小兴安岭霍吉河钼矿床成岩成矿年代学及其地质意义

霍吉河钼矿是小兴安岭地区于近年发现的大型斑岩型钼矿床。本文在对矿化特征分析的基础上,采用LA-ICP-MS锆石U-Pb技术对霍吉河成矿花岗质杂岩测年,获得中细粒花岗闪长岩和斑状花岗岩成岩年龄分别为181.0±1.9 Ma(n=15, MSWD=4.7) 和193.6±1.4 Ma(n=25, MSWD=2.3)。通过辉钼矿Re-Os同位素分析,获得等值线年龄176.3±5.1 Ma(n=5, MSWD=1.3)和加权平均年龄为181.2±1.8 Ma (n=5, MSWD=1.3)。两种方法获得的年龄大致相近,表明成岩与成矿于同一系统形成,成岩大致始于193.6±1.4 Ma,成矿于岩浆期后181.2±1.8 Ma。霍吉河钼矿成岩成矿年龄与乌奴格吐山铜钼矿、兰家沟钼矿和杨家杖子钼矿等矿床辉钼矿Re-Os同位素年龄相近,表明中国东北地区广泛存在早侏罗世岩浆成矿作用。微量元素和同位素显示,霍吉河花岗闪长岩和斑状花岗岩属A型花岗岩,形成于地壳挤压向拉伸转换的构造环境,成矿物质主要来自岩浆。

Petrogenesis and mineralization chronology study on the Huojihe molybdenum deposit Xiao Hinggan Mountains and its geological implication

The Huojihe molybdenum deposit in the Xiao Hinggan metallogenic belt is a large porphyry deposit discovered in recent years. Based on the analysis of characteristics of mineralization, the authors conducted the LA-ICP-MS U-Pb dating of zircon from metallogenic granitic complex and Re-Os dating of molybdenite in Huojihe area. LA-ICP-MS U-Pb ages of zircons from medium-fine grained granodiorite and porphyritic granite are 181.0±1.9 Ma (n=15, MSWD=4.7) and 193.6±1.4 Ma respectively. The molybdenite Re-Os isochrones age is 176.3±5.1 Ma (n=6, MSWD=1.3), with weighted average model age of 181.2±1.8 Ma. The ages from the two methods are close to each other, suggesting that they might have been formed in the same petrogenetic ore-forming system. The petrogenesis started at 193.6±1.4 Ma and the mineralization in the magma occurred at 181.2±1.8 Ma. The ore-forming age of the Huojihe molybdenum deposit is close to the molybdenite Re-Os isochron age of the Wunugetu Cu-Mo deposit and the Lanjiagou and Yangjiazhangzi molybdenum deposits. There existed an early Jurassic magmatic-mineralization event in Northeast China. Trace element and isotope show that granodiorite and porphyritic granite in Huojihe belong to A-type granites. Petrogenesis and mineralization of Huojihe molybdenum deposit were related to changes of the tectonic environment from crust extruding to extending. The mineral source was derived from magma.