶皱和断裂构造特征,探讨了构造对矿(床)体的控制作用,为矿区找矿勘查工作部署提供依据。通过详实的野外实测和综合对比分析表明,锡铁山矿区总体上为单斜层,不发育大型的褶皱构造,但是层内褶皱发育,包括A型褶皱和B型褶皱。发育在滩间山群a段内的A型褶皱,其褶皱枢纽与拉伸线理倾向南东,与矿区矿体的总体倾伏方向一致;而在滩间山群d段内的A型褶皱,其枢纽倾向北西;矿区内发育了多条北西西走向的大型断裂,其编号为F1-F6;分析表明,F1断层发育在早期塑性变形基础之上,晚期叠加了叠瓦逆冲推覆作用,造成了矿体及赋矿围岩的局部倒转;F2断裂大规模的左行走滑-逆冲作用导致了矿区滩间山群不同岩性段地质体的拼合接触,造成了矿区部分含矿地质体的缺失;野外填图揭示出,左行走滑的F3断裂从北西往南东,走向从330°逐渐转变为290°方向,并在南东侧末端,发育了一系列分支的左行走滑-正断层,组成"马尾状"构造,截切了矿体与围岩,并发生了横向错移。以此构造控矿特征为基础,结合矿床成因分析,进一步分析了锡铁山矿区深部的找矿方向,认为矿区南东侧深部具有良好的找矿空间;并以07号勘探线为例,根据F3及其分支断层的错移情况,分析了矿体可能被错移的位置。

Characteristics of ore-controlling structures and ore-prospecting of the Xitieshan lead-zinc deposit, northern edge of the Qaidam basin, NW China

The Xitieshan deposit, one of the large-size lead-zinc deposits located at the northern edge of the Qaidam basin in western China, is related to marine Volcanic-Sedimentary Hosted Massive Sulfur deposit (VSHMS). Most prior researches are focused on the mineralization age, the nature of ore-forming fluid, and the genesis of the deposit by the method of petrology, geochemistry, and isotopic dating. However, the characteristics of ore-controlling structures, which are essential to prospecting and expanding the mining resources, have been controversial for long time, and it is generally believed that it was the fold that controlled the production of ore bodies in the deposit. This paper mainly presents field evidences to discuss the characteristics of folds and faults and its controlling roles to the distribution of ore bodies, and further to provide the basis for the mining prospecting exploration. Our field investigation and comparative analysis showed that there was no large-scale syncline or anticline in the deposit and only a monocline composed of the Ordovician Tanjianshan Group in general, although some interlayered folds were well developed, including A-and B-type. Both the fold hinge and the strench lineation of A-type fold in a-segment of the Ordovician Tanjianshan Group are dipping to SE-ward, consistent with the dipping tendency of the whole ore-bodies in the deposit, but different with those in d-segment of the Tanjianshan Group as dipping to NW-ward. There are six large-scale NWW-trending faults in the deposit, named as F1 to F6 from the northeast to southwest. The F1 fault in the deposit probably developed on the base of ductile deformation in early stage. And the latterly nappe thrusting of the fault resulted in the reverse of ore-bodies and host rocks near the fault. Large-scale sinistral strike-slipping faulting of the F2 fault played important roles on the convergence together of different segments of the Tanjianshan Group, and also the missing of some ore-bearing geological bodies. Field mapping between the Zhongjiangou and Wuminggou areas revealed that the orientation of the F3 fault gradually changed from 330-trending in northwest to 290-trending in southeast. And several branch sinistral strike-slipping and normal faults were identified in the southeastern end area, composing a pattern of horsetail structure in the shape, which truncated ore-bodies and host rocks. Therefore, ore-prospecting directions were proposed based on the ore-controlling structures together with the metallogenic models of the deposit, suggesting that the deep region in the southeastern side should be one of most favorable ore potential areas, and the dislocation places of ore-bodies by the F3 fault and its branch sinistral-normal faults in the prospecting Line 07 were further forecasted for example.