Evaluation of Environmental Impact of Open-Pit Mining, Iran Case study

Introduction

The Folchi method of evaluating the environmental impact of open-pit mining was first applied in Italy. It is a numerical method for evaluating impacts of open pits. This method utilizes the following seven steps:

  • • Evaluation of pre-existing environmental conditions, including geology, geomechanics, hydrology, weather economy, etc.
  • • Identification of impacting factors, which could alter the pre-existing environmental conditions in the mine site
  • • Determination of possible ranges of variation in the existing conditions during mine life identifying the important impacting factors
  • • Singling out the environmental components whose pre-existing conditions could be altered as a result of mining
  • • Correlating each impacting factor and each environmental component
  • • Estimating the specific magnitude for each impacting factor, using previously defined ranges
  • • Calculation of the weighted sum of the environmental impact of each environmental impact on each environmental component

In this method, some parameters, such as general health and safety, social relationship, weather and climatic conditions, vegetations, and animals are defined first. Then consequences of effective mining indexes on each of the environmental component are determined, by applying a rating system for parameters, based on various concerning scenarios. The sum of all the ratings of effective parameters determines the overall effect on each of the environmental indexes. According to this method, impacting parameters are the following:

  • • Alteration of the area’s potential resources
  • • Exposition, visibility of the pit
  • • Interference with surface water
  • • Interference with underground water
  • • Increase in vehicular traffic
  • • Atmospheric release of gas and dust
  • • Fly rock
  • • Noise
  • • Ground vibration
  • • Employment of a local workforce

The possible scenarios for each impacting factor are then considered, and a magnitude is assigned to each of them.

Table 17.1 shows various scenarios and their related magnitude for each impacting factor.

The Folchi method was applied to an important copper open-pit mine in Iran, namely Sarcheshmeh.

This mine is located 50 km south of the city of Rafsanjan in Kerman province and is the largest copper mine in Iran. The geology of Sarcheshmeh porphyry copper mine is very complicated, and various types of rocks can be found. The main minerals are chalcopyrite, chalcocite, covellite, bornite, and molybdenite. Other minerals include molybdenum, gold, and silver. The oxide zone of the deposit consists mainly of cuprite, tenorite, malachite, and azurite. Pyrite, being mineral, which causes acidity in mine sewage. The proven reserve of the deposit is approximately 826Mt with an average grade of 0.7%. The mine worked by open pit. The distance of crusher to mine is 3 km. The annual capacity of the mine mill is 51,000 tons of concentrate with an average grade of 30% and a recovery of 65%. The environmental data related to the Sarcheshmeh mine was evaluated using the Folchi method and magnitude ranges given in Table 15A. Each impacting factor of the proposed mining activities was assessed (Table 17.2). Final scoring for each environmental component can be

TABLE 17.1

Ranges of Magnitude for Impacting Factors (Monjezi, M et. al)

Acting factors

Scenario

Magnitude

Alteration of area’s potential resources

Parks, protected areas

8-10

Urban area

6-8

Agricultural area, wood

3-6

Industrial area

1-3

Exposition, visibility of the pit

Can be seen from inhabited areas

6-10

Can be seen from main roads

2-6

Not visible

1-2

Interference with above groundwater

Interference with lakes and rivers

6-10

Interferences with non-relevant water system

3-6

No interference

1-3

Interference with under groundwater

Water table superficial and permeable grounds

5-10

Water table deep and permeable grounds

2-5

Water table deep and un-permeable grounds

1-2

Increase in vehicular traffic

Increase of 200%

6-10

Increase of 100%-

3-6

No interference

1-3

Atmospheric release of gas and dust

Free emissions in the atmosphere

7-10

Emission around the given reference values

2-7

Emission well below the given reference values

1-2

Fly rock

No blast design and no clearance procedures

9-10

Blast design and no clearance procedures

4-9

Blast design and clearance procedures Peak air overpressure at 1 km distance

1-4

Noise

<141 db

8-10

<131 db

4-8

<121 db

1-4

Ground vibration

Cosmetic damage, above threshold

7-10

Tolerability of threshold

3-7

Values under tolerability threshold

1-3

Employment of local workforce

Job opportunities

7-10

High

3-6

Medium

Low

1-2

TABLE 17.2

Correlation Matrix with Values of the Weighted Influence of Each Impacting Factor on Each Environmental component (Monjezi, M et. al)

