24713877 Education Drilling and Blasting Docs11

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DESIGN OF BLASTING ROUNDS FOR AN INDIAN IRON ORE MINE

By

Satish R. KateDy. General Manager-Marketing (South West Region)IBP Co. Ltd, Nagpur, INDIA

INTRODUCTION

Mining of Iron Ore in India is done by Surface Mining methods and most of the deposits are

massive and are occurring in Hills, surrounded by green forest cover. While majority of iron ore

produced are from mechanized mining systems, some quantities are also produced from semi-

mechanised mines. In mechanized mines, apart from state-of-the-art level of mechanization, the

Run-off-Mine ore is subjected to multi-stage crushing, screening and washing/beneficiation, for

improving the grade and ensure segregating of different size range. The steel plants within the

country have been operating their own captive mines, where both lumps and fines are used in

their furnaces. In case of mines, which exclusively supply ores to export market, the lumps

produced yield very high price and thus efforts are being made to maximize lumps recovery

The mine, where the author had been associated, is an export-oriented mine which supplies

iron-ore to Japanese steel plants.

The present paper has been highlighting the drilling and blasting practices of this mine and

detailed study on the selection of explosives at the mine for –

1) Improving fragmentation level,

2) Reducing number of blast failures in very hard rock conditions (like Steel Grey

Hematite),

3) Reducing the number of oversize boulder generation,

4) Increasing lumps recovery with optimal utilization of explosive energy,5) Improving powder-factor and also cost of blasting,

6) Optimising the number of blast-holes per blasting rounds, thereby reducing cost of

drilling, reducing in the cost of drilling

This mine is designed to produce 5.5 million tones of ROM ore/year and for export of –150 mm

+9.5 mm dumps to Japan.

Copyright © 2004 International Society of Explosives Engineers

2004G Volume 2 - Design of Blasting Rounds for an Indian Iron Ore Mines - A Case Study



MINING COST

Table 1, shows the performance of the mine in last 3 years. During last few years the mine had

faced problem in respect of increase in the cost explosives, cost of drill bits etc. In 2002-03,

powder factor also got dropped by 18%, over the previous year in addition to generation of a

large number of failed blasts, large number of boulders generating per blast etc.

Table: 1, Showing pattern of consumption of Explosives & Drill Bits

Year 2000-01 2001-02 2002-03 2003-04**

Actuals as achieved (Target)

Explosive Qty(T) 1153 1083 1384 1212

Value in Rs.in lacs 247 225 267 252Av. Landed cost of explosive(Rs/T) 21470 20829 19314 20829

Powder Factor Achieved *(T/kg) 6.88 7.51 6.17 7.51

Drill Bit

Qty of 250mm dia bit consumed 32 33 42 NA

Value in Rs. in lacs 31.10 34.33 34.78 NA

Av. Landed cost(Rs./drill bit) 97188 104030 82810 NA

• Powder factor calculated based on total excavation volume.

**The figures for 2003-04, financial year is the target set by the management.

Table: 2, below states the percentage distribution of various consumables:

Explosives 14

POL(HSD,Lubes etc) 33

Drill Bits 2.0

Tyres/tubes 5.7

Spares 33

Consumables 12.3

From these data it can be concluded that explosive as a consumable has great influence on the

overall cost of mining. Besides, it also influences on the overall performance of Shovel,Dumper, and Crusher output. In case of packaged explosives having been used in the mine, the

inventory cost and cost for handling of explosives by manual means has been included in the

above percentage distribution of explosive cost. With the use of Bulk explosives inventory cost

for packaged explosive can be brought down substantially.

Drilling and Blasting

Copyright © 2004 International Society of Explosives Engineers2004G Volume 2 - Design of Blasting Rounds for an Indian Iron Ore Mines - A Case Study



The problems associated with drilling and blasting are a recurrent features ever since the mine

went into production in 1968. In 1980, Indian School of Mines was requested to make an

“Optimization study of drilling and blasting sub-systems’ (Ghose and Singh, 1980) with specia

reference to –

a) Assessment of existing drilling and blasting practices with a view to identifying the

problem areas and seeking solutions thereof;

b) Evaluation of drillability and abrasivity characteristics of the formations which pose

intractable problems vis-à-vis drilling bit life and cost thereof; and

c) Crater studies in the formations for establishing design bases for blasting.

The broad recommendations of this study significantly helped the mine in their effort to

optimize blasting parameters and relative costs. Till 1990, the product mix consisted of Lumps

– 150 mm + 9.5 mm as saleable and fines of –9.5 mm as waste. The initial thrust had been to

generate less fines while designing blasting rounds. This has been changed after the fines have

found ready market.

