2883 Ma commencement of BIF deposition at the northern edge of Congo craton, southern Cameroon: New zircon SHRIMP data constraint from metavolcanics

Abstract

The deposition of BIF is linked to a contemporaneous process in which clastic sediments from the continent were being deposited in the ocean along with the upwelling of hydrothermal fluids at the Mid-Ocean-Ridge (MOR) (Bau and Möller, 1993; Clout and Simonson, 2005 and Beukes and Gutzmer, 2008). Lavas intercalated with BIF provide a direct tool for constraining the timing of BIF formation in a paleobasin. The determination of BIF depositional age is vital to date key events in the evolution of the biosphere. Precise age constraints on the iron formation across the world both advance our understanding of BIF genesis and enable current stratigraphic and tectonic models to be evaluated. This paper dates for the first time BIF deposition within the Ntem Complex at the Northern edge of the Congo Craton by SHRIMP U-Pb method using zircons separated from associated volcanic material (Fig. 1). In addition, zircons separated from a surface BIF sample in the region are also dated to determine if other BIF depositional events occurred after the Archean phase of BIF formation. These results provide new insights for the correlation of Gondwana fragments in Africa (Congo craton) with those of South America (São Francisco craton) and also allow a better comprehension of the relation between volcanism and BIF deposition in pre-Gondwana break-up setting. Overview of geology The Ntem Complex represents the extension of the northern edge of the Congo Craton in Cameroon. Mesoarchean to Neoarchean charnockitic rocks usually of TTG composition (Takam et al., 2009 and Shang et al., 2010) and greenstones associated with metasedimentary formations make up the basement rock suit of the Ntem Complex (Shang, 2001; Pouclet et al., 2007 and Shang et al., 2007). Rocks of the TTG suite are strongly mylonitized and retrogressed along the thrust boundary with the Pan-African Yaounde Group (Takam et al., 2009). Late high-K granites and dolerite dykes generally younger than the TTG and greenstone belts occur as intrusions clearly distinct from the older TTG (Shang et al., 2007, 2010) (See Fig. 2). These have been interpreted as a heat source for remelting TTG and charnockites to generate high-K granites thus suggesting the coeval nature of doleritic magmatism and high-K New SHRIMP data for zircons separated from a metadacite interbedded with banded iron formation (BIF) in the Mbalam region of southern Cameroon provide a 2883±20Ma age for the commencement of BIF deposition in the Congo craton. Separated zircons from the associated metadacite are brown and euhedral to subheral in form with distinct oscillatory zoning typical of magmatic signatures. These zircons lack internal resorption features and serrated zone boundaries as should be expected of zircons inherited from the surrounding basement rocks or multiple magmatic plumbing events. However, zircons from a surface BIF sample collected ~ 60km west of the sequence from which the metavolcanics were sampled show a different age spectrum (Palaeoproterozoic, 1.0-2.0 Ga) suggesting a latter stage of B...

New detrital zircon U-Pb ages from BIF-related metasediments in the Ntem Complex (Congo craton) of southern Cameroon, West Africa

“…The Ntem Complex is part of the Congo craton and represents the oldest lithologic group in Cameroon. This complex hosts several iron deposits at various stages of resource definition and development (see [23][24][25]39] and www.sundanceresources.com.au, www.afferro-mining.com).…”

“…In this paper we characterize metasediments associated with BIF in the Ntem complex and date detrital zircons from them in order to unravel their provenance and the palaeodepositional environment. The mineralogy, age and the structural setting of the BIF have been reported [23][24][25]39].…”

“…Major and trace elements compositions of the samples were obtained by ICP-OES and ICP-MS at a commercial laboratory (Acme Analytical Laboratories Ltd., Vancouver, Canada) and the details are provided in [39].…”

“…Analyses of the zircon grains were also done at the RSES and the procedure is recorded in [39]]. The data were processed using the SQUID I Excel Macro of [43,44] and the decay constants of [45] were employed.…”

Geochemical Constraints on the Origin of Banded Iron Formation‐Hosted Iron Ore from the Archaean Ntem Complex (Congo Craton) in the Meyomessi Area, Southern Cameroon

“…Camiron Ltd., Caminex Ltd., Camina Ltd., Aucam Ltd., G‐stones Resources Ltd.; Divine Mining Ltd., and Geocam Mining Ltd.) have carried out field surveys and preliminary geochemical tests. The exploration results have revealed that the high magnetic anomalies are related to magnetite‐rich BIFs, such as in the Mbalam (Suh et al, ; Chombong & Suh, ), Nkout (Suh et al, ) and Bikoula (Teutsong et al, ) areas. Moreover, new iron‐rich bodies, namely, Elom (Ganno et al, ), Grand Zambi (Ganno et al, ), and Kouambo (Ganno et al, ), have been discovered in the Ntem Complex.…”