摘要
仁布念扎金矿床是近年来在西藏地区新发现的大型独立岩金矿床,矿区内发育有众多煌斑岩脉,但其成因尚不清楚。基于野外地质调查,对矿区代表性煌斑岩样品进行岩相学、磷灰石U-Pb同位素测年和岩石地球化学研究,探讨了煌斑岩的岩石成因。岩相学研究表明,煌斑岩主要造岩矿物包括黑云母、斜长石和少量单斜辉石等,其中斑晶矿物主要为黑云母,基质为斜长石和少量单斜辉石,据此判断其为云斜煌斑岩。岩石TAS分类和K/(K+Na)-K/Al图解表明,岩石属钙碱性钾质系列,富集大离子亲石元素和轻稀土元素,亏损高场强元素和重稀土元素,轻重稀土分馏明显。煌斑岩磷灰石U-Pb定年下交点年龄为(19.9±1.2)Ma,显示其形成于早中新世,综合分析认为,念扎金矿区内的煌斑岩形成于早中新世印度—欧亚大陆碰撞后伸展环境,是具有大洋沉积物性质的流体交代亚洲岩石圈地幔发生部分熔融后沿区域深大断裂上涌而成,其成岩年龄明显晚于金成矿时间。
The Renbu Nianzha gold deposit,recently identified in Xizang,represents a significant independent rock gold deposit.Numerous lamprophyre veins have been identified within the mining area.However,their origin remains ambiguous.Consequently,this study undertook a comprehensive field investigation,collecting representative lamprophyre samples from the site to explore their petrogenesis through petrographic analysis,apatite U-Pb isotope dating,and geochemical characterization.Petrographic analysis reveals that the primary rock-forming minerals in the lamprophyres are biotite,plagioclase feldspar,and minor monoclinic pyroxene.The porphyritic minerals pre dominantly consist of biotite,while the matrix is composed of plagioclase feldspar and minor monoclinic pyroxene,classifying the rocks as mica-plagioclase lamprophyres.The TAS classification and K/(K+Na)-K/Al diagram indicate that these rocks belong to the calc-alkaline potassic series.They are characterized by an enrichment in large ion lithophile elements and light rare earth elements,a deficiency in high field strength elements and heavy rare earth elements,and a pronounced fractionation between light and heavy rare earth elements.The U-Pb dating of apatite within the lamprophyres yields an age of(19.9±1.2)Ma,sug-gesting formation during the early Miocene epoch.A comprehensive analysis indicates that the lamprophyre veins in the Nianzha gold mine area originated in a post-collisional extensional setting associated with the India-Eurasia continental interaction.These lamprophyres are hypothesized to have formed through partial melting of the Asian lithospheric mantle,which had been metasomatized by fluids bearing oceanic sediment charac-teristics,and subsequently ascended along regional deep-seated faults.Notably,the diagenetic age of the lamprophyres is significantly younger than the period of gold mineralization.
作者
王亮
陈柏林
WANG Liang;CHEN Bailin(Chinese Academy of Geological Sciences,Beijing 100037,China;Civil-Military Integrated Geological Survey Center of China Geological Survey,Chengdu 610036,Sichuan,China;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China)
出处
《黄金科学技术》
北大核心
2025年第3期455-466,共12页
Gold Science and Technology
基金
中国地质调查局地质调查项目“冈底斯—藏南成矿带金矿资源潜力动态评价”(编号:DD20220977)
西藏自治区科技计划项目“西藏特提斯演化及其能源资源效应研究”(编号:XZ202401YD0006)联合资助。
