黑龙江省乌拉嘎金矿赋矿花岗闪长斑岩锆石U-Pb年龄、岩石成因及其地质意义

Zircon U-Pb geochronology,petrogenesis and geological implication of ore-bearing granodiorite porphyry in the Wulaga gold deposit,Heilongjiang Province

黑龙江省是我国著名金矿产区之一,发育多个浅成低温热液型金矿,它们与中生代陆相火山-次火山岩有密切的关系,但对这些陆相火山-次火山岩的成因缺乏系统研究,制约了本区金矿的成因认识和矿床勘查。本次研究采用先进的LA-ICP-MS锆石定年法、地球化学Sr-Nd-Pb同位素示踪等方法,对与乌拉嘎浅成低温热液金矿存在密切成因联系的次火山岩(花岗闪长斑岩)进行深入研究。LA-ICP-MS锆石定年法获得乌拉嘎矿区葡萄沟岩体及其南部含矿岩枝的成岩年龄分别为108.2±1.2Ma和106±1.1Ma,与区内宁远村组火山岩成岩时间基本相近,推断金矿成矿时代为早白垩世晚期,与东安金矿和高松山金矿为同期。岩石地球化学确定该岩体为高钾钙碱性(σ=1.83～2.18)偏铝质I型花岗岩特征,结合微量元素和Sr-Nd-Pb研究显示其具有活动陆缘弧岩浆岩特点,进一步得出岩浆源区和成矿物质具有来源于新元古代形成的镁铁质下地壳的部分熔融的属性。早白垩世时,中国东部处于伸展应力体制下,尤其黑龙江构造活动强烈,起源于新生下地壳重融的岩浆活动频繁,结合已有的浅成低温热液金矿床资料显示,推断区内具有巨大的成矿潜力。

Heilongjiang is one of China＇s most famous gold producing districts.Past production in the area was partially from epithermal gold mineralization,which was associated with the Mesozoic subaerial volcanic to subvolcanic intrusions.However,a little work has been done for the petrogenesis of these igneous rocks.In this paper,LA-ICP-MS zircon U-Pb ages,coupled with whole-rock major,trace elements and Sr-Nd-Pb isotopic data are present to constrain the geochronology and the petrogenesis of ore-bearing granodiorite in the Wulaga gold deposit,also discuss the epithermal gold mineralization potential of Heilongjiang Province.Two U-Pb zircon ages from Putaogou granodiorite intrusion and its southern ore-bearing granodiorite porphyry apophysis that occur in the Wulaga gold district are respectively 108.2±1.2Ma and 106±1.1Ma,which are similar to the age of surrounding volcanic rocks.Thus it is inferred that the gold mineralization hosted within the granodiorite porphyry apophysis was also formed in the Early Cretaceous,which was contemporaneous with the Dong＇an gold deposit and Gaosongshan gold deposits.The granodiorite porphyry is the typically I-type,calc-alkaline（σ=1.83～2.18） granitoid with meta-aluminous attributes（A/NCK=0.97～1.16） .Geochemical and Sr-Nd-Pb isotopic features suggest that the granodiorite porphyry was likely derived from partial melting of the Neoproterozoic juvenile mafic low-crust,which is inferred to be the source of partial mineral-forming components by comparing with other gold deposits.Early Cretaceous magmatism favored an extensional regime in NE China,when complex tectonic activities occurred,at the same time as intense low crust-sourced magmatism.This result suggests that there is likely huge mineralization potential for epithermal gold deposits in the Heilongjiang Province,through comparison with regional mining epithermal gold deposits.