柴北缘鱼卡榴辉岩型金红石矿床成矿物理条件

鱼卡榴辉岩型金红石矿床位于柴北缘超高压变质带西侧,是青藏高原发现的第一个超大型金红石矿床。为研究该矿床的控矿因素和成矿机制,在详细的野外地质调查和岩相学研究的基础上,利用电子探针对该矿床榴辉岩中的各特征矿物进行分析。研究表明,粗粒块状高钛榴辉岩的石榴子石保存了较完整的成分环带,从核部到边部,石榴子石的化学成分、矿物包裹体的种类和粒度都具有明显的分带性;细粒片麻状低钛榴辉岩的矿物颗粒较小,石榴子石的成分环带较差。鱼卡榴辉岩的p-T演化特征反映,它们经历了深俯冲阶段的升温升压到早期折返阶段的升温降压,再到之后的降温降压的顺时针演化轨迹。榴辉岩中进变质矿物组合和生长环带的保存说明,榴辉岩的形成经历了相对快速俯冲和折返的动力学过程,钛成矿作用时金红石很少发生转变。超高压变质前后为金红石最主要的成矿期。

An analysis of metallogenic physical conditions of the Yuqia eclogite-type rutile deposit in the North Qaidam

The Yuqia eclogite-type rutile deposit is located on the west side of the northern margin of the Qaidam Basin UHP metamorphic belt. And it is the first ultra-large rutile deposit found on the Tibetan Plateau. In order to study the ore-controlling factors and metallogenic mechanism of this deposit, the authors conducted detailed field geological survey and petrographic study. The characteristic minerals in the eclogite of the deposit were analyzed by electron microprobe analysis. It is shown that the garnets of coarse-grained high-Ti eclogite have preserved relatively complete compositional zoning; from the core to the edge, the garnet has a distinct zonality in chemical composition, type and granularity of mineral inclusions. However, the mineral particles in the fine and gneiss low-Ti eclogite are smaller, and the composition of the garnet is poor. Characteristics of p-T evolution of Yuqia eclogite show that it experienced a clockwise evolutionary trajectory from the temperature and pressure rise of the deep subduction stage to the temperature rise and pressure decrease of the early exhumation stage and then to the decrease of both temperature and pressure. The eclogite belongs to the metamorphic mineral assemblage with the preservation of the growth zone, which suggests that the formation of eclogites went through a dynamic process of relatively rapid subduction and reentry exhumation.