Chilean Mines
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| Chile Mines |
Andacollo Mine
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| Andacollo Mine |
Location: Elqui, Coquimbo, Chile.
Products: Copper
& Gold.
Owner: Royal Gold,Inc.
Ore Type: Porphyry copper-gold
deposit, hosted by altered andesitic and dacitic volcanic rocks, and small
stocks and irregular dykes of potassium-rich tonalitic porphyry.
Overview
The Andacollo mining district is
located in the Coquimbo region of Chile at 30°14’ south, 71°06’ west, some 55
km southeast of La Serena, at a mean elevation of 1030 m within a semi-arid
hilly landscape. Current mining activity in the district is concentrated on
copper and gold. These metals are mined, respectively, from a porphyry copper deposit
and epithermal, manto and vein gold deposits of adularia–sericite type.11,13
Other types of mineralization include mercury veins hosted by carbonate rocks.
The gold veins are controlled by a northwest-trending set of normal faults, whereas
the manto-type mineralization is strata-bound and largely confined to andesite
breccias, dacites and sites of strong fracturing. The lateral and vertical
continuity of the mantos is strongly controlled by rock type, faulting and
intensity of fracturing. The gold deposits have been the focus of a recent
study,11 but comparable information on the Andacollo porphyry has not become
available.
Andacollo’s operating profit from August
22 to December 31, 2007 was $27 million before the effects of the revaluation
of copper inventory to fair value on acquisition and negative pricing adjustments.
The revaluation established a higher value for copper inventories, based on
market prices at the date of acquisition. This increased our cost of sales by
$24 million and the subsequent decline in metal prices resulted in a loss on
the sale of these inventories. In addition, the mine recorded negative pricing
adjustments of $2 million since they acquired it in August 2007. After these adjustments,
Andacollo’s operating profit was $1 million. Copper cathode production in 2008
is expected to be approximately 20,000 tonnes and capital expenditures are
planned at US$190 million, including US$185 million on the hypogene
development.
Geological setting and
Mineralization
The Andacollo deposits are the products of a complex hydrothermal system
and consist of a porphyry copper-gold deposit and peripheral strata-bound manto
gold deposits and veins with minor associated base metals. The hydrothermal
system was part of the Pacific porphyry copper belt which was generated during
development of an Early Cretaceous magmatic arc displaying shoshonitic
petrochemical affiliations. Rocks that crop out in the area include a volcanic
sequence, the Arqueros and Quebrada Marquesa Formations, consisting of andesitc
and dacite flows, volcanic breccias, and pyroclastic rocks of Early Cretaceous
age. Intrusive rocks range from diorite to granodiorite in composition and date
between 87 and 130 Ma. The porphyry copper-gold deposit is zoned vertically
downward from a leached capping through a supergene enrichment blanket to a
hypogene sulfide zone. Alteration is characterized by central potassic (K
feldspar-biotite), phyllic, and peripheral propylitic zones. Abundant northwest-trending
tensional fractures were superimposed on the porphyry copper-gold deposit and
surrounding areas during the later stages of the evolving mineralized system.
The fractures channeled mineralizing fluids from the central parts of the
porphyry copper deposit outward for up to 5 km. Replacement by adularia and
sericite took place together with deposition of gold-bearing pyrite and minor
amounts of zinc and copper where these fluids encountered permeable dacite
flows and andesite flow breccias. The alteration process caused remobilization
of aluminum and alkalies and addition of K 2 O, which attains values of 12 to
13 wt percent. The Andacollo system is interpreted to be a porphyry copper-gold
deposit that is transitional outward to distal epithermal,
adularia-sericite-type contact metasomatic gold orebodies.
Chuquicamata Copper Mine
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| Chuquicamata Copper Mine |
250km north-east of Antofagasta,
1,200km north of Santiago. (22°17'S 68°54'W)
Classification: open pit copper mine.
OreType : Copper porphyry.
Dimension: Size of pit: L=4,500m, W=3,540m, D=800m.
Production: Gold-Copper 650,000 metric
Tons annually. A=2,800m a.s.l.
