摘要
广西大化县透闪石玉矿床产自贫镁碳酸盐岩中,是一种新型透闪石玉矿床,其成矿物质来源及成因研究较为薄弱.对该矿床中围岩、蚀变岩、侵入岩和透闪石玉进行主微量元素和锶同位素对比研究,结果表明:透闪石玉的微量元素和稀土元素配分模式与石灰岩和大理岩相似,且微量元素和稀土元素含量与大理岩相关性较强(相关系数0.931),说明Ca的来源与大理岩有关;透闪石玉87Sr/86Sr与1 000/Sr呈线性负相关关系,说明透闪石玉87Sr/86Sr(0.707 0)主要受大理岩(0.707 5)和辉绿岩(0.706 1)两个端元控制,外推1 000/Sr=0得到的87Sr/86Sr值与辉绿岩一致,说明成矿流体为岩浆热液;透闪石玉Y/Ho值(均值49.10)高于大理岩和辉绿岩(均值分别为44.53、24.30),说明其受岩浆热液作用较强烈.结合大化透闪石玉成矿特点,推测其成矿物质Ca来自大理岩,Si和Mg来自辉绿岩.采用稀土元素配分、δCe、δEu、Zr/Hf、Nb/Ta、Sr/Ba、U/Th、W、V、Cu等指标判断,其氧逸度较高,成矿环境为碱性.广西大化透闪石玉矿床的成矿过程分为4个阶段:基性岩浆侵入→石灰岩变质为大理岩→富含Mg和Si的基性岩浆热液形成→热液交代大理岩形成透闪石玉.
Abstract
Turbidite jade deposit in Dahua,Guangxi,produced in the poor magnesium carbonate rock stratum,is a new type of turbidite jade deposit.The source of its mineralization material and the cause of the study is rel-atively weak.This study has carried out a comparative study by testing the main trace elements and strontium i-sotopes of peripheral rocks,altered rocks,intrusive rocks and tremolite jade in the deposits.The results show that the trace element and rare earth element partitioning patterns tremolite jade are similar to those of limestone and marble,the trace element and rare earth element contents correlate well with marble(correlation coefficient 0.931),suggesting that the source of Ca is related to marble.There is a linear negative correlation between 87 Sr/86 Sr and 1 000/Sr in Dahua stratified tremolite jade,indicating that 87Sr/86Sr(0.707 0)is controlled by marble(0.707 5)and diabase(0.706 1)endmembers.The 87Sr/86Sr value obtained by extrapolating 1 000/Sr=0 is consistent with the 87 Sr/86 Sr value in the gabbro,suggesting that the mineralising fluid is magmatic hydro-thermal;the values of Y/Ho in Dahua stratified tremolite jade(avg.,49.10)are higher than those in marble and diabase(avg.,44.53 and 24.30,respectively),indicating that the marble is more strongly affected by magmatic-hydrothermal action.Combined with the characteristics of Dahua tremolite jade,it is inferred that Ca comes from marble,Mg and Si come from diabase.Using rare earth element composition,δCe,δEu,Zr/Hf,Nb/Ta,Sr/Ba,U/Th,W,V,Cu and other indicators,it determines that their mineralization environment is alkaline with high oxygen fugacity.The formation of tremolite jade deposits in Dahua,Guangxi,is divided into four stages:basic magmatic intrusion → limestone metamorphism to marble → formation of Mg-and Si-rich ba-saltic magmatic hydrothermal fluids→ hydrothermal fluid accounted for the formation of tremolite jade from mar-ble.
基金项目
广西自然科学基金项目(2020GXNSFAA159167)
广西科技基地和人才专项项目(2019AC20007)
维普
万方数据