相山铀矿田北部花岗斑岩黑云母及绿泥石矿物化学特征与地质意义  

Mineral chemistry and geological significance of biotite and chlorite from granite porphyries in the northern Xiangshan uranium orefield

作　　者：刘龙[1] 张树明[1,2] 王利玲 张鑫[1,2] 欧阳军勇 夏寅初 吴志春[1,2] LIU Long;ZHANG Shu-ming;WANG Li-ling;ZHANG Xin;OUYANG Jun-yong;XIA Yin-chu;WU Zhi-chun(State Key Laboratory of Nuclear Resources and Environment,East China University of Technology,Nanchang 330013,China;Fundamental Science on Radioactive Geology and Exploration Technology Laboratory,East China Institute of Technology,Nanchang 330013,China;Shanwei Technical School,Shanwei 516600,China)

机构地区：[1]东华理工大学核资源与环境国家重点实验室,江西南昌330013 [2]东华理工大学放射性地质与勘探技术国防重点学科实验室,江西南昌330013 [3]汕尾市技工学校,广东汕尾516600

出　　处：《地球化学》2021年第6期550-561,共12页Geochimica

基　　金：国家自然科学基金(41862006,41802247);江西省研究生创新基金(YC2020-B159)。

摘　　要：相山铀矿田为中国最大的火山岩型铀矿田,其中北部花岗斑岩型铀矿床资源储量占总储量的36.65%。虽然前人对相山矿田北部花岗斑岩进行了系统研究,但是关于花岗斑岩中矿物化学研究较为薄弱。本次研究运用电子探针技术对相山北部花岗斑岩中黑云母及绿泥石进行了矿物化学分析,并探讨了成岩成矿意义。结果表明:(1)相山北部产铀花岗斑岩黑云母为铁质黑云母。花岗斑岩岩浆结晶温度为721~753℃,平均737℃,氧逸度lgf(O_(2))为-14.8~-15.7,形成压力为112~147 MPa,侵位结晶深度为4.1~5.4 km。岩石成因类型为A型花岗岩,形成于板内拉张构造环境,物质来源于上地壳部分熔融;(2)相山北部绿泥石为蠕绿泥石属于富铁绿泥石,形成于还原环境。绿泥石形成温度为230~271℃,平均值为258℃,属于中温热液作用范围;(3)花岗斑岩中铀的载体主要为黑云母包体中含铀副矿物。矿前期,热液流体交代黑云母形成绿泥石,使得黑云母内含铀副矿物中的铀活化转移为分散吸附状态的铀,被绿泥石等矿物吸附于矿物晶格表面或矿物裂隙为成矿期热液提供了铀源。Xiangshan uranium orefield is the largest volcanic-type uranium deposit in China. Granite-porphyries subtype uranium deposits in the northern part of Xiangshan uranium orefield account for 36.65% of the total reserves. Although systematic studies have been made on granite porphyries in the north of Xiangshan orefield,research on mineral chemistry in granite porphyries is rare. Based on the detailed chemical analyses of biotite and chlorite, this study discusses the formational conditions of biotite and chlorite from granite porphyries in the northern part of Xiangshan uranium orefield and their significance for diagenesis and mineralization. The results are as follows:(1) biotite belongs to Fe-biotite. Chemical composition of biotite suggests that granitic porphyries have high crystallization temperature of 721 ℃ to 753 ℃(average of 737 ℃) and their lgf(O_(2)) range from-14.8 to-15.7. Crystallization pressure for biotite is 112 MPa to 147 MPa with corresponding solidification depth of 4.1 to 5.4 km. Granite porphyries in the northern part of Xiangshan uranium orefield belong to A-type granite formed in the non-orogenic tectonic setting. In addition, granite porphyries originated from partial melting of upper crust.(2) Chlorite in the northern part of Xiangshan uranium orefield is Fe-rich prochlorite formed under reducing conditions. The temperature of chlorite ranges from 230 to 271 ℃(average 258 ℃);hence, it belongs to the region of mesothermal alteration.(3) The main carriers of uranium in granite porphyries are uranium-bearing accessory minerals enclaved in biotite. In the early metallogenic stage, chlorite was formed by hydrothermal metasomatism of biotite, making the uranium in uranium-bearing accessory minerals in biotite activated and transferred into a dispersive adsorbent condition. Active uranium was absorbed by minerals such as chlorite on the surface of mineral lattice or mineral fissures, which provided uranium source for the hydrothermal melt during the metallogenic stage.

关 键 词：黑云母 绿泥石 花岗斑岩 矿物化学特征 成岩成矿 相山北部 

分 类 号：P597[天文地球—地球化学]