Overview
Chuquicamata,
in northern Chile, is the world’s greatest orebody. It was mainly controlled by
initial intrusions (probably at 36 to 33 Ma) through mineralization (last major
hydrothermal event at 31 Ma) to postmineral brecciation and offset by the West
Fault system. The Chuquicamata Porphyry Complex consists of the East Porphyry,
West Porphyry, Banco Porphyry and Fine Texture Porphyry. Potassic
alteration, the early stage of
alteration, affects all porphyries. Veins of quartz molybdenite, up to 5 m wide
and cutting all porphyries, were emplaced between the early and the main
stages. Main-stage veins occupy many of the same structures of the early stage
and may involve massive remobilization of earlier mineralization. The late
stage formed digenite with relatively coarse grained covellite from deep in the
sericitic zone. A leached capping and oxide copper ore, replacing an upper
chalcocite blanket, overlie a high-grade supergene chalcocite body that extends
up to 800 m in depth.
Summary of Geological
Setting
Chuquicamata
is closely related to Eocene, early Oligocene porphyritic intrusions that occur
within the middle to late Cenozoic, north-south striking Domeyko Fault system.
Pre-Oligocene rocks
The
oldest rocks in the Chuquicamata district occur in a north-northeast trending
belt of Paleozoic metasedimentary and metaplutonic rocks. These rocks include gneissic granite, metadiorite, quartz
diorite, and minor tonalite recrystallized in varying degrees to amphibolite.
Eocene-Oligocene intrusions
The
porphyritic rocks in the Chuquicamata pit, with the dominantly barren Fortuna
Complex to the west and the intensely mineralized Chupui Porphyry Complex to
the east, are separated by the major postmineral West Fault. Rocks with
textures essentially identical to those of the Chuqui Porphyry Complex extend
northward at least 9 km through the Radomiro Tomic mine (Cuadra et al., 1997;
Cuadra and Rojas, 2001).
Rock Types
Fortuna
Intrusive Complex
The Fortuna Intrusive Complex borders
to the open pit and contains only low-grade mineralization. It has been structurally
juxtaposed against the intensely mineralized Chuquicamata Porphyry Complex by
large-scale, postmineral movement on the Wets Fault, which is documented by
Dilles et al. (1997), Tomlinson and Blanco (1997), and previous workers. The
Fiesta Granodiorite phase of the Complex is volumetrically dominant and is
intruded by small irregular bodies of San Lorenzo Granodioritic Porphyry and
minor Tetera Aplite Porphyry. Fiesta Granodiorite is weakly mineralized with
copper oxides in the uppermost northwestern benches of the pit. Sulfides occur only
near contacts of the San Lorenzo porphyries.
Pre-Chuqui
porphyry intrusions
The Elena and East Granodiorites are
exposed on the eastern margin of the pit. They intrude metasedimentary rocks
that were originally shale and sandstone with minor limestone. Whereas Elena Granodiorite
is mineralogically and texturally similar to the East Porphyry, the East
Granodiorite is texturally distinctive and clearly older. A radiometric dating
of the Elena Granodiorite indicates a Jurassic (dating of zircon) to Early
Cretaceous age (dating of biotite), published by Ambrus (1979). All of these
rocks at the east edge of the pit are essentially poor of mineralization.
Chuqui Porphyry
Complex
Practically the entire Chuquicamata
orebody is hosted by the Chuqui Porphyry Complex, made up of East, West, Fine
Texture, and Banco porphyries. Their textures vary widely, and most exposures are
affected by some degree of hydrothermal alteration and pervasive cataclastic
deformation. The probably oldest and largest intrusion is the East Porphyry
with hypidiomorphic-granular texture. The West Porphyry is finer grained and
with quartz eyes in an aplitic groundmass. Locally both porphyries are weakly
foliated. Banco Porphyry is more porphyritic and finer grained than East
Porphyry, which it intrudes. From West Porphyry it differs in having an
abundance of small plagioclase crystals in the aplitic mass. The Fine Texture
Porphyry is distinctly finer grained than normal East Porphyry but has also a
hypidiomorphic-granular texture. Contacts with East Porphyry may be abrupt but
usually faulted. Because of the overprinting of most dikes by quartzsericite alteration,
their identification is very difficult. Furthermore is seems, that Banco and
Fine Texture porphyries have been affected by all of the same stage of
alteration and mineralization as the East Porphyry.
