The Chemistry of Manganese Ores through Time: A Signal of Increasing Diversity of Earth-Surface Environments

The Iron Biogeochemical Cycle Past and Present

“…Such environments are found commonly in stratified lakes (Canfield et al, 1995) and marine sediments (e.g. Froelich et al, 1979) and must have contributed to the deposition of the massive Mn ore deposits occasionally found in the rock record (Calvert and Pedersen, 1993;Krauskopf, 1957;Maynard, 2010;Tsikos et al, 2010).…”

“…Particles from the upper part of the chemocline are rich in Mn (oxyhydr)oxides, but these disappear within 5 to 10 meters depth as the settling particles are quickly reduced by aqueous Fe(II) which accumulates in the lower lake. This rapid reaction may place constraints on the circumstances surrounding the massive deposition of MnO 2 as has occurred in some ancient marine basins, and is the basis for massive sedimentary Mn accumulations (Maynard, 2010;Tsikos et al, 2010). The results from Lake Matano suggest that the deposition of massive Mn deposits required either a very shallow water column or that the concentration of Mn 2+ considerably exceeded aqueous Fe(II) in the basin.…”

New insight into the origin of manganese oxide ore deposits in the Appalachian Valley and Ridge of northeastern Tennessee and northern Virginia, USA

“…The coupling of Ba and Mn has been used to describe primary Mn oxide precipitation in a euxinic marine basin environment (Maynard, 2010), but recent reevaluations of the paleoenvironments of the host sediment sequences (the Shady/Tomstown Dolomite, Erwin/Antietam Sandstone, and Rome/Waynesboro Formation) do not find any evidence for early Paleozoic anoxic basins in the study areas (Hageman and Miller III, 2016;Smoot and Southworth, 2014). The source of the Ba is unclear, but Mississippi Valley Type (MVT) hydrothermal ore deposits containing barite are known throughout the Cambrian sediments of the central and southern Appalachains (Kesler et al, 1997 and references therein) and many of these locations either partially or completely overlap with the Mn oxide ore locations described throughout the cental Appalachians ( Figure 1).…”

“…Th, Nb, and Y contents were used to parse out additional geochemical differences within fresh water systems (Figure 17), as the high field strength elements show differences between karst-hosted, sedimentary-hosted, and volcanichosted deposits (Maynard, 2010). Although a karst-hosted origin can be eliminated for all of the samples in this study, there is too much overlap between the other reference units to make any further determinations using this method.…”

“…In most large ore bodies, Mn oxide ores have been assumed to have an abiotic source (Maynard, 2003;Maynard, 2010;Roy, 1992), although several studies do suggest a biogenic origin for Mn oxide oncolites and pisoliths deposited in shallow marine systems (Gutzmer et al, 2002;Ostwald, 1990;Reolid and Nieto, 2010), and for those associated with cherts or black shales (Hein and Koski, 1987;Polgári et al, 2012). Supergene enrichment due to weathering of existing deposits is consistent with the low temperature of associated quartz mineralization (<120 °C) at the Shouns Prospect in the Mountain City Window, as well as a biological source of Mn oxide formation, as downwardmoving Mn 2+ rich fluids would have originated from porewaters in organic-rich soils containing a variety of common Mn oxidizing microbes (He et al, 2008).…”