辽宁省朝阳市小塔子沟金矿1~#脉成矿流体特征及成因

研究区大地构造位置属华北克拉通北缘中段,是中国重要的金、有色金属成矿区段。小塔子沟金矿的容矿围岩为太古宙建平群小塔子沟组变质杂岩,NE和NEE向断裂为主要的容矿断裂,燕山早期北大山二长花岗岩是与成矿关系密切的岩体。矿区内最具工业意义的矿脉是1~#脉,其矿石自然类型为石英脉型。1~#脉石英流体包裹体有富CO_2三相、气液两相和纯气相3种类型。流体盐度介于2.06%～11.72%NaCl_(eqv),集中在2.06%～3.37%NaCl_(eqv),4.69%～6.97%NaCl_(eqv)和9.86%～11.72%NaCl_(eqv);流体密度介于0.689～0.977 g/cm~3;成矿温度在174～348℃,集中在302～348℃和174～187℃。研究表明成矿早阶段流体为低盐度、富CO_2的高温流体,而且富CO_2型和气液两相型包裹体共存;后者可能是由两种不同流体的混合作用造成的不均匀捕获而形成。成矿中晚阶段温度突然降低,盐度明显升高。温度的突然降低导致以CO_2逸失为特征的沸腾,由于沸腾使残余流体盐度和密度升高。通过等容线图解法估算成矿压力范围在16～28 MPa,用静水压力梯度计算成矿深度为1.6～2.8 km。通过与典型的造山型金矿特征对比,该矿床成因类型为浅成造山型金矿,其形成动力学背景为J_1—J_2时期华北与西伯利亚克拉通碰撞对接后的陆内造山。

A study of ore-forming fluid features and metallogenesis of 1~# vein from Xiaotazigou gold deposit, Chaoyang city, Liaoning Province

The studied area is located in the middle section of the north margin of North China craton, which is one of the most important gold and nonferrous metal metallogenic belts. In the Xiaotazigou ore district, the hosted rocks of gold deposit are the Archean metamorphic complex of Xiaotazigou formation, and the orebodies are primarily hosted in EW-striking and NE-striking fractures, while Beidashan monzonitic granite body is closely associated with metallization. The ore natural type of 1~# vein is the quartz vein type;its economic value is the highest in the ore district. Fluid inclusions of quartz crystals in 1~# vein can be classified into types of aqueous two-phase, CO_2-rich three phase and pure gas. The salinities of fluid inclusions range from 2.06% to 11.72% NaCl_(eqv),concentrating in three ranges of 2.06% - 3.37% NaCl_(eqv),4.69% - 6.97% NaCl_(eqv) and 9.86% - 11.72% NaCl_(eqv). The densities of fluid inclusions range from 0.689 to 0.977 g/cm~3. The homogenization temperatures of fluid inclusions range from 174 ℃ to 348 ℃,concentrating in two ranges of 302 - 348 ℃ and 174 - 187 ℃. During the early ore-forming stage, the ore-forming fluids were characterized by high temperature, low salinity, and the coexistence of CO_2-rich three phase and aqueous two-phase. The reason for the coexistence is that the mixture of two different kinds of fluids caused non-uniform capture. During the middle-late ore-forming stage, the ore-forming fluids were characterized by the fall in temperature,and the rise in salinity. The abrupt fall in temperature resulted in boiling characterized by CO_2 loss, from which the salinity and the density of remnant fluids were raised. According to the diagram of coexistence surface,the ore-forming pressure can be calculated and it is in the range of 16 - 28 MPa, the ore-forming depth is in the range of 1.6 - 2.8 km. In contrast to other orogenic gold deposits worldwide, Xiaotazigou gold deposit is defined as epizonal orogenic gold deposit and the intracontinent collision was its metallogenic dynamic background.