湘南黄沙坪多金属矿床花岗斑岩的矿物化学及其对矽卡岩白钨矿成矿的指示意义

发布时间：2018-02-03 08:30

本文关键词： 黄沙坪矿床花岗斑岩铌铁矿黑钨矿黑云母白钨矿电子探针原位LA-ICP-MS 成矿物质和流体　出处：《岩石学报》2017年03期 　论文类型：期刊论文

【摘要】：黄沙坪多金属矿床是湖南最大的铅锌生产基地,并且在与矿床内花岗斑岩接触的矽卡岩带产有隐伏的大型矽卡岩型白钨矿和中型规模的辉钼矿。钨-钼矿化的时代为晚侏罗世,与矿床内花岗斑岩侵入时代一致。然而,已有研究认为,由于该花岗斑岩规模很小,矽卡岩型白钨矿的成矿热液应来自深部岩浆房而非此花岗斑岩。为此,我们对花岗斑岩进行了仔细的镜下观测,并且对其中的副矿物和黑云母以及矽卡岩中的白钨矿进行了电子探针成分分析,应用原位LA-ICP-MS方法测定了矽卡岩中白钨矿的稀土元素含量,试图对白钨矿矿化的物质和流体来源提供确切的证据。通过研究,首次在矿床内花岗斑岩中发现了与未蚀变黑云母伴生的黑钨矿和铌铁矿,表明花岗斑岩至少在岩浆结晶作用晚期或岩浆-热液过渡阶段早期就已发生钨的矿物富集,为确定花岗斑岩是控制钨矿化的成矿岩体提供了依据。此外,发现花岗斑岩中的黑云母(属铁叶云母)含有极高的氟含量(3%),指示其应形成于富含氟的高分异岩浆。研究进一步揭示,矽卡岩中白钨矿的轻稀土元素配分模式与花岗斑岩十分一致,而重稀土元素则显著亏损,而且Eu的含量较花岗斑岩更为富集。这暗示形成白钨矿的成矿流体应直接来自花岗斑岩,即:在早期无水矽卡岩阶段,石榴子石的沉淀导致流体中的重稀土亏损而Eu相对富集;白钨矿随后再从这种流体中沉淀。此外,白钨矿的Eu含量与Sm、Gd含量具有负相关关系,表明Eu的分配是相对独立的行为,主要以Eu2+存在,从而指示沉淀白钨矿的流体具有还原的性质。结合前人的研究成果及本文所提供的新证据,我们认为,形成矽卡岩型白钨矿的钨和成矿热液应来自高分异且富F的花岗斑岩,而所需的钙则可能来自于碳酸盐围岩,即矿床内花岗斑岩应是形成钨钼矿床的物质来源,驱动热液活动的能量来源,和寻找隐伏钨矿床的重要找矿标志。
[Abstract]:Huangshaping polymetallic deposit is the largest production base of lead and zinc in Hunan. In addition, in the skarn belt in contact with granitic porphyry within the deposit, there are concealed large skarn type scheelite and medium scale molybdenum ore. The age of tungsten molybdenum mineralization is late Jurassic. In accordance with the age of granitic porphyry intrusion in the deposit, however, it has been suggested that, due to the small scale of the granitic porphyry, the ore-forming hydrothermal solution of skarn type scheelite should come from the deep magmatic chamber rather than the granitic porphyry. We have carefully observed granitic porphyry under microscope, and have made electron probe analysis of accessory minerals and biotite and scheelite in skarn. The content of rare earth elements of scheelite in skarn has been determined by in situ LA-ICP-MS method in order to provide exact evidence for the material and fluid source of scheelite mineralization. Wolframite and niobite associated with unaltered biotite were first found in granitic porphyry. The results indicate that granitic porphyry has been enriched in tungsten minerals at least in the late magmatic crystallization or magmatic hydrothermal transition stage, which provides a basis for determining that granitic porphyry is a ore-forming rock controlling tungsten mineralization. It is found that biotite in granitic porphyry contains extremely high fluorine content indicating that it should be formed in high fluorine rich heterogeneous magma. The distribution pattern of light rare earth elements of Scheelite in skarn is very consistent with that of granitic porphyry, while the heavy rare earth element is significantly depleted. Moreover, the EU content is more abundant than granitic porphyry, which suggests that the ore-forming fluid forming scheelite should come directly from granitic porphyry, that is, in the early anhydrous skarn stage. The precipitation of pomegranate results in the depletion of heavy rare earth and the relative enrichment of EU in the fluid. In addition, there is a negative correlation between EU content and Sm Gd content, indicating that EU distribution is a relatively independent behavior, mainly in the form of Eu2. This indicates that the precipitated scheelite fluid has the property of reduction. Combined with the previous research results and the new evidence provided in this paper, we believe that. The tungsten and ore-forming hydrothermal solution of skarn type scheelite should come from the granitic porphyry with high diversity and rich in F, and the calcium needed may come from the carbonate surrounding rock, that is, the granitic porphyry in the deposit should be the material source for the formation of W-Mo deposit. The source of energy driving hydrothermal activity and the important prospecting criteria for searching for hidden tungsten deposits.
【作者单位】：南京大学地球科学与工程学院内生金属矿床成矿机制研究国家重点实验室;河海大学海洋学院海洋地质研究所;
【基金】：国家重点基础研究发展计划(2012CB416705) 国家自然科学重点基金项目(41230315) 中国地质调查局项目(1212011085407)联合资助
【分类号】：P618.2;P618.67
【正文快照】： 1引言黄沙坪钨钼铅锌多金属矿床位于华夏地块湘南地区,属于钦杭成矿带中段范围(周永章等,2015;图1a)。该地区以广泛出露的中生代岩浆活动以及与其紧密联系的多金属矿化为特征,包含多个世界级大型、超大型多金属矿床,例如与花岗岩有关的柿竹园、新田岭矽卡岩型白钨矿床,荷花坪

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