川西新台子金矿床的矿化特征及成矿流体特征研究

MINERALIZATION AND ORE-FORMING FLUIDS OF THE XINTAIZI GOLD DEPOSITINWESTERNSICHUANPROVINCE,CHINA

川西新台子金矿床位于龙门山造山带和鲜水河韧性平移断裂带的复合交接部位,是“姑咱-孔玉-丹巴”金成矿区的重要组成之一。该矿床产于泥盆系下统危关群第一岩组的千枚岩中。本次研究通过电子探针测试、流体包裹体显微测温、LA-ICP-MS扫面测试、自然金成矿流体的热力学模拟等方法研究新台子金矿床的矿化特征及成矿流体特征。根据野外调查与镜下观察,新台子金矿床的含金石英细脉主要赋存在早期贫矿石英脉的裂隙中,热液作用可分为早期的黄铁矿-石英阶段和晚期的自然金-多金属硫化物-石英阶段,自然金主要与晚期的黄铁矿和闪锌矿等金属硫化物共生。电子探针查明自然金的成色值范围介于918.9~945.9,且晚期黄铁矿中Au,As,Zn的含量较高。流体包裹体的均一温度范围介于189~349℃,盐度w(NaCl_(eqv))介于0.6%~13.7%,估算压力值范围介于2~15MPa。LA-ICP-MS扫面测试显示AsAu,Ag,Co,Ni.Cu,Pb,Zn,Sb元素以及Au/Ag比值(>0.1)在晚期黄铁矿中较高,而在早期黄铁矿中较低。基于实验结果的热力学模拟揭示,温度降低和氧逸度升高可能是促发金沉淀的机制,金成色值的变化可能是晚期流体的温度降低所致。根据早期贫矿石英脉被晚期含金石英细脉充填的矿化特征,以及中低温、低盐度、低压的H_(2)O-NaCl成矿流体特征,本次研究认为新台子金矿床属于浅成的造山型金矿。

The Xintaizi gold deposit in western Sichuan is situated at the junction of the Longmenshan o-rogenic belt and the Xianshuihe ductile fault belt,making it a pivotal component of the"Guzan-Kongyu-Danba"gold metallogenic area.This deposit is found within the first layer phyllite of the Lower Devonian Guiguan Group.This study investigates the characteristics of mineralization and the ore-forming fluids of the Xintaizi gold deposit using electron probe microanalysis,microthermometry of fluid inclusions,LA-ICP-MS surface scanning tests,and thermodynamic simulation of native gold ore-forming fluids.Field in-vestigations and microscopic observations reveal that the gold-bearing quartz veins in the Xintaizi gold de-posit predominantly occur within fractures of early quartz veins,with native gold primarily associated with late-stage metal sulfides such as pyrite and sphalerite.The hydrothermal processes related to mineraliza-tion can be classified into two stages:an early pyrite-quartz stage and a late native gold-polymetallic sul-fide-quartz stage.Electron probe microanalysis indicates that the fineness value of native gold ranges from 918.9 to 945.9,with high contents of Au,As,and Zn in pyrite formed during the late stage.Homogeni-zation temperature of fluid inclusions ranges from 189 to 349℃,with salinity between 0.6 and 13.7% Na-Cleqv,and estimated pressures ranging from 2 to 15 MPa.LA-ICP-MS scanning tests demonstrate that concentrations of As,Au,Ag,Co,Ni,Cu,Pb,Zn,Sb,and Au/Ag ratios(>0.1)are higher in pyrite formed during the late stage,but lower in pyrite formed during the early stage.This comprehensive analy-sis sheds light on the complex mineralization processes at the Xintaizi gold deposit,contributing valuable insights for further geological and mineralogical research in similar regions.Thermodynamic simulations,based on experimental results,indicate that a decrease in temperature and an increase in oxygen fugacity are key factors promoting the precipitation of gold.The changes in gold composition may be attributed to a decrease in the temperature of the ore-bearing fluid during the late stages.The Xintaizi gold deposit is characterized by early lean-bearing quartz veins overlain by late gold-bearing quartz veins.The ore-forming fluid,characterized by H_(2)O-NaCl,exhibits low temperature,low salinity,and low pressure conditions,suggesting that the Xintaizi deposit can be classified as a hypabyssal orogenic gold deposit.