华南变质基底对铀成矿作用的制约

Based on previous studies on the granite and metamorphic basement from Southern China, this study will select the basement rocks closely related with uranium deposit, and the basement rocks without uranium deposit as the objects of this study. The relationship between basement rocks and uranium mineralization is the core content of this study. Through the studies of petrography, geochemistry, the spectrum of zircon geochronology and Nd-Hf isotopic composition, we will discuss the characteristics of sediment sources and the sedimentary environment of the basement rocks, and try to recovery the protolith rocks. According to genesis of the granites with and without uranium deposit, we will distinguish the rocks and its characteristics of two kinds of granites, and will reveal the uranium enrichment mechanism during the evolution process of the basement rocks, and will find out its constraints on later uranium mineralization, and typical signs of uranium-bearing basement rocks. This study will provide a theoretical basis for uranium exploration, and then discuss the uranium metallogenic regularity in Southern China. It will give guiding significance for uranium prospecting in China.

在前人对华南花岗岩和基底变质岩研究的基础上，本项研究拟选定与铀矿床密切相关的基底岩石（如猫尖洞铀矿床、白面石铀矿床，广东下庄铀矿床、长江铀矿床、广西苗儿山产铀花岗岩及相山火山岩型铀矿床及其周围的震旦、寒武及元古宙地层），以及不含铀矿床的基底岩石（如江西中部及北部，湖南西北部的震旦、寒武纪元古宙地层）为研究对象，以基底与铀成矿的关系为核心内容，通过岩相学、岩石地球化学、锆石年代频谱和Nd-Hf同位素组成的研究，讨论基底岩石的沉积物源区特征和原岩沉积环境等方面的原岩恢复工作，结合前人对含铀花岗岩和不含铀花岗岩的成因研究，甄别两类花岗岩的基底层位和特征，揭示基底岩石形成演化过程中铀的富集机制，及其对后期铀成矿的制约作用，找出产铀基底的典型标志，为铀矿勘探提供一定的理论依据，从而深入探讨华南铀成矿规律，对于我国下一步的铀矿勘查具有一定的指导意义。

通过对华夏地块（铀矿有关）和扬子地块东南缘（铀矿无关）的前寒武纪基底变质岩研究发现，前者的碎屑锆石年龄峰值主要集中在900-1000Ma，后者的峰值主要位于800-900Ma之间。峰值不同表明两者具有截然不同的物质来源和地球化学特征。前者源自于长石石英砂岩再循环，地球化学组成等同于0-20%铁镁质岩石加80-100%的长英质岩石构成；后者为中性-中酸性火成岩再循环的产物，地球化学组成类似于10-40%的铁镁质岩石加60-90%的长英质岩石。与后者相比，前者具有较高铀（1.82-12.22ppm，平均3.74ppm）、钍（8.37-48.0ppm，平均18.50）和稀土元素总量（平均225ppm），以及较高的成熟度。我们认为华夏地块具有高U、Th含量和高成熟度可能是制约花岗岩型铀矿床之所以产出在华夏板块而非扬子地块东南缘的关键因素之一。