Open File Report 1994-07

Open File Report 1994-07

OFR 1994-07

Regional Stratigraphic - Structural Study. Orientation Heavy Mineral Stream Sedimentary Study., Southern Alberta Rift, Southwest Alberta

Author(s) Gilmour, W.R. Date 1994-03-01

The intent of the 1993 field program was to follow up the fieldwork that was conducted under Canada-Alberta MDA project M92 04 002 during 1992 (Williamson et al., 1993). The 1993 program consisted of two separate studies. (1) One study comprised the stratigraphic-structural examination and geological mapping of selected stratigraphic sections in rock units ranging from Proterozoic to Cenozoic in age. The intent of this work was to search for changes in sedimentary facies, paleocurrent directions and other such geological features that would indicate the location and duration of the Southern Alberta Rift in southwest Alberta. (2) The second study comprised the orientation heavy mineral sampling of three selected drainages in southwest Alberta. The intent of this work was to determine if selected heavy mineral fractions in stream drainage sediments provide a better 'anomaly' to 'background' contrast as compared to that found by the standard stream silt sampling methodology.

The major contributions from the 1993 stratigraphic-structural study are: (1) definite stratigraphic evidence for rift-related influences on sedimentation patterns in Middle Proterozoic to Cenozoic strata and, less definitively, (2) stratigraphic and structural data that more precisely indicate the inferred margins, particularly the southern margin, of the Southern Alberta Rift. Strata of the Purcell Supergroup contain several notable features that indicate rift-influenced effects on sedimentation patterns. These syndepositional tectonic effects on sedimentation patterns were mainly found in strata of the Appekunny, Grinnell, Siyeh and Sheppard Formations. The effects of rift-related tectonism are not as obvious in Phanerozoic strata, and an accurate estimation of the rift margins during the Phanerozoic could not be defined by the 1993 field work. However, several features occur within Phanerozoic strata that indicate repeated episodes of syndepositional tectonism that may have been related to reactivation of structures associated with the Southern Alberta Rift. With respect to the location of the margins of the Southern Alberta Rift, it must be kept in mind that the original delineation of the rift boundaries was interpreted from geophysical evidence by Kanasewich (1968) and Kanasewich et al. (1969), hence the inferred margins of the Southern Alberta Rift in southwest Alberta are not accurately known. Nonetheless, the existence of well-defined depocentres and associated facies variations found by the 1993 program comprise hard field evidence that rift-related effects are preserved in the Proterozoic rocks of the Clark Range and have permitted a better understanding of the position of at least the inferred southern margin of the Southern Alberta Rift. This information, coupled with suitable mineral deposits models, will assist in the exploration for various types of metallic mineral deposits in southwest Alberta.

The orientation heavy mineral stream sediment survey has proven successful in detecting known elastic sediment-hosted copper-silver mineralized zones in Proterozoic strata, and carbonate-hosted zinc-lead-silver mineralized zones in Paleozoic strata. The heavy mineral survey results commonly show a contrast between anomalous and background values that is about an order of magnitude greater than that which exists in the standard geochemical stream silt survey results in southwest Alberta. Therefore, the use of heavy mineral concentrates from stream sediments to obtain this better anomaly to background contrast can play a significant role in both identifying specific mineralized zones and in evaluating the mineral potential of drainage basins. Further studies of the regional heavy mineral content of stream drainages are required in southwest Alberta to: (a) confirm the heavy mineral technique's applicability to other areas with differing geological and geomorphological conditions, (b) confirm and refine which of the various heavy mineral fractions provide the best anomaly to background contrast for each element of exploration interest, and (c) more precisely determine the background, threshold and anomalous classifications for each element and heavy mineral fraction.