THE POTENTIAL INFLUENCE OF A TRIANGLE ZONE GEOMETRY ON THE LOCATION OF GOLD DEPOSITS IN SEDIMENTARY ROCKS: AN EXAMPLE FROM THE RACKLA GOLD BELT, YUKON TERRITORY, CANADA

Gold deposits in the eastern Nadaleen Trend (NT) of northeastern Yukon Territory are hosted in strongly deformed, unmetamorphosed, Neoproterozoic carbonate and siliciclastic rocks and display characteristics similar to Carlin-type deposits in Nevada. Deformation was primarily mid-Cretaceous and thin-skinned. It resulted in regional east-trending folds and thrusts, and locally at the NT, hundred meter-scale moderately to steeply SSW-plunging chevron folds crosscut by a dextral east-trending fault. The structural complexity of the NT may be a result of its location in a zone of regional stratigraphic and structural transitions. Neoproterozoic and Paleozoic platform rocks exist to the west and north and associated basin rocks to the east and south. Also, regionally extensive east-trending faults, including the Dawson Thrust and Kathleen Lakes Fault, end within 10 km of the NT. Furthermore, the combination of south-vergent thrust faults at and north of the NT, and north-vergent thrust faults elsewhere, result in a triangle zone geometry across the NT. We believe that gold was concentrated through funneling of ore fluids into the triangle zone and subsequently into the hinge zones of moderately to steeply SSW-plunging anticlines. The interpretation of gold concentration into a zone of complex geology within a triangle zone may have implications for gold exploration elsewhere.

In contrast to structures across the NT, those to the east are consistently north vergent, and to the west, rocks are undeformed north of the triangle zone. The variation in deformation can be explained in numerous ways, including differences in displacement and/or competence of the rocks, and/or the existence of a basement structure, such as a south-dipping basement normal fault west of the NT. We consider the existence of a basement normal fault (inspired by the platform-to-basin transitions), because it would explain (1) undeformed rocks north of the triangle zone west of the NT, where north-directed fold-thrust movement was obstructed by the basement fault, (2) continuous north-vergence east of the NT, where no obstruction occurred, and (3) tectonic wedging and multiple backthrusts across the NT, as a result of north-directed fold-thrust movement overriding the terminal part of the basement fault.