Geometric Analysis of the Itakpe Open Pit Mine

TABLE OF CONTENTS

ABSTRACT

DEDICATION

ACKNOWLEDGEMENTS

LIST OF FIGURES

ABBREVIATIONS

CHAPTER ONE INTRODUCTION
1.1 BACKGROUND OF THE STUDY
1.2 STATEMENT OF THE PROBLEM
1.3 OBJECTIVES OF THE STUDY
1.4 SCOPE OF THE STUDY
1.5 SIGNIFANCE OF THE STUDY
1.6 THE STUDY AREA
1.7 GEOLOGY OF THE AREA

CHAPTER TWO LITERATURE REVIEW
2.1 ORE AND ORE RESERVE
2.2 NIGERIAN IRON ORE RESERVE
2.3 ITAKPE IRON ORE RESERVE
2.4 MINE AND MINING
2.5 OPEN-PIT MINING
2.6 EXTRACTION OF AN OPEN-PIT MINE
2.7 OPEN-PIT AND ORE BODY CONFIGURATIONS
2.8 EQUIPMENTS USED IN OPEN PIT MINING
2.9 GEOMETRIC ANALYSIS OF AN OPEN-PIT MINE

CHAPTER THREE METHODOLOGY
3.1 BASIC TERMS
3.2 LIMITING STRIPPING RATIO APPROACH
3.3 GEOMETRIC SECTION OF THE MINE
3.4 CALCULATIONS

CHAPTER FOUR RESULTS

CHAPTER FIVE CONCLUSION

REFERENCES

ABSTRACT

In mine planning and design, it is of utmost importance to have the basic knowledge of geometry as it is necessary in the in the graphical representation of the mine and also in the estimation of the mine’s production rate.

Using the limiting stripping ratio approach, I can establish the overall slope angle of the mine using the mine surface intercept method of which the overall slope should be inclined at an angle of 53⁰. The mine divided into benches of 10m intervals would enable easy estimation of the production rate as the given deepening rate would aid in calculations.

All these would enable easy design of the mine as well as its planning prior to when production commences.

DEDICATION

This work is dedicated to the Almighty God for his inspiration and guidance, and to my mother, Mrs. Hannah Oniuwe.

ACKNOWLEDGEMENTS

I would like to express my deepest appreciation to all those who provided me with the possibility to complete this research project. A special gratitude I give to the Almighty God for seeing me through this period. To my mother, Mrs. Hannah .E. Oniuwe and sister Mrs. Cynthia .U. Ogbonna for their continuous support, in terms of encouragement and finances, my other siblings.

Furthermore, I would like to acknowledge with much appreciation, the crucial role of my H.O.D and Supervisor, Dr. J.I Nwosu who made sure that that I really understood the project work to the fullest and for his constant presence.

Also, many thanks go to the staff of the National Iron Ore Mining Company (NIOMCO) Itakpe, who gave me the permission to make use of their data and also explore the mine. And to the entire staff of the Department of Geology and Mining Technology.

Last but not the least, special thanks go to my favourite people, Joseph Amadi, Ibinabo Kalio, Christiana Uduosoro, Selina Nabiebu et al. You all made my days at the University of Port Harcourt Awesome.

LIST OF FIGURES

Abbildung in dieser Leseprobe nicht enthalten

ABBREVIATIONS

Abbildung in dieser Leseprobe nicht enthalten

CHAPTER ONE INTRODUCTION

1.1 BACKGROUND OF THE STUDY

Itakpe mine, owned and operated by the National Iron Ore Mining Company (NIOMCO), is located at Itakpe in Okehi Local Government Area of Kogi State, Nigeria. The mine complex includes a series of surface mining operations that use open-pit mining method to extract iron ore. The mine has an estimated reserve of 145 million tonnes grading 35% iron metal.

Exploration work on the Itakpe Iron Ore deposit was started in 1963, by the Geological Survey of Nigeria together with the Canadian Aero Service Limited and the Italian Technical Association

The use of geometric method involves the use of graphic representation of the shape of deposit and properties (features) of minerals in the earth’s interior. Methods of calculating and keeping track of the changes in reserves, and methods of solving geometric problems related to carrying out on mining work.

This method is also used in analysing the production rate of the mine which includes the data gotten from the following:

- Estimated cost of mining which include;
- Labour costs
- Exploration and development costs
- Capital cost of the mine
- Mining cost
- Processing cost
- Miscellaneous cost of operation
- Royalties
- Taxes ( Federal, State and Local)
- Revenues

- Financing
- Working capital necessary
- Depreciation method used
- Depletion allowance

- Factors limiting production
- Technical factors
- Market
- Finance
- Reserve

- Stripping ratio

- Deepening rate

All of these would be represented in statistical graphs, charts, tables and equations with which I would be able to a clear breakdown of the productivity of the mine.