A large part of the copper at Chuquicamata occurs in veins and
veinlets filling faults and faultrelated shatter zones. In the main orebody
practically all of these fractures have been opened and mineralized more than
once. Early-stage veinlets of quartz and quartz-K feldspar contain no or only
very minor sulfide. They are cut by more continuous quartz veins, to 5 cm wide,
containing minor molybdenite and traces of chalcopyrite. Large banded quartz veins,
known as blue veins, are typically 1 m or more in width. They contain abundant
molybdenite and truncate the previous veins. Furthermore, they are commonly
surrounded by sericitic alteration, but this is due to superposition of younger
pyritic veins following the same structures. Veins and veinlets of the main stage
contain pyrite, chalcopyrite, bornite, and digenite, decreasing amounts of
quartz and increasingly well-developed sericitic alteration halos. Locally, the
earliest of these veins appear to contain pyrite without Cu sulfide (Lindsay et
al., 1995). Relatively late main stage veins contain enargite ± pyrite and
minor sphalerite. Later on, veinlets and fractures are filled with relatively
coarse grained covellite (to 1 mm) and digenite with and without pyrite.
Hypogene Alteration and
Mineralization
Just like El Salvador and many other
porphyry copper deposits, vein relationships lead to the definition of an early
stage defined by K feldspar stable alteration and early quartz veinlets, a
transitional stage defined by quartz-molybdenite veining, and a main-stage
defined by pyrite-bearing veins with sericitic halos. A more unusual and
controversial late stage is defined by coarse-grainedcovellite-digenite
veinlets without pyrite and possibly hypogene sphalerite rims on other sulfides
(Fréraut, et al., 1997).
Supergene Mineralization and
Alteration
After Taylor (1935) and Jarrell (1944) the
rich oxide copper orebody has been largely mined out, but considerable
resources of lower grade material remain in the north end of the pit and beyond
(North zone, Fig. 1; Cuadra et al., 1997; Ossandón and Zentilli, 1997). Oxide
ores contain a large variety of minerals but in chief antlerite, brochantite,
atacamite, chrysocolla, and copper pitch. Also residuals of chalcocite are
implied. The ore was overlain by leached capping and was an eastward and upward
extension of the chalcocite zone, indicating it was a supergene chalcocite
enrichment blanket oxidized in situ. It is the upper of two chalcocite blankets
with a leached horizon in between. A lower enrichment zone has more reactive
alteration assemblages and contains decreasing chalcocite and/or covellite
proportions downward. In the central zone of intense brecciation, the two
enrichment blankets (copper leaching and chalcocite enrichment) merge and reach
their maximum depth.
Mining and processing
Coldec uses conventional open pit mining methods at
Chuquicamata. A conventional truck-and-shovel operation constitutes the mining
activity. Large quantities of the ore are crushed within the pit. Underground
conveyors transport the crushed ore to the mill bins.
An Outokumpu flash smelter is installed for smelting the
concentrate. The concentrate is then passed through a converter with electric
furnace. After the slag is cleaned, the concentrate passes through four Pierce
Smith converters. Blister copper is then sent to six anode furnaces. The
electrolytic refinery has a capacity of 855,000t per annum. Three anode casting
wheels were installed and are fed by the furnaces.
Underground mining at Chuquicamata
The new underground mine, scheduled begin operations in 2019,
will comprise of four production levels, a 7.5km main access tunnel, five clean
air injection ramps, and two air-extraction shafts.
The tunnels will deepen the mine by nearly 787m by the end of
production in 2060. The underground mine will be developed at an estimated cost
of $4.2bn and will produce an estimated 140,000 tonnes of ore per day. It mine
is expected to produce 366,000t of copper and 18,000t of fine molybdenum per
year.
Sinclair Knight Merz undertook the conceptual engineering of the
mine, including identification, option studying and analysis for ore excavation
and handling. For ore extraction, panel caving and macro blocks were studied.
Three extraction panels were identified at different depths for both options.
Excavation panels identified for panel cavings were at 1,841m, 1,697m and
1,409m above sea level and 1,841m, 1,625m and 1,409m for macro blocks.
The copper ore reserves of the Chuquicamata underground mine are
estimated to be 1,700mt grading 0.7% copper and with an average molybdenum
content of 502ppm.
