TRACE MINERAL ANALYSIS OF GLACIOGENIC SANDS FROM THE GREAT MIAMI RIVER SYSTEM IN SOUTHWESTERN OHIO: EVALUATING COMPLEX MINERAL ASSEMBLAGES AND THE POTENTIAL OF CRITICAL RESOURCE MINERALS

Rare earth elements (REEs) are a critical resource for energy efficiency and economic independence as are several other metals (e.g., silver). The extent and nature of REE-bearing minerals at the trace level in common aggregates is often not considered in mining and production operations, as the primary focus is often on products related to construction infrastructure, transportation, and traditional geotechnical applications. Geologic settings exist where such minerals may occur at trace concentrations in potentially recoverable forms. One such setting is extensive glacial deposits of southwestern Ohio where REE-bearing minerals may occur in the fine sand size fraction of quarried aggregates. This is because these minerals are hard, dense, resistant to alteration, and likely ultimately sourced from Canadian igneous and metamorphic rocks during the last glacial maximum. Whether these minerals are common, and/or occur at concentrations to be of economic interest within these regional glaciogenic sands (or elsewhere) is currently uncertain.

A preliminary scanning electron microscopy (SEM) investigation of samples near Ross, Butler County, Ohio from both the active sediment load of the Great Miami River and an active sand and gravel mine has identified several minerals of potential interest. Rare earth element-bearing phosphates are observed to occur in the active sediment load of the Great Miami River on the order of 10 micrometers in diameter. Silver flakes of a range of morphologies are also observed in sample material from an active sand and gravel mine from older (presumed Pleistocene) deposits approximately 7 km to the northeast. Trace or minor gold is observed in some silver flake particles, with some approaching gold contents of ~5%.

These preliminary analyses open up several questions regarding the diversity and occurrence of trace minerals in glaciogenic sands in southwestern Ohio and throughout similar settings across the Midwest of the United States. The origin, concentration, and spatial distribution of these minerals, and variation thereof, should be examined in further detail to assess the geologic and economic relevance of these minerals in these settings.