Compositional variations in manganese carbonate micronodules from the Lower Proterozoic Nsuta deposit, Ghana: product of authigenic precipitation or post-formational diagenesis?

The genetic significance of carbon and oxygen isotopic variations in Mn-bearing carbonates from the Palaeo-Proterozoic (∼2.2GA) Nsuta deposit in the Birimian of Ghana

“…Carbonate petrography indicates isotope values that concentrate within this zone (i.e I) are from manganese carbonate ore and Mn bearing phyllite that show least deformation and/or veining. In addition, primary sedimentary structures, as are mineral compositions, appear 27 to be much more preserved (Nyame et al 2002). Such carbonates are, therefore, referred to as least altered.…”

“…Contrary to the observations of John et al (1999), however, all available evidence suggests the metamorphism was low-grade. The preponderance of microcrystalline and microconcretionary carbonates, the presence of zoning and evidence of metastability as exemplified by carbonate mineral chemistry in some host rock microconcretions (Nyame 1998;Nyame et al 2002) suggest greater preservation of original depositional and/ or early diagenetic conditions of carbonate formation.…”

“…John et al (1999) and few other workers have argued that Birimian rocks, Nsuta inclusive, were metamorphosed to amphibolite facies and retrograded to greenschist facies conditions. According to Nyame et al (2002), however, available evidence suggests pervasive low grade greenschist facies metamorphism in the Nsuta rocks.…”

Geochemical studies on Permian manganese deposits in Guichi, eastern China: Implications for their origin and formative environments

“…Al 2 O 3 /TiO 2 ratio is the most useful indicator for the provenance of sedimentary rocks (Hayashi et al, 1997;Taylor and Mclennan, 1985) and acidic tuffs as well (Zhou and Kyte, 1988), because of remaining virtually constant during surface weathering and alteration of rocks (Hayashi et al, 1997). Volcanic activity not only generated volcanic-sedimentary Mn ore deposit (Liakopoulos et al, 2001;Nyame et al, 2002), but also provided source materials for other types of Mn deposits (Fan and Yang, 1999;Levasseur et al, 2004). An important source of the manganese in this area probably came from sea-floor volcanism or hydrothermal activity, perhaps associated with syn-sedimentary faults.…”

“…In contrast, Proterozoic, Devonian, Cretaceous and Oligocene Mn deposits are widely found elsewhere in the world ( Fig. 1) (Brusnitsyn and Zhukov, 2012;Fitzgerald and Gillis, 2006;Jach and Dudek, 2005;Munteanu et al, 2004;Nyame, 2008;Nyame et al, 2002;Polgári et al, 2012Polgári et al, , 2005Roy, 2006;Salas et al, 2008;Sethumadhav et al, 2010).…”