黑龙江争光金矿床方铅矿黄铁矿Rb-Sr年龄及地质意义

Rb-Sr Age of Galena and Pyrite from the Zhengguang Gold Deposit,Heilongjiang Province and its Geological Significance

争光金矿床位于兴安地块东缘黑龙江省多宝山铜钼-金矿集区南东端,矿体产于早奥陶世闪长岩与下奥陶统多宝山组地层接触带及多宝山组中,为大型金矿。因缺乏精确的成矿年代学研究,其成矿时代一直存在争议。本文在争光金矿床地质背景和岩石矿物学研究的基础上,对矿区内12件矿石样品中共生矿物方铅矿和黄铁矿进行Rb-Sr同位素年代学研究。结果显示,方铅矿^(87)Rb/^(86)Sr、^(87)Sr/^(86)Sr值分别为0.0853~1.2090、0.708066~0.714793,Rb-Sr等时线年龄跨度较大,为482.0±270 Ma(MSWD=9.20),(^(87)Sr/^(86)Sr)t=0.70753±0.00067;黄铁矿^(87)Rb/^(86)Sr、^(87)Sr/^(86)Sr值分别为1.431~3.^(86)2、0.717346~0.733799,Rb-Sr等时线年龄为474.9±3.3 Ma(MSWD=0.41),(^(87)Sr/^(86)Sr)t=0.70767±0.00013。在方铅矿和黄铁矿共生矿物组合的Rb-Sr等时线图解中,方铅矿和黄铁矿样品点具有良好的线性关系,去除5个不谐和点外,获得组合等时线年龄为477.8±3.2 Ma(MSWD=1.14,n=7),(^(87)Sr/^(86)Sr)t=0.707553±0.000083,Rb-Sr同位素年龄显示该矿床形成于早奥陶世。矿集区内的斑岩型多宝山铜钼矿床、铜山铜钼矿床空间上与争光金矿床分布紧密,它们与区内古生代早奥陶世的花岗质岩浆活动有关,属于多宝山铜钼-金多金属成矿系统。

The Zhengguang gold deposit is a large-sized gold deposit located at the southeast end of the Cu-Mo-Au ore concentration area in Duobaoshan,Heilongjiang province,on the eastern edge of the Xing’an block.The ore bodies occur in the contact zone of the Early Ordovician diorite and the Duobaoshan Formation.The origin of the deposit is still controversial,mainly due to the lack of accurate chronological results.In this paper,we report new Rb-Sr isotopic dating results of the paragenetic galena and pyrite from 12 ore samples.The ^(87)Rb/^(86)Sr and ^(87)Sr/^(86)Sr ratios of galena vary in ranges of 0.0853–1.2090 and 0.708066–0.714793,respectively.The Rb-Sr isochron of galena yields an ages with large uncertainty,which is 482.0±270 Ma(MSWD=9.20),with(^(87)Sr/^(86)Sr)t=0.70753±0.00067.The ^(87)Rb/^(86)Sr and ^(87)Sr/^(86)Sr ratios of pyrite are 1.431–3.^(86)2,0.717346–0.733799,respectively.The Rb-Sr isochron age of pyrite is 474.9±3.3 Ma(MSWD=0.41),with(^(87)Sr/^(86)Sr)t=0.70767±0.00013.The paragenetic galena and pyrite exhibit a good linear relationship in the Rb-Sr isochron diagram.When five discordant spots were eliminated,the combined isochron of seven concordant spots yields an isochron age of 477.8±3.2 Ma(MSWD=1.14),with(^(87)Sr/^(86)Sr)t=0.707553±0.000083.We argue that the Rb-Sr isochron age of 477.8±3.2 Ma represents the age of ore-formation,which means that the deposit was formed in the Early Ordovician.Therefore,the Zhengguang gold deposit and the neighboring porphyry Duobaoshan Cu-Mo deposit and the Tongshan Cu Mo deposit are likely related to the Early Ordovician granitic magmatism in the region and belong to the Duobaoshan Cu-Mo-Au polymetallic mineralization system.