新疆东准噶尔顿巴斯套金矿床成因:H-O-C-S-Pb同位素制约

Origin of the Dunbasitao Gold Deposit in Eastern Junggar, Xinjiang: H-O-C-S-Pb Isotopic Constraints

顿巴斯套金矿床位于新疆东准噶尔阿尔曼泰构造带东段北东侧,是目前该带上发现的典型金矿床。矿床中主要矿体赋存于下石炭统姜巴斯套组下段浅变质含碳细碎屑岩中,受NWW向的陡倾断裂构造控制。与金矿化密切相关的蚀变类型为毒砂-黄铁矿化、硅化和绢云母化。根据矿物共生组合及相互穿切关系,可将成矿期划分为四个成矿阶段:石英脉阶段、粗粒黄铁矿-石英脉阶段、细粒黄铁矿(毒砂)-石英脉阶段和石英-碳酸盐阶段,其中第三阶段为主成矿阶段,形成于张性环境。H-O同位素数据显示,主成矿阶段流体δ^(18)O和δD组成分别为1.1‰～3.9‰和-115.5‰～-120.6‰,指示成矿流体以岩浆热液为主,后期有部分大气水的参与; C同位素研究显示,成矿流体中δ13C的范围为-24.7‰～-25.4‰,是深源无机碳与地层有机碳不同程度的混合碳,深源流体对金的成矿具有重大影响,同时地层有机质也参与了金的运移和卸载;矿石中黄铁矿和毒砂的δ^(34)S分别为3.0‰～5.8‰和4.2‰～5.6‰,数值比较集中,指示成矿物质硫源具有岩浆硫特征,有深源硫参与;矿石中黄铁矿的Pb同位素组成基本一致, ^(206)Pb/^(204)Pb、^(207)Pb/^(204)Pb、^(208)Pb/^(204)Pb分别为17.875～18.102、15.483～15.625和37.699～38.148,指示成矿物质铅源以地幔铅为主,并同化了壳源铅,应是一种分别来自地幔和上地壳的混合铅。综合矿床地质特征及多元同位素分析,认为顿巴斯套金矿床为岩浆热液成因的构造破碎蚀变岩型金矿床,为早二叠世伸展构造背景下的构造-岩浆-流体活动综合作用的产物。

The Dunbasitao gold deposit is located in the northeastern part of the eastern Aermantai structural belt in Eastern Junggar,Xinjiang.It is the only one gold deposit found in the belt.Ore bodies are hosted in the first member of the Lower Carboniferous Jiangbasitao Group that comprises low-grade metamorphic clastic rocks.The deposit is controlled by the NWW trending and steeply dipping fault structures.The dominant types of alteration related to the gold mineralization include arsenopyrite-pyritization,silicification and sericitization.The hydrothermal ore-forming processes can be divided into four stages accoding to the mineral assemblages and the crosscutting relationships,i.e.,quartz vein;coarse-grained pyrite-quartz vein;fine-grained pyrite-arsenopyrite-quartz vein;and quartz-carbonate vein.The third stage is the main ore-forming stage,which was formed in an extensional environment.Theδ18O andδD values range from 1.1‰to 3.9‰and from?115.5‰to?120.6‰,respectively.The H-O isotopic signatures indicate that the ore-forming fluids was dominated by magmatic water with the participation of some meteoric water.Theδ13C values of the ore-forming fluid range from?24.7‰to?25.4‰,indicating that carbon of ore-forming fluid is a mixture of inorganic carbon from deep source and organic carbon from strata at varing proportions.It is obvious that gold mineralization is closely related to the deep-source fluid,and the organic carbon derived from sedimentsry strata in this area plays an important role on transportation and unloading of the deep-sourced gold.Theδ34S values of the pyrite and arsenopyrite form the Dunbasitao ores range from 3.0‰to 5.8‰and from 4.2‰to 5.6‰,respectively,indicating the sulfur is mainly magmatic origin with the participation of deep-source sulfur.The 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb values of the pyrite from the Dunbasitao ores range from 17.875 to 18.102,from 15.483 to 15.625,and from 37.699 to 38.148,which suggest a mixed Pb source of the mantle and upper crust.Based on the H,O,C,S and Pb isotope geochemical signatures of the ores,combined with the comprehensive studies on geological characteristics and metallogenic tectonic setting of the ore deposit,we argue that the Dunbasitao gold deposit is an altered rock type deposit which is a type of structure-controlled magmatic hydrothermal ore mineralization,and formed in an extensional setting related to lithospheric extension in the Early Permian in Eastern Junggar.