投稿时间：2021-02-20
修订日期：2022-04-29
网络发布日期：2022-07-07
中文摘要:陕西宁强县中坝锰矿床形成于扬子地块西北缘伸展裂陷沉积环境内，是近年新发现的锰矿床，赋存于下寒武统牛蹄塘组黑色岩系内，含锰岩系岩性主要为含碳粉砂质板岩、含碳泥质板岩、硅质岩，夹有灰岩条带和灰岩透镜体，矿石类型为层状、似层状的含锰硅质岩及条纹条带状的含锰灰岩，含锰矿物主要为硬锰矿，可见极少量的菱锰矿。对中坝一带MnⅠ号锰矿体常量及微量元素地球化学特征分析表明：中坝锰矿体相对围岩亏损Ti和Al元素，SiO2/Al2O3比值较高，Th含量低，Y/Ho比值高，且含锰岩系的PAAS标准化的稀土元素配分模式具有轻稀土元素亏损、重稀土元素富集、Ce负异常、Y正异常的特征，与现代海水稀土元素配分模式一致，说明海水自生沉积作用对含锰岩系中元素的富集具有重要影响，陆源碎屑物质的影响较小；含锰岩系的Al/（Al+Fe+Mn）、Fe/Ti、（Fe+Mn）/Ti、U/Th、Sr/Ba比值、δEu及SiO2-Al2O3图解、Fe/Ti-Al/（Al+Fe+Mn）图解、Lg （U）-Lg （Th）图解、Fe-Mn-（Cu+Co+Ni）×10图解、La/Yb-REE图解、δEu-Mn图解均表明锰矿沉积为热水沉积和正常海水混合作用的结果。含锰岩系的δCe、V/Cr、V/（V+Cr）、Ni/Co比值、富集U、V、Mo等特征表明锰矿形成于还原-硫化的沉积环境。中坝锰矿的形成机制为在弱碱性、还原、富CO32-的条件下，Mn2+和CO32-结合形成菱锰矿而沉淀。由此总结出中坝锰矿的成矿模式为：在早古生代，富含Fe、Mn多金属的硅质热水溶液沿着刘家坪古火山通道上涌，上涌的热水与海水混合，在弱碱性、还原、富CO32-的条件下，Mn2+和CO32-结合形成菱锰矿而沉淀，形成Fe、Mn硅质岩，且在沉积凹陷处成矿更有利，溶于海水中的Mn同碳酸盐一同沉淀，形成含锰灰岩。
Abstract:The Zhongba manganese deposit in Ningqiang County, Shaanxi Province is formed in the sedimentary environment of the extensional rift on the northwestern margin of the Yangtze block. It is a newly discovered manganese deposit in recent years. It occurs in the Lower Cambrian Niutitang Formation black shale series, and the main lithology of manganese-bearing rock series is carbon-bearing silty slate, carbon-bearing argillaceous slate, and siliceous rock, with limestone bands and limestone lenses. The ores are stratiform and layer-like manganesebearing siliceous rock and striped-banded manganese-bearing limestone, the manganese-bearing minerals are mainly psilomelane, with a very small amount of rhodochrosite. The analysis of the major and trace elements geochemical characteristics of the orebody MnⅠ at the Zhongba deposit indicates that:the manganese ore is depleted in Ti and Al relative to the wall rock, and the ratio of SiO2/Al2O3 is higher, with low Th content and high Y/Ho ratio, the PAAS standardized REE patterns of manganese-bearing rock series have the characteristics of depletion in light REE, enrichment in heavy REE, Ce negative anomaly and Y positive anomaly, which is consistent with the REE patterns of modern seawater, indicating that the seawater authigenic sedimentation has an important impact on the enrichment of elements in manganese bearing rock series, and the impact of terrigenous clastic materials is small. the Al/(Al+Fe+Mn), Fe/Ti, (Fe+Mn)/Ti, U/Th, Sr/Ba, δEu and SiO2-Al2O3 diagram, Fe/Ti-Al/(Al+Fe+Mn) diagram, Lg(U)-Lg(Th) diagram, Fe-Mn-(Cu+Co+Ni)×10 diagram, La/Yb-REE diagram, δEu-Mn diagram of the manganese-bearing rock series show that the manganese ore deposition is the result of the mixture of hot water and normal seawater. The characteristics of δCe, V/Cr, V/(V+Cr), Ni/Co and enrichment of U, V, and Mo in the manganese-bearing rock series indicate that manganese ore was formed in a reduction-sulfur rich depositional environment. The formation mechanism of the manganese ore is that, under the conditions of alkalescence, reduction and rich CO32-, Mn2+ and CO32-combine to form rhodochrosite and precipitate. The ore-forming model of the Zhongba manganese deposit is summarized as follows:in the Early Paleozoic, the Fe and Mn polymetallic rich siliceous hot water solution ascended along the Liujiaping volcanic channel; the upwelling hot water solution was mixed with sea water, resulting in the formation of rhodochrosite and precipitation of Fe-Mn siliceous rocks under the conditions of alkalescence、reduction and rich CO32-. The ore-forming conditions in the sedimentary depression zone are more favorable, and the Mn dissolved in the seawater precipitates together with the carbonate forming the manganese-bearing limestone.
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基金项目:本文得到中陕核工业集团公司科技攻关项目（编号：61180102）、中陕核工业集团公司院士工作站科研项目（编号：R-YS190101）、陕西省自然科学基础研究计划项目（编号：2021JQ-985）和陕西省地勘基金项目（编号：61201405264）联合资助
引用文本：
纪冬平,王朋,高政伟,仇金林,江宏君,程博兴,王淮.2022.陕西宁强县中坝锰矿床地球化学特征及成矿模式[J].矿床地质,41(3):469~488JI DongPing,WANG Peng,GAO ZhengWei,QIU JinLin,JIANG HongJun,CHENG BoXing,WANG Huai.2022.Geochemical characteristics and metallogenic model of Zhongba manganese deposit in Ningqiang County, Shaanxi, China[J].Mineral Deposits41(3):469~488
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