OPTIMALISASI PROSES PELEBURAN (SMELTING) BIJIH TIMAH (Sn) UNTUK MENINGKATKAN KADAR DAN KUALITAS LOGAM TIMAH YANG DIHASILKAN

THESIS WORK

PROPOSAL

THE INFLUENCE OF ROCK CHARACTERISTICS TO BLASTING GEOMETRY AT GRASSBERG GOLD MINE

OF PT. FREEPORT INDONESIA COMPANY-TEMBAGAPURA

By:

DESRIZAL03003120013Transcribed as Students Thesis Work Requirement

Majoring Mining Engineering

MINING ENGINEERING DEPARTMENTENGINEERING FACULTY

SRIWIJAYA UNIVERSITY

2004STUDENTS IDENTITY AND APPROVAL OF THESIS WORK 1. Title :The Influence of Rock Characteristics to Blasting Geometry at Grassberg Gold Mine of PT. Freeport Indonesia Company-Tembagapura

2. Applicant

a. Name :Desrizalb. Gender: Male

c. Students ID No : 03003120013d. Semester: IX (Nine)

e. Faculty/Major: Engineering/Mining Engineering

f. Institution: Sriwijaya University

3. Location of Thesis Work : Grassberg Surface Mine of PT. Freeport Indonesia Company Tembagapura - Papua

Indralaya, September 2004Applicant,

DesrizalNIM. 03003120013A. TITLE

The Influence of Rock Characteristics to Blasting Geometry at Grassberg Gold Mine of PT. Freeport Indonesia Company-Tembagapura

B. DEPARTMENT

Mining Engineering

C. INTRODUCTION

PT. Freeport Indonesia Company is located in Tembagapura, Papua, on the Jayawijaya Mountains and move on the field of gold mining. This Company is operating as an affiliate of Freeport McMoRan Copper and Gold.

Fragmentation is a term used to describe the size distribution of rock boulders and particles produced when explosives break a solid mass of rock.

The safety factors of blasting operation itself include; ground vibration, fly rock distribution, hazardous blasting gas, direction of rock breaks and the sound of the explosion.

To achieve optimum blasting it is necessary to make sufficient planning which include blasting geometry influenced by the rock characteristics.

The rock characteristics at Grassberg gold mine of PT. Freeport Indonesia Company are grouped in six rock classification, which are:

1. very soft rock

2. soft rock

3. medium rock

4. hard rock

5. very hard rock

6. extremely hard rock

Generally the blasting patterns used by PT. Freeport Indonesia Company at Grassberg gold mining operation from the data of 31 July 2003 are:

Ore Pattern9m x 8m x 17m

Blasthole diameter: 12 inches

Explosive: ANFO

Powder factor: 0.15 to 0.25 kg/tonne

Blasthole Drill: D90K

Waste Pattern10m x 11m x 17m

Blasthole diameter: 12 inches & 15 inches

Explosive: ANFO

Powder factor: 0.12 to 0.15 kg/tonne

Blasthole Drill: D90K

For extremely hard rock blasting, the powder factor may reach 0.5 kg/tonne or 1:2 blasting ratio, which means using explosive to 500 grams for each tonne of rock.

D. SCOPE OF WORK

The discussion of this thesis work is focused in the study of the influence of rock characteristics to geometry of blasting at Grassberg gold mine of PT. Freeport Indonesia Company Tembagapura.

E. GOALS OF WORK

The goals of this thesis work are:

1. To do direct observation of drilling and blasting operations commenced at mining fronts of Grassberg gold mine of PT. Freeport Indonesia Company.

2. To observe the result of blasting operation consisting fragmentation result and rock-breaks size distribution.

3. To analyze and synthesize the data from direct observation with secondary data of previous blasting observation.

4. To make final conclusion and suggestions of the study of the influence of rock characteristics to blasting geometry.

F. BENEFITS OF WORK

The benefits of this thesis work are to give information and suggestions to measure near future blasting geometry suitable to existing rock characteristics at mining fronts of Grassberg gold mine of PT. Freeport Indonesia Company.

G. METHODOLOGY

1. Study of literatures from books and journals relevant to the theme of the thesis work to study the theory of rock and blasting.

2. Gathering of data which conclude:

Primary data, consisting data from direct observation of drilling and blasting operations at the mining fronts and sampling of rock-breaks from blasting.

