GOLD GRAIN COUNTS IN GLACIAL TILLS, VERMILION GREENSTONE BELT, NORTHEASTERN MINNESOTA

A small orientation project to determine the variability of glacial till in the Mud Creek area of northeastern Minnesota's Vermilion Greenstone Belt demonstrates that gold grains and pathfinder elements are present at elevated levels in some basal till samples, and anomalous samples have high contrast to regional background levels. Clastic and chemical variations within the sample set are sufficient to consider using the basal till as a sample media for gold dispersal mapping. Several of the 32 samples in the sample population returned anomalously high concentrations of pathfinder elements and gold grains, up to 1,282 gold grains per 10 kg of –2mm sample, and pristine gold grain proportions up to 98%; 8,050 ppb gold in HMC (nonmagnetic heavy mineral concentrates); and 1,050 ppb gold in –63um fraction of till. A suite of bedrock grab samples collected as reference mineralization returned assays up to 12,247 ppb Au, and silver concentrations up to 42,500 ppb. Analytical results for the till sample set confirm the hypothesis that clastic dispersal trains of mineralized material exist in tills in the area. These results are proportionately comparable to more extensive regional evaluations conducted in neighboring Ontario, and confirm anomalous soil and fine fraction gold values found in earlier Vermilion Greenstone Belt studies. The gold grain counts add a transport distance value to the chemical measurements of gold content in the soils and till. Particulate gold is more abundant in basal till samples than in the thin surface drape of meltout till, and till having a lacustrine sediment component. Till analysis in this part of the Vermilion Greenstone Belt, particularly for gold grains, provides a capability to positively detect areas of local, previously unrecognized mineralization both inside and outside of areas of detailed bedrock geologic mapping.