1.2 STATEMENT OF THE PROBLEM

The National Iron Ore Mining Company (NIOMCO), operators of the Itakpe mine should have a concise system that analyses the production rate and cash flow for the period of time that the mine would be in operation. This system is usually computerized in other to obtain quick and precise analysis.

However, a computerized system although very easy to understand and operate, might lead to people having little or no knowledge of how the actual system works in real life analysis. In cases of computational errors, an analyst who has little knowledge of production rate analysis would find it difficult in tracing and rectifying these errors. Hence, theoretical knowledge is required.

This process might be time consuming but it would definitely save the company a lot when these documents are not only stored in computer devices but also stored in prints where they could be filed and kept in cabinets. The Analyst would be able to interpret the cash flows and revenues generated, state the profits and losses incurred in the process of operation, give a proper rundown on all expenditures made, thereby saving the company from running into losses due to ignorance.

1.3 OBJECTIVES OF THE STUDY

The purpose of this analysis is to give a complete break down on the production rate of Itakpe mine.

The specific objectives include:

- To compare the annual production rates
- To identify factors that limit mine production rate and then develop a means of overcoming such factors
- To analyse the production rate from commencement of operation till date
- To give estimates that will be feasible.

1.4 SCOPE OF THE STUDY

The area of this study covers the Nigerian Mining Sector, especially ore mining. However, this study is specifically focused on the Itakpe mine which is operated by the National Iron Ore Mining Company (NIOMCO).

1.5 SIGNIFANCE OF THE STUDY

This study will be greatly beneficial to a number of companies operating in the mining sector. Not only will it be useful for production rate calculations, it would also be useful for auditing purposes.

Another set of interest groups that will benefit from this study are the government, the community where the company operates, where taxes and royalties can be monitored with ease.

The last beneficiary of this study is the international community particularly in the area of mining and solid minerals. With this analysis, they would know if investing in the mining sector in Nigeria is profitable or not.

1.6 THE STUDY AREA

Itakpe mine is located at Itakpe in Okehi Local Government Area of Kogi State within the latitude 07◦ 36’ 20”N of the equator and longitude 06◦ 18’ 35”E of the Greenwich Meridian. Its climatic condition consists of wet and dry seasons, an average temperature of 30◦C (79◦F), 82% humidity, and wind speed of 2km/h. the town is accessible by both rail and road.

[Figure removed by the editorial staff due to copyright reasons.]

(FIG 1.1) Map Of The Area (Google Maps, 2016)

1.7 GEOLOGY OF THE AREA

Itakpe iron ore deposit is a magnetite hematite mineralization of 14 ore layers of 14.8% Fe to 41% Fe with an overall average grade of 36% ( NIOMOC Project Report, 1980, Vol 2). This deposit lies within the Precambrian crystalline rocks. The host rocks for the deposit include ferruginous and ore free quartzite, migmatites and other stratified rocks. Average content of SiO2=44%, Al2O5=9.6%, phosphorus=0.05%, and Sulphur content=0.1%. the low level of phosphorus and Sulphur implies that they are within tolerable level

[Figure removed by the editorial staff due to copyright reasons.]

(miningnigeria.com.ng).

(FIG 1.2) Geology Of The Area (Dr. J.I Nwosu, 2103)

[Figure removed by the editorial staff due to copyright reasons.]

(FIG 1.3) Geological Map Of Itakpe Iron Ore Deposit (Dr. J.I Nwosu, 2103)

CHAPTER TWO LITERATURE REVIEW

2.1 ORE AND ORE RESERVE

An ore is a type of rock that contains sufficient minerals with important elements that can be extracted from the rock (Wikipedia).

An ore deposit is an accumulation of ore. An ore reserve is an economically mineable part of a mineral resource where appropriate assessments and studies have been carried out to show that the deposit can be mined at a profit after consideration of all factors impacting a mining operation (nordicmining.com).

An ore reserve is transitory. What this means is that a location that housed certain ores today might have none after a while (after much exploitation), it will become extinct or a location that did not contain ore deposit in the past could later contain ore due to accumulation over time.

Most ore deposits are named after their locations, for example Itakpe mine located at Itakpe, Nigeria, the Witwatersand located at Witwatersand, South Africa.

