COMBINED MICRO-ANALYSES OF CARBONACEOUS MATERIAL ASSOCIATED WITH APATITE IN AN EOARCHEAN BANDED IRON FORMATION FROM THE NUVVUAGITTUQ SUPRACRUSTAL BELT, QUEBEC, CANADA

Banded iron formations (BIFs) are among the oldest types of sedimentary rocks on Earth and organic remains of primitive microorganisms may be preserved in them. Establishing the pathways of carbon that produced graphite is challenging because Eoarchean metasedimentary rocks, such as those from the Isua Supracrustal Belt (ISB), Akilia Association, and Nuvvuagittuq Supracrustal Belt (NSB) have been highly metamorphosed. Protracted metamorphic events could potentially introduce foreign sources of carbon in rocks or produce ¹³C-depleted graphite from decarbonation reactions or by other non-biological pathways. Preliminary analyses of organic carbon in microdrilled powders from NSB BIFs revealed δ¹³C_org values down to -35‰ and there are hints that values may be even more ¹³C-depleted. Apatite grains mapped in thin sections of amphibole+magnetite BIFs from the NSB were found to be metasomatic in origin as they were often associated with complex networks of remobilized magnetite and amphibole veinlets. In comparison, quartz+amphibole+magnetite BIFs also from the NSB have apatite grains mostly in the quartz matrix and these are occasionally associated with carbonaceous material (CM). Laser scanning Raman analyses of these mineral associations revealed that the CM has strong G- and D-band peaks (at ~1575 cm^-1 and ~1345 cm^-1, respectively) characterized by low full widths at half maximums (FWHM) consistent with partly disordered graphite that likely crystallized at high temperature. One such particle of graphite associated with apatite was found to host curled graphite structures identified by an unusually strong D*-band (at ~2700 cm^-1). This apatite-associated graphite particle was extracted with a focused ion beam (FIB) extraction technique in preparation for transmission electron microscopy (TEM) and synchrotron-based scanning transmission X-ray microscopy (STXM). These new results will be compared with similar microscopic mineral associations from BIFs from the ISB and from the quartz-pyroxene rock from the Island of Akilia. This multidisciplinary and multi-techniques approach provides nanoscale resolution characterization of the structure and geochemistry of graphite and has great potential to shed light on the origins of graphite in Eoarchean metasedimentary rocks.