Cordilleran base metal

veins and replacement

bodies as "normal"
constituents of
porphyry systems
Llus Fontbot

Earth Sciences, University of Geneva, Switzerland

l
 Outline

Normal constituent of porphyry style systems

Overview of main Characteristics

Mineralogical zoning (ore and alteration

minerals)

Evolution in time

Origin of mineralizing fluid (brine, vapor,

single phase fluid?)
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 2
Cordilleran base metals deposits
are "normal" constituents in
porphyry style systems
A type among others within the magmato-hydrothermal
porphyry system:

porphyry copper deposits,

intermediate and high sulfidation Au and Ag deposits
Cu, Cu-Fe, Au, and Zn-Pb skarn deposits
"Cordilleran" (~ "zoned base metal deposits")
"distal" Au deposits

All types do not coexist in each single porphyry system!

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 3

Schematic relations: HS and IS epithermal deposits
And roots of porphyry systems Sillitoe and Hedenquist, 200

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 4

Cordilleran Base Metal Deposits
are
Economically Interesting
Targets
Butte: >0.6 billion oz Ag, > 4 billion lb Zn, > 16 billion lb of Cu, > 4
billion lb Zn, > 0.8 billion lb Pb, > 2.5 million oz Au.
Gold equivalent: > 80 million oz.

Cerro de Pasco: >1.5 billion oz Ag, >8 billion lb Zn, >2.5 billion lb Pb,
>2 billion lb Cu, >2 million oz Au.
Au equivalent: > 60 millons oz

Colquijirca District: >500 million oz Ag, >6 billion lb of Cu, >6 billion
lb Zn, >2 billion lb Pb, >2 million oz Au.
Au equivalent: > 50 million oz

Morococha, San Cristobal, Yauricocha, Huarn, Quiruvilca, Julcani,

Hualgayoc, Casapalca (?)

Bisbee, Magma, and Tintic (USA), Bor (Serbia)

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 5

Cordilleran Base Metal Deposits
are
Economically Interesting
Targets (cont.)
Historically, a most important base-metal and Ag ore-
type.

Today, in Peru, Cordilleran base metal deposits

account for more than 50% of the Zn and Pb
production and more than 60% of Ag production.

Resources of largest known deposits (80 - 100 million

oz Au equivalent) are comparable to those of
very large porphyry copper deposits (e.g. 2000 million
t and 1% Cu, i.e., Au equivalent: > 145 million oz).

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 6

 What are Cordilleran Base Metal
Deposits?

In short: (Mostly) epithermal base metal (Cu-Zn-Pb)

deposits formed in late stages of a porphyry system.

Still another new name???

Not really new: long time known deposit class for polymetallic
veins occurring in the upper part of porphyry copper systems
(e.g., Sawkins (1972), Einaudi (1977, 1982, 1994):
Cordilleran base metal lodes".

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 7

What are Cordilleran Base Metal
Deposits?
Other terms:
Butte-type vein deposits, zoned Cu-Zn-Pb-Ag
deposits", zoned base metal veins, high
sulfidation/intermediate sulfidation base
metal veins

Problem with these terms:

not always HS or IS and therefore not not
always so well zoned
not only veins but also large replacement
bodies.
generally epithermal, but T up to 350 C
have been recorded
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 8
 Typical tonnages, grades

In some systems, the Cordilleran stage is

well developed (e.g., Bisbee, Arizona;
Yauricocha, Cerro de Pasco, Colquijirca,
Peru....).
Typical tonnages, grades

Underground: 2 - 10 Mill t, 2-5%Cu, 5-

15%Zn+Pb, 3-5 oz/t Ag
Open pit: 30-150 Mill t, 1-2%Cu, 2-
10%Zn+Pb, 1-3 oz/t Ag

Not always present:

In other districts the Cordilleran stage is
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 9
 Main characteristics of
Cordilleran base metals deposits
(1) Close association in time and space with
calc-alkaline igneous activity- Same
producing areas as porphyry - Cu or high
sulfidation epithermal Au-Ag deposits
(2) Mainly epithermal: deposition at shallow
levels below the paleo-surface and generally
at temperatures below 300C (temperatures
up to ~350C also recorded)
(3) Deposition "late" in the evolution of the
porphyry system
(4) Cu-Zn-Pb-(Ag-Au-Bi-Sn-W) metal suites.
High
G4 Cordilleran Ag/Au
Base Metal ratios.
Deposits, Llus Fontbot, v. 06.12, slide 10
 Main characteristics of
Cordilleran base metals deposits

(5) Much richer in sulfides (up to more than 50

% total sulfides) than porphyry copper ores
(6) Mainly occurrence as open-space fillings in
silicate host rocks and as replacement in
carbonate rocks,
(6) Frequently: well-developed zoning (ore and
alteration minerals)
(7) Frequent early pyrite-quartz (W)
assemblage that can be extensive and form
large bodies (and can be zoned to Zn-Pb
ores)
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 11
 Cordilleran deposits, the
Colquijirca and Cerro de
Pasco examples

