About YGS | Contact Staff | YGS News | Site Map | Links
5. Finlayson/Frances Lake
Donald Murphy
Yukon Geological Survey
The discovery of rich massive sulphide deposits with high precious metal values in 1994-97 focused attention on Devono-Mississippian felsic volcanic rocks of eastern Yukon-Tanana Terrane. At the time of the discoveries, the stratigraphy, structure and nature of relationships with adjacent terranes of this structurally complex and variably metamorphosed assemblage of rocks were not known at a scale suitable for focused mineral exploration. To address these deficiencies and aid in ongoing mineral exploration, Yukon Geological Survey initiated a program of 1:50 000-scale geological mapping; conducted an airborne multiparameter geophysical survey which was jointly funded with the Geological Survey of Canada; and implemented a systematic lithogeochemistry study of the metavolcanic rock units in the terrane which was partnered with companies involved in local exploration, the Mineral Deposits Research Unit at the University of British Columbia and the Geological Survey of Canada.
This work forms the basis for a new understanding of the geological evolution of Yukon-Tanana terrane and the setting of the massive sulphide deposits. In the Finlayson Lake district, the terrane is made up of several unconformity-bound volcano-sedimentary successions reflecting the Devono-Mississippian to Permian evolution of paired arc-backarc systems. Massive sulphide deposits or prospects occur in all of the successions: Kudz Ze Kayah, GP4F, and Fyre Lake occur in the Grass Lakes succession; Wolverine occurs in the overlying Wolverine succession; and basalt of the uppermost Campbell Range succession hosts the Money prospect and underlie areas where soils are anomalous in copper. Based on geological and geochemical considerations, the rock-hosted deposits mainly occur in a back-arc setting. Coeval volcanic rocks with an arc-like geochemical and geological character lie to the west and southwest in the hanging wall of the Money Creek thrust.
Stratigraphic data collected in the Finlayson Lake project is an important benchmark in the understanding of the geological evolution of the so-called pericratonic terranes, and is the focus of a joint Geological Survey of Canada, Yukon Geological Survey, British Columbia Geological Survey National Mapping Program (NATMAP) project.