ABSTRACT An organic-rich (gyttja) lake sediment geochemical survey was conducted over Lower Precambrian volcanic and associated rocks in northeastern Minnesota, for the purpose of determining the applicability of this method for evaluation of mineral resource potential and reconnaissance exploration. Two hundred and seventy samples were collected from 75 lakes over an area of 200 square miles (520 sq. km.).
A weak aqua regia leach on unignited gyttja produced the best contrast over background. Statistical analysis of the data indicates that trace element distributions are greatly dependent upon the limnological environment of each lake; trace elements tend to be concentrated in the organic and/or inorganic fractions of the gyttja; and, of all parameters considered, LOI (loss-on-ignition) is the best single indicator of limnological environment.
Due to the variations in lake environments and trace element accumulation in the gyttja, parameters other than the element concentrations were considered. However, the study indicated, even though a perfect datum for comparing lakes was not possible, the element concentrations for arsenic, cobalt, copper, nickel, lead, and zinc provided the best datum for comparing all 75 lakes.
Several significant anomalies were located by the survey. Anomalous copper was found in a lake near an interesting copper prospect. Copper, lead, titanium, and zinc appear to reflect bedrock composition; chromium, magnesium, and nickel reflect both bedrock composition
and glacial dispersion.
Report 73-3-1: Gyttja Lake Sediment Exploration Geochemical Survey of E. L. Vermilion-Ely Area, St.Louis Co. and Lake Co., MN; organic-rich lake sediment survey in T61N-63N R11W-16W; element maps (plates 1-11) & references.
(41 pages, 8.5 x 11 inches, 2.46 MB)
Authors: D.G. Meineke, M.K. Vadis, and A.W. Klaysmat
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See MN DNR Report 376, Minnesota Lake Sediment Geochemistry Surveys for compiled GIS geochemistry data from historic MN DNR lake and stream sediment survey reports including this report, 73-3-1.
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