Origin of the bedrock values of placer deposits

As a land surface is lowered by dissection, the gold always tends to remain on or near bedrock while the lighter particles are sluiced away. Gold sufficiently coarse to form commercial placers (particles exceed 1 milligram) may not travel horizontally much farther than it drops vertically with respect to its original sitein bedrock. Greatest concentration occurs in narrow valleys during active degradation. Lesser concentrations and dissemination may form at higher levels in gravels when the stream becomes more aggradational later in the erosional cycle. Similar considerations apply to marine placers. (For original paper, see ibid., v. 62, p. 852-853, 1967.)

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