Secondary data, consisting data of previous drilling and blasting operations, geotechnical data of Grassberg gold mine and bore machine specification.H. LITERATURE REVIEW

FRAGMENTATION

The significance of fragmentation cannot be underrated because, to a large degree it is the measure of the success of a blast: it influences the operational and maintenance costs of subsequent operations and equipment including such unit operations as excavating or loading, haulage and crushing or size of reduction plant. Therefore both drilling and blasting are clearly related to cost optimization of subsequent operations.

Poor fragmentation results in oversize or large boulders involving secondary breaking costs to reduce them to a size which can be handled economically, safely and efficiently by loading and haulage equipment.

Rock fragmentation factors, however, may be considered under three groups of parameters:

(a) Explosive parameters, which include explosive density, velocity of detonation, gas volume and available energy.

(b) Charge loading parameters, including charge diameter and length, stemming, coupling and type and point of initiation.

(c) Rock parameters related to rock density, strength (compressive and tensile), texture and propagation velocity.

Excessive production of fines or undersize rocks is also undesirable because it indicates possible wastage of explosives; economic size reduction could be achieved by the correct utilization of crushing installations. However, under certain circumstances, fragmentation may be improved by adoption of one or all of the following measures (these apply to bench or quarry blasting):

1. Reduce hole depth; i.e. use shallow holes with improved distribution of explosive.

2. Reduce spacing between adjacent holes in a row.

3. Reduce burden distance.

4. Use an explosive with greater gas generation (heave) and less brisance.

5. Use short delay detonators.

BLASTING GEOMETRY

Blasting operation is an operation to break solid rock mass by using explosive and with sufficient planning without excluding safety factors to gain suitable break result, or effective and economic.

In order to fracture rock (or to break ground) the explosive charge must be placed within the rock at some distance behind the face.

The rock mass must have one or more free faces. The drill holes are placed at right angles to the plane(s) of the face and the rock is blasted in the direction of the free face. This is necessary, first, because broken rock occupies a greater space than solid rock and must have room to expand (swell); second, it allows the rock to be broken in tension rather than in shear where there is no free face or tight conditions.

Aspects which have an effect on blasting operations are:

Rock:

Presence and extent of free faces

Strength of rock blasted

Structure of rock

Explosive:

Type, strength and nature

Loading density and confinement

Detonation:Instantaneous or sequential

Blast hole:

Size, type and depth of hole

Amount of loaded hole

Burden

Operational:

Safety

Statutory regulation

Climatic conditions

Shape of excavation

Quantity of rock

Permissible concussion

Degree of fragmentation

Loading procedure and equipment

The discussed aspects in this thesis work are only those relevant to rock characteristics influence to blasting geometry.

Blasting geometry is consisting burden, blast hole depth, sub-drilling, stemming, and spacing (Figure 1)

1. BURDEN

The burden distance is the distance between the bottom of the hole and the free face, and corresponds with the line of least resistance. Burden distance should be less than hole depth to prevent surface cratering.

Factors that should be noticed in burden are:

Burden should be the distance from the charges perpendicular to nearest free face and the direction of breaking.

The distance of burden depends on the characteristics of rock, characteristics of explosive, etc.

A blasting design formula for single holes gives burden in the following empirical equation (Andersens equation).

Where B = burden

D = diameter of blast hole, m

L = depth of blast hole, m

C = constant determined empirically

(Applies to NG based explosive and ANFO)

The formula derived by Andersen allows burden distance to be determined from readily available physical dimensions. The formula is modified for multi-shot firing where spacing affects the burden adopted.

(a) Burden distance

(b) Spacing

(c) Free face

(d) Blasthole

(e) Charged blast hole

(f) Sub-drilling

(g) Stemming

FIGURE 1

DIAGRAM OF BENCH BLASTING DESIGN

2. SPACINGSpacing is the distance of blast holes arranged in one row adjacent to pit wall. Generally spacing depends on the burden, length of blast hole, location of primer, delay time and direction of rock structure.

The fundamental factor that must be noticed in determining spacing is whether there is an interaction between nearest charges. If each blasthole is detonated separately with long delay time, to allow each blast hole to explode perfectly, hence there will be no interaction between each existing energy wave. If the delay time is short, interactions will happen and causing complex effects.