Pascua Lama mine
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| Pascua Lama mine |
Location: Andes Mountains, on the Chilean-Argentine
border.
Products: Gold,
Silver, Copper.
Owner: Barrick Gold.
The Mine life: The mine life is expected to be 25 years.
Deposite Type:
The gold, silver and copper
mineralisation and alteration assemblages at Pascua-Lama are associated with a
structurally controlled acid sulphate hydrothermal system hosted by intrusive and
volcanic rock sequences of the Upper Palaeozoic and Middle Tertiary age.
Alteration and mineralisation are of the high-sulphidation, epithermal type.
Throughout the Pascua-Lama district, the alteration and mineralisation appear
to have been strongly controlled by structure. This control is most evident
along the Esperanza, Pedro and Quebrada de Pascua fault systems. As is typical
with high-sulphidation epithermal deposits, the principal metal commodities at Pascua-Lama
are gold and silver, the copper content is sub-economic.
The presence of hypabyssal intrusive host
rocks that are not related to mineralisation is unusual for high sulphidation
deposits, making Pascua-Lama (along with Barrick’s Alto Chicama deposit in
Peru, which is hosted by meta-sedimentary rocks) somewhat unique among deposits
of this type.
Overview
Pascua-Lama is located
at an altitude of 3,800m to 5,200m. The Chilean part of the mine constitutes
75%, while 25% is located in Argentina. The development activities of
Pascua-Lama were stopped in April 2013, following a Chilean court's orders on
issues of sanitation and violation of the Glacier monitoring plan. The Diaguita
indigenous community filed a petition for the closure of the project. Barrick
Gold's plea to reopen the project was rejected by a local appellate court in
Copiapó, Chile, on 24 April 2013.
The Chile's Supreme
Court, however, issued a ruling in September 2013 overturning the Copiapó court
order. Following the ruling, Barrick Gold will construct a water management
system at the Chilean section of the mine in order to receive environmental
approval for the project. The water management system is expected to be
completed by the end of 2014.
Barrick Gold announced
its decision to temporarily suspend the Pascua-Lama project, in October 2013,
in order to reduce its debt burden. Construction of facilities required for
obtaining the environmental approval will, however, be completed. The company
plans to resume the mine's development in future.
The Argentinean segment
was to include critical infrastructure such as the processing plant and
tailings storage facility.
Barrick Gold had
estimated the development capital cost of Pascua-Lama to be $3bn at 2009
prices, but the construction delay increased the estimated capital costs of the
project to approximately $8bn to $8.5bn at 2012 prices. The development of the
mine would have created more than 5,500 jobs during construction and more than
1,600 jobs during production phase.
Geological Setting
The Pascua-Lama deposit is situated at the crest of the high
cordillera of Region III, along the international border between Chile and
Argentina and on the northern edge of a major mineralised trend known as the El
Indio belt. This trend, along which a number of major precious metal deposits
are located (including the nearby Veladero mine), stretches 47km south of
Pascua-Lama to the world-renowned El Indio deposit and adjacent Tambo deposit
(both closed).
The geology in the region is dominated by extrusive volcanic rocks
that are locally intruded by hypabyssal stocks of varying size and numerous
dikes and sills (Figure 6-1). Volcanic activity began with deposition of the
Permian Guanaco/Zonso felsic ash flows from a caldera 15km east of Pascua-Lama
and subsequent intrusion of the Permian-Triassic Chollay crystalline felsic
rocks along the extent of the El Indio belt. These events were followed by
intrusion of the Triassic Pascua-Lama granite complex in the immediate vicinity
of the Project. Deposition of extrusive volcanic rocks and continued intrusive
activity resumed in the Oligocene with the Bocatoma diorite stocks (33-36Ma),
the Tilito dacite ash flows (27.2-17.5Ma) the Escabroso mafic andesite and
andesitic flows (21.0-17.5Ma), and the Cerro de Las Tortolas I andesites (16.0
±0.2 -14.9 ±0.7Ma), after which volcanic activity decreased markedly in the
vicinity of the El Indio belt. Subsequent activity was confined to the Vacas
Heladas intermediate dacitic domes, lava flows and felsic tuffs (12.8-11.0Ma),
and the Late Miocene rhyodacite dikes at Pascua. The most recent activity in
the region included deposition of the post mineralisation silicic Vallecito rhyolites
south of Pascua-Lama in the vicinity of Cerro de Las Tortolas, and the Upper
Pliocene Cerro de Vidrio rhyolite. All ages are from Bissig et al., (2000a
& 2001) and Martin et al.,(1995).
