Open File Report 1994-19

Open File Report 1994-19

OFR 1994-19

Investigation of Potential Paleoplacers in the Cretaceous Strata of the North Saskatchewan River Watershed

Author(s) Horachek, Y. Date 1994-03-01

In the order of one tonne of gold has been produced from the North Saskatchewan River since the middle of the 19th century. Most of this gold probably came from the segment of river between Devon and Elk Point as it is known to contain the richest placers in Alberta. Samples by Alberta Research Council from this area contain from 13.6 ppb to 141 ppb of gold. This portion of the river intersects basal strata of the Scollard Formation, the Horseshoe Canyon Formation and the Belly River Formation . These formations and their equivalents in the foothills are part of a clastic wedge of post-Jurassic sediments that resulted from erosion of the Rocky Mountain and the gold-bearing Omineca Belts which were formed by a Middle Jurassic to Paleocene orogeny in eastern British Columbia.

Depositional environments of the Cadomin, Hoadley, Mountain Park and the Entrance conglomerates, and coarse sandstones and conglomerates of the Brazeau Formation (all part of the post-Jurassic clastic wedge) were locally favourable for deposition of gold. The volcanic grain content of these clastics which is an indicator of their origin in the Omineca Belt ranges from trace amounts to over 60%. Similar rocks contain gold paleoplacers in many parts of the world. In Alberta the Burmis magnetite paleoplacer in the basal sandstone of the belly River Formation (the lower Brazeau equivalent) is an example of such a deposit.

The Brazeau and Cadomin Formations were the main targets of this prospecting program in which 134 samples were collected from 92 sites.

The Brazeau Formation was sampled at 61 sites from which 78 samples were collected. Most samples are conglomeratic sandstones or conglomerates. The Cadomin Formation was sampled at 25 sites from which 47 samples were collected. All of these samples are conglomerate.

Nine samples were collected from Hoadley and Mountain Park conglomerates from six sites. Thirteen samples were collected from 5 to 16 ppb of gold. Five samples assayed between 10 and 16 ppb of gold. Three of the five highest values are from samples of Cadomin conglomerate. The remaining two samples are of the Brazeau Formation and contain 10 and 13 ppb Au. Most of the samples assayed less than 5 ppb which is considered a background value.

In the Brazeau Formation elevated gold values occur as local "concentrations" which are laterally well distributed throughout the area sampled. Most samples were collected from the lower Brazeau. Of the fewer samples taken from the upper Brazeau, one indicated a gold content slightly above background value (7 ppb Au).

In the Cadomin Formation the increased gold values were found at the base of the formation as well as in the middle part of it.