Publication Type:

Journal Article

Authors:

Jones, L. R.; Lafrance, B.; Beaumont-Smith, C. J.

Source:

Exploration and Mining Geology, Canadian Institute of Mining, Metallurgy and Petroleum, Montreal, QC, Canada, Volume 15, Number 1-2, p.89-100 (2006)

ISBN:

0964-1823

Keywords:

Canada, chemical ratios, deformation, dikes, faults, folds, geochemistry, gold ores, Greenstone Belts, Hudsonian Orogeny, Hydrothermal alteration, intrusions, Lynn Lake Manitoba, major elements, Manitoba, metabasalt, metaigneous rocks, metal ores, Metallogeny, metamorphic belts, Metamorphic rocks, metasomatism, mineral deposits, genesis, Mineral exploration, mines, mining geology, ore grade, orogenic belts, Paleoproterozoic, petrography, Precambrian, proterozoic, structural analysis, structural controls, tectonics, textures, tholeiitic composition, Trace elements, upper Precambrian, Wasekwan Group, Western Canada

Abstract:

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 S (sub 2) foliation. At the Burnt Timber deposit, S (sub 2) is folded by centimeter- to meter-scale, Z-shaped, F (sub 3) chevron folds that have an axial planar S3 crenulation cleavage. Within the 20 to 30 m-wide core zone of the shear zone, S (sub 2) and F (sub 3) are transposed parallel to S (sub 3) and the volcanic rocks are strongly sheared parallel to S (sub 3) . The presence of a steeply plunging stretching lineation, together with dextral shear sense indicators along both S (sub 2) and S (sub 3) 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 (> or =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.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2007-008137<br/>Burnt Timber Mine<br/>Johnson shear zone<br/>Lynn Lake Belt<br/>Pool Lake Suite