Metallogenic process of the Precambrian graphite ores in the North China Craton and its response to the evolution of the Earth surface environment

Abstract

The North China Craton (NCC) is China's primary graphite production region, with over 90 % of the graphite ores from its Precambrian strata. Precambrian graphite ore formation in the NCC reflects coupled geological and environmental processes, but their relationship mechanism remains unclear. This paper, from the perspective of the evolution of earth surface environment, systematically analyzes the distribution pattern and metallogenic mechanism of Precambrian graphite ores in the NCC. Precambrian graphite ores are predominantly located at the margins of the craton and are primarily hosted within Paleoproterozoic strata. Precambrian graphite ores in the NCC are mainly regional metamorphic, with organic-derived carbon as the primary protolith carbon source. Their metallogenic process is a comprehensive response to the drastic changes of the surface lithosphere, biosphere, hydrosphere and atmosphere in the early Earth: 1) Numerous rift basins, formed by continental breakup and post-glacial sea level rise, provided ample space for carbon-rich protolith deposition. Concurrently, marine species innovation and biological productivity surges, linked to atmospheric oxygenation events, supplied the organic matter (OM) necessary for extensive carbon-rich protolith formation. 2) Cratonization and rift-related dynamic heat flow triggered regional metamorphism, activating carbon to form graphite crystals. These crystals grew further through thermal contact metamorphism, ultimately forming large-scale graphite ores. Although there is limited research on the feedback mechanisms of graphite mineralization on Earth's surface environmental evolution, the sedimentary areas for organic-rich protolites and regional metamorphic zones for carbon mineralization in the Precambrian period are superimposed to resulted in the formation of favorable metallogenic zones, where the magmatic thermal contact metamorphic zones are favorable exploration targets for high-grade crystalline graphite ores in the NCC.