Anomalous gold occurrences in Cretaceous and Tertiary conglomerates and gravels of Alberta

Abstract

Reconnaissance surveys of lithified Cretaceous conglomerate and generally nonlithified Tertiary gravel in outcrop in southern to central Alberta indicate anomalous values of detrital gold at several levels. Background gold levels are considered to be 2 to 5 ppb, based on about 200 analyses. The highest gold values of up to 910 ppb were obtained from an igneous-clast conglomerate in the Albian Blairmore Group, southern Rocky Mountain Foothills. Tertiary gravels of Swan Hills and Cypress Hills have values between <2 and 21 and <2 and 44 ppb respectively. The basal Cretaceous Cadomin Formation of the Alberta Foothills has values of 2 to 5 ppb with one value of 17 ppb. Gold occurrences in the foreland basin deposits appear to have been influenced by the position of the drainage divide associated with the accretionary prism to the west. "Windows" of gold deposition exist in the succession owing initially to exposure of Omineca Belt primary gold deposits due to uplift, followed by cutoff of source by lateral eastward-stepping of the drainage divide. The Western Canada foreland basin contains three such gold deposition "windows", the last of which is still open. Although the gold values obtained for this study may not yet be of direct economic interest, some occurrences are anomalous and should be investigated further.