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| 新疆阿希金矿:古生代的低硫型浅成低温热液金矿床 | |
| 引用本文： | 翟伟,孙晓明,苏丽薇,贺小平,吴有良.新疆阿希金矿:古生代的低硫型浅成低温热液金矿床[J].地学前缘,2010,17(2):266. |
| 作者姓名： | 翟伟 孙晓明 苏丽薇 贺小平 吴有良 |
| 作者单位： | 1. 中山大学,海洋学院,广东,广州,510275 2. 中山大学,海洋学院,广东,广州,510275;中山大学,地球科学系,广东,广州,510275 3. 广州市地质调查院,广东,广州,510440 4. 新疆阿希金矿,新疆,伊宁,835000 |
| 摘 要： | 新疆阿希金矿床为一形成于古生代的低硫型浅成低温热液金矿床,矿床产于伊犁—中天山板块北部中天山北缘活动大陆边缘的吐拉苏火山岩断陷盆地中。其赋矿围岩为大哈拉军山组安山质火山岩和火岩碎屑岩,矿体呈脉状产于古火山口外围的环形断裂带中,主要金属矿物有自然金、银金矿、黄铁矿、白铁矿、毒砂、赤铁矿、褐铁矿以及微量的浓红银矿、硒银矿、硫锑铜银矿、角银矿等,非金属矿物有石英、玉髓、菱铁矿、方解石、绢云母、冰长石等,围岩蚀变作用主要有硅化、绢云母化、碳酸盐化和青盘岩化。矿床以富集Au、Ag、As、Sb、Bi、Hg、Se、Te、Mo元素组合为特征,Ag/Au比值小,为0.46～11.1。氢、氧、碳、硫及稀有气体同位素组成特征显示其成矿流体主要为循环大气降水;成矿流体盐度主要为0.7%～3.1%NaCl_(eqv),平均为2.2%NaCl_(eqv);成矿温度为120～240℃,平均190℃;最大成矿深度约700 m。沸腾作用是引起成矿流体中矿质发生沉淀富集的主要成矿机制,成矿作用过程中流体处于近中性pH值的还原环境,成矿时代介于晚泥盆世晚期((363.2±5.7)Ma)到早石炭世维宪期。其一系列特征显示该矿是一个典型的、形成于古生代的低硫型浅成低温热液型金矿床。矿床得以保存与矿床形成后很快被阿恰勒河组沉积盖层覆盖有关,从上新世开始由于印度板块对欧亚板块的碰撞挤压作用,天山造山带被快速抬升遭受风化剥蚀作用使矿床重新露出地表而被发现。阿希金矿的发现对于在中、新生代以前的造山带中寻找浅成低温热液型金矿床具有重要的借鉴和指导意义。 |
| 关 键 词： | 阿希金矿 低硫型浅成低温热液金矿 古生代 成矿流体 沸腾作用 矿床保存 |
Axi gold deposit: A Paleozoic low-sulfidation type of epithermal gold deposit in Xinjiang, China |
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| Zhai Wei,Sun Xiaoming,Su Liwei,He Xiaoping,Wu Youliang.Axi gold deposit: A Paleozoic low-sulfidation type of epithermal gold deposit in Xinjiang, China[J].Earth Science Frontiers,2010,17(2):266. | |
| Authors: | Zhai Wei Sun Xiaoming Su Liwei He Xiaoping Wu Youliang |
| Abstract: | Axi gold deposit, occurring in the Tulasu volcanic fault-basin in the Paleozoic active-continental-margin on the north side of the Yili-Central Tianshan Plate, is a low-sulfidation type of epithermal gold deposit formed in the Paleozoic era. The host rocks are andesitic and volcaniclastic rocks of the Paleozoic Dahalajunshan Formation, and the ore bodies occurred as veins in annular faults of an old caldera. Ore-related minerals consist mainly of native gold, electrum, pyrite, marcasite, arsenopyrite, hematite, limonite, and trace amounts of pyrargyrite, naumannite, polybasite, cerargyrite, etc, whereas gangue minerals consist mainly of quartz, chalcedony, sericite, calcite, siderite, adularia, etc. The main wall-rock alterations were silicification, phyllic alteration, carbonatization and propylitization. The deposit is characterized by enrichments of Au, Ag, As, Sb, Bi, Hg, Se, Te and Mo relative to average crust, and low Ag/Au ratios (0.46 - 11.1). The compositions of hydrogen, oxygen, carbon, sulfur and noble gas isotopes indicate that ore-forming fluids of the Axi gold deposit consisted predominantly of circulating meteoric water. The salinities of ore-forming fluid vary mainly from 0.7 to 3.1 wt% NaCl_(eqv), with an average of 2.2 wt% NaCl_(eqv). The homogenization temperatures are mainly of 120 to 240 ℃, with an average of 190 ℃, the fluid density is 0.73 to 0.95 g/cm~3, and thus the estimated maximum mineralization depth is about 700 m. The boiling of the ore-forming fluid had occurred, leading to the supersaturation of the hydrothermal solution and the deposition of ore metals. This is the main mineralization mechanism for quartz-vein type ores in Axi. The ore-forming fluid was buffered to a near-neutral pH in a reduced environment during mineralization. Geochemical and geological characteristics show that Axi is a typical Paleozoic low-sulfidation type of epithermal gold deposit. The preservation of this Paleozoic Axi deposit required a rapid covering by the sedimental cover of Aqialehe Formation after the formation of the deposit. Beginning in the Pliocene, the Tianshan had dominated by rapid thrusting and uplifting as a result of the collision and compression between India and Eurasia, which led to part of the deposit cover being eroded and the deposit reemerged. The discovery of Axi is therefore critical for guiding the exploration of epithermal gold deposits in pre-Mesozoic orogenic belts. |
| Keywords: | Axi gold deposit low-sulfidation type epithermal gold deposit Paleozoic ore-forming fluid boiling preservation of ore deposit |
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