新疆喀什凹陷乌拉根铅锌矿床有机质特征及其地质意义

Characteristics and geological significances of the organic matter in the Wulagen Zn-Pb deposit,Kashi sag,Xinjiang

乌拉根铅锌矿床位于新疆喀什凹陷北部,矿区及外围发育大量有机物质,有机质与铅锌成矿的关系备受关注。文中采用有机质抽提、族组分分离、定量及饱和烃色谱-质谱等实验分析方法对铅锌矿区有机物质及外围油砂中氯仿沥青"A"和生物标志物进行分析,研究铅锌矿区及外围有机质特征及其地质意义,并对有机质与铅锌矿化的关系进行了探讨。结果表明,近矿围岩和外围油砂中氯仿沥青"A"族组成及其饱和烃的主要生物标志物特征均较相似,CPI=1.11～1.17,Pr/Ph=0.68～1.08,C27、C28、C29规则甾烷具有C27>C28<C29的分布特征,规则甾烷/17α(H)-藿烷为0.55～0.93,C29/C30藿烷=0.36～0.52,说明矿区及外围有机质来源一致,且主要为陆相页岩。生物标志物特征OEP=1.01～1.15,C31-αβ22S/(22S+22R)=0.56～0.58,βα-莫烷/αβ-藿烷=0.13～0.21,表明矿区及外围有机质的成熟度均较高。所有样品的Pr/Ph比值均较低(小于0.85),且所有样品均检出一定量的伽马蜡烷,说明有机质经历了较高盐度的还原条件。本次研究的所有样品的饱和烃气相色谱基线"鼓包"现象不明显,说明有机质生物降解作用弱。结合矿区地质、岩相学、矿相学和岩石地球化学特征,认为成矿流体为盆地油田卤水,而下白垩统克孜勒苏群第五岩性段紫红色岩石的褪色就是这种含有有机质的还原性流体造成的。由于成矿流体中有机质烃类与赋矿地层中SO2-4发生反应生成H2S,而H2S的生成是铅锌大量沉淀成矿的主要原因。

Wulagen zinc-lead deposit in Xinjiang Province is located in north margin of Kashi sag. Large quanti- ty of organic matter exists in the mining area and the periphery of Wulagen zinc lead deposit, and the relation ship between organic matter and zinc-lead mineralization has attracted the attention. By the organic extraction, family components separation and quantitative, saturated hydrocarbons chromatogram-mass spectrum, the chloroform bitumen ＂A＂ and biomarkers were analyzed, and the characteristics of the organic matter and its geological significances and the relationship between organic matter and zinc-lead mineralization were dis- cussed. The chloroform bitumen＂A＂ family components and main eigenvalues of biomarkers in the wall-rocks and the periphery of Wulagen zinc-lead deposit have a similar and smaller variational range （CPI= 1.11 - 1.17; Pr/Ph=0. 68- 1. 08; Cer, Ce8 and C29 sterane has a pattern of C27〉C28〈C29; steranes/17a（H）-hopanes= 0. 55 - 0. 93; C29/C30 hopanes=0. 36 - 0. 52）, indicating that the organic matter have the same nature and origin, and the organic matter were derived mainly from continental shale. The features of biomarkers （OEP= 1.01 - 1.15%C431aBhopane 22S/（22S＋22R）=0. 56 - 0. 58; flrMO alkyl/aBhopane=0. 13 - 0. 21） show a high maturity of the organic matter in the mining area and the periphery of Wulagen zinc-lead deposit. The Pr/Ph ratio of the samples were low （〈0. 85） and all samples were detected having a certain amount of gammaeerane, indicating that organic matter has undergone a high salinity and reduction conditions. The ＂hump＂ phenomenon of gas chromatography base- line of saturated hydroearbons is not obvious, suggesting that the organic matter biodegradation effect was weaker. Combining these with the characteristics of geology, petrography, mineragraphy and geochemistry of the mining area, it is suggested that the ore-forming fluids was the basin oil-field brine, which contained organic matter with reduction fluid and thus made the fifth member of Lower-Cretaceous Kezilesu Group purple rock faded. Because the hydrocar- bons of organic matter in ore-forming fluids reacted with SO24- to produce H2 S, the H2 S generation was the main cause of the lead and zinc precipitation and mineralization.