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661铀矿床位于浙江省境内,是赣杭铀成矿带东段重要的火山岩型铀矿床之一,矿体赋存于晚中生代磨石山群九里坪组流纹岩中。对采自该矿的与铀成矿相关的方解石进行了系统铅同位素测定。结果表明,该矿床不同阶段方解石具有一致的Pb同位素组成和较窄的变化范围,暗示成矿过程中铅可能来自于同一的且较为均一的铅源,少量晚期样品仅表现为206Pb/204Pb的增大,指示后期流体可能通过淋滤作用加入了部分早沉淀的铀。通过与基底陈蔡群变质岩和磨石山群火山岩铅同位素组成对比发现,矿石具有与磨石山群火山岩一致的铅同位素组成和变化趋势。在铅构造模式和铅同位素Δγ-Δβ成因图解中矿石和火山岩均显示出造山带铅或地壳与地幔混合的俯冲带岩浆作用铅特征,这与华东南地区的火山岩成因上主要由中下地壳熔融,并不同程度加入了地幔组分的结果一致。这些证据表明火山岩铅为该矿床的主要铅源。
Located in the territory of Zhejiang Province, the 661 uranium deposit is one of the important volcanic-type uranium deposits in the eastern section of the Gan-Hang uranium metallogenic belt. The ore body occurs in the rhyolite of the Juriping Formation in the Late Mesozoic. The systematic lead isotope determination of calcite associated with uranium mineralization collected from this mine was conducted. The results show that the calcite at different stages has the same Pb isotopic composition and narrow variation range, suggesting that the lead may originate from the same and more uniform source of lead in the ore-forming process. The small amount of late-stage samples only show the increase of 206Pb / 204Pb Large, indicating late fluid may be added by leaching part of the early precipitation of uranium. By comparison with the lead isotopic compositions of the basement Chencaidun volcanic rocks and the Shaoshishan volcanic rocks, it is found that the ore has the same lead isotopic composition and variation tendency as the volcanic rocks of the Moshishi Group. Both lead and crustal and mantle mixed lead and magmatic lead characteristics are shown in the lead tectonic model and lead isotope Δγ-Δβ genetic mapping. This is consistent with the fact that the volcanic rocks in southeastern China are mainly composed of middle and lower crustal melting , And consistent with the results of the addition of mantle components to varying degrees. The evidence shows that volcanic lead is the major source of lead in the deposit.