北秦岭东段晶质石墨矿床地质特征及成因探讨

Geological characteristics and genesis discussion of crystalline graphite deposits in the east section of North Qinling orogenic belt

北秦岭东段石墨矿是近年来陕西省新发现的大中型优质大鳞片晶质石墨矿床矿产地。矿体赋存于秦岭岩群雁岭沟岩组地层中,具有明显的层位特征。含矿岩石以石墨大理岩、石墨片麻岩、石墨石英片岩为主,石墨矿物呈浸染状集合体产出,鳞片片径大多大于0.147 mm,以正目石墨为主。本文通过变质岩原岩恢复、石墨碳质来源、成岩成矿环境等角度,对研究区晶质石墨矿矿床成因进行探讨,认为研究区δ^(13)C具有中间碳同位素特征,为有机物在还原环境下分解不彻底造成,其碳质来源于元古代沉积的含碳有机质。石墨矿品位及其分布主要与沉积相有关,推测晶质石墨由浅海相沉积的碎屑岩-钙泥质岩-碳酸盐岩中的有机碳在区域变质作用下变质形成。北秦岭东段晶质石墨矿为沉积变质成因。

The graphite deposit in the east section of North Qinling orogenic belt is a newly discovered large and medium-sized high-quality crystalline graphite deposit in Shaanxi Province in recent years.Theore body occurs in Yanlinggou Formation of Qinling Rock Group and has obvious stratigraphic characteristics.The ore bearing rocks are mainly composed of graphite marble,graphite gneiss,and graphite quartz schist.Graphite minerals are produced as disseminated aggregates,with scales mostly larger than 0.147 mm in diameter and mainly composed of orthorhombic graphite.This article explores for the genesis of crystalline graphite deposits in the study area from the perspectives of metamorphic rock restoration,graphite carbon source,and diagenetic and ore-forming environment.It is considered that the research area δ^(13)C has intermediate carbon isotope characteristics,which are caused by incomplete decomposition of organic matter in a reducing environment.Its carbon source comes from carbonaceous organic matter deposited in the Proterozoic era.The grade and distribution of graphite ore are mainly related to the sedimentary facies,and it is speculated that crystalline graphite is formed by the metamorphism of organic carbon in clastic rocks,calcareous mudstone rocks,and carbonate rocks deposited in shallow marine facies under regional metamorphism.The crystalline graphite deposits in the east section of North Qinling orogenic belt are of the sedimentary metamorphic origin.