This document discusses porphyry copper deposits and the processes of hypogene and supergene mineralization. It describes how primary sulfide minerals react in the presence of oxygenated groundwater to form secondary sulfides and then supergene oxides, carbonates, sulfates, and phosphates. This leaves gossan, or iron oxide, at the surface as a marker for sulfide prospecting. The document also briefly discusses alteration minerals formed from the reaction of hydrothermal fluids with igneous rocks, and compares porphyry copper deposits, which form at depths under 6 km, to shallow epithermal deposits formed less than 1 km deep.

1. Porphyry Copper
Deposits

2. Copper Resources

6. (Idealized Porphyry Alteration/Mineralization (Lowell and Gilbert, 1970

9. Potassic Alteration
Bornite
Chalcopyrite
High Grade Ore
Porphyry Ore and
Alteration Textures
Phyllic Alteration

12. Supergene
Hypogene
Chalcopyrite
Bornite
Malachite
From Hypogene to Supergene

13. Sulfide minerals are unstable in
the presence of oxygenated
groundwater. Primary (hypogene)
sulfides react to form secondary
(supergene) sulfides, and then
supergene oxygen-bearing
minerals such as oxides,
carbonates, sulfates, and
phosphates, depending on the
anions that are available in the
groundwater. At the surface,
red/orange colored iron oxides
(gossan) are left behind and
become a marker for sulfide
mineral prospecting.
See Table 19.3, page 382 for
names of some minerals in the
oxidized part of the supergene
zone.

14. .Gossan at the Lavender Pit overlook, Bisbee Arizona

15. Enriched zone
Leached zone
Mineralized gravel
Primary zone
Mineralized bedrock
Barren gravel
Supergene enrichment
Leached zone – acidity creation
+FeS2 + H2O + 7/2O2= Fe2+ + 2SO4
2- + 2H
-CuFeS2 + 4O2= Fe2+ + Cu2+ + 2SO4
2
Oxidised zone – Fe and Cu oxides, acidity creation
+2Fe2+ + 2H2O + 1/2O2 = Fe2O3 + 4H+ + 2Cu+ + H2O = Cu2O +2H
Enriched zone – reduction and sulphide deposition
2Cu+ + SO4
2- = Cu2S +4O2

16. The silicates in igneous rocks
(feldspar, hornblende and
micas) are altered by reaction
with hydrothermal solutions to
form characteristic alteration
minerals:
Propylite (chlorite and epidote
form)
Argillite (clay minerals form)
Sericite (mica forms from
clays)
Secondary or Supergene Hydrothermal
Minerals

23. intrusives which were saturated
by water as they intruded in
shallow areas of the crust (less
(. than 6 km depth
The developing hydrothermal
systems are characterized by the
interaction, to different degrees,
of fluids coming directly from
the parental intrusive and from
.meteoric surface waters
Porphyry copper deposits Epithermal deposits
originate in or nearby porphyritic Hydrothermal deposits
formed at shallow depths at
depths of less than 1 km in a
hydrothermal system
dominated by surface waters
with only a small contribution
.by magmatic fluids
Epithermal deposits include a
wide variety of ores: Au, Au-
Ag, Ag, Pb, Zn, Cu, Sn, Sb, U
. and Hg
Comparison between the the porphry copper
deposits and the epithermal deposits

24. Schematic diagram oft he tectonic setting of porphyry, epithermal and skarn deposits | Image Credit: MBG