新疆北部弧-盆转化体系下铁氧化物-铜-金矿床的流体演化特征:来自卤族元素和稀有气体同位素的证据

Fluid evolution of iron oxide-Cu-Au(IOCG)deposits in the basin inversion setting,North Xinjiang:constraints from halogen and noble gas composition of fluid inclusions

东准噶尔北缘和东天山雅满苏带是中国新疆北部地区两个重要的晚古生代铁氧化物-铜-金矿化潜力区,以老山口、乔夏哈拉和黑尖山矿床作为典型矿床代表。研究表明两区域的铁氧化物-铜-金矿床均产出于盆地闭合的弧盆转化体系下,且具有明显的铁、铜-金两阶段矿化。卤族元素和稀有气体同位素作为可靠的流体示踪剂,被应用于探究这一特定构造环境下的铁氧化物-铜-金矿床的流体演化和矿床成因。结果显示老山口、乔夏哈拉和黑尖山矿床的成矿流体具有明显的混合流体端员特征:(1)岩浆流体端员,主要参与黑尖山矿床磁铁矿阶段,I/Cl、Br/Cl和^40Ar/^36Ar比值分别为(16.3~18.0)×10^-6、(1.03~1.06)×10^-3和352~437;(2)海水表源蒸发成因盐卤水端员,主要参与老山口矿床铜-金矿化阶段,I/Cl、Br/Cl和^40Ar/^(36) Ar比值分别为(77.1~87.7)×10^-6、(1.53~1.80)×10^-3和672~883;(3)蒸发岩溶解或者深度水-岩反应成因的盐卤水/沉积岩地层水端员,主要参与到老山口、乔夏哈拉矿床的磁铁矿阶段以及黑尖山、乔夏哈拉矿床的铜-金矿化阶段,综合I/Cl、Br/Cl和^40Ar/^36Ar比值分别为(477~26 301)×10^-6、(0.39~1.28)×10^-3和288~510。明显的多阶段矿化和铜-金矿化阶段以非岩浆富Ca高盐度卤水为主的特征与世界范围内的IOCG型矿床极为相似,表明新疆北部的铁氧化物-铜-金矿床应为IOCG型矿床。

Represented by the Laoshankou,Qiaoxiahala and Heijianshan deposits,the northern margin of East Junggar and the Yamansu belt of East Tianshan are two important potential belts for iron oxide Cu-Au(IOCG)mineralization in North Xinjiang.All IOCG deposits in these two regions formed in a basin inversion setting and show significant two-stage mineralization.In this study,we used halogen and noble gases as reliable tracers to track the fluid sources and evolution of these deposits.The results showed that three different fluid end members are mainly involved in the mineralization processes of the three deposits:(1)the magmatic hydrothermal fluid,with I/Cl,Br/Cl and ^40Ar/^36Ar ratios of(16.3-18.0)×10^-6,(1.03-1.06)×10^-3 and 352-437,respectively,in the magnetite stage of the Heijianshan deposit;(2)surfacederived basin brine by seawater evaporation,with I/Cl,Br/Cl and ^40Ar/^36Ar ratios of(77.1-87.7)×10^-6,(1.53-1.80)×10^-3 and 672-883,respectively,in the copper gold stage of the Laoshankou deposit;and(3)basin brine or formation water by water-rocks reaction and evaporate dissolution,with I/Cl,Br/Cl and^40Ar/^36Ar ratios of(477-26301)×10^-6,(0.39-1.28)×10^-3 and 288-510,respectively,as the main mineralizing fluids in the magnetite stage of the Laoshankou and Qiaoxiahala deposits and for the Cu-Au mineralization of the Qiaoxiahala and Heijianshan deposits.The obvious multi-stage mineralization and involvement of Ca-rich hypersaline non-magmatic brines in the Cu-Au stage in the iron oxide Cu-Au deposits in North Xinjiang resemble the characteristics of other IOCG type deposits in the world.