Types,Characteristics,and Genesis of Lower Carboniferous Baizuo Formation Dolomite in Super-Large Huize Pb-Zn Orefield
Zhao Sibo
Liu Yingchao
Yue Longlong
Ma Wang
Zheng Ning
Tang Bolang
Abstract：The origin of dolomite in dolostone-hosted Mississippi valley-type(MVT)lead-zinc deposits has long been controversial.The Huize super-large lead-zinc deposit,situated in the Sichuan-Yunnan-Guizhou adjacent region,exemplifies a typical MVT deposit hosted within dolostones and dolomitized limestones,making it an ideal object for addressing the aforementioned issue.This study focuses on disseminated,banded,and blocky distal dolomite from the Lower Carboniferous Baizuo Formation of the Huize orefield.Through comprehensive petrographic analysis and cathodoluminescence(CL)microscopy,coupled with the examination of major elements,LA-ICP-MS in-situ compositional data,and carbon,oxygen,and strontium isotopic analyses,it systematically investigates the genesis of these dolomites.These characteristics indicate that the dolomite in the Baizuo Formation underwent formation through three distinct stages.The first stage—replacement powdered dolomite(Dol 1)—exhibits selective and fabric-retentive replacement,characterized by a blue-purple CL,a MgO/CaO ratio of 0.68,low iron(Fe)and manganese(Mn)contents,weak light rare earth element(LREE)depletion,negative europium(Eu)and cerium(Ce)anomalies,and a positive lanthanum(La)anomaly.The second stage—replacement fine-coarse crystalline dolomite(Dol 2)—shows fabric-retentive replacement and recrystallization,displaying a dark red-orange CL,a MgO/CaO ratio of 0.71,higher Fe and Mn contents compared to the first stage,slight LREE depletion,a negative Eu anomaly,and slightly negative to positive Ce anomalies.C-O and Sr isotopes fall within the range of Early Carboniferous seawater.The third stage—coarse crystalline dolomite cement(Dol 3)—fills cavities in dolostone,exhibiting alternating dark red and bright red CL bands,an average MgO/CaO ratio of 0.68,higher Fe and Mn contents,enriched middle rare earth elements(MREE),negative Eu anomalies,and no Ce anomalies.The results indicate that dolomitizing fluid in the first stage originated from localized oxidizing seawater.In the second stage,the dolomitization fluid comprised oxidizing to weakly oxidizing,saline shallow-burial pore waters.The third stage dolomitizing fluid is suggested to be Mn-rich deep-burial pore waters or residual seawater in a reducing environment.Based on the findings,in this paper it establishes the formation process of widespread dolomitization in the Baizuo Formation of the Huize Pb-Zn orefield.(1)The seepage-reflux dolomitization in near-surface to shallow burial environments lead to the formation of Dol 1 and Dol 2;(2)Recrystallization processes within burial environments alter dolomiteto form coarse crystalline dolostone;(3)During the post-diagenetic deep burial stage,Dol 3 precipitates in the cavities of the coarse crystalline dolostone.Therefore,the dolomite at both the proximal and distal extents exhibit similar characteristics and genetic mechanisms,and the dolomite in proximity to the ore body may have undergone alteration by hydrothermal fluids.
Keywords：Mississippi valley-type lead-zinc depositHuize lead-zinc orefieldBaizuo Formationdolomite genesismineral deposits
Publication Date：2025-04-30
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：27( 1353-1379 )