Impacting factors

Environmental Components

Human Health and Safety

Social

Relationship

Water

Quality

Air

Quality

Use of Territory

Flora

and

Fauna

Above

Ground

Underground

Landscape

Noise

Economy

Alteration of area’s

Med

Min

Nil

Nil

Max

Min

Nil

Nil

Max

Nil

Nil

potential resources

0.80

0.77

0

0

5.71

0.63

0

0

2.86

0

0

Exposition, visibility

Nil

Min

Nil

Nil

Med

Nil

Nil

Nil

Max

Min

Nil

of the pit

0

0.77

0

0

2.86

0

0

0

2.86

2.00

0

Interference with

Max

Nil

Max

Nil

Nil

Max

Med

Nil

Max

Nil

Nil

above groundwater

1.60

0

4.44

0

0

2.50

6.67

0

2.86

0

0

Interference with

Min

Nil

Max

Nil

Nil

Nil

Nil

Med

Nil

Nil

Ni

under-groundwater

0.40

0

4.44

0

0

0

0

6.67

0

0

01

Increase in vehicular

Max

Max

Nil

Nil

Min

Max

Nil

Ni

Min

Nil

Nil

traffic

1.60

3.08

0

0

1.43

2.50

0

01

0.71

0

0

Atmospheric release

Max

Min

Min

Max

Nil

Max

Min

Nil

Min

Nil

Ni

of gas and dust

1.60

0.77

1.11

10.00

0

2.50

3.33

0

0.71

0

01

Fly rock

Max

Nil

Nil

Nil

Nil

Med

Nil

Nil

Nil

Nil

Nil

1.60

0

0

0

0

1.25

0

0

0

0

0

Noise

Med

Max

Nil

Nil

Nil

Min

Nil

Nil

Nil

Max

Nil

0.80

3.08

0

0

0

0.63

0

0

0

8.0

0

Ground vibration

Max

Med

Nil

Nil

Nil

Nil

Nil

Min

Nil

Nil

Nil

1.60

1.54

0

0

0

0

0

3.33

0

0

0

Employment of local

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Max

workforce

0

0

0

0

0

0

0

0

0

0

10.00

Total

10

10

10

10

10

10

10

10

10

10

10

Rating of Environmental Parameters in the Case Study of Mines (Monjezi, M et. al)

TABLE 17.3

Impacting Factors

Sarcheshmeh

Alteration of area’s potential resources

3

Exposition, visibility of the pit

3

Interference with the above groundwater

7

Interference with the under groundwater

7

Increase in vehicular traffic

9

Atmospheric release of gas and dust

10

Fly rock

5

Noise

7

Ground vibration

7

Employment of local work force

7

acquired by multiplying Table 17.2 into Table 15C. The overall effect on each environmental component is calculated by summing the weighted magnitudes of all the impacting factors (Table 17.3).

The Folchi method indicates that specific aspects of environmental impact can be quantified. The most significant impacts in the Sarcheshmeh copper mine are air quality, above ground, and flora and fauna with score values of 100, 80, and 77.6, respectively. The sum of scores for the environmental components can be calculated and then evaluated. The sum of components of scores for the Sarcheshmeh copper mine is 766. The evaluation indicates that some remedial measures must be taken for the affected environmental components, such as air quality and water condition, which are essential for the living creatures. A plant for converting sulphur dioxide to sulphuric acid has been constructed for the Sarcheshmeh mine which has been seriously affecting air quality. Additionally, the Sarcheshmeh mine has seriously affected the water quality in the area as indicated in the Table 17.4 and shows high ground vibration for the Sarcheshmeh mine for which reducing charge per delay is a reasonable solution.

This evaluation indicates that the Folchi method accounted for many environmental parameters that were not recognized by other approaches. This method is the best approach for evaluating mine operations. This method can be potentially used as an environmental regulation tool as needed. There are several advantages to applying this method. The method makes it possible to simplify complex analysis by splitting it in a number of easily quantified components, which can be treated one at a time, being reconstituted in a standardized matrix to give a total magnitude value. This value can then be used to compare mining operations of different types. This is a key requirement for using it as a regulatory tool.

 
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