陕西省煎茶岭金矿C、H、O、S、Pb同位素地球化学示踪

C, H, O, S, Pb Isotopic Geochemistry of the Jianchaling Gold Deposit,Shaanxi Province

陕西省煎茶岭金矿床位于勉一略一阳三角区东北部，勉略缝合带南侧。矿体受F1-45断裂及次级断裂控制。根据矿物共生组合及脉体穿切关系，可将成矿期划分为三个阶段：（I）石英一黄铁矿一白云石细脉，含少量硫化物，变形强烈，形成于变形早期或同构造变形期；（Ⅱ）石英一多金属硫化物一碳酸盐细脉，发育大量铬云母；（Ⅲ）白云石一方解石一石英一雄黄一雌黄细脉，形成于张性环境。H、o同位素数据显示，早阶段成矿流体的6D值平均为-76．5％o，6180。值变化于7．5％o～21．1％o，类似于变质水，晚阶段8D值为一81％o，6180w变化于2．5％o～7．7％o，接近大气降水线，指示初始成矿流体为变质流体，晚阶段向大气降水演化。C同位素研究显示，早阶段成矿流体6”Cc02为-2．4‰-2．6‰，中阶段成矿流体δ13Ccoz为一1．9‰-0．4‰，晚阶段为-5．0‰～1．6‰，指示早阶段成矿流体来源于碳酸盐岩地层的变质分解，晚阶段有大气降水的混入。矿石S同位素显示较高的正值，集中于10‰～15‰，与断头崖组地层一致，指示成矿物质与断头崖组地层有关。相比于赋矿围岩，矿石Pb同位素具有更低的放射性成因铅，指示成矿物质需要有另一更低放射性成因铅的物质端元，即地幔物质的加入。总之，初始成矿流体以变质流体为主，成矿流体及成矿物质可能主要来源于围岩，另有少量深部（地幔）物质加入。

The Jianchaling gold deposit in Shaanxi province, China, is located to the south of the Mianlue suture zone. The ore bodies were controlled by fault F1-45 and the secondary faults. The hydrothermal ore-forming processes can be divided into three stages according to the mineral assemblages and the crosscutting relationships of the veinlets as follows: (I) quartz-pyrite-dolomite vein with poor sulfides which was strongly deformed in a compressional or transcompressional setting; (II) quartz-polymetallic sulfides vein, characterized by large amount of fuchsite; and (III) dolomite-calcite-quartz-orpiment-realgar veinlets. The δ18OW and δD values of early stage fluids range from 7.5‰ to 21.1‰, with an average of 13.3‰, and from-85‰to-70‰, with an average of-77‰, respectively;while theδ18OW of late stage fluids range from 2.5‰to 7.7‰, with an average of 6.5‰, and the average value of δD is-81‰. This H-O isotopic signature suggests a shift from metamorphic water towards meteoric water. δ13CCO2 values of the ore-forming fluid range from -2.4‰ to 2.6‰ in stage I, from -1.9‰ to 0.4‰ in stage II, and from -5.0‰ to 1.6‰ in stage III, respectively, indicating that the ore-forming fluids were derived from metamorphic devolatilisation of carbonate strata. The δ34S values of the Jianchaling ores (10.0‰~14.3‰) suggest that the sulfur was mainly sourced from evaporation strata. The Pb isotope ratios of the ores have less radiogenic Pb isotope than the host rocks, and suggest that the ore-forming fluids, which interacted with the wallrocks to form ores, must have been sourced from a depleted mantle or a depleted subducting oceanic slab. In combination with the H, O, C, S and Pb geochemical signatures of the mineral systems, we argue that the initial ore-forming fluid is mainly metamorphic extracted from the dehydration of the wall rocks, and the ore-forming materials might have derived mainly from the wall rocks with mantle input.