Preliminary Study On The Characteristics And Genesis Of Nanhuashan Graphite Deposit In Yihuang,Jiangxi Province

The Nanhuashan graphite deposit is located in the Wugongshan uplift belt of the Yun(Kai)-Kui(Ji)front edge pleat belt in the southeast orogenic belt of the Huaxia plate.The main stratigraphy of the mining area are Nanhua-Sinian System Hongshan Formation(NhZh)and Cambrian System Waiguankeng formation((?)1-2W).The graphite ore is deposited at the bottom of the Waiguankeng formation,the ore bodies are stratified and layered-like.Through the light microscopic and scanning electron microscopic(SEM)observation,the main minerals of the metamorphic rocks are quartz,muscovite,biotite,plagioclase,graphite,sillimanite,and so on.The lithology is mainly schist-granitic-quartzite,indicating the degree of metamorphism is middle to high grade.The mineral composition,mineral morphology and their correlation of metamorphic rocks suggest that their original rocks are sedimentary rocks and are a set of argillaceous clastic rocks.Based on the analysis of the major,trace and rare earth elements in the metamorphic rock series of the deposit and the related geochemical diagrams,it is further inferred that the primary rock of the metamorphic rock series is sedimentary rock,and its material source is probably felsic rock of the upper crust;the tectonic environment of the primary rock may be continental margin environment.The main,trace and rare earth elements of late Caledonian granite in the mining area indicate that it is S-type.The granite occurs in the continental collision fold belt and is the product of orogenic belt.Carbon isotope measurements of graphite in representive ores show that organic carbon is the main source of carbon in the graphite deposits.Previous measurements show that the metallogenic age of adjacent graphite deposits is 424 Ma,which coincides with the Caledonian granite diagenetic age(415 Ma)within the range of measurement error.It is speculated that the genesis of graphite deposits is closely related to Caledonian magmatic intrusion in the area.The magamatic activity provided heat source for the metamorphic processes.Based on the above analysis and regional tectonic evolution,it is inferred that the geotectonic location of the mining area is in a stable rift basin from late Neoproterozoic to Early Paleozoic,forming a hydrostatic stagnant environment and depositing a set of hydrostatic shallow-sea muddy-sandy clastic sedimentary formations represented by the Waiguankeng Formation,which is the source bed of graphite deposits.The Caledonian tectonic movement in this area underwent extensive regional metamorphism,which provided temperature and pressure conditions for the recrystallization of organic carbon into flaky graphite ore.Based on the geological and geochemical charateristics,the genesis of the Nanhuashan graphite deposit can be identified as sedimentary metamorphic type.The formation and late superimposed alteration of the deposit mainly experienced three stages:(1)deposition of organic matter enriched sedments,(2)formation of graphite ore caused by regional metamorphism,and(3)the alteration caused by later structural and magmatic activities.