METAL CONCENTRATIONS IN COVER OVERLYING DULUTH COMPLEX NI-CU-PGE DEPOSITS, NE MINNESOTA
In a first round of field work, samples of unconsolidated material overlying the Spruce Road, Wyman Creek, and Skibo deposits in the Duluth Complex, along with background areas, were collected to determine effective sampling methods and to characterize the geochemical signature from the deposits in the overlying cover. Peat and sediment samples were collected with depth in conjunction with groundwater samples and were analyzed for major and trace element chemistry. Results show enrichment of median concentrations for Ni (262 ppm), Cu (439 ppm), Pd (15 ppb), and Pt (8.5 ppb) in Spruce Road samples (n=13) relative to background sites (median Ni= 45 ppm, Cu=63 ppm, Pd 2.5 ppb, Pt 5 ppb, n=12). Samples from Wyman Creek (n= 4) and Skibo (n=11) are not elevated in these elements when compared to background sites. Relative to sediment, peat samples are elevated in Ni, Cu, Pd, and Pt for Spruce Road and background sites. Peat samples from Wyman Creek and Skibo are similar to background peat samples. Both the 1976 survey over the Mesaba deposit and our preliminary data from Spruce Road, Wyman Creek, and Skibo indicate that Ni and Cu anomalies exist in the unconsolidated cover over Ni-Cu-PGE deposits, with the most substantial anomalies occurring in peat. It remains unclear to what degree these anomalies are caused by underlying mineralized bedrock versus mineralized till within the cover itself. Future sampling will attempt to address this uncertainty along with other processes-based questions related metal accumulation in peats.