Regional Geochemical Analysis of Lower Paleozoic Strata, Western Wisconsin

Abstract

Lower Paleozoic clastic strata of western Wisconsin were deposited during a series of transgressive marine incursions into the mid-continent in Cambrian to Ordovician time. These strata consist of intercalated sandstone, siltstone and shale that form a series of fining-upward/coarsening upward stratigraphic cycles resulting from repetitive sea level changes. The coarser grained units (i.e. Wonewoc and Jordan Fms.) are highly valued by the silica sand industry for their consistent grain size, shape and rounding. The finer grained units (Eau Claire and Lone Rock Fms.) are too fine grained to be utilized for silica sand and are considered waste rock by the silica sand industry. The materials need to be removed, stored and reclaimed during the mining process. Concern has been raised about potentially high levels of trace metals and phosphorous in these units that could pose an environmental hazard. A regional analysis of the whole rock major and trace metal geochemistry of these finer-grained units will constrain the composition of these rocks and permit an assessment of the environmental danger posed by these strata. Initial results indicate that these strata do not contain elevated levels of trace metals and do not represent an environmental hazard.