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 12

 Geology

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 13

 Colquijirca
Marcapunta volcanic complex

Smelter deposit Colquijirca deposit

N
500 m

Cu-(Au-Ag) zone: enargite

Zn-Pb-Cu-(Ag) zone:
sphalerite-galena-
chalcopyrite
Zn-Pb-(Ag) zone: sphalerite
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 14 -galena
 Colquijirca

Cu-(Au-Ag) zone: enargite

Zn-Pb-Cu-(Ag) zone:
sphalerite-galena-
60 m chalcopyrite
Zn-Pb-(Ag) zone: sphalerite
-galena
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 15
 Colquijirca
Early silica-pyrite stage Main ore stage Late ore sta

G4 Cordilleran Base Metal Deposits, Llus Fontbot, <1

v. 06.12, slide 16 >1-<5 >5-<10 >10
Colquijirca, Early silica-pyrite stage

1 cm
2 cm

sheelit
e
rutil
e rutil
e
zirco
n

50 m 50 m
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 17
lquijirca, Main ore stage, enargite zo
z

2 cm 1 cm

enargite

dickite

0.5 1 cm
cm
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 18
lquijirca, Main ore stage, enargite zo
z

enargite

colusite

200 50 m
m

Au-(Ag)
telluride alunite
s
+
electrum
tennanti
te

pyrite II
goldfieldit
e 50 m 1 cm
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 19
Colquijirca, Main ore stage, Cu zone
woodhouseit
quartz e

alunite

1 mm
alunite 50 m

colusite

100 100
m m
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 20
uijirca, Main ore stage, chalcopyrite

kaolinit sphalerit
e e aikinite

emplectit
e
tennantit
e
bornite
chalcopyri
100 te 100
m m

tennantit
e

matildite

stromeyerit tennantit
e e
50 m 50 m
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 21
quijirca, Main ore stage, sphalerite z
sphalerit
e
sphalerit
e
galena

alunit
e
alunit
e 100 50 m
m

hematit
e
sphalerit
e
galena

kaolinite
sphalerit 400 m
e Mn-Zn-
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 22 siderit
 Colquijirca, Late stage

100 m

tennanti
te

bornite chalcosite digenite

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 23

 Cerro de Pasco
A
1st mineralization stage:
- Pyrite-quartz body
- Pipe-like pyrrhotite
bodies Matagent
- Zn-Pb ores (bearing Fe- e syncline
rich sphalerite)

2nd mineralization stage:

- Cu-Ag-(Au-Zn-Pb)
enargite-pyrite veins
- Zn-Pb-(Bi-Ag-Cu)
carbonate replacement
A
bodies (bearing Fe-poor
sphalerite)

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 24

 Cerro de Pasco
1st mineralization stage

Modified after Einaudi

(1977)

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 25

 Cerro de Pasco

pyrrhotit
e,
quartz,
wolframi
pyrrhotite,
te
sphalerite,
chalcopyrit
e, stannite

pyrrhotite,
Fe-rich
sphalerite, Pyrrhotite
arsenopyrit Transition body Transition
e, zone zone
Pyrite-quartz Zn-Pb ores
chalcopyrit body
eCordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 26
G4
 Cerro de Pasco

35.0 10.0 mol% FeS

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 27

 Cerro de Pasco
pyrrhotite

galena

sphalerite

100 m pyrite
Pipe-like pyrrhotite ores: pyrrhotite, arsenopyrite, Fe-rich
sphalerite
Alteration mineral: quartz

=> LowBase
G4 Cordilleran sulfidation statev. 06.12,
Metal Deposits, Llus Fontbot, assemblages
slide 28
 Stage superposition at Cerro de
Pasco

Massive
ore with
Fe- Fe-rich sl
poor sl (early
vein
stage)
(Main
ore
stage)

Central part of the

pit, in the vicinity
20cm of the silica-pyrite
body
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 29
 Zoning of alteration minerals and of
ore minerals are "parallel" but do
not correlate 1:1
Alteration minerals Ore mineral assemblages (-)
Association (/)
AA Advanced Argillic (qtz-
alunite, barite),
core

Cu-(Au): /py-en, py, en, cc,

(cv), Sn, W, and Bi
A Argillic alteration,dickite, minerals/
kaolinite,
to

AA (A), ((S))
rim

S qtz-sericite
Cu-(Ag-Bi) /py-bn, (py-cp),
ten, /py-cp, bn/Bi
From

D qtz, calcite, rhodochr,

siderite, hematite sulfosalts/ ; A, (AA), (S)

Zn-Pb-Ag py-sl, gn, (tt, arg,

cp); D, (A), ((AA, S))
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 30
 Caution!

