Abstract The Quartzite-type crystalline graphite deposit of East China, which is developed in the South Sulu ultrahigh-pressure (UHP) metamorphic belt, represents a medium-sized crystalline graphite deposit. The ore bodies primarily occur within the Banzhuang Formation of the Donghai Group, with their strata-bound occurrence, indicating a sedimentary-metamorphic origin. In this study, petrological, mineralogical and geochemical investigations were conducted on the ore-bearing strata. The quartzite-type graphite ores mainly consist of graphite-bearing diopside quartzite and graphite-bearing sericite-quartz schist. These ores typically occur as lenticular bodies that predominantly preserve early-stage ductile deformation features. The characteristic mineral assemblage (diopside + quartz + calcite + graphite + garnet) suggested amphibolite-facies metamorphic conditions, with the ore type classified as massive crystalline graphite. Major element geochemistry revealed enrichment in SiO 2 and Al 2 O 3 , moderate contents of Fe 2 O 3 and K 2 O, and depletion in CaO and MgO. Protolith analysis indicated the quartzite-type graphite ores were derived from graywacke and claystone deposited in a continental margin to continental island arc setting. Carbon isotope analysis revealed that the organic carbon isotopes (δ 13 C) ranged from −30.8 % to −32.2 %, indicating that the graphite was of biogenic origin. Raman spectroscopy analysis demonstrated well-developed crystallinity of the graphite, suggesting its formation under medium-to high-temperature metamorphic conditions between 430 and 655 °C. Zircon U–Pb geochronology of the graphite ores revealed a dominant age population with a weighted mean age of 733 ± 16 Ma, indicating that magmatic rocks formed during the middle-late Neoproterozoic served as the primary source for the terrigenous clastic components in the Quartzite-type crystalline graphite deposit’s metamorphic sequence. Subsequently, these rocks underwent medium- to high-grade metamorphism accompanied by regional dynamo-thermal metamorphism, which transformed the organic matter into crystalline graphite. It was noted that the ore-bearing strata could be affected by Cretaceous magmatic activity of 110 Ma.
Zhang et al. (2026) studied this question.