南岭燕山期骑田岭复式岩体钨、锡成矿差异机制研究

Spatial distribution shows that the eastern sector of the Nanling Range is characterized by extensive W mineralization, while Sn mineralization becomes stronger westwards. The Qitianling composite pluton, as a typical metallogenetic pluton in the Nanling Range, which hosts the Furong tin deposit in the south and the Xintianling tungsten deposit in the north, is an ideal research subject to study the mechanisms of the difference of the tin and tungsten deposits. According to the previous researches, this project mainly focuses on (1) systematic analyses in terms of petrology, mineralogy, geochemistry and isotope geochemistry of the granites associated with tin and tungsten mineralization; (2) detailed in-situ micro-analyses on minerals of the Furong tin deposit and the Xintianling tungsten deposit. The aims of the project are to disclose (1) the petrogenesis of the granites associated with the tin and tungsten mineralization; (2) the difference of the fluorine content and oxygen fugacity of the granites associated with tin and tungsten deposits and their effects on the mineralization; (3) the composition evolution of the ore-forming fluid and the mechanism of the tin-tungsten mineralization. Finally, with synthesizing the data of the metallogenetic granites and the tin-tungsten deposits, this project would provide new mechanisms of the difference of the tin and tungsten deposits hosted in the Qitianling pluton, which can throw light on the mechanisms of the difference of the tin and tungsten deposits in the Nanling Range.

南岭地区钨矿床和锡矿床空间分布整体呈“东钨西锡”的特点。骑田岭岩体为南岭地区燕山期成矿复式岩体的典型代表，其南部形成芙蓉锡矿田而北部形成新田岭钨矿，同一岩体南北成矿类型截然不同，是研究南岭地区钨锡矿化空间差异机制的理想岩体。本项目在已有研究基础上，通过（1）对骑田岭南、北成矿岩体进行岩石学、矿物学、地球化学和同位素的研究；（2）对南部芙蓉锡矿田和北部新田岭钨矿田进行矿床学和精细的矿物原位微区分析研究。揭示（1）南部成锡矿岩体与北部成钨矿岩体的岩石成因；（2）南部成锡矿岩体与北部成钨矿岩体的F含量和氧逸度的差异，及其对钨、锡成矿作用的影响；（3）芙蓉锡矿田和新田岭钨矿成矿流体演化和成矿机制。最终综合钨锡成矿岩体、矿床学研究数据，建立骑田岭钨、锡成矿差异形成的模式，为南岭地区钨、锡成矿差异提供重要信息。

南岭地区在中生代具有大规模钨锡成矿作用，钨矿床和锡矿床空间分布整体呈“东钨西锡”的特点。为揭示南岭钨、锡成矿差异机制，本项目对南岭地区骑田岭复式岩体、新田岭矽卡岩型钨矿、屋场坪矽卡岩型锡矿床开展了系统的岩石学、地球化学、矿物微区分析研究，取得如下主要研究成果：（1）通过对骑田岭南、北成矿岩体的系统研究，结合区域资料，揭示南岭地区成锡矿岩体具有更多的地幔物质加入和更高的F含量；成钨岩体地幔物质加入较少，F含量较低；并提出富F特征可能与地幔物质的加入有关。该结论也得到华南燕山晚期钨成矿岩体研究的支持。（2）复式岩体各岩体之间即不是简单的分离结晶关系，也不是源区多期次部分熔融的结果，而是花岗质岩浆演化过程中，堆晶体与粒间熔体分离的结果。此模式得到了角闪石成分特征，微量元素模拟和全岩Li同位素数据的支持。我们进一步利用矿物温压计将粒间高硅熔体抽离的温压条件限定为750~780℃、~3.1kbar。（3）矽卡岩型钨矿中的三期石榴石形成于流体演化的不同阶段。从早期到晚期，石榴石由近封闭、低氧逸度环境，转变为开放的、高氧逸度环境。石榴石的Nd同位素变化指示，早期石榴石主要从岩浆流体中沉淀，而晚期石榴石的沉淀则需要更多围岩地层物质的加入。矽卡岩型钨、锡矿床中的富集轻稀土、亏损重稀土的石榴石具有最高的钨、锡含量，暗示成矿作用与围岩地层流体的大量加入有关。