Drift prospecting applied to volcanogenic massive sulphide (VMS) and other greenstone belt related deposits is well documented. Case studies outline best practices for the use of indicator minerals, till geochemistry and gold grain recovery across Canada and other formerly glaciated terrain. While Nunavut’s Izok lake deposit has been the subject of such case studies, the Northwest Territories is notably absent from this body of literature. With the prospect of an all-season road crossing the Slave Geological province, the Northwest Territories Geological Survey has launched multiple efforts to support exploration in greenstone belt settings, including this multi-year till sampling campaign. This presentation outlines the indicator mineral and geochemical results from till collected during the summers of 2016 and 2017. A total of 155 till samples were collected and analyzed for indicator minerals and till geochemistry. Ninety-two of these samples were also analyzed for gold grain recovery. Till sampling sites were selected to outline contrasts between regional backgrounds and multiple historical metallic showings found on a rough transect from the Sunrise deposit to the south and the Point Lake area to the north. Both of these areas were also the subject of additional sampling to characterize local dispersal patterns.
Indicator minerals recovered in samples collected down-ice of known greenstone belt related mineralization include chalcopyrite, gahnite, spinel and rutile. Other potential indicator minerals such as scheelite, arsenopyrite, sphalerite and loellignite were less common but also recovered from samples of interest. Thirty-three out of the 92 samples analyzed for gold returned positive results ranging from 1 to 3 grains of irregular to abraded shape. The two best samples returned estimated gold values of 17.9 and 18.8 ppb from till. Those values correspond to known mineralization; respectively the TIP showing in the Camsell lake area and the Sunset deposit in the Beaulieu river area.
Till geochemistry was analyzed using ICP-MS after partial and near total digestion using the less than 0.063 mm size fraction. Cu, Ga, and Pb are found to be the most reliable indicator elements as they most commonly have anomalous values down ice of known greenstone belt related mineralization. Ag, As, Bi, Cd, Fe, and Mn, though less commonly anomalous, also provided easily identifiable outliers. Interestingly, Co, Mo, U, Zn and REE anomalies were also identified. Multiple till samples anomalous in gold concentrations as well as indicator minerals are consistent with geochemical anomalies, such as in the Beaulieu River area, the Camsell Lake and in the eastern part of the Point Lake area. Indicator mineral, gold grains recovery and till geochemistry were all successful at identifying anomalies down ice of known bedrock mineralization, even in areas of thin and discontinuous till, commonly believed to be less conducive to drift prospecting in the Slave Geological Province.