The Penokean orogen and southern Animikie basin of cast-central Minnesota contain numerous carbonaceous units. The carbon content of these units ranges from as little as 1-2 wt.% to as much as 44 wt.%; the thickness of these units ranges from a few inches to over 500 feet. By using published values for the energy content of some Finnish and Swedish carbonaceous rocks, it is possible to estimate the energy content in samples from this study. These values indicate that a ton of rock with 44 wt.% graphite contains approximately as much energy as one ton of lignite or a half ton of bituminous coal. This suggests that such a rock contains roughly $13.50-19.00/ton worth of energy. In certain localities, the carbonaceous units also contain significant precious and base metal concentrations. Values of as much as 350 ppb gold and 6 ppm silver were recorded.
McSwiggen, Peter L.; Morey, G.B..
Information Circular 28. Graphite in Early Proterozoic Rocks of East-Central Minnesota.
Minnesota Geological Survey.
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