黑龙江先锋北山金矿床火山岩地球化学特征、LA-ICP-MS锆石U-Pb定年及地质意义

黑龙江省先锋北山金矿床地处完达山造山带西南段,矿体主要赋存在流纹岩、岩屑晶屑凝灰岩和流纹质角砾岩中。文章系统研究了与成矿密切相关的火山岩的地球化学特征,同时,对其进行了LA-ICP-MS锆石U-Pb测年。与成矿相关的火山岩(流纹岩、岩屑晶屑凝灰岩、流纹质角砾岩)表现出高硅、富碱,贫铝、镁、钙的特征,属碱性系列岩石;具有弱的Eu负异常;富集大离子亲石元素K、Rb、Th等;亏损高场强元素Ta、Nb、P、Ti等。同时,Ba、Sr、Eu等元素亦表现为亏损,具有典型的同碰撞环境的地球化学特征。LA-ICP-MS锆石U-Pb测年显示,流纹岩、流纹质角砾岩和石英闪长玢岩的206Pb/238U谐和年龄分别为(116.98±0.47)Ma、(116.98±0.42)Ma和(108.48±0.99)Ma。结合矿区侵入接触关系,限定先锋北山金矿床的形成时间介于(116.98±0.47)Ma~(108.48±0.99)Ma,即早白垩世晚期。该矿床的形成与太平洋板块的俯冲和佳木斯与完达山地块的拼合有着密切的关系,系古太平洋板块构造体制由挤压变为伸展背景下的产物。

Geochemical characteristics and LA-ICP-MS zircon U-Pb dating of Xianfengbeishan gold deposit in Heilongjiang Province and their geological significance

The Xianfengbeishan gold deposit is located in the southwest part of Wandashan orogenic belt. The orebodies occur in rhyolite, crystal fragments and debris tuff and rhyolitic breccia. The geochemistry of volcanic rocks related to mineralization was systematically studied in this paper. Meanwhile, LA-ICP-MS zircon U-Pb dating of volcanic rocks was conducted. The mineralization-associated volcanic rocks (rhyolite, crystal fragments and debris tuff and rhyolitic breccia) are rich in silicon and alkalis and poor in aluminum, magnesium and calcium, belong to alkaline series rock and are characterized by weak Eu negative anomaly, enrichment of K, Rb and Th, strong depletion of Ta, Nb, P and Ti, and also depletion of Ba, Sr and Eu, suggesting geochemical characteristics of typical syn-collision setting. LA-ICP-MS zircon U-Pb dating results show that weighted average ²⁰⁶Pb/²³⁸U ages of rhyolite, rhyolitic breccia and quartz diorite porphyrite are (116.98 ± 0.47) Ma, (116.98 ± 0.42) Ma and (108.48 ± 0.99) Ma. Combined with the relationship of intrusive contact, the authors hold that the formation age of the Xianfengbeishan gold deposit is between 116.98 Ma and 108.48 Ma, i.e., the late period of Early Cretaceous. The mineralization of Xianfengbeishan gold deposit was closely associated with subduction of Pacific Plate and collage of Jiamusi and Wandashan Plate, being a product of tectonic regime change from compression to extension.