Sediment-hosted copper deposits are formed by fluid mixing in permeable sedimentary and (more rarely) volcanic rocks. Two fluids are thought to be involved: an oxidized brine carrying copper as a chloride complex, and a reduced fluid that commonly formed in the presence of anaerobic sulfatereducing bacteria. For a sediment-hosted copper deposit to form, four conditions are required: (1) an oxidized source rock, (2) a brine to mobilize copper, (3) a reduced fluid to precipitate copper, and (4) conditions favorable for fluid mixing (Haynes, 1986a, b; Sverjensky, 1989; Ruffell and others, 1997). Sediment-hosted copper deposits are restricted to a narrow range of layers within a sedimentary sequence but do not necessarily follow sedimentary bedding.
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Mineralization is independent of igneous processes. Host rocks comprise two types: calcareous or dolomitic siltstone, shale, and carbonate rocks of marine or lacustrine origin; and non marine sandstone, arkose, and conglomerate. In addition, the iron oxide copper-gold and basaltic copper deposit sub models may be applicable within some of the areas studied. Deposits of the reduced-facies subtype (model 30b.1; Cox and others, 2003), also termed coppershale or stratiform copper deposits, are hosted by reduced-facies marine or lacustrine rocks such as green, black, or gray shale, siltstone, thinly-laminated tidal facies or reefoid carbonate rocks, and dolomitic shale. The deposits consist of stratabound, disseminated copper sulfide minerals that occur in reduced-facies sedimentary rocks, which overlie, or are interbedded with, red-bed sedimentary sequences or subaerial basalt flows. Copper is mobilized in the red beds by oxidized brines and is derived from reduction of sulfate in marine or lacustrine sedimentary rocks (Davidson, 1965). Finegrained clastic rocks and carbonate rocks host 69 percent of deposits and occurrences (Lindsey, 1982; Cox and others,
Mineralization is independent of igneous processes. Host rocks comprise two types: calcareous or dolomitic siltstone, shale, and carbonate rocks of marine or lacustrine origin; and non marine sandstone, arkose, and conglomerate. In addition, the iron oxide copper-gold and basaltic copper deposit sub models may be applicable within some of the areas studied. Deposits of the reduced-facies subtype (model 30b.1; Cox and others, 2003), also termed coppershale or stratiform copper deposits, are hosted by reduced-facies marine or lacustrine rocks such as green, black, or gray shale, siltstone, thinly-laminated tidal facies or reefoid carbonate rocks, and dolomitic shale. The deposits consist of stratabound, disseminated copper sulfide minerals that occur in reduced-facies sedimentary rocks, which overlie, or are interbedded with, red-bed sedimentary sequences or subaerial basalt flows. Copper is mobilized in the red beds by oxidized brines and is derived from reduction of sulfate in marine or lacustrine sedimentary rocks (Davidson, 1965). Finegrained clastic rocks and carbonate rocks host 69 percent of deposits and occurrences (Lindsey, 1982; Cox and others,