大横路铜钴矿含矿地层的物源区属性和沉积环境:对钴富集的制约  

Characteristics and depositional environments of the source rocks of the ore-bearing strata in the Dahenglu Cu-Co deposit:Constraints on the cobalt enrichment

作　　者：刘超辉 王慧宁[2] 朱志勇 田忠华 孙逊[3] LIU ChaoHui;WANG HuiNing;ZHU ZhiYong;TIAN ZhongHua;SUN Xun(School of Civil and Resource Engineering,University of Science and Technology Beijing,Beijing 100083,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;Guangzhou Marine Geological Survey,China Geological Survey,Guangzhou 511458,China)

机构地区：[1]北京科技大学土木与资源工程学院,北京100083 [2]中国地质科学院地质研究所,北京100037 [3]中国地质调查局广州海洋地质调查局,广州511458

出　　处：《岩石学报》2024年第10期2988-3009,共22页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2022YFC2903502);国家自然科学基金项目(92062214、42172221)联合资助.

摘　　要：大横路铜钴矿床位于胶-辽-吉古元古代构造带北段,是我国目前探明的以钴为主的大型变沉积岩容矿型铜钴矿床。然而,关于该矿床的含矿地层物源属性及沉积时的氧化还原条件,以及二者与钴成矿之间的联系尚不清楚。本次研究以采自钻孔的贫Co和富Co变碎屑岩以及老岭群地表出露的变质碎屑岩和碳酸盐岩作为研究对象,开展了详细的全岩地球化学以及C-O-S同位素研究,对比含矿与不含矿地层的物源属性、风化程度以及沉积时水体氧化还原环境的差异,进而探讨它们对Co(富Co硫化物)富集的制约。钻孔及地表的大栗子组变碎屑岩的地球化学特征表明含矿的大栗子组样品相对老岭群其他组样品更加富集Fe_(2)O_(3)^(T)和Sc且具有更低的Zr/Sc比值,这表明含矿地层中具有更多的镁铁质岩石来源的碎屑物质的输入。这与大栗子组中Hf含量小于8300×10^(-6)以及ε_(Hf)(t)值大于+2.3的碎屑锆石的比例更高是一致的。富Co的绢云千枚岩(变质页岩)相比贫Co样品具有更高的校正后化学蚀变指数CIA(大于83)、化学风化指数CIW(大于89)和斜长石蚀变指数PIA(大于85),这表明前者的母岩区经历了较高程度的化学风化,导致了含矿岩石中具有更高的黏土矿物含量。此外,富Co样品显示了更低的Fe^(3+)/Fe^(2+)比值,表明了其形成于相对较为还原的沉积环境。综上所述,在大横路铜钴矿的赋矿岩石大栗子组绢云千枚岩的原岩沉积时,其更高的基性源区组份、母岩区较高的化学风化程度以及相对较为还原的沉积环境为Co的初始富集提供了有利条件。这一研究结果为深入探讨该类型矿床的成矿机制提供了重要依据。The Dahenglu Cu-Co deposit,located in the northern part of the Paleoproterozoic Jiao-Liao-Ji orogenic belt,is a large metasedimentary-hosted Cu-Co deposit.Currently,there is a lack of research on the relationship between the sedimentary source feature and depositional redox condition of the ore-bearing strata and the cobalt mineralization.This study selects the representative borehole samples that are minimally affected by deformation,hydrothermal and epigenetic oxidation alteration,as well as the surface meta-siliciclastic and carbonate rocks of the Laoling Group,as key research objects.Detailed petrographic,whole-rock geochemistry and stable isotope studies are conducted to compare the differences between the ore-bearing and barren samples.Geochemical characteristics reveal that the ore-bearing samples of the Dalizi Formation have relatively higher Zr/Sc ratios,and Fe_(2)O_(3)^(T) and Sc contents compared to meta-siliciclastic samples from other formations of the Laoling Group,indicating more detritus derived from the Late Neoarchean and Middle Paleoproterozoic mafic rocks in the ore-bearing strata.This is consistent with the fact that a higher proportion of detrital zircons with Hf content less than 8300×10^(-6) andε_(Hf)(t)values greater than+2.3 occurred in the Dalizi Formation.When compared to the Co-poor samples,the Co-rich ones exhibit higher corrected CIA(chemical index of alteration;>83),CIW(Chemical Index of Weathering;>89)and PIA(Palgioclase Index of Alteration;>85),indicating a higher degree of chemical weathering in the source rocks,which leads to higher clay mineral contents in the ore-bearing rocks.Additionally,the Co-rich samples display lower Fe^(3+)/Fe^(2+)ratios,suggesting a more reducing depositional environment.In summary,the deposition of sericite phyllites of the Dalizi Formation which is also the host rock of the Dahenglu Cu-Co deposit was characterized by higher mafic source compositions with higher clay mineral contents resulting from a higher degree of chemical weathering in the sour

关 键 词：胶-辽-吉古元古代构造带 大横路铜钴矿 地球化学 物源属性 成矿地质背景 

分 类 号：P618.41[天文地球—矿床学] P618.62[天文地球—地质学]