南非Postmasburg地区锰矿床地质特征及成因分析

Geological Characteristics and Genesis Analysis of Deposits in Postmasburg Area,South Africa

以南非Postmasburg地区Bishop、Paling两个矿区为研究载体,将研究区的地层划分为6个岩性单元,自下而上分别为白云岩单元、铁锰矿体单元、铁质细砂岩/铁质砾岩单元、泥质粉砂岩单元、石英岩/Gamagara页岩单元和Paling页岩单元。识别出了沉积受变质型、堆积型和锰质软泥或锰土型三类矿床,并讨论了其成因模型。根据地层序列特征,将研究区的发育与演化过程划分为4个阶段。分析表明:锰质软泥或锰土是富锰白云岩遭受溶蚀后的残余物。沉积序列各单元为渐变关系,而与白云岩单元之间为不整合接触关系。三种矿床类型都与白云岩的岩溶系统有关,锰质软泥或锰土中的锰来源于富锰白云岩,另外两种则可能来源于安山岩。两次岩溶系统之后分别形成了沉积受变质型矿床和堆积型矿床。成矿后期矿体受到Marthaspoort石英岩的保护而保存下来。

Bishop and Paling mining areas in Postmasburg district are taken as the target of research, and six lithologieal units are identified for the stratum, which are dolostone unit, iron—manganese ore unit, ferruginous fine sandstone/ferruginous conglomerate unit, politic sihstone unit, quartz/Gamagara shale unit and Paling shale unit. Three types of ores, sedimentary—metamorphism, cumulate type, and manganese mud or wad type, are identified and the genetic models are discussed. According to the depositional sequence, the development and evolution process of the study area is divided into four stages. The result shows that manganese mud or wad is the residues of the manganese-rich dolostone after corrosion. The units in the depositional sequence have a gradual transition relationship while the depositional sequence is unconformable with dolostone. All of the three types of ores are related to the karst system, and Mn in the manganese mud or wad origins from manganese-rich dolostone, while in the other two types probably origins from andesite. The sedimentary—metamorphism type and cumulate type of ores are formed after karst system respectively. The orebodies are preserved with the protection of Marthaspoort quartz after metallogenesis.