2.2 NIGERIAN IRON ORE RESERVE

Nigeria has several deposits of Iron ore, but the purest deposits are in and around Itakpe.

Itakpe mine located at Itakpe hills, Okehi Local Government Area of Kogi State is operated by the National Iron Ore Mining Company (NIOMCO). The mine has an estimated reserve of about 145million tones of ore with 36% iron grade.

The National Iron Ore Mining Company (NIOMCO) founded in 1979, was given the mission to explore and exploit iron ore in various parts of the country and then process and supply iron ore concentrates to the Ajaokuta Steel Company (ASCL) in Ajaokuta, Kogi State and Delta Steel Company (DSCL) in Aladja, Delta State. They also export concentrates.

Nigeria’s vast iron ore reserves comprises two main types which are;

- Banded Iron Formation (BIF) deposits which occur in folded bands and lenses associated with the Precambrian metasediments schist belts.
- The cretaceous sedimentary (oolitic) iron deposits which are small, rounded accretionary masses formed by repeated deposition of thin layers of iron mineral.

2.3 ITAKPE IRON ORE RESERVE

The Itakpe iron ore reserve lies in the banded iron formation (BIF) which occurs in metamorphosed folded bands associated with Precambrian basement complex rocks which include low grade metasediments, high grade schists, gneisses, and migmatites.

The banded iron formation occurs in narrow bands and lenses, interbedded with phyllites and schists. The iron formation bands vary in thickness from about 3cm to 5cm.

The main types of banded iron formation which have been identified are the oxide silicate and sulphide types. The oxide type which is represented by silica iron oxide assemblage is the most widespread of the iron formation types.

2.4 MINE AND MINING

A mine is an excavation in the earth from which valuable minerals or other geological materials are extracted from an orebody, lode, vein, seam, reef or placer deposits. These deposits form a mineralized package that is usually of economic importance.

Mining is the extraction of these valuable minerals or geological materials from the earth’s surface.

There are two types of mining which are :
- Surface Mining
- Underground Mining

Surface mining is the removal of the earth’s surface (Overburden) in order to reach the buried ore deposit. Here the ore deposits are usually not buried too deep in the earth. Mining methods include

- Open pit mining
- Open cast mining
- Quarrying
- Underwater mining

Underground mining also known as hardrock mining consists of digging tunnels or shafts into the earth to reach buried ore deposits. Here, the ore deposits are usually buried deep in the earth.

My report is focused on Open Pit Method, a technique under Surface Mining.

2.5 OPEN-PIT MINING

Open-Pit Mining is a surface mining technique of extracting rocks or minerals from the earth by their removal from an open pit or borrow. This mining method is used when deposits of economically useful minerals or rocks are found near the earth’s surface, that is where the overburden is relatively thin or the material of interest is structurally unsuitable for tunneling.

Open-pit mines are typically enlarged until either the mineral resource is exhausted or an increasing ratio of overburden to ore makes further mining uneconomic. Once this occurs, the exhausted mines are then converted to landfills for disposals of solid wastes.

[Figure removed by the editorial staff due to copyright reasons.]

(FIG 2.1) Open-Pit Mine (MARTIN, n.d.)

2.6 EXTRACTION OF AN OPEN-PIT MINE

Open-pit mines are dug on benches, which describe the vertical levels of the hole. These benches are usually of forty to sixty metre intervals, depending on the machineries that are being used. These benches are usually stepped with an inclination of 70⁰. A haul road is usually situated at the side of the pit, forming a ramp up which trucks can drive, carrying ore and waste rock. The waste rock is then piled up at the surface near the edge of the open pit forming a waste dump.

[Figure removed by the editorial staff due to copyright reasons.]

(FIG 2.2) Diagram of an extracted open-pit mine (MARTIN, n.d.)

2.7 OPEN-PIT AND ORE BODY CONFIGURATIONS

This describes the attitude of the bedrock on which the ore body lies. They could be either of the following:

- Flat lying seam or bed, flat terrain e.g platinum reefs, coal
- Massive deposit, flat terrain e.g iron ore or sulphide deposits
- Dipping seam or bed, flat terrain e.g anthracite
- Massive deposit, high relief e.g cupper sulphide
- Thick bedded deposits, little overburden, flat terrain e.g iron ore, coal.

The Itakpe mine deposit is a thick bedded deposit with little overburden on a high relief.

