CHARACTERIZATION OF MANGANESE OXIDES FROM SHENANDOAH VALLEY (VIRGINIA): FORMATION CONDITIONS AND ENVIRONMENT

Manganese oxide nanomaterials, including MnO and MnO₂, have attracted great interest for environmental purposes and industrial application. In spite of their economic and environmental significance, geoscientists continue to debate how manganese oxides form and what mechanisms determine which of the manganese oxides are likely to form. Manganese ores are found in many parts of the United States, however they do not occur in economically viable concentrations in most regions in the eastern United States. However, deposits of manganese oxides and iron oxides are abundant in the Shenandoah Valley and have been mined there for more than 100 years. The present study focuses on eight manganese oxide samples from the abandoned Crimora Mine (Augusta County, Virginia). Over 160,000 tons of manganese ore were mined at Crimora in the period of maximum production from 1882 to 1915. The mine workings are scattered across about 0.8 Km² area. The ore body occurs as irregular masses and lenses in clay bed on quartzite bedrock. The origin of manganese oxide deposits in the Shenandoah Valley is still uncertain and the clear mineralogical identification of the manganese oxides is limited. This research aims to identify the minerals belonging to the manganese oxide group in Crimora samples and to elucidate the origin of manganese deposits that occur in residual clays along the western slopes of the Blue Ridge based on mineralogical and physical features. The mineralogical and chemical characterization of samples from Crimora mine was performed using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and inductively coupled plasma - optical emission spectrometry (ICP-OES). A comparison with literature data and chemical data from this study was carried out to shed light on the past environment and conditions under which the Crimora manganese oxides formed. Results on Crimora samples suggest a mixed origin in different environments with varying biological, sedimentary, and low temperature hydrothermal conditions. A complex origin with variable conditions is in agreement with the irregular conglomerate masses and lenses observed in the Crimora ore body.