THE EARLY SILURIAN WOODSTOCK FERROMANGANESE DEPOSITS, NEW BRUNSWICK, CANADA: A STRATIGRAPHIC, DEPOSITIONAL, AND PALEOENVIRONMENTAL ANALYSIS

The Woodstock manganiferous banded iron formations (BIF's) are known to be one of the largest Mn resources in North America and were mined as a source of Fe from 1848 to 1884. Six major ferromanganiferous bodies were identified by gravimetric surveys (circa 1954) and are hosted within the Late Ordovician to Early Silurian White Head Formation and conformably overlying Silurian Smyrna Mills Formation. The strike of these BIF's extends from Jacksontown to Plymouth, western NB (Canada), and similar deposits are known to occur nearby in Maine (USA). These BIF's have sharp, conformable contacts and are associated with red shale and (or) green shale facies, that have been deformed and metamorphosed to subgreenschist-grade during the Devonian Acadian Orogeny. Mineralogic data from four drill holes (archived core) at the Plymouth Mn-Fe deposit exhibit a Mn-rich assemblage of braunite (Mn⁺²Mn₆⁺³SiO₁₂), hausmannite (Mn₃O₄), with crosscutting veins of sursassite (Mn⁺²₂Al₃(SiO₄)(Si₂O₇)(OH)₃) with 12.0% Mn and 17.86% Fe within the main ore assemblage.

Geologic mapping of the I-95 highway section from Houlton, Maine to Woodstock, NB and areas south of the highway section identified several previously unknown BIF's trending parallel to the northeast strike of the bedrock within Irish Settlement (~5 meters thick) and Green Road (~0.3 meters thick) areas of NB. Sharp contacts between the BIF's and the surrounding strata indicate a rapid change in redox and depositional conditions. The Green Road exposure comprises a BIF with interbedded and crosscutting pyrite. Asymmetrical ripple marks within this outcrop, and regional strata, indicate a shallow marine depositional environment for the ferromanganiferous units and surrounding stratigraphic facies.