Deposits Formed by Sedimentary and Surficial Processes - Metals and Society: An Introduction to Economic Geology - page 139

WEATHERING
ZONES

MINERALS

Mineralized vein Weathered surface

Leached
capping
(gossan)

Hydrated iron
oxides

Water seepage

Cu 2+

Leached
zone

Cu 2+

Copper
carbonates,
oxides
silicates, etc

Oxidized
ores
Water table
(redox barrier)

Secondary
sulfide
enrichment

chalcocite,
covellite,
bornite

Primary, unaltered
hypogene ore

chalcopyrite,
pyrite

Fig. 5.10 Supergene enrichment zone (From Webb and Rowston ( 1995 ))

Perhaps the best-known examples of supergene enrichment zones are those that
overlie porphyry copper deposits. Primary ore in the Chuquicamata deposit
(discussed in Chap. 4) contains only about 0.8% Cu but it was overlain by a thick
layer of supergene enrichment in which the copper grade was 2-3%. In addition,
flow of acidic solutions from the main ore body transported dissolved copper
downstream where it was redeposited in gravels to form a secondary ore body
called the Exotica deposit. This deposit contained an additional 300 t of ore, also
with about 2% Cu.

References

Butt CRM, Lintern MJ, Anand RR (2000) Evolution of regoliths and landscapes in deeply
weathered terrain - implications for geochemical exploration. Ore Geol Rev 16:167-183
Freyssinet Ph, Butt CRM, Morris RC, Piantone P (2005) Ore-forming processes related to lateritic
weathering. Econ Geol 100th Anniversary Volume:681-722
Frimmel HE, Groves DI, Kirk J, Ruiz J, Chesley J, Minter WEL (2005) The formation and
preservation of the Witwatersrand goldfields, the largest gold province in the world. In:
Hedenquist JW, Thompson JFH, Goldfarb RJ, Richards JP (eds), 100th Anniversary Volume,
Society of Economic Geologists, pp 769-797