3. STEMMING

The section of blast hole uncharged by explosive between explosive charge and the bore hole collar is usually filled by stemming material. The length of the stemming must not be less than burden distance so as to minimize fly rock from cratering off the upper portion of the blast hole.

4. LENGTH OF BLAST HOLE

The length of the blast hole must not be less than the burden distance. This is to avoid overbreak or cratering. The location of the primer will also effect the depth of the bore hole.

5. SUB-DRILLINGThe objective of sub-drilling is to gain full face explosion effect as expected. The toes on the floor after blasting operation will add problems to succeeding blasting operation, or in loading and transporting operation. In some rock mass the value of sub-drilling must not be smaller than 0.20, the usual value of KJ is 0.30. The value of KJ depends on the structure and type of rock, also the direction of the bore hole.

On elevating rock the value of KJ needed is smaller. Even on vertical bore hole sub-drilling is rarely needed.

POWDER FACTOR

Powder factor (Pf) is a value to determine the amount of blasted or broken material to certain amount of explosive. Powder factor is affected by blasting pattern and free face.To measure Pf it is necessary to know the area (A) to be blasted, length of bench (L), length of the charge of each blast hole (PC), loading density (de) and material density ratio (dr).

dr= SG (62,4) / 2000 = 0,0312 (SG)

(tonne/cuft)

W= AL (dr)

(tonne)

E= (de) (PC) N

(lb)

Pf= W/E

(tonne/lb)

W= blasted rock or material

(tonne)

N= amount of bore hole

In actual field situation the value of W is gain by measurement prior to blasting operation and after the blasted material is utterly loaded. This measurement is undergone in some frequency to get the average value of each similar blasting pattern.

The value of E is gain from the amount of explosive charged to blast holes in each detonation. The average value of E is the average value of E in each blast hole. The value of Pf is the quotient of average W and average E.FIRING METHOD

Simultaneous firing charges in blast holes so they mutually assist one another are fundamental to surface mining operations. However restriction on the size of the simultaneous blast may apply because the ground vibration produced often result in damage to adjacent structures and consequent complaints. The principle of mutual assistance is retained by using short delay (milliseconds) firing methods which reduce or minimize blast vibration. Consequently, because vibration is related to the weight of explosive detonated in any single short delay period and not to total weight of the blast, the overall size of the blast may be increased.

CHARGE MASS CALCULATION

For successful blasting, the bore hole must be drilled to give an achievable burden distance. It is also necessary to obtain a loading density in the bottom portion of the blast hole.

The quantity of explosive, required for each blast hole may be determined by the following equation. Note that this applies to a specified explosive (powder) factor (kg/tonne).

Equation:

Q = B x S x D x d x E (kg)

WhereQ = mass or quantity of explosive

B = burden distance (m)

S = spacing

d = density factors of the rock (tonnes /m3)

D = hole depth (face height)

E = powder factor (kg/tonne)

I. ACCOMPLISHMENT TIME AND SCHEDULE PLAN OF WORK

The accomplishment time of this thesis work will be commenced from 1 November 2003 to 1 February 2004

DETAILED SCHEDULE OF THESIS WORK

NoWorkSchedule of Work

Weeks

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1Administration and field orientation

2Gathering primary data

3Gathering secondary data

4Analysis and data processing

5Report making and presentation

J. REFERENCE

______, 2000, Ensiklopedi Pertambangan, Edisi 3, Pusat Penelitian dan Pengembangan Teknologi Mineral, Bandung.

, 2001, Diktat Kursus Juru Ledak Kelas II, Pusat Pendidikan dan Pelatihan Teknologi Mineral dan Batubara, Bandung.

Arthur B. Cummings, 1973 SME Mining Engineering Handbook, Volume 1, Society of Mining Engineering of The American Institute of Mining, Metalurgical, and Petroleum Engineers, Inc, New York.

K. A. Sweet, 1984, Mining 1, Technical Publication Trust, Perth.

Made Astawa Rai, Dr. Ir., Suseno Kramadibrata, Dr. Ir., Mekanika Batuan, Jurusan Teknik Pertambangan, Institut Teknologi Bandung

Moehim Kartodharmo, M. Bambang Sugeng, 1996, Supervisory Teknik Peledakan Diklat Angkatan VII 21 29 Agustus 1996, Jurusan Teknik Pertambangan, Institut Teknologi Bandung.

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