Graphite from Palaeoproterozoic enhanced carbon burial, and its metallogenic legacy

Abstract

The episode of widespread organic carbon deposition marked by peak black shale sedimentation during the Palaeoproterozoic is also reflected in exceptionally abundant graphite deposits of this age. Worldwide anoxic/euxinic sediments were preserved as a deep crustal reservoir of both organic carbon, and sulphur in accompanying pyrite, both commonly >1 wt %. The carbon- and sulphur-rich Palaeoproterozoic crust interacted with mafic magma to cause Ni–Co–Cu–PGE mineralization over the next billion years, and much uranium currently produced is from Mesoproterozoic deposits nucleated upon older Palaeoproterozoic graphite. Palaeoproterozoic carbon deposition has thus left a unique legacy of both graphite deposits and long-term ore deposition.

The origin and fate of organic carbon in graphite-manganese bearing rocks and implications for the Lomagundi-Jatuli Event

“…A major criticism of the canonical LJE model is the lack of geological evidence for organic-rich rocks in the Palaeoproterozoic era 12,13,14 . However, the global occurrence (Figure 1A) of graphite-rich rocks chrono-correlated with the LJE reinforces the idea that large amounts of organic matter were buried during this time interval 15 . Furthermore, detailed analysis of some of these occurrences indicate that they are associated with Mn-rich rocks that are temporally related to the Great Oxidation Event (GOE) 16 .…”

“…This way, our work helps to solve the enduring puzzle of the most signi cant positive carbon isotope anomaly in the history of our planet. Furthermore, as noted by Parnell et al 15 , the presence of Paleoproterozoic graphite deposits around the globe suggests that an unusually high amount of carbon burial may have had a signi cant impact on Earth's carbon budget following the GOE. Supporting this view, the association of metamorphosed organic-rich successions with manganese sequences, as reported in this study, reinforces a causal link between manganesecarbonaceous sedimentation and the climatic-biological crisis 59 .…”

“…Based on the above assumptions, we believe that during these orogenic events, crustal thickening due to regional metamorphism of organicrich rocks has led to devolatilization and consequent graphitization of these ancient organics. Hence, the prolonged duration of the Lomagundi event could be attributed to the elevated gross primary organic productivity and e cient sequestration of organic carbon that occurred during the mountain-building period 15 . This way, our work helps to solve the enduring puzzle of the most signi cant positive carbon isotope anomaly in the history of our planet.…”

A Case History of Graphite Exploration in North Norway Integrating Various Geophysical Surveys

“…Parnell et al [19] highlighted that more than 80% of the world's major graphite deposits can be traced back to paleoproterozoic rocks formed about 2.0-2.2 Ga. Paleoproterozoic graphite is found on every continent and in abundance with high-grade graphite deposits containing high levels of total carbon in the Baltic (Fennoscandian) Shield stretching across Norway, Sweden, Finland, and Russia. We focus on graphite mapping in Northern Norway, specifically the Vesterålen province where > 50 occurrences have been found.…”

Proterozoic large igneous provinces and implications for paleogeographic and paleoenvironmental reconstructions

“…通过不同层位火山灰(或斑脱岩)夹层的高精度锆石 CA-ID-TIMS U-Pb 定 年，有望获得元古宙时期黑色页岩的沉积速率. 另外，由于大部分元古宙黑色页 岩富含页岩气等能源矿产 [105,106,108,111,112] ， 黑色页岩变质后还会形成石墨等战略性 矿产资源 [113] ，元古宙黑色页岩的资源能源潜力也是未来值得关注的方向之一. (6) 与大火成岩省相伴的区域性抬升剥蚀作用研究：前岩浆期穹窿状地壳抬 升是与大火成岩省及地幔柱相伴生的一种普遍现象 [114,115] .…”