| Natural Presence |
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  Copper
occurs naturally in the environment in a variety of forms. It can
be found in various concentrations in the geosphere, atmosphere, hydrosphere,
and biosphere.
Very high concentrations of copper ore deposits exist on all continents
of the earth. In these ores, the copper can occur in sulfide deposits
(in the minerals chalcopyrite, bornite, chalcocite, and covellite),
in carbonate rocks (in the minerals azurite and malachite), in silicate
deposits (in the minerals chrysycolla and dioptase), and as pure "native"
copper metal.
Much more commonly, trace concentrations of copper may be found in
almost all ordinary rocks and soils. The mean concentrations of copper
in rocks range from a low of 2 parts per million (ppm) in sandstones,
to 4 ppm in limestones, to 15 ppm in granites, to 70 ppm in black
shales, and to 90 ppm in basalts.
Copper can be released from these rocks during the natural course
of weathering, where it can find its way to soils, lakes, rivers,
and oceans. Upon entering water bodies, much of the copper precipitates,
and the remaining copper either remains suspended in particles or
is dissolved into the aqueous phase. The ratio of copper that precipitates
versus what remains in the aqueous phase is a function of the chemical
parameters of the water. |
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