2.8 EQUIPMENTS USED IN OPEN PIT MINING

The following equipment are used in open-pit mining method:

- Bucketwheel Excavators
- Load Haul Dump (LHD) Trucks
- Bulldozers
- Back Hoes
- Loaders
- Mills

Abbildung in dieser Leseprobe nicht enthalten

(FIG 2.3) Backhoe (Oniuwe, 2016)

Abbildung in dieser Leseprobe nicht enthalten

(FIG 2.4) Coach (Oniuwe, 2016)

Abbildung in dieser Leseprobe nicht enthalten

(FIG 2.5) Locomotive (Oniuwe, 2016)

Abbildung in dieser Leseprobe nicht enthalten

(FIG 2.6) Bulldozer (MARTIN, n.d.) (Oniuwe, 2016)

[Figure removed by the editorial staff due to copyright reasons.]

Abbildung in dieser Leseprobe nicht enthalten

(FIG 2.7) Haul Truck (MARTIN, n.d.)

2.9 GEOMETRIC ANALYSIS OF AN OPEN-PIT MINE

This is a graphic representation of the shape of deposit and properties (features) of minerals in the earth’s interior. Methods of calculating and keeping track of the changes in reserves, and methods of solving geometric problems related to carrying out on mining work.

The mine deposit is usually a complex body in shape and structure. Using limited data on the deposit obtained during an analysis of its value, it is necessary to reproduce the most probable shape of the deposit, determine the mineral’s condition of occurrence among other rocks and also determine the distribution of the mineral’s properties that are important for production. In developing methods that make it possible to solve these problems, geometrical analysis makes use of ordinary method of geometry, mathematical statistics and probability theory. There are two large groups among the various shapes of deposits:

- Beds or Bedlike deposits
- Deposits of irregular shape

There are some differences between the geometrical analytical problems solved in reference to these two groups of deposits. In geometrical analysis of a mine, the concepts of angle of strike and dip are important. They determine the position of the deposit in the earth’s interior. The elements of occurrence are very simple to find for regular bed deposits. When direct measurements are impossible, geometrical analysis allow for indirect determinations. When the beds of the rock and of the mineral are deformed into folds and parts of the rock are broken off and re-displaced, geometrical analysis works out methods to determine the elements of the folded shape and methods of searching for the displaced parts of the bed.

CHAPTER THREE METHODOLOGY

In achieving the geometry of a mine, several approaches are used. In my report, I will be using the stripping ratio approach under which I will be using the limiting stripping ratio to determine the overall slope limit.

3.1 BASIC TERMS

Stripping Ratio

This is the ratio representing the volume of the waste to the volume of ore. Mathematically, it is defined as :

S.R= Volume of Waste

Volume of Ore

It has no unit.

Limiting Stripping Ratio

This is the economically allowable stripping ratio i.e the stripping ratio beyond which the ore will no longer be economically viable.

It can also be defined as the maximum ratio at which the exploitation of the deposit is viable. Above this stripping ratio, the exploitation of the deposit is no longer viable.

3.2 LIMITING STRIPPING RATIO APPROACH

From the above definition of limiting stripping ratio, there are components which when put together mathematically, can be determined.

These components are:

- The cost of waste removal
- Cost of processing per tonne of ore
- Cost of mining

Applying these using already available data from the National Iron Ore Mining Company (NIOMCO), we have the following;

- Cost of mineral processing per tonne (Cp) = #400
- Cost of waste removal per tonne (Cw)= #500
- Cost of mining per tonne (Cm)= #600
- Cost per tonne of ore of concentrate (P) = #2800,this is achieved by multiplying the price per tonne of concentrate (#8000) by the concentrate yield (3.5)

Therefore, P = Cm + Cp + CwK

Where K is the limiting stripping ratio

2800= 600 + 400 + 500k

2800= 1000 +500K

500K = 2800 – 1000

500K = 1800

K = 1800/500K = 3.6

3.3 GEOMETRIC SECTION OF THE MINE

Here, the mine is represented diagrammatically where it is divided into benches which are 10m apart, each bench having a haul road of 40m and mine working of 30m. The benches are inclined at an angle of 70⁰ while the overall slope angle which intersects the earth’s surface is inclined at an angle of 53⁰.

With the limiting stripping ratio at 3.6, I can then achieve my overall pit slope through surface intercept method by representing the mine diagrammatically where the mine is broken into its various benches till I reach the pit bottom.

From the diagram below, the mine is divided into 8 benches, 8 excavation sequences. In each sequence, both ore and waste are excavated hence the use of stripping ratio to know when it becomes unprofitable to exploit.

Also, in each sequence, the volume of ore and waste are determined using simple geometric shapes and formulae in order to determine their operating stripping ratios.

