北山地区南金山金矿床的^(40)Ar-^(39)Ar同位素年代学及其流体包裹体特征

^(40)Ar-^(39)Ar Geochronology and Fluid Inclusion Features of the Nanjinshan Gold Deposit, Beishan Mt.,Gansu Province

本文对甘肃北山地区肃北县南金山金矿床的成矿年代学和成矿流体进行了系统研究。40Ar-39Ar同位素测年结果表明,南金山金矿石中绢云母的40Ar/39Ar坪年龄为242.8±0.8Ma,相当于印支早期,略晚于南金山金矿床附近闪长岩中黑云母的40Ar/39Ar坪年龄(244.2±0.3Ma),这表明印支早期闪长岩对南金山金矿床的形成起着重要的控制作用。流体包裹体研究表明,成矿流体的形成温度主要为160～240℃,属于中低温范围;成矿流体的盐度变化于0.88%～11.81%(NaCleq),并主要集中在6%～7%(NaCleq)之间,属于中低盐度范围;估算的成矿压力集中在100～160MPa。成矿过程中可能存在高盐度流体与低盐度流体的混合。结合前人研究成果,南金山金矿床应该属于与侵入岩有关的中低温热液型金矿床。

The studies on ore-forming geochronology and ore fluid are conducted deeply in this paper. According to the isotopic dating, the sericite from the gold ore yields a ^40Ar-^39Ar age of 242.8±0.8 Ma,which is a little bit later than the ^40Ar-^39Ar age of 244.2 ± 0. 3 Ma obtained from the biotite of diorite near the ore district. It indicates that the ore-forming process was controlled by Indosinian magmatism. Based on the study on fluid inclusions, the homogenization temperatures are concentrated between 160 and 240℃, with the Salinities from 0. 88 to 11.81% （NaCleq） [a mode between 6%-7% （NaCleq）], and estimated pressure mainly from 100 to 160 MPa. The mixing between fluids with high- and low-salinities may existed during ore-forming. Combined with the results from previous studies, the Nanjinshan gold deposit belongs to the intrusion-related meso- to epi- thermal gold deposit.