Open File Report 1995-07

Open File Report 1995-07

OFR 1995-07

Geology of Devonian Limestones in Northeast Alberta

Author(s) Cotterill, D.K. Hamilton, W.N. Date 1995-03-01

This study of the Devonian rocks in northeast Alberta grew out of a broader MDA project, to evaluate the resource potential of limestones in Alberta for industrial use. Northeast Alberta is the only area in the province outside the Rocky Mountains belt where limestone rocks are found in outcrop. These rocks are part of a Devonian sedimentary succession which onlaps crystalline rocks of the Precambrian Shield to the northeast. The Devonian rocks include variably argillaceous limestones and dolomites that crop out extensively in the valleys of the major rivers and their tributaries draining the area. Evaporites and redbed clastics also comprise part of the succession in the deeper subsurface, but do not crop out in the study area.

Although most of the Devonian outcrops have been mapped and described by previous workers, no 3-dimensional framework existed into which the outcrop data could be referenced. Devonian geology had been viewed simply as a wedge of carbonate and evaporite strata resting undisturbed on Precambrian crystalline basement. However, a more complex picture was becoming apparent from scattered evidence of fault tectonics, salt collapse structures, and widespread karstification. A better model of the structural and stratigraphic framework was needed to evaluate the resource potential for these Devonian rocks.

The resource focus initially was on industrial mineral aspects of limestone. During the course of the work, some anomalous assay results for precious metals in the Devonian rocks were reported, suggesting a much broader resource potential that included the potential for hosting metalliferous deposits.