秦岭大巴山地区紫阳毒重石矿床成因:矿石组构、氧化还原敏感元素和碳-氧同位素证据  

Ore-genesis of the witherite deposit in Ziyang,Shaanxi Province:Evidence from ore texture,redox-sensitive trace elements and C-O isotopes

作　　者：罗莉[1] 皮道会[1,2] 杨競红[1] 吴赫嫔[1] 

机构地区：[1]南京大学内生金属矿床成矿机制研究国家重点实验室,地球科学与工程学院 [2]中国地质大学资源学院,武汉430074

出　　处：《岩石学报》2012年第12期4021-4030,共10页Acta Petrologica Sinica

基　　金：科技部973项目(2013CB835000);国家自然科学基金项目(40803013;41230102)联合资助

摘　　要：秦岭大巴山地区钡矿资源极为丰富,以蕴含世界罕见的层状毒重石矿床为特色。本研究在紫阳毒重石矿床中发现了玫花瓣状结构,经显微镜观察和电子探针分析表明,玫花瓣体由板柱状重晶石呈放射状排列而成,与前人报道的矿物组成明显不同。紫阳灰黑色毒重石矿石有较高的V、Ni、Cr、U、Mo含量,较低的Th/U比值(<0.04),较高的V/(V+Cr)比值(>0.8)和V/(V+Ni)比值(>0.9),指示寒武纪紫阳毒重石矿床的沉积环境为较还原的环境。紫阳毒重石矿石的C同位素分布在-10.9‰～-16.0‰,O同位素分布在18.1‰～22.3‰之间,表明毒重石中CO32-是有机质通过氧化作用或脱羧基(生物有机质降解)作用提供的低13C的碳与同期海水提供的高13C的水溶性HCO3-或CO32-的混合来源。综合研究表明,该区毒重石矿床的形成可能与寒武纪早期的海底热液成矿作用有关。Qinling-Daba Mountains region is extremely rich in mineral resources of barium,characterized by widespread occurrence of the world＇s unique stratiform witherite deposit.In this study,we found the rose petal-like structure of witherite ores in the witherite deposit at Ziyang,Shaanxi Province.Microscope observation and electron microprobe analysis showed that the rose petal-like structure is composed by slab and column barites.This structure may have formed from pore fluids during early diagenesis.Redox-sensitive trace element analysis indicates high concentrations of V,Ni,Cr,Mo and U in the witherite ores,with low Th/U ratios（〉0.04）,and high V/（V＋Cr）（〉0.8） and V/（V＋Ni） ratios（0.9）,suggesting a reduced sedimentary environment for the witherite deposition.Carbon and oxygen isotope analysis show the witherite ores have δ^13C values of-10.9‰--16.0‰ and δ^18Ovalues of 18.1‰-22.3‰,indicating a 12C-rich biogenic carbon source possibly resulting from degradation,polycondensation and dehydroxylation of bio-organic matter in sediments at the early stage of diagenesis,mixing with a 13C-rich seawater-derived HCO^3-or CO3^2-.In combination all the previous and present data,we suggest that the deposition of the witherite ores were likely related to the Early Cambrian sea-floor hydrothermal fluids.

关 键 词：毒重石矿床 玫花瓣状结构 氧化还原敏感元素 碳氧同位素 紫阳矿床 南秦岭 

分 类 号：P578.61[天文地球—矿物学] P595[天文地球—地质学]