Enrichment mechanisms of Sn-Cs-Tl in the Himalaya leucogranite

Abstract

关键金属是全球高科技产业不可或缺的战略性资源，其富集机制和成矿作用是目前国际矿床学研究的热点之一。我们对喜马拉雅带吉隆和亚东地区淡色花岗岩开展系统的地球化学研究，发现侵入到藏南拆离系的淡色花岗岩含有较高的Sn、Cs、Tl、Be、W、B、Li和Bi。全岩元素地球化学分析表明，这些淡色花岗岩具有如下特征：（1）富集关键金属元素；（2）为原始岩浆经历斜长石、锆石、独居石、磷灰石、云母分离结晶作用后的残余熔体；（3）关键元素的富集和矿化与花岗岩高度分离结晶作用密切相关。随着分异程度的增强，岩浆变为富挥发分的高SiO₂体系，关键金属元素在残余熔体中富集，并且最后可能形成具有工业价值的矿床。由于地球化学特征的相似性，Cs和Tl呈类质同象替代钾、铷进入云母中。富集关键金属元素的花岗岩在时间上和空间上属于与藏南拆离系相关的同构造侵位花岗岩，藏南拆离系的活动促使了原始岩浆的广泛分离结晶作用，以及后期的关键金属元素（如Rb、Cs和Tl）的富集。;Critical elements are the indispensable strategic resource for global high-tech industries, and the mechanisms for the enrichment and mineralization for such elements is currently one of the key areas in the international mineral deposit studies. In the Gyirong and Yadong areas along the Himalayan orogen, a systematic geochemical study of leucogranites indicate that the leucogranites which invaded the Southern Tibet Detachment System (STDS) contain a relatively elevated content of Sn, Cs, Tl, Be, W, B, Li and Bi. Whole-rock element geochemical data indicate that (1) these leucogranites are enriched in critical elements; (2) they represent the residual melts, which resulted from fractional crystallization of plagioclase, zircon, monazite, apatite, and mica of more primitive magmas; and (3) enrichment and mineralization of critical elements are closely related to the evolution of such highly fractionated granites. As magmas evolved into high SiO₂ and volatile magmas by intensive fractional differentiation, critical elements with a high fluid compatibility are enriched in the residual melt and might eventually form economic ore deposits. Due to geochemical similarity, Cs and Tl are incorporated into mica by replacement of K or Rb. These granites enriched with critical elements are syntectonic granites spatially and temporally associated with the STDS whose activities promote extensive fractional crystallization of the more primitive magmas and later enrichment of critical elements such as Rb, Cs, and Tl.

Topics & Concepts