冀东高板河矿床硫同位素特征及其对高于庄组硫化物及锰矿石成矿机制的约束  

Sulfur isotopic characteristics of the Gaobanhe deposit in East Hebei Province and their constraints on the processes of sulfide and Mn mineralization from the Gaoyuzhuang Formation

作　　者：高兆富[1] 朱祥坤[1] GAO ZhaoFu;ZHU XiangKun(MNR Key Laboratory of Isotope Geology,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]中国地质科学院地质研究所,自然资源部同位素地质重点实验室,北京100037

出　　处：《岩石学报》2024年第1期267-281,共15页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2022YFC2903401);地质联合基金(U2244210);中国地质调查项目(DD20221649);中国地质科学院基本科研业务费专项经费(J2012)联合资助.

摘　　要：河北兴隆县高板河矿床是我国典型的中元古代喷流-沉积(SEDEX)型多金属硫化物矿床,其矿石及赋存围岩类型多样,目前不同类型矿石的主导成矿机制及其成因关系尚存争议。本文聚焦该矿床代表性矿石的硫同位素特征,发现与富锰黑色页岩密切相关的条带状/纹层状黄铁矿矿石和含锰白云岩赋矿的块状、浸染状及脉状硫化物矿石的硫同位素组成呈明显的两端元分布特征:前者主要由自形程度较好的黄铁矿微晶组成,相对富集重的硫同位素(δ34 S值在+6.7‰~+27.1‰之间);而后者以粗粒他形黄铁矿为主,硫同位素组成明显偏轻(δ34 S值总体在-10.0‰~+5.0‰之间)。不同于传统SEDEX模型强调局限盆地硫化水体环境,本文结合前人对该时期海平面及沉积相变化的认识,提出高板河矿化是海侵向海退转化过程中局部热液喷流活动加强的产物。底板黑色页岩上覆于浅水台地相碳酸盐岩地层以及其下部赋存白云质结核等地质证据指示该套富锰黑色页岩属于海侵成因。海侵过程使得潮下带深水区域形成局部硫化水体环境,低浓度海水硫酸盐几乎完全被还原,使得具有明显沉积特征的条带状/纹层状黄铁矿矿石富集重的硫同位素,其δ34 S平均值与前人报道的同时期海水硫酸盐硫同位素组成基本一致。相比之下,含锰碳酸盐岩中大量叠层石出现、硫化物矿层的下伏围岩由黑色页岩横向上过渡为碳酸盐岩的“穿时”特征共同指示层状矿体形成于海侵向海退转换过程中的沉积相突变带。同时,广泛发育的热液交代等地质特征指示碳酸盐岩中硫化物成矿过程中热液活动加强,由于潮间带碳酸盐岩沉积-早期成岩环境中硫酸盐浓度较高,水岩界面附近发生硫酸盐热化学还原作用产生较大的硫同位素分馏,因此碳酸盐岩赋矿的块状、浸染状及脉状矿石的硫同位素相比海水硫酸盐明显偏轻。综上�The Gaobanhe deposit is one of the most typical Mesoproterozoic SEDEX polymetallic sulfide deposits in China.However,the types of its mineralization and the dominant mineralization process of its different ore types and their genetic relationships are still controversial.Here,we focus on the sulfur isotope characteristics of typical ore types,i.e.,the laminated/banded pyrite ores and the massive and vein-type sulfide ores,in the Gaobanhe deposit to study their sulfur isotope compositions.The laminated/banded pyrite ores are closely associated with Mn-rich pyritic black shales,while the massive and vein-type sulfide ores are mainly hosted in dolomite.A bimodal distribution of the sulfur isotope compositions occurred in these two types of ores:the fine-grained pyrites corresponding to the bedding-parallel layers or laminations are significantly enriched in heavy sulfur isotopes(δ34 S=+6.7‰~+27.1‰),while the coarse-grained,anhedral pyrites corresponding to main stage of sulfide mineralization(pyrite mounds,massive mineralization)have significantly lower sulfur isotope compositions(mostly between-10.0‰and+5.0‰).Unlike the traditional SEDEX model,which emphasizes the sulfate-limited water environment,we suggest that the Gaobanhe sulfide mineralization is a product of the enhanced hydrothermal activity during the transition of the transgressive-regressive sequence.Geological evidence,such as the presence of dolomitic nodules in the lower part of the black shale overlying on the shallow carbonates,indicates that this set of manganese-rich black shale belongs to the product of a large-scale marine transgressive event which led to the formation of a local sulfidic water environment.In this scenario,the complete reduction of seawater sulfate makes the bedding-parallel layers or laminations significantly enriched in heavy sulfur isotopes whose average value is generally consistent with the previously reported sulfur isotopic composition of coeval seawater sulfate.In contrast,the presence of a large number of stroma

关 键 词：高板河 SEDEX 中元古代 硫化物 硫同位素 

分 类 号：P597.2[天文地球—地球化学] P618.32[天文地球—地质学]