Ore deposits related

to intermediate to

felsic intrusions –

Porphyry Cu-Mo

Deposits - Examples

- GLY 361 -

Lecture 9

SOUTH AMERICA

Subduction of Nazca plate beneath South American plate emplacement of a series of porphyritic, calc-alkaline

plutons in the mid to late Oligocene.

- CHILE -

Chilean Deposits

• Deposits occur in 3 discrete north trending belts that are based on the ages of the contained deposits – become progressively younger in an eastward direction from: – early Cretaceous (~130 Ma),

– through Paleocene (66 – 58 Ma),

– to late Eocene to early Oligocene (42 – 31 Ma).

• The Eocene to early Oligocene belt is the principal repository of Cu in the world.

Chuquicamata Cu-Mo

- CHILE -

Large open pit mine 1,240 km north of the capital Santiago de

Chile.

4.3 km long, 3 km wide and 850 m deep and its smelter and

electrolytic refinery (855,000 tonnes p.a.) are amongst the world's

largest.

Second deepest open-pit mine in the world after Bingham

Canyon Mine, Utah, USA.

By far the largest total production of approximately 29 million

tones of copper

Despite over 90 years of intensive exploitation it remains one of

the largest known copper resources.

Chuquicamata

• Copper has been mined for centuries at Chuquicamata as was shown by the discovery in 1898 of "Copper Man", a mummy dated at about 550 A.D. which was found trapped in an ancient mine shaft by a fall of rock.

• Early operations mined high grade veins (up to 10-15% Cu) and disregarded the low grade disseminated ore. Mining never really developed satisfactorily in the early days because of the lack of water, the isolation and lack of communications, lack of capital and fluctuations in the copper price.

• The modern era started when a method of working low grade oxidised copper ores was developed. Production started in May 1915.

• Production for many years came from the oxidised capping of the orebody but by 1951 the oxidised reserves were largely exhausted.

• Mining then focussed on the huge reserves of

underlying secondary sulphides.

Overview of the supergene enrichment of

the Chuquicamata porphyry copper deposit

with the associated Exotica deposit, Chile.

Münchmeyer (1996)

El Galeno and Michiquillay

Porphyry

Cu–Au–Mo Deposits

- PERU -

In Peru, the localities of deposits,

occurring within the batholiths, were

controlled by preexisting joint

systems.

El Galeno and Michiquillay are early to middle Miocene Cu–Au–Mo porphyry-related deposits located in the auriferous Cajamarca district of

northern Peru.

• Associated with multiple dioritic intrusions hosted within Lower Cretaceous quartzites and shales.

• Emplacement of the porphyry stocks (17.5–16.5 Ma) in a hanging wall anticline was structurally controlled.

• Early potassic alteration associated with py and cpy mineralization. A quartz–magnetite assemblage that occurs at depth has completely replaced potassically altered rocks.

• Late- and post-mineralization stocks are spatially and temporally related to weak phyllic alteration.

• High Au grades are associated with early intrusive phases located near the centre of the deposit.

• Highest Cu grades (~0.9% Cu) - supergene enrichment blanket; high Mo grades - contacts with the metasedimentary rocks.

El Galeno

486 Mt at 0.57% Cu, 0.14 g/t Au

and 150 ppm Mo.

• Associated with a Miocene (20.0–19.8 Ma) dioritic complex that was emplaced within the hanging wall of a back thrust fault.

• Hosted in quartzites and limestones. The NE-trending deposit is crosscut by NNW-trending prospect-scale faults - influenced both alteration and metal distribution.

• In the SW and NE of the deposit, potassic alteration zones contain moderate hypogene grades (0.14 g/t Au and 0.8% Cu) and are characterized by cpy and py mineralization.

• Core: lower grade (0.08 g/t Au and 0.57% Cu) phyllic alteration that overprinted early potassic alteration.

• Supergene enrichment blanket of 45–80 m thickness with an average Cu grade of 1.15%, overlain by a deep leached cap (up to 150m).

544 Mt at 0.69% Cu, 0.15 g/t Au,

100–200 ppm Mo and 0.5-5.0 g/t Ag.

Michiquillay

Michiquillay

Michiquillay

Michiquillay

Bingham Canyon Porphyry Cu-Mo

Deposit

- USA -

It is the largest man-made excavation on earth.

Locality map of

the Bingham

Porphyry Copper

Deposit,

Utah, USA

•Mining started in 1865 and some 194 Mt were mined up to 1929.

•In 1929, 17,724,100 t were mined by electrically operated steam

shovels with a capacity of 50,000t per day.

•The ore was concentrated by flotation and 148,000 t of refined

copper was produced together with 116,087 oz Au 1,050,075 oz Ag.

•Ore reserves were 640 Mt at a grade just above 1% Cu.

