湘南新田岭氧化性S型花岗岩成因及其钨成矿作用

The granites associated W mineralization are reduced S-type. Preliminary survey indicates that Xintianling granite is in all probability oxidized W-bearing one. This proposal will deal with the source features, genesis of this granite and its relationship with W mineralization. The chemical compositions, morphology and paragenesis of rock-forming minerals and accessory minerals (such as zircon and apatite), especially Ti- and Fe-oxide, will be investigated. The contents of magnetite and ilmenite will be evaluated. The evolutional process and genesis of Xintianling granite will be revealed based on study of mineralogy and rock geochemistry. The analysis of trace elements of apatite and zircon by LA-ICP-MS will be carried out. Combined with the chemical compositions of the whole rock and biotite, magnetic susceptibility and the trace element geochemistry of the zircon and apatite, the redox state of the granite will be assessed. Deposit geology, ore-forming stages and alteration zoning will be studied. Based on the changes in the chemical compositions of skarn minerals from the different ore-forming stages, the formation conditions will be investigated. On the basis of analysis of the O-H-S-Pb isotopic compositions of ores and fluid inclusions, property, source and evolution of ore-forming fluids are discussed. Dating of the tungsten deposit will be carried out and combined with timing of the granites, the relationship between the granites and the W-deposit will be revealed. A comparative study of the oxidized and reduced W-bearing granites will be systematically carried out. This study not only deepens understanding the relationship between granite and W-metallogeny, but also benefits exploration for W-deposits.

南岭成矿带与钨矿化有关花岗岩都是还原性S型花岗岩。初步调查研究发现新田岭花岗岩可能是一个高氧化性含钨花岗岩。因此，本项目选择湘南新田岭花岗岩及其有关钨矿床系统开展花岗岩的的源区特征、成因及其与钨成矿关系研究。开展造岩矿物和副矿物（如锆石、磷灰石），特别是钛铁氧化物的化学成分、形貌、矿物相互关系研究。利用矿物特征的变化示踪岩浆演化过程，结合岩石地球化学探讨岩石成因,开展磷灰石、锆石等矿物微区微量元素分析，结合磁化率测试、全岩化学成分和黑云母成分分析，揭示花岗岩的氧化性质。研究钨矿床的矿床地质特征、蚀变期次和成矿阶段。研究不同阶段矽卡岩矿物的矿物化学特征，揭示矽卡岩的形成环境。开展矿床地球化学研究，探讨成矿流体性质、来源和演以及矿床成因。系统对比高氧化性含钨花岗岩与还原性含钨花岗岩的差异。这项研究不仅可以丰富花岗岩成岩成矿理论，加深对花岗岩成矿的理解，而且对指导找矿也具有重要的意义。

新田岭矽卡岩型钨矿是华南大型钨矿之一。新田岭含矿花岗岩主要由中心相的中粒黑云母二长花岗岩和边缘相的细粒黑云母正长花岗岩组成。花岗岩Fe-Ti-Mn氧化物主要为磁铁矿、红钛锰矿和钛铁矿，磁铁矿明显多于钛铁矿，磁铁矿/钛铁矿比值一般大于4。黑云母二长花岗岩和黑云母正长花岗岩平均磁化率分别为827×10–6 emu/g，后者平均磁化率为190×10–6 emu/g，明显高于华南其他钨锡花岗岩。新田岭含矿花岗岩锆石Ce4+/Ce3+比值>100。这些特征表明新田岭含钨花岗岩为氧化性花岗岩，明显不同于华南其他还原性S型钨锡花岗岩。花岗岩中锆石U-Pb定年和矽卡岩中辉钼矿定年表明，成矿与花岗岩具有密切的成因联系，两者均形成于中侏罗世。成矿花岗岩为高钾钙碱性、弱过铝质，亏损Ba、Nb、Sr、P和Ti，富集U、Ta、Pb、Hf，轻重稀土比值较大，Eu负异常显著，具有S型花岗岩特征。中粒黑云母二长花岗岩的初始87Sr/86Sr值和εNd（t）分别为0.7115~0.7133和-7.1~-8.8，εHf（t）值介于-5.4~-16.0之间。细粒黑云母正长花岗岩的初始87Sr/86Sr和εNd（t）分别为0.7129~0.7198和-8.1~-9.5，εHf（t）值介于-4.1~-10.0之间。岩石地球化学和同位素特征表明，花岗岩的分异演化程度相对较低，由贫粘土矿物的变质杂砂岩部分熔融而成，细粒黑云母正长花岗岩与中粒黑云母二长花岗岩来源于同一岩浆分异演化。花岗岩氧逸度高可能与源区岩石缺乏有机质有关。研究表明，华南至少存在两类花岗岩源区，即高成熟度的富碳变质泥岩源区和缺乏有机质的贫粘土矿物的变质沉积岩源区。新田岭矽卡岩型钨矿分为进变质矽卡岩、退变质矽卡岩、脉状矿化和硫化物四个形成阶段，退变质矽卡岩为主要钨成矿阶段，脉状矿化为次要矿化阶段。大规模钨沉淀与流体氧逸度变化有关。不同阶段矿物成分记录了成矿环境和成矿流体成分演化特征。C-H-O-S-Pb同位素研究表明，成矿流体和钨主要源自于花岗岩岩浆。