河南嵩县大石门沟钼矿床辉钼矿Re-Os同位素年龄及地质意义

Re-Os isotopic dating of molybdenites from the Dashimengou molybdenum deposit in Songxian County,Henan Province,and its geological significance

河南省嵩县大石门沟钼矿床是近年来在豫西地区新发现的大型钼矿床,采用辉钼矿Re-Os精细测年技术,对与成矿相关的5个含辉钼矿角砾岩样品、3个含辉钼矿的破碎石英样品进行同位素年代学测定,获得了模式年龄:模式年龄变化范围(156.1±3.4)^(228.0±4.1)Ma,模式年龄明显分为2组:一组为(208.4±3.1)^(228.0+4.1)Ma,平均年龄(218.07±4.3)Ma,加权平均年龄(217.1±8.5)Ma,另一组为(156.1±3.4)^(160.9±3.3)Ma,平均年龄(158.6±3.35)Ma,加权平均年龄(158.6±4.7)Ma。结果表明,大石门沟钼矿成矿时代为印支期、燕山晚期。2个期次的成矿作用又与该区隐爆角砾岩的两次隐爆有关。印支期的成岩成矿发生在东秦岭钼矿带碰撞造山后的构造体制从挤压到伸展的转折期,上地幔、下地壳的部分熔融产物上涌在地壳薄弱的NW向与NE向构造交叉部位隐爆产生。燕山晚期成矿作用继承、改造和叠加印支期成矿作用,两者一起构成东秦岭钼矿带中生代成矿作用大爆发的完整旋回。

The Dashimengou molybdenum deposit in Songxian County of Henan Province is a newly discovered large molybdenum deposit in western Henan. Five samples of molybdenite-bearing breccia and there samples of molybdenite-bearing broken quartz related to mineralization were selected for precise molybdenite Re-Os dating, and the model ages obtained are from （156.1±3.4） Ma to （228.0±4.1） Ma. The model ages can be obviously divided into two groups：the Re-Os model ages of the first group range from （208.4 ± 3.1） Ma to （228.0 ± 4.1） Ma, with an average model age of （218.07 ± 4.3） Ma and a weighted average model age of （217.1 ± 8.5） Ma;the second group range from （156.1 ± 3.4） Ma to （160.9 ± 3.3） Ma, with an average model age of （158.6 ± 3.35） Ma and a weighted average model age of （158.6 ± 4.7） Ma. The results show that the Dashimengou molybdenum deposit was formed in the Indosinian and Late Yanshanian periods. The ore-forming processes of the two phases were related to two cryptoexplosion events of the hydrothermal breccia. The rock-forming and ore-forming activity of Indosinian period occurred in the transition period of the tectonic regime from compression to extension after collision orogenic movement of the East Qinling molybdenum ore belt. The upwelling of partially melted upper mantle and lower crust produced cryptoexplosion at the intersections of NW-and NE-trending structures. Late Yanshanian mineralization seems to have been the inheritance, transformation and superposition of the Indosinian mineralization, and the ore-forming processes of these two periods constituted the full cycle of the Mesozoic metallogenic explosion of the East Qinling molybdenum ore belt.