扬子北缘埃迪卡拉纪锰矿层中的古氧化还原条件对锰矿成矿过程的影响  

Redox conditions of the Ediacaran in northern margin of Yangtze Block and their implications for metallogenic processes

作　　者：王萍 崔旭 赵海彤 杜远生[3] 栾进华 张雄 罗旭 王健 WANG Ping;CUI Xu;ZHAO Haitong;DU Yuansheng;LUAN Jinhua;ZHANG Xiong;LUO Xu;WANG Jian(School of Resources and Environment,Henan Polytechnic University,HenanJiaozuo 454003,China;Chongqing Key Laboratory of Resource and Environmental Effects of Major Geological Events,Chongqing Institute of Geology and Mineral Resources,Chongqing 401120,China;School of Earth Sciences,China University of Geosciences(Wuhan),Wuhan 430074,China;Chongqing Huadi Resources Environment Technology Co.,LTD.,Chongqing 401120,China)

机构地区：[1]河南理工大学资源环境学院,河南焦作454003 [2]重庆地质矿产研究院,重大地质事件资源环境效应重庆市重点实验室,重庆401120 [3]中国地质大学(武汉)地球科学学院,湖北武汉430074 [4]重庆华地资环科技有限公司,重庆401120

出　　处：《古地理学报》2025年第2期338-350,共13页Journal of Palaeogeography:Chinese Edition

基　　金：国家自然科学基金项目(编号:42202111);生物地质与环境地质国家重点实验室开放基金(编号:GBL22107);河南省博士后基金(编号:HN2022027);河南省高等学校重点科研项目(编号:24A170019)资助。

摘　　要：扬子板块北缘埃迪卡拉纪锰矿赋存于陡山沱组上部的黑色页岩中,主要分布在城口次级盆地的边缘,目前对于锰矿形成时的氧化还原条件以及成矿模式等问题仍然存在争议,需要进一步研究。对于锰矿的成矿模式,目前主要有2种观点:一种认为菱锰矿直接从缺氧水体中沉淀,另一种认为水体中的Mn^(2+)首先被氧化,然后在沉积物中被还原成菱锰矿。本研究以陡山沱组上部的锰矿层为研究对象,对其进行系统的矿物组成和地球化学分析。结果显示,锰矿层中发现了少量的水锰矿,而水锰矿是一种锰的氧化物矿物,意味着在含锰矿物形成时,存在锰的氧化物中间产物,最终转化为菱锰矿。此外,锰矿层中TOC和TN具有明显的正相关关系,表明地层中的氮主要来源于有机质;TOC与Mn含量具有明显的负相关关系,表明锰矿形成过程中需要消耗有机质;锰矿层具有很高的δ^(15)N值(+7.22‰~+10.06‰,平均值+9.22‰),可能与有机氮的硝化作用有关,^(14)N富集的NH^(+)_(4)优先被氧化,导致剩余有机氮具有较高的δ^(15)N值,反映了当时表层水体处于氧化状态。因此,认为陡山沱组锰矿经历了Mn^(2+)被氧化然后被还原成菱锰矿的阶段,其成矿过程受到水体氧化还原状态的影响。该研究成果有助于进一步了解埃迪卡拉纪海洋的生物地球化学循环过程。The Ediacaran manganese deposits located in the northern margin of the Yangtze Block are found within the black shales of the upper Doushantuo Formation,predominantly occurring along the margin of the Chengkou Sub-basin.However,several key issues remain contentious,such as including the redox conditions and the metallogenic processes,which quire further investigation.Two primary metallogenetic models have been proposed:(1)rhodochrosite precipitates directly from an anoxic water column;and(2)dissolved Mn^(2+) is initially oxidized to Mn-oxides,which are then reduced to rhodochrosite within the sediments.This study focuses on the Mn-bearing layers of the Doushantuo Formation,analyzing the high-resolution mineral compositions and geochemical characteristics.The results reveal the presence of minor amounts of manganite,a Mn-oxide mineral,within the manganese deposits.This finding indicates that Mn-oxides likely served as a precursors in the formation of rhodochrosite formation.Additionally,a significant positive correlation between total organic carbon(TOC)and total nitrogen(TN)indicates that nitrogen in the sediments primarily originates from organic matter.Conversely,a negative correlation between TOC and manganese(Mn)content implies that organic matter is consumed during the process of manganese deposition.The Mn-bearing layers are characterized by elevated δ^(15)N values(+7.22‰ to +10.06‰,mean +9.22‰),which can be attributed to the nitrification of organic nitrogen.During this process,^(14)N-enriched NH~+_(4) is preferentially oxidized,resulting in an increase in the δ^(15)N of residual organic nitrogen.This implies that oxic conditions prevailed in the surface waters during the formation of rhodochrosite formation.Therefore,it is concluded that the manganese ore of the Doushantuo Formation underwent a stage of Mn^(2+) oxidation followed by reduction to rhombosite,with its mineralization process being influenced by the redox state of the water.This research further contributes to the understanding of the

关 键 词：埃迪卡拉系 陡山沱组 锰矿 氧化还原条件 氮同位素 

分 类 号：P611.22[天文地球—矿床学]