利用宽谱系岩墙群进行勘查靶区预测的初步尝试: 以南阿拉套山为例

本文提出了一种利用宽谱系岩墙群(WSDS)进行内生金属矿床勘查靶区预测的新方法。南阿拉套山出露有一套由二叠纪煌斑岩质、玄武质、安山质、英安质和流纹质岩墙(脉)组成的岩墙群,可称为宽谱系岩墙群。该岩墙群侵位于花岗质岩基及其围岩中,是区内最晚一期岩浆活动的产物。以下特征暗示岩墙群的形成伴随着大规模含矿流体活动:(1)许多岩墙岩石具有气孔状构造,且含有大量含水暗色矿物; (2)部分岩墙岩石具有多斑斑状结构,基质为隐晶质或玻璃质结构; (3)部分岩墙岩石含有浸染状硫化物; (4)各类岩墙具有相似的不相容元素和成矿元素分配型式; (5)不同时代、不同岩性的地层具有相似的成矿元素分配形式。因此,宽谱系岩墙群及其围岩经受过含矿流体的浸润和改造,可作为确定性找矿标志。岩墙群的空间展布形式同时受区域性裂隙系统和局部性裂隙系统控制,可以解释为岩墙同时侵位于先存裂隙和自生长裂隙中。因此,宽谱系岩墙群是熔体-流体流快速侵位的产物,具有较强的成矿潜力。岩墙的空间展布形式可能暗示了含矿流体的运移方式,因而可以用来预测成矿金属大规模堆积的可能位置:(1)流体在运移路径上与碳酸盐岩相遇的部位; (2)流体在运移路径上与块状少裂隙火成岩体相遇的部位; (3)流体运移路径上适度破碎的断裂交汇部位; (4)流体在运移路径上与高渗透率地层相遇的部位; (5)岩墙密集区的小岩体。据此,可在南阿拉套山划出为六个勘查靶区(A、夏尔敖腊靶区,B、米尔其克岩体靶区,C、勒根乌苏-科克塔舒根乌苏靶区,D、阿尔夏提靶区,E、布图哈马尔西南岩体靶区,F、诺尔特靶区),涵盖了区域矿产调查发现的20个矿点(床)中的8个。如果将预测靶区的范围稍微扩大,则可以涵盖15个矿点(床)。据此,可以认为利用宽谱系岩墙群进行成矿预测是有效的。

A preliminary attempt for targeting prospecting districts using the wide composition-spectrum dike swarms: An example of the South Alatao Mountains, Xinjiang, China

This article is contributed to propose a new methodology for targeting prospecting districts of the endogenic ore deposits, using the Wide composition-Spectrum Dike Swarm(WSDS). A Permian dike swarm, which consists of the lamprophyric, the basaltic, the andesitic, the dacitic, and the rhyolitic dikes, is extensively exposed in the South Alatao Mountains, and can be felled to the WSDS. The WSDS intrudes the Permian granitic plutons and their country rocks, and is the products of the latest epoch of magmatism in this region. The WSDS generation is accompanied by violent activity of the ore-bearing fluids because(1)many dike's rocks have the fumarolic structure, and contain numerous water-bearing mafic minerals; (2)a part of the dike's rocks have poly-phenocryst porphyritic texture with a cryptocrystalline or glassy matrix; (3)a part of the dike's rocks contain disseminated sulphides; (4)all dikes have the similar pattern of the incompatible and the ore-forming elements; (5)all the strata and plutons have the similar pattern of the ore-forming elements. Accordingly, we can conclude that the WSDS and their country rocks are infiltrated and chemically modified by the ore-bearing fluids, and can be considered as the deterministic targeting element. The spatial patterning of the dike swarm is controlled by both the regional and the local fracture system. This can be explained by emplacement of the dike magmas into both the pre-existing and the self-propagating fractures. Therefore, the WSDS is resulted from the melt-fluid flows through rapid ascending and emplacement, and has a stronger potentiality to produce ore deposits. The spatial patterning of the dike swarm may suggest transport of the ore-bearing fluids, and thus can be used to predict the localities where the ore-forming metals have extensively cumulated. Along the transport paths of ore-bearing fluids, the ore-forming metals are largely discharged at the places where the fluid flow encounters:(1)carbonate rocks; (2)massive igneous blocks, in which fractures are poorly developed; (3)moderately broken regions cross-cut by faults; (4)strata with a high permeability; (5)minor magma bodies in the fields where the dikes are clustered. Accordingly, six prospecting regions can be targeted from the South Alatao Mountains. They are: A. the Xiaeraola, B. the Mierqike intrusion, C. the Legenwusu-Keketashugenwusu, D. the Aerxiati, E. the southwest Butuhamaer intrusion, and F. the Noerte. The divided prospecting regions cover 8 of the 20 mineralized points discovered in previous regional investigations. When the prospecting regions are slightly enlarged, they can cover 15 of them. It is clear that the new methodology is effective.