矽卡岩矿床的汇流扩容空间控矿机制及其对深部找矿的意义:以铜陵—安庆地区为例

The controlling mechanism of ore formation due to flow-focusing dilation spaces in skarn ore deposits and its significance for deep-ore exploration:Examples from the Tongling-Anqing district

本文以铜陵—安庆地区凤凰山铜矿和安庆铜矿为例,通过野外地质分析和计算模拟实验探讨了浅成岩体冷却过程中接触带上汇流扩容空间对矽卡岩矿体的控制。在凤凰山矿田和安庆矿田,围绕新屋里岩体和月山岩体的接触带上矿体的分布极不均匀,形成大规模矽卡岩矿体的位置既与接触带本身的特征有关,也与构造变形有关。矿体的边界特征以及与矿体密切相关的角砾岩的特征表明水压致裂在赋矿扩容空间的形成过程中可能起重要的作用。矿体的围岩蚀变特征以及流体包裹体地球化学特征显示来自岩体和围岩的流体的混合以及高压流体的减压沸腾可能是矿石沉淀的主要机制。新屋里岩体和月山岩体的同构造冷却过程力学变形—传热—流体流动耦合动力学计算模拟结果显示:所有矿体都位于汇流扩容空间内,且主矿体位于最大最强的汇流扩容带内,这表明力—热—流耦合作用形成的汇流扩容空间不仅控制了矿体的位置,也控制了矿体的规模。在铜陵—安庆地区开展深部找矿勘查,应该将重点放在大规模高强度的汇流扩容区,特别是还没有发现大规模矿体的汇流扩容区,凤凰山和安庆铜矿深部找矿已取得的成果证明了汇流扩容空间控矿模式对这一地区深部找矿勘查具有重要意义。

Controlling of flow-focusing dilation spaces on skarn ore formation during cooling of hypabyssal intrusion is discussed by field investigation and computational modeling experiments on the Fenghuangshan and Anqing copper deposits in the Tongling-Anqing district. In this district, the ore-body distribution along the contact zones of Xingwuli and Yueshan intrusions is very non-uniform. The location of large-scale skarn ore-bodies are related not only to features of the contact zones but also to the structural deformation. The characteristics of ore-body boundaries and ore-related brecciation indicate that hydrofracture might play an important role in the formation of ore-hosting spaces. Both the alteration features of country rocks and the fluid inclusion of ore bodies suggest that the major ore-depositing mechanism might be caused by the mixing of fluids from intrusion and country rocks and/or depressurizing boil of high pressured fluids. The computational modeling of coupled mechanical deformation-thermal transfer-fluid flow geodynamics of the Xingwuli and Yueshan intrusion during their syn-tectonic cooling demonstrates that all existing ore bodies are located in the flowfocusing dilation spaces and, further more, the major ore-bodies must be in the most intensive and largest scale dilation zones, suggesting that fluid-focusing dilation spaces resulted from coupled mechano-thermo-hydrological processes must control not only the location but also the scale of the skarn ore bodies. According to this model, deep exploration for hidden ore-bodies should target at the largest and most intensive dilation zones, especially in the dilation zones where no ore-bodies having been discovered. The deep ore discovering accomplishments in the Fenghuangshan and Anqing mines have demonstrated the important significance of the model for deep ore exploration.