Regional
structure in and around the gold deposits and prospects in the El Indio belt is
dominated by northerly-trending high angle reverse faults, normal faults and fold
belts oriented parallel to the major structural grain of this portion of the
Andean Cordillera. Pascua-Lama is positioned near the center of a northerly
trending graben that contains nearly the entire Tertiary volcanic sequence that
is distributed along the spine of the cordillera in Chile and Argentina. This
graben is bounded by two high angle reverse fault zones, the Baños del Toro/Chollay
located 10km west of the deposit and the El Indio zone situated 16km to the
east. The graben is cut at Pascua and El Indio by strong, west-northwest
fracture zones, which form loci for mineralisation. Large elliptical fracture
zones are also present immediately to the east and/or northeast of both El Indio/Tambo
and the Pascua-Lama/Veladero deposit areas, and these zones may have
contributed to host rock permeability.
Metallurgy and Mineral Processing
The
Pascua-Lama (and Esperanza) ore is extremely complex and highly variable,
ranging from relatively straight forward oxide zones which are amenable to cyanide
leaching, to highly altered sulphide zones containing soluble sulphate minerals
with some cyanide-amenable gold/silver and some refractory gold/silver hosted
in sulphides. The majority of silver occurs in an enriched blanket of secondary
mineralisation in the upper zones of the deposit with silver grades typically four
to five times those of the underlying primary zones.
The
deposit is hosted in a high-sulphidation hydrothermal system consisting of
acidic material that requires a washing stage to remove soluble iron and copper
sulphate salts that are detrimental to subsequent processing. Ore material in
the deposit is classified as two main types:
Non-Refractory
and Refractory, both ore types are crushed, wet ground and washed in similar circuits.
The washed Non-Refractory ore is subject to direct cyanide leaching only with
pregnant solution which is recovered from the counter current decantation
(“CCD”) circuit, treated in a conventional Merrill Crowe (zinc precipitation)
circuit to produce gold/silver doré. The washed
Refractory
ore is subject to flotation with cyanide leaching of the flotation tails.
Solution recovery and precious metal production from the leached tails is via
the CCD and Merrill Crowe circuits to produce gold/silver doré. The flotation
circuit produces a final gold/silver rich concentrate of nominally 12% copper
for export to smelters.
The proposed nominal plant capacity is 45,000t/d of ore, 30,000t/d
for Non-Refractory ore and 15,000t/d for Refractory ore, according the
following schedule:
• Year 1, Q1: Two lines,
30,000t/d Non-Refractory ore;
• Year 2, Q4: Three lines,
45,000t/d Non-Refractory ore; and
• Year 3, Q3: Two lines,
30,000t/d Non-Refractory ore and one line, 15,000t/d Refractory ore.
Mine Production and Mineral Reserve Estimate
SRK audited the Mineral Reserve estimate that was prepared by Barrick
(Table 2). SRK is of the opinion that the estimation strategy and methods
employed meet or exceed current industry standards and the reserves have been
classified according to CIM guidelines. The LoM plan was based on calculations
prepared in mid-2008 for the Feasibility Study and not the end of year Mineral
Reserve estimate disclosed in this report.
The difference between the LoM plan and the Mineral Reserve
estimate is not considered material to Silver Wheaton.
Mining commences in 2011 with pre-stripping. The amount of pre-stripping
required is 66.4Mt and this is scheduled to be mined in an 18-month period using
the owner’s equipment. The first ore is produced in late 2012. The production phase
commences in 2013. The LoM production schedule is shown in Table 3.
The average ore plus waste mining rate is 66.0 Mt/y, comprising
18.3Mt/y of ore and 48.8Mt/y of waste. The average overall strip ratio is
2.71:1, exclusive of the pre-production period. The average overall strip ratio
inclusive of the pre-production period is 2.88:1.
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