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Exploration and Mining Geology; January 2006; v. 15; no. 1-2; p. 89-100; DOI: 10.2113/gsemg.15.1-2.89
© 2006 Canadian Institute of Mining, Metallurgy & Petroleum
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Structural Controls on Gold Mineralization at the Burnt Timber Mine, Lynn Lake Greenstone Belt, Trans-Hudson Orogen, Manitoba

L.R. JONES1, B. LAFRANCE1 and C.J. BEAUMONT-SMITH2

1 Mineral Exploration Research Centre, Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6.
2 Manitoba Industry, Trade, and Mines, Geological Survey of Manitoba, 360 - 1395 Ellice Ave., Winnipeg, Manitoba R3G 3P2.

The Burnt Timber gold deposit is located in the Paleoproterozoic Lynn Lake greenstone belt of the Trans-Hudson Orogen, Manitoba. The deposit occurs along the Johnson shear zone, and is hosted by enriched and depleted tholeiitic volcanic arc basalts cut by feldspar porphyry dikes. The Johnson shear zone is a regional, belt-parallel structure characterized by the intensification of the regional S2 foliation. At the Burnt Timber deposit, S2 is folded by centimeter- to meter-scale, Z-shaped, F3 chevron folds that have an axial planar S3 crenulation cleavage. Within the 20 to 30 m-wide core zone of the shear zone, S2 and F3 are transposed parallel to S3 and the volcanic rocks are strongly sheared parallel to S3. The presence of a steeply plunging stretching lineation, together with dextral shear sense indicators along both S2 and S3 on horizontal surfaces, suggest that the Johnson shear zone is a dextral transpression zone.

Gold was introduced in pyritic, biotitic, and carbonatized mafic volcanic rocks along the core of the shear zone. Mylonitic mafic volcanic rocks contain localized high-grade zones (≥10 g/t Au) that differ from wider carbonatized, low-grade zones (<3 g/t Au) by the presence of deformed gold-bearing quartz-pyrite veins. High-grade zones are also associated with swarms of quartz-pyrite veins that cut across sericitized and carbonatized feldspar porphyry dikes, which acted as brittle, competent bodies during shearing. Gold deposition in the high-grade zones was controlled by the channeling of hydrothermal fluid along the core of the shear zone during shearing of the volcanic rocks, and brittle fracturing of the porphyry dikes.

Key Words: Structural controls • Gold mineralization • Burnt Timber mine • Lynn Lake • Trans Hudson






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