Geology and geochemistry of sedimentary ferromanganese ore deposits, Woodstock, New Brunswick, Canada
University of New Brunswick
The Early-Silurian Woodstock Fe-Mn Deposits are a series of six, northeast-trending, low grade manganiferous-iron deposits in western New Brunswick that collectively represent the largest Mn resource in North America (194,000,000 tonnes; 13% Fe and 9% Mn). Recent expansion of Route 95 has allowed a more detailed local stratigraphy, mineralogy, and geochemistry of the Fe-Mn deposits within the context of the regional stratigraphy to ascertain the genesis of these deposits. Geological mapping during the field seasons of 2008 and 2009 has revealed six Lithofacies Associations (O, I, II, III, IV, V) within the area, that, generally, are lying conformably on top of each other. However complications due to folding and interbedding have resulting in juxtaposition of the lithofacies associations so they are not always in stratigraphic order. These lithofacies associations are composed of a turbidite-rich section of blue grey calcareous sandstone (O) overlain by black pyritic mudstone (I), associated mineralized and nonmineralized green (II) and red siltstone (III), and laminated to massive grey green calcareous sandstone (IV and V). Na/Mg ratios, chondrite-normalized REE patterns, and mineralogical evidence of rapid changes in ocean redox conditions suggest the Fe-Mn mineralized lithofacies were formed in the offshore zone of a continental shelf on a stable cratonic margin. Al-Fe-Mn ternary and SiO[subscript 2]/Al[subscript 2]O[subscript 3] binary plots developed from archived drill core data indicate the Fe-Mn mineralization was initially derived from hydrogenous-detrital sources without any indication of a hydrothermal input as a source of Fe and Mn.