热液金刚石压腔在流体包裹体研究中的应用——以川西甲基卡伟晶岩型矿床为例  

Application of Hydrothermal Diamond-Anvil Cell in Fluid Inclusions:An Example from the Jiajika Pegmatite Deposit in Western Sichuan,China

作　　者：李胜虎[1] 李建康[2] 张德会[1] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]国土资源部成矿作用与资源评价重点实验室中国地质科学院矿产资源研究所,北京100037

出　　处：《地质学报》2015年第4期747-754,共8页Acta Geologica Sinica

基　　金：中央级公益性科研院所基本科研业务费专项基金(编号K1409);国家自然科学基金项目(编号41372088);中国地质大调查项目(编号1212011220805)联合资助的成果

摘　　要：流体包裹体是赋存在矿物中的流体样品,均一实验是以其研究成岩成矿流体演化的重要步骤和内容。但某些深成岩或矿床中的流体包裹体,如我国川西甲基卡伟晶岩型锂矿中的富CO2包裹体,因具有较大的内压,当利用传统的热台在1个大气压下加热时,容易发生爆裂而无法观测到均一行为和均一温度。因此,本文利用热液金刚石压腔(HDAC),以H2O为压力介质对流体包裹体施加外压,完成了甲基卡矿床No.134号脉石英中富CO2包裹体的均一实验。实验结果表明,随着外压的增大,均一温度呈降低的趋势,说明流体包裹体在被捕获后并非严格的等容,从而警示我们以后再对深成矿床中具有高内压的流体包裹体进行显微测温时应选用HDAC以获得更为可靠准确的数据。补充富CO2包裹体的均一实验数据后,石英中的H2O-CO2-NaCl包裹体表现出良好分异现象,随着均一状态自液态CO2→CO2与H2O临界相→液态H2O相变化,均一温度和盐度也随之降低,且比锂辉石中的包裹体具有更低的盐度和更大的温度变化范围。这些热力学特征说明,在锂辉石型伟晶岩形成过程中,锂辉石和石英先后结晶,分别主要捕获富子晶包裹体和H2O-CO2-NaCl包裹体,同时Li+不断向锂辉石结晶前锋聚集,使参与流体的Li+含量降低,致使石英中流体包裹体的盐度呈现出降低的趋势。Fluid inclusions contain the important signatures of metallogenic fluid and homogenization experiment is one of the high-tech experimental means to investigate the characteristics of rock- and ore-forming fluids. But for some fluid inclusions in some plutons or deep deposits, for example, CO2-rich fluid inclusions in pegmatitie of Jiajika deposit, western Sichuan, have high internal pressure, and it is impossible to test the homogenization temperature when heated at atm on conventional heating table because they tend to blast. Therefore, this study employed hydrothermal diamond-anvil cell （HDAC） to heat CO2-rich fluid inclusions in quartz from No. 134 pegmatite dyke in the Jiajika deposit under elevated pressure with pressure medium of H2O. The experimental results show that the homogenization temperatures of fluid inclusions decreased with the increase of elevated pressures, indicating that fluid inclusions are not isometrical exactly after entrapment. Therefore, it gives some warning that it is better to choose HDAC as the microthermometric testing tool in order to get more reliable and accurate data for fluid inclusions with high internal pressure which come from hypogenic ore deposits. Combining the homogenization results by using HDAC and Linkam THMSG600, we found that the homogenization temperatures and salinities of H2O-CO2-NaCl inclusions decrease with change of homogenization states from liquid CO2 to the critical phase of CO2 and H2O, and to liquid H2O, have lower salinity and wide temperature range than that inclusions in spodumene. These thermodynamic features indicate that spodumene crystallized earlier than quartz and both entrapped crystal-rich inclusions and CO2-bearing fluid inclusions. Because Li＋ tends to concentrate before crystallization of spodumene and causes decrease of Li＋ content in the fluid, the salinity of fluid inclusions in quartz decrease generally during the crystallization.

关 键 词：热液金刚石压腔 均一实验 流体包裹体 伟晶岩 甲基卡 

分 类 号：P619.241[天文地球—矿床学]