| |
| OPEN PIT SURFACE MINE |
-
- Fig. 1, above shows an illustration of a Open Pit Surface Mine. The
definition of a open pit mine is "an excavation or cut made at the
surface of the ground for the purpose of extracting ore and which is open
to the surface for the duration of the mine’s life." To expose
and mine the ore, it is generally necessary to excavate and relocate large
quantities of waste rock. The main objective in any commercial mining operation
is the exploitation of the mineral deposit at the lowest possible cost
with a view of maximizing profits. The selection of physical design parameters
and the scheduling of the ore and waste extraction program are complex
engineering decisions of enormous economic significance. The planning of
an open pit mine is, therefore, basically an exercise in economics, constrained
by certain geologic and mining engineering aspects.
A bench may be defined as a ledge that forms a single level of operation
above which mineral or waste materials are mined back to a bench face.
The mineral or waste is removed in successive layers, each of which is
a bench. Several benches may be in operation simultaneously in different
parts of, and at different elevations in the open pit mine.
-
- Open pit mines can be used in coal mining, and they are used extensively
in "hard rock" mining for ores such as metal ores, copper, gold,
iron, aluminum, and many minerals. In a open pit coal mine, the pit bottom
would be the bottom mined coal seam elevation, since it is usually feasible
to extract multiple seams when surface mining coal. In a hard rock mine,
the bottom of the pit would be the lowest level (elevation) that mining
would be conducted on the ore being mined.
Planning must account for both environmental protection, beginning as early
as the initial exploration, and for reclamation. It is critical that planning
alleviate or mitigate potential impacts of mining for two key reasons:
(1) the cost of environmental protection is minimized by incorporating
it into the initial design, rather than performing remedial measures to
compensate for design deficiencies, and (2) negative publicity or poor
public relations may have severe economic consequences. From the start
of the planning process, adequate consideration must be given to regulatory
affairs. The cost of compliance may be significantly reduced when taken
into account in the design or planning process, in a proactive manner,
rather than being addressed on an ad hoc basis as problems develop or enforcement
actions occur.
-
- From the beginning of the mine design planning stage, data gathering
and permitting, environmental considerations are important, although benefits
from a strictly economic sense may be intangible. From exploration, where
core holes must be sealed and the site reclaimed, through plan development,
the impacts on the environment must be considered. These impacts include
aesthetics, noise, air quality (dust and pollutants), vibration, water
discharge and runoff, subsidence, and process wastes; sources include the
underground and surface mine infrastructure, mineral processing plant,
access or haul roads, remote facilities, etc. If mining will cause quality
deterioration of either surface water or groundwater, remedial and treatment
measures must be developed to meet discharge standards. The mine plan must
include all the technical measures necessary to handle all the environmental
problems from initial data gathering to the mine closure and reclamation
of the disturbed surface area.
-
- Reclamation plans include many of the following concerns: drainage
control, preservation of top soil, segregation of waste material, erosion
and sediment control, solid waste disposal, control of fugitive dust, regrading,
and restoration of waste and mine areas. The plan must also consider the
effects of mine subsidence, vibration (induced by mining, processing, transport,
or subsidence), and impact on surface water and groundwater. These environmental
items often dictate the economics of a planned mining operation and determine
its viability.
-
-
|
|
|
|
