南秦岭镇安核桃坪钨铍矿床成矿时代及成矿模式探讨
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本文为国家重点研发计划项目(编号2017YFC0602700)、中国地质调查项目(编号DD20190173;DD20190379)和中国博士后科学基金资助项目(编号2017M610960)联合资助成果。


Metallogenic epoch and metallogenic model of the Hetaoping W- Be deposit in Zhen’an County, South Qinling
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    摘要:

    秦岭造山带是中国中央造山带重要组成部分,近年来取得了一系列钨的找矿突破,尤其是在南秦岭镇安地区新发现了首例铍矿达到工业品位的核桃坪钨多金属矿床。在详细的野外地质工作基础上,本文通过对该矿床开展年代学及微区原位元素/同位素地球化学研究,限定其成矿时代和物质来源,旨在查明其成矿机制并建立成矿模式。利用Ar- Ar法获得铬云母坪年龄为201. 4±2. 10 Ma,金云母坪年龄为196. 6±2. 38 Ma,指示区域内大规模钨(钼、铍)等稀有金属矿化与印支晚期- 燕山早期后造山阶段的酸性岩浆活动关系密切。LA- ICP- MS微区原位分析结果显示,白钨矿中Mo、Nb、Ta等元素相对富集,且由氧化物早阶段至晚阶段Nb/Ta比值显著降低,87Sr/86Sr比值显著升高,反映氧化物早阶段的成矿物质来源以深源酸性岩浆为主,而演化至氧化物晚阶段,壳源的成矿物质逐渐增多。本区白钨矿呈轻稀土富集特征,指示石榴子石、透辉石等矽卡岩矿物先于白钨矿和绿柱石沉淀,相对富钾的热液环境有利于Be在氧化物早阶段富集沉淀。综合南秦岭地区地质背景以及各钨矿床的地质特征,镇安西部地区钨多金属矿床成矿作用受到了岩浆、地层及构造的多重制约,含矿热液与碳酸盐岩围岩相互作用产出矽卡岩化似层状矿(化)体,而在裂隙中充填交代形成脉状矿(化)体。成矿机制可以归纳为“隐伏岩体+特定层位+两组性质的断裂控矿”,深部勘探过程中可以借鉴华南“五层楼+地下室”的勘查模型,重点探寻不同岩性界面层间破碎带控制的层状矿体。该成矿模式对区域上同类型钨矿的深部找矿和综合评价也具有重要的参考价值。

    Abstract:

    Qinling orogenic belt is an important part of China’s Central Orogenic belt. In recent years,a series of tungsten prospecting breakthroughs have been made, especially for the newly discovered Hetaoping W- polymetallic deposit in the southern Qinling Mountains, which has an industrial grade of Be resources in Zhen’an, Shaanxi Province. Based on the detailed field geological work, this paper studies chronology and in- situ element/isotope geochemistry of the deposit in order to define its metallogenic age and material source, find out its metallogenic mechanism and establish its metallogenic model. The plateau ages of fuchsite and phlogopite obtained by Ar- Ar method are 201. 4±2. 10 Ma and 196. 6±2. 38 Ma, indicating that the large- scale mineralization of rare metals such as W, Mo and Be is closely related to the acid magmatism of the post- orogenic stage during the late Indosinian to the early Yanshanian. LA- ICP- MS in- situ analysis shows that Mo, Nb and Ta are relatively enriched in scheelite, and the Nb/Ta ratio decreases significantly from the early to late stages of oxide, while the 87Sr/86 Sr ratio increases significantly, reflecting that the source of ore- forming material in the early stage of oxide is mainly deep- sourced acidic magma, while the crust- sourced ore- forming material increases gradually from the late stage of oxide. Scheelites were characterized by light rare earth enrichment, indicating that garnet, diopside and other skarn minerals enriched in the skarn stage precipitate prior to scheelite and beryl. Relatively K- rich hydrothermal environment was conducive to enrichment and precipitation of Be in the early stage of oxide. Considering the geological background and geological characteristics of tungsten deposits in the southern Qinling, the metallogenesis of tungsten polymetallic deposits in the western Zhenan area are multi- restraint of magma, strata and structure. The ore- bearing hydrothermal reacted with carbonate host rocks and produced skarnized layered ore bodies, and filling and metasomatizing in fissures to form veined ore bodies. The metallogenic mechanism can be summarized as “hidden rock mass+specific horizon+two distinct structurals”. In the deep exploration process, we can draw lessons from the exploration model of “five storeys+basement” in South China, especially focusing on the exploration of layered ore bodies controlled by interlayer fracture zones of different lithologic interfaces. The metallogenic model also has important reference value for deep prospecting and comprehensive evaluation of similar type of tungsten polymetallic deposits in the southern Qinling orogenic belt.

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代鸿章,王登红,刘丽君,黄凡,王成辉.2019.南秦岭镇安核桃坪钨铍矿床成矿时代及成矿模式探讨[J].地质学报,93(6):1342-1358.
DAI Hongzhang, WANG Denghong, LIU Lijun, HUANG Fan, WANG Chenghui.2019. Metallogenic epoch and metallogenic model of the Hetaoping W- Be deposit in Zhen’an County, South Qinling[J]. Acta Geologica Sinica,93(6):1342-1358.

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历史
  • 收稿日期:2019-04-22
  • 最后修改日期:2019-05-31
  • 录用日期:2019-06-03
  • 在线发布日期: 2019-06-12