Geological characteristics and genesis of crystalline graphite deposits in the North margin of Upper Yangtze Block

Graphite ore is a kind of important national strategic protection resource.In order to deepen the understanding of the genesis of crystalline graphite ore in the northern margin of the Upper Yangtze Block, the ore-bearing strata, ore body characteristics, ore structure and ore geochemical characteristics of many graphite deposits in the area have been studied.It was found that graphite ore was mainly distributed in the Nanjiang-Wangcang area of Sichuan, forming a graphite mineralization zone extending about 60 km from the northeast-southwest direction, and graphite ore has a tendency to increase the thickness of the ore body and the degree of crystallinity in this direction.The main and trace element proxies (SiO₂, Al₂O₃, V/Cr, Ni/Co, etc.) reflect the formation of the ore-bearing rock series in a relatively limited, oxygen-deficient shallow carbonate platform environment.This environment is conducive to the preservation of carbon, which provide material sources for graphite ore formation.The δ¹³C of graphite ore is between -24.9‰ and -14.2‰, which overlaps the distribution range of δ¹³C of organic matter, indicating that the carbon of graphite ore comes from biological organic matter.The surrounding rock of the graphite mine contains characteristic metamorphic minerals such as sericite, biotite, garnet, andalusite, indicating that it is a set of low-green schist facies shallow metamorphic rocks.The fixed carbon content in the contact part of the magmatic rock and the graphite ore increases significantly and is accompanied by the increase of the scale structure, indicating that the thermal contact metamorphism of the rock mass promotes the further enrichment of the graphite ore.A three-stage metallogenic model of graphite deposits in the study area is initially proposed, inclunding the Mesoproterozoic primary carbonaceous sedimentation enrichment stage, Mesoproterozoic to Neoproterozoic regional metamorphic graphite nucleation stage, and Neoproterozoic rock mass thermal metamorphic crystal growth and mineralization stage.This study will provide basic materials for in-depth understanding of the formation mechanism of graphite ore in the study area and the genesis of China's crystalline graphite ore.