Minnesota DNR mineral tests find gold grains

Recent minerals testing near Soudan, MN, showed some unusually high counts of gold grains, according to the Minnesota Department of Natural Resources (DNR). Of the 32 samples collected to characterize sediments in the area, 28 had counts ranging from 0 to 10 grains, which is normal, but four samples contained unusually high gold counts ranging from 67 to 641 grains. The gold particles are microscopic in size, too small to be visible to the unaided eye. Finding gold grains in the area isn’t a big surprise. The area was prospected during the 1860s Vermilion gold rush and some bedrock gold mineralization was found during an exploration episode in the 1980s. But the recent discovery of high numbers of pristine gold grains may be significant. “These are the highest gold grain counts we’ve seen in Minnesota,” said project leader David Dahl, a DNR geologist in Hibbing. “Samples with more than 30 gold grains are uncommon. The fact that 45 to 98 percent of the gold grains in the high count samples are pristine suggests they haven’t been moved long distances by glaciers.” The raw test samples consisted of two-gallon pails of glacial till - unsorted sand, gravel and clay above the bedrock - from widely separated sites on public lands. The test area is north of Highway 169 between Soudan and Ely, part of the Vermilion greenstone belt. Overburden Drilling Management, Ltd., Nepean, Ontario, processed the samples. “We collected some samples down-ice from known gold occurrences in the bedrock to see how much gold might be carried in glacial till,” Dahl said. “But, other samples with high pristine gold counts are not linked to known sources.” “This indicates a potential for the existence of one or more previously unrecognized local sources,” said Dr. Harvey Thorleifson, Minnesota Geological Survey director. Thorleifson, an authority on indicator mineral methods, helped design the project. “With the current high price of gold and a state mineral lease sale scheduled for Oct. 13, mineral exploration interest in the area may increase,” said Dennis Martin, DNR senior geologist for mineral resources. The mineral lease sale is a competitive process by sealed bid. If public lands are leased, further exploration and testing will likely be done to determine whether the high gold grain counts can be traced to a bedrock source. If there is exploration interest, land owners in the area might receive inquires from exploration companies. “Project results so far suggest that glacial till can be useful in mineral evaluations of the greenstone belt,” Martin said. “There is enough variation in the gold grain values to warrant further mapping activities.” Martin cautioned, however, that the discovery of more gold grains doesn’t mean gold mining is on the horizon. “This is further evidence of gold in Minnesota,” Martin said. “Whether gold mining will ever be economically feasible in this area is yet to be determined.” Geological mapping and research in the area have been ongoing by the University of Minnesota Natural Resources Research Institute and the Minnesota Geological Survey. The DNR is the administrator of state mineral rights for public lands. Revenue from state mineral leasing of School Trust lands benefits school districts and the University of Minnesota. Revenue from tax forfeit lands benefits the local taxing district. The gold grain report is available from the Minnesota DNR. Additional information will be released to the public as it becomes available. Information on Minnesota mineral leasing can be found on the DNR Web site at http://www.dnr.state.mn.us/lands_minerals/leasesale/index.html For more information on the orientation project, contact David Dahl at dave.dahl@dnr.state.mn.us.