Gold, tin, uranium and other elements in the Proterozoic Nonacho sediments and adjacent basement rocks near MacInnis Lake, District of Mackenzie

Heavy mineral layers in a pink arkose-quartz-rich conglomerate unit of the Nonacho Group contain notable amounts of U, Th, Sn, Nb, Ta and Au. Enrichment in Th, Sn, Nb, Ta and to a lesser extent in U is related to the detrital dispersal and accumulation of thorite-uranothorite, cassiterite and a suspected but undetected Nb-Ta mineral. These minerals probably originated from sources to the west of the Nonacho basin. in the Fort Smith belt. The clastic minerals are consistently enriched in the heavy mineral layers throughout the arkose-conglomerate unit although Sn appears to be more concentrated towards the base of the sedimentary pile. A decline in the concentrations of the various clastic minerals from south to north is also apparent and reflects increasing distance from source. Hydrothermal enrichment in U and Au is super-imposed upon the detrital pattern in the arkose-conglomerate unit. This activity appears to have been confined to the area adjacent to the southeastern shore of MacInnis Lake and is probably related to hydrothermal activity that led to the formation of nearby U-Cu-Au-Ag veins in basement rocks as well as in Nonacho Group sediments. Uranium is believed to have precipitated in the intergranular spaces of heavy mineral layers in the arkose-conglomerate unit as a result of interaction with Ti compounds and/or in response to reducing conditions associated with the presence of magnetite. Gold is more erratically distributed and is not confined to the heavy mineral layers