•The operating costs was 87c/t (6.65c/lb Cu, and copper content was

19.89 lb/t and the recovery was 17 lb/t.

•Due to market conditions the production was curtailed in 1930.

Lindgren (1933)

History

•The understanding of this deposit (first studies already in 1905)

greatly contributed to our understanding of porphyry copper

deposits and resulted in the highly successful application of the

porphyry copper deposit model in exploration elsewhere.

•Most of the bulk mining methodology nowadays in use were first

developed here.

•Similarly, many extraction metallurgical processes were first

developed here, this include the concentration of ore minerals by

flotation methods.

Economic Geology Milestones

PRODUCTION

In 2003, Bingham Canyon mined 135.2Mt of rock in the open pit and

milled 46.1Mt of ore grading 0.67% Cu, 0.027% Mo, 0.29g/t Au and

3.02g/t Ag, together with smaller amounts of Bi, Pt, Pd, Se and Re.

Replacement and vein deposits in sedimentary and igneous rocks

peripheral to the porphyry center yielded 2.9 Mt of Pb-Zn with lesser

amounts of Cu, Au and Ag from approximately 47 Mt of ore.

The concentrator yielded 1.15Mt of concentrates containing 281,800t

Cu, 8,800t Mo, 305,000oz Au and 3.55Moz Ag.

Refined Cu production was constrained by an acid-plant failure and by

low copper/high sulphur grades.

The smelter-refinery complex converted 1.06Mt concentrate to

230,600t Cu, 308,000oz Au and 2.96Moz Ag.

http://www.mining-technology.com/projects/bingham/index.html#bingham3

RESOURCES:

- The existing pit will be worked out by 2013.

- Open pit and then underground mining will continue

after that.

- As of end 2003, open-pit reserves: 28Mt proven ore @

0.56% Cu, 0.35g/t Au and 3.16g/t Ag.

- + a further 529Mt probable ore of slightly lower grade.

- In addition, there are 321Mt of ore @ 0.70% Cu, 0.27g/t

Au, 2.69g/t Ag and 0.035% Mo that Kennecott intends to

block cave, plus 13.5Mt of skarn ore grading 1.89% Cu

that can be mined underground.

http://www.mining-technology.com/projects/bingham/index.html#bingham3

N-S cross section showing Geology

Latite porphyry dykes

Quartz monzonite

porphyry

Limestone

Quartzite

Monzonite and quartz

monzonite

E.C. John (1978)

Mineralization is related to a quartz monzonite porphyry, intruded into

a open syncline formed by Carboniferous (Pensylvanian) quartzite

with numerous limestone lenses.

The low- grade (< 1%Cu) protore in the quartz monzonite porphyry

was enriched by supergene processes.

The leached surface zone (21m deep) contained oxidized ore.

The supergene mineralization comprised a cc blanket (1.5% Cu and

0.018 oz/t Au 0.25 oz/t Ag) consisting of covellite at the top grading

into covellite and cc.

Geology

Minerals: py, cpy, bn, molybdenite.

Setting: disseminations, fracture fillings, and in quartz veinlets

Zonation:

• Inner weakly mineralized to barren zone minor cpy and

molybdenite with < 2% py

• Molybdenite zone

• bn + cpy zone

• cpy zone

• py zone

• Zone of skarn Pb-Zn mineralization

• The distribution of these zones in the pit depends on the

elevation at which they are intersected.

Hypogene Mineralization:

N-S Cross Section showing Sulphide Mineralized Zones

E.C. John (1978)

N-S cross section showing bornite distribution

E.C. John (1978)

Plan of bornite

distribution in pit

Lower bornite zone

Higher bornite zone

Pit outline

E.C. John (1978)

Alterations

Conditions: High temperature alteration caused by hydrothermal

fluids corresponding to the late magmatic environment.

Alteration assemblage (neo mineralization):

This will depend on the composition of the rocks affected but

normally consists of:

Quartz showing resorbed grain boundaries

K-feldspar

Biotite

Intermediate plagioclase

Potassic Alteration:

E-W cross section illustrating metal zoning in the Bingham district.

Data on west are projected up to 500m from intersection of fissures

with north-dipping limestone beds.

Mining:

-Rotary drilling/blasting – shovel/truck – in-pit crushing system,

with 2 to 4 blasts per day.

-A major recent investments was an in-pit, semi-mobile gyratory

crushing unit linked to the Copperton Concentrator by an 8km

conveyor system.

- This reduced haulage distances from the working faces

substantially but even so the mine needs a large fleet of

Caterpillar mechanical drive and Komatsu electric-drive trucks,

mostly of 218t-capacity, to service ten P&H electric rope shovels.

http://www.mining-technology.com/projects/bingham/index.html#bingham3

The Bingham mine has its own climate zones.