The observed patterns may be complicated by

prograde evolution: Cu-(Au) prograding
over Cu(Ag-Bi) and over Zn-Pb-Ag zones
retrograde evolution: typically Cu(Ag-Bi)
and Zn-Pb-Ag zones retrograding over
Cu-(Au) zone
superposition of pulses

It is important to distinguish between

- mineral assemblages (without reaction borders, in
apparent equilibrium)
- mineral associations

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 31

 Fluid origin

Brine? If yes, how

could reach dense
fluids shallow
depths?

Vapor? If yes, why

Zn and Pb rich?

Contracted (deep)
vapor/Single-
phase fluid?
Heinrich (2005)
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 32
 Brine? If yes,
how could reach
dense fluids
shallow depths?

Vapor? If yes,
why Zn and Pb
rich?

Reminder:
Single-phase
The
fluid?/(deep)
"Single phase
contracted
intermediate-density
vapor?
fluid" could ascend
without crossing the
two-phase boundary
and condenses out
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 33
minor mass of saline
 Brine and vapour FI in porphyry copper deposits

Ulrich, T., Gnther, D, Heinrich, C.A. (1999) Nature, v. 399, p. 676-679.

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 34
 Cerro de Pasco - Fluid isotope
signature

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 35

 Colquijirca - Fluid isotope
signature

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 36

 Colquijirca - Fluid isotope
signature
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 37
 Results of FI and stable isotope
studies
(Colquijirca, Bendez, 2006; Cerro de Pasco, Baumgartnerr et al., 2008, Morococha,
Kouzmanov et al ., 2008)
Early and Main stage

- Moderate to low salinities (< ~12 % NaCl eq.)

- Mixing of magmatic fluids with isotope equilibrated
waters
- Possible to retrace cooling ( ~350C to ~200C)

Alunite in Main stage:

- Mixing trend of magmatic fluid with meteoric water (in
part no mixing, only magmatic signature)
Ore Fluid origin
Brine? If yes, how could Yes, Diluted brine!
reach dense fluids shallow
depths?
Pulses of vapor are
responsible for alunite
Vapor? If yes, why Zn and Pb precipitation
rich?
Difficult if taking into
G4 Cordilleran
Contracted vapor/Single-
Base Metal Deposits, Llus Fontbot, v. 06.12, slide 38 account the traced
 Very acidic fluids
between diluted brine and acidic fluids derived from SO2-bearing

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 39 (Bendez, 2006)
 Less acidic fluids
ly diluted brine enters the epithermal environment

Only diluted brine Diluted brine and vapor pulse

(Bendez, 2006)
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 40
 Timing of Cordilleran
mineralization as part of a porphyry
system
HS Cordilleran
lodes

D veins

A-B qtz veinlets

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 41 Einaudi, M, 1996
 Today

Polymetallic lodes cutting D-veins,

Toromocho,
G4 Cordilleran Base MetalMorococha,
Deposits, Llus Fontbot, Peru.
v. 06.12, slide 42
Timing at Cerro de Pasco

Baumgartner, Fontbot &

Vennemann (2008)
 Timing at
Colquijirc
a

Bendez, Page, Spikings,

Pecskay and Fontbot (2008)

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 44

 Early barren quartz-alunite
ledges

Au-(Ag)
high
sulfidation
epithermal Cordilleran base
metal veins and
replacement
deposits

Porphyry copper
Skarn
Zn-Pb-(Ag-Cu)

Modified from Muntean and Einaudi (2002)

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 45
 Cordilleran base metal deposits -
Conclusions
Economically important (Cu-Zn-Pb-Ag-Au-Bi-(Sn-W))
Typical constituents in the upper part of porphyry
copper systems
Main characteristics: zoned and rich in sulfides
The cores may bear HS and AA mineral assemblages,
but Cordilleran base metal deposits are a separate
deposits class which
is rich in sulfides
crosscuts "porphyry veins" and epithermal Au-Ag
deposits
older by n 100.000 years than the later (in dated
examples)

Diluted magmatic brines (tapped when the system is

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 46
 Recent References

Bendez, R , Page, L, Spikings, R, Pecskay, Z and Fontbot, L, 2008. New

40Ar/39Ar alunite ages from the Colquijirca District, Peru. Evidence of long

period of magmatic SO2 degassing during formation of epithermal Au-Ag

and Cordilleran polymetallic ores. Mineralium Deposita, v. 43, p. 777-789.

Baumgartner, R, Fontbot, L and Vennemann, T, 2008. Mineral zoning and

geochemistry of epithermal polymetallic Zn-Pb-Ag-Cu-Bi mineralization at
Cerro de Pasco, Peru. Economic Geology, 103: 493-537.

Kouzmanov, K., A. Bendez, H. Catchpole, M. Ageneau, J. Prez & L.

Fontbot, 2008 The Miocene Morococha district, central Peru: large-scale
epithermal polymetallic overprint on multiple intrusion-centered porphyry
system PACRIM 2008

More documents to download in:

http://www.unige.ch/sciences/terre/mineral/ore/min_ore.htm

G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 47

 From Einaudi, 199
G4 Cordilleran Base Metal Deposits, Llus Fontbot, v. 06.12, slide 48