Open File Report 1995-05

Open File Report 1995-05

OFR 1995-05

Stratigraphy, Structure and Mineral Occurrences of the Aphebian Waugh Lake Group, Northeastern Alberta

The sedimentary and volcanic rocks of the Waugh Lake Group, contain well preserved primary structures and comprise diverse facies assemblages that can be arranged into a coherent stratigraphic system. The Waugh Lake Group has an estimated measured thickness of 1120 m, and consists of five rock units of formation rank. The Martyn Lake Formation consists of rhythmically bedded, turbiditic sedimentary rocks, that are overlain by strata of the Doze Lake Formation which comprise the lower sedimentary and volcanic assemblage. The rocks of the latter formation are conformably overlain by a distinctive green, brown- to black-grey weathering, mafic sedimentary rock-unit (Sederholm Lake Formation), which is, in turn, succeeded by a second sedimentary and volcanic assemblage (Johnson Lake Formation) and capped by the youngest rock-unit of the Waugh Lake Group (Niggli Lake Formation) which is dominated by mafic volcanic flows and breccia.

The strata of the Waugh Lake Group were deposited in a composite back-arc/strike-slip rift basin that evolved from a marine-dominated tectonically quiescent initial stage (Martyn Lake Formation) into a largely continental depositional regime characterized by syndepositionally active tectonism and related volcanism in the overlying Waugh Lake formations. The rift basin model is supported by the occurrence of bimodal volcanism, latero-vertical facies transitions, significant local thickness variations within members and soft-sediment deformation.

Deeply weathered, mineralized rusty shear zones (gossans) within the Martyn Lake Formation may be related to thrust faulting. These gossan zones contain schists with minor (1-10%) pyrite, trace arsenopyrite and gold contents of up to 3.2 g/t. The preferred location of sulfides in the shear zones indicate that the enrichment is shear-related and that sulfides are remobilized throughout the shearing process. The mineralization (redistribution of sulfides) is syn- to epigenetic in relation to deformation in the shear zones under greenschist facies conditions.

Iannelli, T.R., Langenberg, C.W. and Eccles, D.R. (1995): Stratigraphy, structure and mineral occurrences of the Aphebian Waugh Lake Group, northeastern Alberta; Alberta Research Council, ARC/AGS Open File Report 1995-05, 122 p.