腾冲地块那俄铍矿床成矿时代和流体包裹体特征研究
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1.云南省地质调查院(云南省地质科学研究院);2.云南大学地球科学学院;3.云南省地质勘查基金管理中心

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云南省地质勘查(D202101)和滇西地区战略性关键稀有金属矿产成矿规律及找矿预测(Y202305)项目资助。


Mineralization timing and characteristics of fluid of Na’e beryllium deposit in the Tengchong terrane
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1.Institute of Yunnan Geology Survey(Institute of Yunnan Geological Sciences);2.College of Earth Science, Yunnan University;3.Yunnan Geological Survey Fundation Management Center

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    摘要:

    铍(Be)广泛应用于国防尖端科技和战略新兴领域,是一种国家亟需的战略性资源,面向找寻铍潜力的资源区是快速解决我国铍资源困境的“捷径”。腾冲地块是东特提斯造山带的重要组成部分,经历了复杂的地质构造过程,其中早白垩世-新生代以来岩浆活动频繁,发育大量与岩浆作用相关的锡(钨)稀有金属矿床(点),地质调查评价表明该区域可能形成潜在的铍、铷、铌、钽等稀有金属矿床。那俄铍矿床是腾冲地块中发育的典型花岗伟晶岩型矿床,花岗伟晶岩侵入到早白垩世二长花岗岩围岩中。本文对花岗伟晶岩和二长花岗岩围岩开展锆石U-Pb年代学,对花岗伟晶岩中绿柱石和石英开展流体包裹体研究,从而探讨那俄铍矿床成矿年代及成矿物理化学条件。LA-ICP-MS锆石U-Pb年代学研究显示,那俄地区含绿柱石花岗伟晶岩年龄为44.3Ma~46.9Ma,二长花岗岩围岩年龄为122.9Ma,表明那俄铍矿床形成于始新世,二长花岗岩围岩形成于早白垩世,两者不存在演化关系。结合腾冲地块岩浆活动和构造演化历史,我们认为那俄铍矿床可能是印度-欧亚板块碰撞后构造背景下地壳物质熔融的产物,为典型的造山期后LCT伟晶岩型铍矿床。绿柱石和石英中流体包裹体特征显示,那俄铍矿床中主要发育气液两相NaCl-H2O包裹体以及少量纯液相水包裹体、CO2包裹体,成矿流体具有中低温(172.0℃~299.4℃)、低盐度(0.70%~3.87% NaCl eqv.)、低密度(0.723 g/cm-3~0.913g/cm-3)的特征。成矿流体压力和深度估算,表明那俄铍矿床形成于低压浅层环境。腾冲地块锂铍地球化学异常中心与腾冲地块主要锡矿化、伟晶岩带分布一致,暗示腾冲地块稀有金属成矿作用与锡矿化、伟晶岩带关系密切。结合区域已发现铌钽、铷、锂等矿化点,表明腾冲地区存在较大的稀有金属成矿潜力。该研究结果对理解那俄铍矿床的成因和地质背景提供了重要的科学依据,同时也为腾冲地区的稀有金属矿产勘查和开发提供了有益的指导。

    Abstract:

    Beryllium (Be) is widely used in advanced science and technology and strategic emerging fields, and is an urgent strategic resource for our country. The Tengchong terrane, which has experienced a complex geological structural process, is an important part of the East Tethys Orogenic belt. In this terrane, frequently magmatic activities occurred during the Cretaceous-Cenozoic stage and a large number of tin (tungsten) -rare metal deposits (mineralizatioin) related to magmatism have been discovered. Geological survey and evaluation indicate that potential beryllium, rubidium, niobium, tantalum rare metal deposits may be formed in this area. The Na"e beryllium deposit is a typical granitic pegmatite type deposit discovered in the Tengchong terrane. The granitic pegmatite intruded into the wall rock of the early Cretaceous monzogranite. In this paper, we study zircon U-Pb chronology of granite pegmatite and monzogranite (the wall rocks) and fluid inclusion of beryl and quartz from the granite pegmatite to discuss the ore-forming age and physical and chemical conditions of the Na’e beryllium deposit. LA-ICP-MS zircon U-Pb dating yield ages of granitic pegmatite are 44.3 Ma~46.9 Ma, that of monzogranite is 122.9 Ma, indicating that the Na’e beryllium deposit was formed in Eocene and the wall rock of monzogranite was formed in Early Cretaceous. Thus, we suggest that they have no evolutionary relationship. Combined with the magmatic activities and tectonic evolutionary history of the Tengchong terrane, we suggest that the Na’e beryllium deposit may be the product of crustal material melting in a post collision tectonic setting caused by the convergence between India and Eurasia plates, and is a typical LCT pegmatite type beryllium deposit at a post orogenic stage. Beryl and quartz from the Na’e beryllium deposit have vapor-liquid two-phase NaCl-H2O inclusions and a small amount of pure liquid phase water inclusions and CO2 inclusions. The ore-forming fluid is characterized by medium-low temperature (172.0 oC~299.4 oC), low salinity (0.70%~3.87% NaCl eqv.), and low density (0.723 g/cm-3~0.913 g/cm-3). According to the estimation of pressure and depth for ore-forming fluid, the Na’e beryllium deposit was formed in a low-pressure shallow environment. The concentration center of lithium and beryllium in geochemical anomaly map is consistent with the tin mineralization and pegmatite belts, suggesting that the rare metal mineralization is closely related to tin mineralization and pegmatite belt in the Tengchong terrane. In combination with the discovery of niobium, tantalum, rubidium, lithium mineralization in this district, we suppose that there is a potential for rare metal mineralization in the Tengchong terrane.

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  • 收稿日期:2023-07-12
  • 最后修改日期:2023-09-13
  • 录用日期:2023-09-15
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