Geochemical exploration feasibility study within the zone of continuous permafrost, Coppermine River region, N W T
Authors: Hornbrook E H W , Allan R J 
Published: September 2015

During the summer of 196 9, the author s conducted a geochemical exploration feasibility study in the Coppermine River Basalt Belt, immediately north of Dismal Lakes, Coppermine Rive r are a, N. W. T. primarily to evaluate geochemical exploration methods in
areas of continuous permafrost, The study was secondarily concerned with the detection of copper mineralization in this basalt series. Because this was a feasibility study , samples were collected from a variety of surficial materials, O / A , B and C horizons o f s oils; mineral soil samples
from silty frost boils; stream sediment s ; vegetation and lake waters, Most of t h e sample s cam e from the vicinity o f a known copper ore body (the 47- Zone of the Coppermine River L td.) and a miner a li zed quartz vein (the 1 3 - Showing of the Coppermine Rive r Ltd.). Lake waters were
sampled in 25 lakes over an area of about 100 square miles. Background frost boils were sample d on a 25 - mile traverse line across the study area. Analysis of all samples was by hot nitric acid leach and atomic absorption spectroscopy. A study of copper con centration in 25 lakes revealed that 4
lakes were anomalous, 7 were threshold and 14 were background. Anomalous concentrations were greater than 15 ppb Cu, threshold were about 8 ppb and background about 2 ppb. Significantly, 2 of the 4 anomalous lakes were adjacent to the 47 - Zone. Anomalous concentrations of copper in stream
sediments were found only in the two streams which crossed the 47-Zone. For these two, concentrations immediately downstream from the ore body were three to four fold (about 3, 000 ppm Cu) those upstream from the ore body (about 800 ppm Cu) in a background area. O/A horizons were not an entirely
satisfactory sample material for exploration purposes because of prolonged time and effort required for collection. Anomalous and regional background B horizon concentrations, 1, 000 ppm Cu and 70 ppm Cu respectively, defined an anomalous zone immediate! y downslope from the 47-Zone ore body. Silty
frost boils were collected on only one line across this ore body. A comparison of the anomalous to background ratios for silty frost boils, B horizon and O /A horizon on this line shows the following: silty frost boils, 60 - fold; B horizon, 25-fold; and O/A horizon 50 - fold. At three sites
material from the C horizon in the thawed zone , immediately above the permafrost in the vicinity of the 47 - Zone, had substantially higher (17-fold in one case) copper concentrations than B horizon material at the same sites . The phenomenon of increasing copper concentrations with depth was
also found in silty frost boils at the 13-Showing, but the increase was considerably less pronounced (a maximum of 2-fold) and occurred only very close to the mineralized quartz vein. Regional background obtained by analysis of 8 silty frost boil samples collected on a 25 - mil e traverse is in the
order of 45 ppm Cu (range from 20 to 71 ppm Cu). At the 13 - Showing analysis of silty frost boil surface sample s showed dispersion of Cu to be limited to 100 to 200 feet downslope from t h e vein. Results of biogeochemical studies (76 samples were collected over the 47- Z one) indicate that
flowering shrubs in stream valleys and certain lichens have an exploration potential. Dispersion of metals in this area by both physical and chemical processes is sufficient to develop geochemical halos in lakes, stream sediments and soils. Based on the results of this feasibility study, the
following multistage approach for geochemical mineral exploration in the Coppermine Basalt Belt would appear to be effective: (1) lake water analysis (one axis of the lake should be at least 1, 000 feet, followed by (Z) stream sediment analysis (sample every 1, 000 feet), followed by (3) silty
frost boil surface soil analysis (sample every 100 feet on traverse lines or grids).