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Journal of the Geological Society

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Placer deposits symposium

Gilbert-Commonwealth Associates of Michigan

Report of a whole-day joint meeting of the Institution of Mining and Metallurgy and the British Geomorphological Research Group held at Burlington House, 15 November 1984. The meeting was organized by Professor F. K. G. Hosking, Dr Ian Reid, Dr D. G. Sutherland and Professor M. F. Thomas, and convened by Drs Reid and Sutherland.

At this joint meeting, some 160 participants explored those areas where process geomorphology is instrumental in the identification of metalliferous palaeosediments. Water transport and reworking of debris are fundamental controls on placer concentration by mechanical processes, and chemical deepweathering of land surfaces is a feature of environments where residual enrichments are concentrated.

The initial session, chaired by K. F. G. Hosking, was an immediate reminder of the global span and regional diversity of the topic. D. G. Sutherland’s overview featured the main areas in the world of placer deposits. He examined the fundamental role of chemical deep weathering in releasing minerals from the host rock, noting the temperature and moisture conditions required. Climate is also important and controls the volume of runoff, which then determines the amount of debris moved. The climatic changes of the past, particularly during the last 2 Ma, were emphasized.

T. K. Smith’s talk featured an area of former hydraulic mining in the Sierra Nevada in the San Juan placer gold deposits. The significance of the unlikely name of his study area, the Red Dog–You Bet district, was only explained during the informal discussions, which were a conspicuous feature of

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This 250-word extract was created in the absence of an abstract.