Information Circular 43. Background Levels of Mercury and Arsenic in Paleoproterozoic Rocks of the Mesabi Iron Range, Northern Minnesota

Abstract

This study was primarily designed to calculate background levels of mercury and arsenic in the Biwabik Iron Formation of the Mesabi range. A second objective was to evaluate the ability of various laboratories to provide analytical data for mercury and arsenic that is reasonably priced yet sufficiently reliable for the purpose of environmental screening. Mercury and arsenic where present in sufficient concentrations are considered to be hazardous substances. They may be naturally occurring, of anthropogenic origin, or some combination thereof. To establish natural background levels and to reduce the possibility of anthropogenic sources, 191 samples of the Biwabik Iron Formation were collected from drill-core sites located south of the Mesabi range (Fig. 1). Ten samples of the overlying Virginia Formation were also analyzed for comparison. Four of the selected sites were jointly drilled by the Minnesota Geological Survey and the Iron Range Resources and Rehabilitation Board (IRRRB) in 1966 and 1967; principal facts for these holes are summarized in Pfleider and others (1968). The fifth site, U.S. Steel 17,700 was drilled sometime in the 1950s, and the core was donated to the Minnesota Geological Survey in the late 1960s; principal facts for it are summarized in Morey and others (1972).