88
This chapter presents both open-pit and alluvial mining as case studies to assess
the sustainability of gold mining. In recent years, open-pit mining has been seen as
the preferred method, while alluvial is seen as slightly less conventional (Norgate
and Haque 2012). The case study mine sites are located in Antioquia, Colombia.
The open-pit mine is located in South-East Antioquia, and the alluvial mine-site is
in North-East Antioquia.
Generally, an extractive process can be understood as inclusive of both the prospecting and exploration stage and the separation of the mineral of interest. For both
systems the operational process included the cut and stripping stage, the extraction
stage, and finally the processing and transformation of a gold ingot. Data was supplied annually over a 6-year period for alluvial mining and an 11-year period for
open-pit mining.
7.2.1.1 Open-Pit Mining
Figure 7.1 below depicts the open-pit mining extractive process. Land is prepared
through removal of the vegetation cover and organic soil in the clearing and stripping
stage, and residual biomass is then stored for future land restoration. Mineral
excavation is then carried out by conventional extraction methods, which may
include drilling, blasting, loading, and hauling.
Ore beneficiation is carried out through physical-chemical processes. It begins
with the size reduction of the excavated mineral by means of primary crushing and
both primary and secondary milling. Irrigation water is used in this step to minimize
the detrimental impacts of total particulate matter (PST) emitted. This stage
produces two different process lines; the first flow moves straight onto the flotation
process. The flotation process helps to concentrate the sulfide minerals containing
gold (96.3% of gold and 79.5% of silver are recovered in this stage, respectively).
Then, the mineral resulting from flotation goes through an intensive leaching
process (34.7% and 10% of gold and silver are recovered in this process,
respectively). Finally, tailings are stored in a tailing pond. Then it is directly
transported to the gold recoverable by gravity (GRG) process.
Gold and other metals extracted from both the leaching process (cyanidation)
and gravimetric separation are adsorbed on activated carbon in a carbon-in-pulp
circuit (CIP). They are then released into an elution column under certain conditions
of pressure and temperature. This gold-rich solution continues the electrowinning
process where a selective precipitation is made through electrolysis. Once the
electrowinning of gold and silver is obtained, it is sent to the casting furnace.
Assuming no losses in the smelting and casting process, approximately 1904 ton/
year of gold and 2155 ton/year of silver are produced, which amounts to around 952
gold ingots and 1077 silver ingots, with a 900 millesimal fineness.
Tailings are conformed by flotation tails. Evidence shows that 96.5% of the total
industrial wastewater is generated in the beneficiation process, with leaching and
carbon adsorption tails corresponding to the remaining 3.5%. These last two are
treated by a detoxification system, in which the solution of circuit is oxidized by
N. A. Cano Londoño et al.
This chapter presents both open-pit and alluvial mining as case studies to assess
the sustainability of gold mining. In recent years, open-pit mining has been seen as
the preferred method, while alluvial is seen as slightly less conventional (Norgate
and Haque 2012). The case study mine sites are located in Antioquia, Colombia.
The open-pit mine is located in South-East Antioquia, and the alluvial mine-site is
in North-East Antioquia.
Generally, an extractive process can be understood as inclusive of both the prospecting and exploration stage and the separation of the mineral of interest. For both
systems the operational process included the cut and stripping stage, the extraction
stage, and finally the processing and transformation of a gold ingot. Data was supplied annually over a 6-year period for alluvial mining and an 11-year period for
open-pit mining.
7.2.1.1 Open-Pit Mining
Figure 7.1 below depicts the open-pit mining extractive process. Land is prepared
through removal of the vegetation cover and organic soil in the clearing and stripping
stage, and residual biomass is then stored for future land restoration. Mineral
excavation is then carried out by conventional extraction methods, which may
include drilling, blasting, loading, and hauling.
Ore beneficiation is carried out through physical-chemical processes. It begins
with the size reduction of the excavated mineral by means of primary crushing and
both primary and secondary milling. Irrigation water is used in this step to minimize
the detrimental impacts of total particulate matter (PST) emitted. This stage
produces two different process lines; the first flow moves straight onto the flotation
process. The flotation process helps to concentrate the sulfide minerals containing
gold (96.3% of gold and 79.5% of silver are recovered in this stage, respectively).
Then, the mineral resulting from flotation goes through an intensive leaching
process (34.7% and 10% of gold and silver are recovered in this process,
respectively). Finally, tailings are stored in a tailing pond. Then it is directly
transported to the gold recoverable by gravity (GRG) process.
Gold and other metals extracted from both the leaching process (cyanidation)
and gravimetric separation are adsorbed on activated carbon in a carbon-in-pulp
circuit (CIP). They are then released into an elution column under certain conditions
of pressure and temperature. This gold-rich solution continues the electrowinning
process where a selective precipitation is made through electrolysis. Once the
electrowinning of gold and silver is obtained, it is sent to the casting furnace.
Assuming no losses in the smelting and casting process, approximately 1904 ton/
year of gold and 2155 ton/year of silver are produced, which amounts to around 952
gold ingots and 1077 silver ingots, with a 900 millesimal fineness.
Tailings are conformed by flotation tails. Evidence shows that 96.5% of the total
industrial wastewater is generated in the beneficiation process, with leaching and
carbon adsorption tails corresponding to the remaining 3.5%. These last two are
treated by a detoxification system, in which the solution of circuit is oxidized by
N. A. Cano Londoño et al.