Abstract: Within the Sixtymile River drainage basin, Quaternary placer deposits include tributary valley bottom gulch gravel, a broad main valley alluvial plain, and high level terrace systems in both tributary and main valley settings. After downcutting, paleo-Miller Creek underwent valley widening during alluvial fan erosion and sedimentation. During this time, the main Sixtymile River valley was also being laterally eroded during braidplain aggradation. Terrace development and incision through both fan and braidplain sediments coincided with significant debris flow sedimentation. The Sixtymile River changed from a braided environment to single channel meandering environment during terrace development.

Incision of Miller Creek through the fan surface to present levels probably coincided with downcutting of the Sixtymile River. Economic concentrations of placer gold are found in:: 1) the upper Miller Creek terrace where coarse-grained, massive and angular flood flow gravel forms a crude pay streak above the bedrock surface; 2) the distal Miller Creek terrace where discontinuous concentrations of gold were formed over a broad paleo-surface of lag gravel prior to fan aggradation; 3) laterally discontinuous pockets in the main Sixtymile valley terrace which was originally part of an aggraded braidplain sequence; and 4) lower, but still economic placer concentrations in gravels of the alluvial plain in the main Sixtymile valley.

Authors: Hughes, R.L. and Morison, S.R.

Citation: Hughes, R.L. and Morison, S.R., 1986. Placer gravels of Miller Creek, Sixtymile River area, 116 B,C. In: Yukon Geology Volume 1, J.A. Morin and D.S. Emond (eds.), Exploration & Geological Services Division, Indian & Northern Affairs Canada, p. 50-55.

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