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OVERVIEW OF MINING AND ITS IMPACTS
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- University Of Limpopo (UL)
IT GIVES YOU THE OVERVIEW OF MINING,IMPACTS TO THE ENVIONMENT AS WELL
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1. Overview of Mining and its Impacts1
Proposed mining projects vary according to the these metal ores are the subject of this Guidebook.
type of metals or materials to be extracted from the The Guidebook does not discuss the mining of
earth. The majority of proposed mining projects ores that are extracted using strip mining methods,
involve the extraction of ore deposits such as including aluminum (bauxite), phosphate, and
copper, nickel, cobalt, gold, silver, lead, zinc, uranium. The Guidebook also does not discuss
molybdenum, and platinum. The environmental mining involving extraction of coal or aggregates,
impacts of large-scale mining projects involving such as sand, gravel, and limestone.
1.1 PHASES OF A MINING PROJECT
There are different phases of a mining project, EIA for the exploratory phase of a mining project
beginning with mineral ore exploration and because the impacts of this phase can be
ending with the post-closure period. What profound and because further phases of mining
follows are the typical phases of a proposed may not ensue if exploration fails to find sufficient
mining project. Each phase of mining is quantities of high-grade mineral ore deposits.
associated with different sets of environmental
impacts. 1.1.2 Development
1.1.1 Exploration If the mineral ore exploration phase proves that
there is a large enough mineral ore deposit, of
A mining project can only commence with sufficient grade, then the project proponent may
knowledge of the extent and value of the mineral begin to plan for the development of the mine.
ore deposit. Information about the location and This phase of the mining project has several
value of the mineral ore deposit is obtained during distinct components.
the exploration phase. This phase includes
surveys, field studies, and drilling test boreholes 1.1.2.1 Construction of access roads
and other exploratory excavations.
The construction of access roads, either to
The exploratory phase may involve clearing of provide heavy equipment and supplies to the
wide areas of vegetation (typically in lines), to mine site or to ship out processed metals and
allow the entry of heavy vehicles mounted with ores, can have substantial environmental impacts,
drilling rigs. Many countries require a separate especially if access roads cut through ecologically
Chapter 1 3
, sensitive areas or are near previously isolated In almost every case, metallic ores are buried
communities. If a proposed mining project under a layer of ordinary soil or rock (called
involves the construction of any access roads, then ‘overburden’ or ‘waste rock’) that must be moved
the environmental impact assessment (EIA) for the or excavated to allow access to the ore deposit.
project must include a comprehensive assessment The first way in which proposed mining projects
of the environmental and social impacts of these differ is the proposed method of moving or
roads. excavating the overburden. What follows are brief
descriptions of the most common methods.
1.1.3.1 Open-pit mining
Open-pit mining is a type of strip mining in which
the ore deposit extends very deep in the ground,
necessitating the removal of layer upon layer of
overburden and ore.
In many cases, logging of trees and clear-cutting
or burning of vegetation above the ore deposit
may precede removal of the overburden. The
use of heavy machinery, usually bulldozers and
dump trucks, is the most common means of
Erosion near a mining road, Pelambres mine, Chile
removing overburden. Open-pit mining often
PHOTO: Rocio Avila Fernandez
involves the removal of natively vegetated areas,
1.1.2.2 Site preparation and clearing and is therefore among the most environmentally-
destructive types of mining, especially within
If a mine site is located in a remote, undeveloped tropical forests.
area, the project proponent may need to begin
by clearing land for the construction of staging
areas that would house project personnel and
equipment. Even before any land is mined,
activities associated with site preparation and
clearing can have significant environmental
impacts, especially if they are within or adjacent
to ecologically sensitive areas. The EIA must
assess, separately, the impacts associated with site
preparation and clearing.
1.1.3 Active mining
Open-pit mine in Cerro de Pasco, Peru
Once a mining company has constructed PHOTO: Centro de Cultura Popular LABOR, Peru
access roads and prepared staging areas that Because open-pit mining is employed for ore
would house project personnel and equipment, deposits at a substantial depth underground, it
mining may commence. All types of active usually involves the creation of a pit that extends
mining share a common aspect: the extraction below the groundwater table. In this case,
and concentration (or beneficiation) of a metal groundwater must be pumped out of the pit to
from the earth. Proposed mining projects allow mining to take place. A pit lake usually
differ considerably in the proposed method for forms at some point in time after mining stops and
extracting and concentrating the metallic ore. the groundwater pumps are turned off.
4 Guidebook for Evaluating Mining Project EIAs
, 1.1.3.2 Placer mining off-site. Mining projects that only involve the
reworking of abandoned mine waste piles avoid
Placer mining is used when the metal of interest the environmental impacts of open-pit mining
is associated with sediment in a stream bed or and placer mining, but still entail environmental
floodplain. Bulldozers, dredges, or hydraulic jets impacts associated with purification (beneficiation)
of water (a process called ‘hydraulic mining’) of metals from the waste piles.
are used to extract the ore. Placer mining is
usually aimed at removing gold from stream 1.1.4 Disposal of overburden and
sediments and floodplains. Because placer waste rock
mining often occurs within a streambed, it is
an environmentally-destructive type of mining, In almost every project, metallic ores are buried
releasing large quantities of sediment that can under a layer of ordinary soil or rock (called
impact surface water for several miles downstream ‘overburden’ or ‘waste rock’) that must be moved
of the placer mine. or excavated to allow access to the metallic ore
deposit. For most mining projects, the quantity
1.1.3.3 Underground mining of overburden generated by mining is enormous.
The ratio of the quantity of overburden to the
In underground mining, a minimal amount of quantity of mineral ore (called the ‘strip ratio’)
overburden is removed to gain access to the ore is usually greater than one, and can be much
deposit. Access to this ore deposit is gained by higher. For example, if a proposed mining project
tunnels or shafts. Tunnels or shafts lead to a more involves the extraction of 100 million metric tons
horizontal network of underground tunnels that of mineral ore, then the proposed mining project
directly access the ore. In an underground mining could generate more than one billion metric tons
method called ‘stoping’ or ‘block caving,’ sections of overburden and waste rock.
or blocks of rock are removed in vertical strips
that leave a connected underground cavity that is These high-volume wastes, sometimes containing
usually filled with cemented aggregate and waste significant levels of toxic substances, are usually
rock. deposited on-site, either in piles on the surface
or as backfill in open pits, or within underground
Although underground mining is a less mines. Therefore, the EIA for a proposed mining
environmentally-destructive means of gaining project must carefully assess the management
access to an ore deposit, it is often more costly options and associated impacts of overburden
and entails greater safety risks than strip mining, disposal.
including open-pit mining. While most large-
scale mining projects involve open-pit mining,
1.1.5 Ore extraction
many large underground mines are in operation
around the world.
After a mining company has removed overburden,
extraction of the mineral ore begins using
1.1.3.4 Reworking of inactive or
specialized heavy equipment and machinery,
abandoned mines and tailings
such as loaders, haulers, and dump trucks, which
transport the ore to processing facilities using
Some mining projects involve the reworking
haul roads. This activity creates a unique set
of waste piles (often tailings) from inactive or
of environmental impacts, such as emissions of
abandoned mines, or older waste piles at active
fugitive dust from haul roads, which an EIA for a
mines. Typically, this is proposed when more
proposed mining project should assess separately.
efficient methods of metal beneficiation have
made it economical to re-extract metals from
old mining waste. The material from the piles
may be sent to processing facilities on-site or
Chapter 1 5
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