陕西凤太矿集区柴蚂金矿床成矿时代的^(40)Ar-^(39)Ar年龄证据

Evidence of ^(40)Ar/^(39)Ar age data for ore-forming time of Chaima gold deposit in Fengtai ore concentration area,Shaanxi Province

柴蚂金矿床位于陕西凤太矿集区的西北部,矿体产于长沟-八卦庙向斜和长沟-打柴沟背斜核部和两翼的NWW向脆韧性剪切构造带中,赋矿地层为上泥盆统星红铺组的斑点状铁白云质粉砂质千枚岩。金矿化类型包括石英脉型和蚀变岩型2种。成矿过程划分为早期石英-碳酸盐阶段、主成矿期石英-碳酸盐-硫化物阶段和晚期石英脉阶段。对主成矿阶段热液蚀变形成的绢云母开展40Ar/39Ar测年研究,获得坪年龄为(219.0±2.0)Ma,指示其成矿作用始于219 Ma左右,即晚三叠世。前期工作获得该阶段碳酸盐矿物的Sm-Nd同位素年龄为(203.0±1.6)Ma,2个年龄值可能限定了成矿作用的上限与下限。结合前人有关区域地质与成矿作用的研究成果分析认为,柴蚂金矿床属于造山型金矿床,其成矿作用的多阶段性与剪切带长期演化过程中的构造递进变形密不可分。

The Chaima gold deposit is located in the northwest of the Fengxian-Taibai （Fengtai） ore concentration area in Shaanxi Province. It is developed within a NWW-trending brittle-ductile shear zone. The orebodies are hosted in spotted ankerite-silty phyllite of Upper Devonian Xinghongpu Formation and occur in the limbs and cores of the Changgou-Baguamiao syncline and Changgou-Dachaigou anticline. The ores are mainly altered rock type and quartz-vein type. The gold mineralization could be divided into three stages：the early quartz-carbonate stage, the main quartz-carbonate-sulfide stage and the late quartz stage. In this paper, the ^40Ar-^39Ar dating was carried out on the sericite resulting from hydrothermal alteration in the main mineralization stage, yielding a plateau age of （219.0±2.0） Ma, which shows that the mineralization of the Chaima gold deposit started from 219 Ma. Combined with the carbonate minerals Sm-Nd isotopic age of （203.0±1.6） Ma obtained before, the age data may define the upper and lower limits of gold mineralization. Combined with previous work on the regional geology and polymetallic mineralization, the authors hold that the Chaima gold deposit is an orogenic gold deposit, whose multiple stages of mineralization were inseparable with the progressive deformation of the shear zone during the long-term tectonic evolution in Triassic.