喜马拉雅琼嘉岗伟晶岩型锂矿成矿地质特征和形成机制

Geological features and ore-forming mechanism of the Qiongjiagang super-large pegmatite lithium deposit in Himalaya,China

西藏喜马拉雅琼嘉岗伟晶岩型锂矿是喜马拉雅稀有金属成矿带标志性的伟晶岩型矿床。其成矿地质特征、成矿机理-机制和含矿性评价的研究对喜马拉雅稀有金属成矿带的形成机制和找矿勘查工作研究具有重要意义。中国科学院地质与地球物理研究所在2021~2023年期间对喜马拉雅琼嘉岗伟晶岩型锂矿形成机制研究中,获得如下认识:(1)琼嘉岗锂辉石伟晶岩的主矿体主要顺矽卡岩化大理岩和钙质千枚岩面理侵入,中部整体上呈板状近水平(10°~20°),主矿体两侧倾角相对较大(30°~50°);(2)琼嘉岗矿床的富锂矿物主要为锂辉石(包括3个期次),次为透锂长石、锂绿泥石、锂云母等,其他稀有金属矿物包括绿柱石、日光榴石、羟硅铍石、铌锰矿-铌铁矿、锡石等,围岩蚀变主要为矽卡岩化并含有少量锡矿化;(3)琼嘉岗锂矿中花岗岩-伟晶岩的演化和成矿受岩浆结晶分异过程控制,锂辉石伟晶岩矿体的形成与系统大量流体出溶有关,花岗质熔体演化的早期阶段稀有金属可能达到饱和;(4)钾长石Ti温度计和流体包裹体等容线相交法揭示出从电气石白云母花岗岩到锂辉石伟晶岩呈现降温趋势,锂辉石伟晶岩石英形成时流体的捕获温度为410~475℃,捕获压力为180~240MPa,结合含锂矿物相关系揭示出降压是锂辉石伟晶岩形成的重要机制;(5)建立了琼嘉岗锂矿的成矿模式,指出高度结晶分异、流体出溶和降压过程控制了琼嘉岗锂辉石伟晶岩的形成,流体交代作用形成了稀有金属矿化;(6)长石结构和化学成分(Rb、Cs、Sr、Ba、K/Rb和形成温度)、石榴子石组成(高水含量、高Mn/(Mn+Fe)的锰铝榴石)、副矿物组成及其包裹矿物类型是琼嘉岗及周边伟晶岩含矿性评价的有效指标。

The Tibetan Himalayan Qiongjiagang pegmatite-type lithium deposit is a landmark rare-metal deposit in the Himalayan belt.Uncovering the geological characteristics of the mineralization,the mechanism of mineralization,and the evaluation of mineral directors in the pegmatites will be of great significance to the research on the formation mechanism and prospecting of the Himalayan rare metal belt.Institute of Geology and Geophysics,Chinese Academy of Sciences(IGGCAS)has made the following findings on the formation mechanism of the Himalayan Qiongjiagang pegmatite-type lithium deposit in 2021~2023:(1)the main ore body of the Qiongjiagang spodumene pegmatites mainly occurred along the foliation of the skarnization marble and calcareous phyllite strata,and the central part of the main ore body is generally sub-horizontal,with large dips on both sides of the main ore body;(2)the ore minerals in the Qiongjiagang ore bodies consist of spodumene(including three stages),petalite,cookeite,lepidolite,beryl,helvite,bertrandite,columbite-group minerals and cassiterite;(3)the evolution and mineralization characteristics of the Qiongjiagang granite-pegmatites are controlled by the fractional crystallization and differentiation processes,the fluid exsolution is genetically related to the lithium mineralization,and the magma source may be saturated with rare-metal elements at the early stage of granitic melt evolution;(4)K-feldspar Ti thermometer and isochores from microthermometric measurement of the fluid inclusions show a temperature decreasing trend from tourmaline leucogranite granite to spodumene pegmatite,and depressurization in the formation of the spodumene pegmatites by estimating pressure-temperature conditions(trapping temperature:ca.410~475℃;trapping pressure:ca.180~240MPa);(5)establish the ore deposit model of Qiongjiagang lithium deposit,pointing out that the high degree of crystallizing differentiation,fluid exsolution and depressurization drive the formation of the Qiongjiagang spodumene pegmatites,and late-magmatic metasomatism is responsible for the formation of rare-metal mineralization;(6)Feldspar composition(Rb,Cs,Sr,Ba,K/Rb and formation temperature),garnet composition(high-water content and high Mn/(Mn+Fe)ratio),and paragenesis and types of mineral inclusions in the accessary minerals are effective indicators for evaluating of the mineralization of the Qiongjiagang pegmatites.