Abbildung in dieser Leseprobe nicht enthalten

(FIG 3.1) Geometric Shapes (Oniuwe, 2016)

Abbildung in dieser Leseprobe nicht enthalten

(FIG 3.2) Geometric Section Of The Mine

(the overall slope angle makes an intersect with the surface) (Oniuwe, 2016)

3.4 CALCULATIONS

In order to determine the stripping ratios, the tonnages of ore and waste excavated are determined by converting the areas of the shapes to volumes, then from volumes to tonnes. This can be achieved by the following examples:

Using a rectangle of 30m length and 10m width, we attain the tonnage by;

Area of rectangle = length * width

= 20*10

=200m2

To obtain the volume, we multiply the area by 1000

200*1000

= 200000m3

To convert to tonnage in terms of ore, we multiply the volume by 3.5

= 200000 * 3.5

=750000tons

To convert to tonnage in terms of waste, we multiply the volume by 2.5

= 200000 * 2.5

= 500000tons

From the above answers, the ratio of the volume of waste to the volume of ore is 500000 : 750000 which gives a stripping ratio of 0.75. This implies that for 1ton of ore that was extracted, 0.75ton of waste was also extracted.

With the values obtained from the calculations, I will them to solve for the production rate of the mine by using the deepening rate method.

The deepening rate is the amount of depth one goes down the mine annually, usually in metres.

The deepening rate is 12m/yr and the bench height is 10m,

Therefore, the fraction of the year would be:

10m

12m = 0.83

In terms of production rate for ore, the quantity of ore mined per bench will be divided by the fraction of year then the value obtained will be multiplied by the specific gravity (3.6).

i.e quantity of ore = 425200

fraction of year 0.83 = 512,289 * 3.6 = 1.8million

the same method goes for all extraction sequences.

In terms of production rate for waste, the same method is applied;

i.e quantity of waste = 520000

fraction of year 0.83 = 626506 * 3.6 = 2.3million

CHAPTER FOUR RESULTS

From the methods applied, the results obtained were arranged in a table from which graphs were plotted to show the various distributions.

Abbildung in dieser Leseprobe nicht enthalten

The above table gives a breakdown of the amount of ore and waste extracted in each sequence and also shows the production rate for each. Going down the table, we can see the various amount of ores and waste extracted.

GRAPH OF STRIPPING RATIO AGAINST DEPTH

Abbildung in dieser Leseprobe nicht enthalten

(FIG 4.1) Graph showing the relationship between stripping ratios and the benches (Oniuwe, 2016)

From the above graph, the limiting stripping ratio which has a value of 3.6 was achieved at a depth of 35m into the mine.

Also from the graph, it can be seen that the most ore was extracted at on the 6th bench while the least ore was extracted on the first bench.

GRAPH OF PRODUCTION RATE FOR ORE AGAINST DEPTH

Abbildung in dieser Leseprobe nicht enthalten

(FIG 4.2) Graph showing the relationship between the production rate of ore and the benches (Oniuwe, 2016)

From the above graph, the production rate of ore is highest on the 4th, 5th and 8th benches.

GRAPH OF PRODUCTION RATE OF WASTE AGAINST DEPTH

Abbildung in dieser Leseprobe nicht enthalten

(FIG 4.3) Graph of production rate of waste against the benches (Oniuwe, 2016)

From the above graph, the most waste was extracted from the 6th bench while the least was extracted from the 1st bench.

CHAPTER FIVE CONCLUSION

The geometric analysis of Itakpe open-pit mine gives a precise breakdown on the extraction sequence and production rate, this has been proven to be of huge importance in the mining engineering when mine planning and design is involved. This shows how simple geometry can be applied in solving complex mining construction issues and also analyzing the production rate of the mine.

REFERENCES

Open-Pit and Mine Planning and Design 3rd Edition

Mninigengineersworld.blogspot.com

EMMANUEL. O. AKINRINSOLA and JACOB I.D. ADEKEYE (1993)

Geostatistical Ore Reserve of the Itakpe Iron Ore Deposit Okene, Kogi State

Dr. J.I NWOSU, Dr. KINGSLEY OKENGWU, Dr. ALIMI ADESOJI (2013)

NIOMOC Project Report; 1980, Vol 2

Annual Report of Mines Laboratory, NIOMCO 1988-1997

PROMERANTSEV. V.V (1990)

Mineral Processing Analysis

En.wikipedia.org/wiki/itakpe_mine

Miningnigeria.com.ng/2016/03/11/iron-ore-in-nigeria/

[...]