Overview
The wholly owned AGA Mineracao mining complex is located in southeastern
Brazil, in the state of Minas Gerais, close to the city of Belo Horizonte, with
operations in the municipalities of Nova Lima, Sabara and Santa Barbara.
Ore is sourced from the Cuiaba and Lamego underground mines and
processed at the Cuiaba and Queiroz plants, while the Corrego do Sitio
open pit mine has a heap-leaching facility.
Reorganisation of the corporate structure was completed during the first
half of 2010, combining the Cuiaba/Lamego/Queiroz and the Corrego do Sitio and
Sao Bento operations to capture operating and financial synergies. The new
company is called AngloGold Ashanti Corrego do Sitio Mineracao (AGA
Mineracao).
Location
The wholly owned AGA Mineracao mining complex is located in
southeastern Brazil, in the state of Minas Gerais, close to the city of Belo
Horizonte, with operations in the municipalities of Nova Lima, Sabara and Santa
Barbara.
Geology and Mineralization
Gold mineralization is localized in the Basal Iron Formation. The Basal Iron
Formation is subdivided along strike into 3 portions: Orebody No. 1; Orebody
No. 2; and the Sao Bento/Pinta Bem or Orebody No. 3. The Basal Iron Formation
has its greatest thickness in the No. 1 Orebody area where it attains 35 m and
at least 6 periods of gold/sulphide mineralization are evident. The ore zone is
distinctly banded and consists of alternating layers of sulphide and iron
carbonates. Gold occurs in close association with sulphides and may be free, on
crystal boundaries or enclosed in sulphide grains.
The banded iron formation (BIF) orebodies in this district have great
vertical continuity and have been mined to depths of 2,500 meters along a down
dip length of up to 4,800 meters. The BIF ore horizon at Sao Bento has been
mined continuously from surface to the current mining depth of 1,100 meters at
the 23 rd level. Diamond drill holes have intersected the ore horizon to the
31st level at the Anglogold property boundary. The ore horizon shows unbroken
continuity in the deepest drill holes and offers the potential to develop
additional ore reserves to depth. Access to deeper ore can be gained from the
existing Sao Bento shaft which has the capacity to be deepened to the 31 st
level without major changes to the existing hoisting equipment.
Mining & Operation
AngloGold Ashanti Corrego do Sao Mineracao (AGA Mineracao) comprises two
operational units, namely the Cuiaba and the Corrego do Sitio complexes. The
Cuiaba complex includes the Cuiaba and Lamego mines and the Cuiaba and Queiroz
plants. In operation for 26 years, the Cuiaba mine is principally a
cut-and-fill mine accessed by ramp and shaft. Lamego is a new mine developed to
mine an underground sulphide ore.
The first stage of the processing of the ore from Cuiaba and Lamego mines is in
the gold plant at the Cuiaba complex, where concentrate is produced. The
material is then transported 15km by aerial ropeway to the Queiroz plant where
milling, flotation, roasting, leaching, precipitation and refining occur. Total
capacity of the complete circuit is 1.65Mt/year and recoveries of 93% are
achieved.
The Corrego do Sitio operation comprises one surface (oxide) and two
underground (sulphide) mines, as well as a heap leach pad and sulphide plant,
the latter originally acquired from Eldorado late in 2008 and since
refurbished.
At AGA Mineracao, production in 2011 was 361,000oz, 7% higher than the prior
year. The higher output followed the ramp-up at Lamego and the start of
production from Corrego do Sitio. Production was, however, negatively impacted
by lower tonnage at Cuiaba, due mainly to geotechnical and fleet availability
issues.
Given the increased mining depth to more than 1,100m at Cuiaba by the end of
2011 and the resultant rise in working temperatures, a refrigeration plant was
commissioned to service the deeper areas of the mine.
At Lamego, where tonnages improved by 15%, the drill method was changed to
cross-cut instead of driving the ramp down to the mine's deepest levels so as
to improve knowledge of the orebody at depth. Now, more than 2.5 years of
reserves are estimated to be available at current production rates, following
development of ore drives from level 3.1 to level 4 at the Carruagem orebody.
This enables a high level of mining flexibility.
While the scheduled maintenance shutdown at the pyrometallurgy plant at
Queiroz was undertaken during the year, there was an unexpected shutdown of
Plant A to undertake screening of the catalyst bed and removal of the roasters.
Three new flotation cells were added to the Cuiabá plant and the wall of the
tailings dam was lifted to cope with incremental production.
At Corrego do Sitio, the underground sulphide mine was developed and the
orebodies prepared for the start of production during 2011. This mine had
reached production capacity of 40% by year-end. The underground mine produced
171,000t in 2011. The metallurgical plant was commissioned in January 2012. The
oxide heap leach plant improved its productivity 18% by increasing bench
heights on the heap leach by 1m to 7m.
Processing
Ore is treated by conventional grinding and milling in an autogenous mill
and subsequently processed by flotation to separate the gold bearing sulfides
from the tailings. Concentrate is treated by an oxidation process, either
through two bioxidation reactors using the BIOX process and/or through 2
autoclaves.
Gold is recovered in a six-stage CIL circuit to produce dore.
