内蒙古白乃庙铜矿床稳定同位素地球化学特征及其地质意义

内蒙古白乃庙铜矿床位于中亚造山带温都尔庙加里东增生带铜多金属成矿带，矿床包括南、北两个矿带，南矿带矿体产于白乃庙组绿片岩中，北矿带矿体主要产于加里东期花岗闪长斑岩体内。成矿作用大致分为早、中、晚3个阶段，分别以石英－黄铁矿，石英－黄铜矿、辉钼矿，石英、方解石－方铅矿、闪锌矿组合为标志。同位素测试结果显示：石英流体包裹体中的δ¹⁸O_H2O值在-3.2‰~5.5‰之间，δD变化范围为-94.2‰~-69‰，随着成矿作用的进行，δD基本不变，δ¹⁸O_H2O逐渐降低；热液方解石的δ¹³C_PDB为-5.4‰~-2.4‰，δ¹⁸O_SMOW为-3.1‰~10.9‰，随着成矿作用的进行，δ¹³C_PDB基本不变，δ¹⁸O_SMOW逐渐降低；硫化物的δ³⁴S值变化范围为-0.6‰~-6‰，显示出幔源硫的特征。碳、氢、氧、硫同位素显示南、北矿带不同成矿阶段流体主要来自岩浆系统，且南、北矿带间没有明显差异，但南矿带流体显示有更多大气降水和壳源物质的加入。结合矿床地质特征分析，认为在加里东期古洋壳经俯冲作用发生部分熔融形成花岗闪长岩岩浆，并沿着裂隙上升到浅部，带来成矿物质，对原始矿源层的成矿物质进行活化富集，在白乃庙岛弧带形成白乃庙斑岩铜矿床。

Stable Isotopic Geochemistry of the Bainaimiao Copper Deposit in Inner Mongolia and Its Geological Significance

The Bainaimiao copper deposit in Inner Mongolia is located in the Ondor Sum Caledonian copper polymetallic zone of the Central Asian Orogenic Belt. Copper mineralization in Bainaimiao is comprised of the northern and southern zones. The host rock of the southern zone is greenschist of the Bainaimiao Formation, while orebodies in the northern zone mainly occur in the Caledonian granodiorite porphyry. The metallogenic processes can be divided into early, middle, and late stage, which is characterized by mineral assemblages of quartz-pyrite, quartz-chalcopyrite±molybdenite, and quartz±calcite±galena-sphalerite, respectively. The δ¹⁸O_H2O and δD values of fluid inclusions in quartz range from -3.2 ‰ to 5.5 ‰ and from -94.2 ‰ to -69 ‰, respectively. The δD values are relatively constant, whereas the δ¹⁸O_H2O values decrease gradually from early to late stage. In addition, the δ¹³C_PDB and δ¹⁸O_SMOW values of hydrothermal carbonate minerals range from -5.4 ‰ to -2.4 ‰ and from -3.1 ‰ to 10.9 ‰, respectively. The δ¹³C_PDB values keep steady, and the δ¹⁸O_SMOW values reduce gradually during the mineralization processes. The δ³⁴S values of the sulfides range from -0.6 ‰ to -6 ‰ and are typical of mantle source. The C-H-O-S isotopic compositions of the southern and northern zones show that ore-forming fluids of different stage are mainly derived from magma system, and there are no obvious differences between these two zones. However, the fluids in the southern zone exhibit closer affinity to meteoric water and crustal substances. Combined with geological features of the deposit, it is concluded that the Bainaimiao deposit was produced by granodioritic magma that formed by anatexis under subduction environment, and the magma arose along fissures up to the shallow crust. These processes gave rise to the activation and enrichment of ore metals from source beds of the Bainaimiao strata, and the formation of the Bai naimiao porphyry copper deposit.