Preparation of drilling block:

The rock type being heterogenous they can be broadly categorized as under –

Rock type Bulk density Specific gravity

Steel Grey Hematite(SGH) 4.28 4.20

Banded Grey Hematite 4.10 4.50

Blue hematite 2.29 4.00/4.20Laminated Ore 1.85 3.20

Laterite Ore 1.89 3.20

Blue Dust 2.47 3.00

Banded hematite Quartzite - 3.00

Yellow - 3.30

Shale - 2.50

Selection of explosive type and blast-hole pattern is undertaken in consultation with Geology

Department taking into cognizance distribution of the above rock type and the process Plant

Manager for quality consistency (at an average Fe content of + 67%).

(a) Blasthole pattern The height of the bench varies from 12 to 14 m and the holes are drilled by 250mm

dia.drills. The following pattern has been broadly followed after several trials using

‘crater test’ results.




Rock type Burden Spacing S:B ratio

Steel Grey Hematite 6.0 7.0 1.17

Banded Grey Hematite 5.5 6.5 1.18

Banded hematite 6.0 7.0 1.17

Blue Dust 6.5 8.0 1.23

Laterite Ore 6.5 7.5 1.15

Shale 7.0 9.0 1.29

DRILLING

All primary drilling is done by 250mm dia blast-hole drills of IR make. Secondary blasting is

done by 100 mm crawler mounted drills. In each bench for better floor management and

elimination of toe, 10 % sub-grade drilling is done. This has led to smooth floor, elimination of

undulations, toes etc, when explosive of right quality and quantity is used.

EXPLOSIVES

Cartridged/packaged explosives

With the entry of a number of cartridge explosive suppliers to the mine, the mine management

had faced severe problems due to blast failures, toes at every blast, over-sized boulders, etc. In

order to improve upon the blast performance, IBP Co. Ltd was insisted by the mine

management to supply their cartridge slurry explosives, comprising of high energy base andbooster explosive. IBP’s products were identified for use in very hard and hard rock conditions.

Table 3, shows the performance of cartridge explosives supplied by 4 different manufacturers.

Briefly speaking, from amongst the 4 suppliers only Manufacturer 1, had been allowed to

conduct blasts in all types of rock conditions and others have been blasting in medium hard to

soft strata conditions. Besides, boulders generation posed additional problem of secondary

blasting & slowing down in the cycle time per dumper trip.

BULK EXPLOSIVES

In order to avail the benefits of bulk explosives, the mine had gone for introduction of bulk

explosives. Initially they conducted trials with three manufacturers, who supplied Site Mixed

Re-pumpable Emulsion explosives.

Repumpable Emulsion based bulk explosives (SME)




The three manufacturers have conducted blasting with their emulsion explosives in all types of

rock and at Table 4 & Table 5, their blast wise details are presented.

It has been observed that the trials with SME had not given any marked improvement in Powder

factor values vis-à-vis packaged explosives. One of the manufacturers had gone for deck

loading.

Manufacturer 1, with SME explosives, explosive per M. of hole depth varied from 55 to 62

kg/m. Since, pattern was not expanded with SME powder factor values continued to remain

within 4.7 to 5.5 T/kg. This manufacturer pumped straight emulsion as well as Heavy Anfo &

introduced deck to the thickness of 1.0m.

Manufacturer 2: In the 9 blasts conducted average powder factor varied between 4.83 to 5.9

T/kg. In this case also qty of explosive per hole was not reduced as compared with LD

charge/hole varied between 370 to 420 kgs. Density of the explosive was 1.05 – 1.03 having

VOD of 5000 + 300.

IBP Co. Ltd had been given an opportunity to undertake trials with their Bulk Explosives

system. IBP which supplies Site Mixed Slurry, Site Mixed Emulsion and HANFO in Indian

Mines had evaluated different options in selecting Bulk explosives.

The main considerations being –

1) Charge per M. of hole length,

2) Density of products to be used,

3) Energy Factor required for different benches,

4) Optimising blasting pattern etc.

IBP chose to supply SITE MIXED SLURRY EXPLOSIVES (SMS), to this mine in view of the

following techno-economic considerations –

1) Charge density per M in 250mm dia blast hole drills vary from 37 kg to as high as 49

kg/M, with varying densities,

2) Density of SMS can be varying from 0.65 to 1.0 gm/cc,

3) Calculation of Energy Factor (Kcal/CuM) of SMS per bench per blast.

Selection of SMS explosive on the basis of ENERGY FACTOR

Powder factor was a good indicator of the explosive energy used to break a quantity of rock and

normally explosive energy increased with density of explosive. However, with slurries

watergels and emulsions the energy can greatly, even though the explosive density remains the

same. Consequently, a better method is needed to relate the amount of explosive energy




required to fragment a given quantity of rock. This is known as energy factor. The energy factor

describes the energy distribution within a given unit of rock. Energy distribution within a blast

is measured by the energy factor (EF) a ration of the explosive energy (kcal) to quantity of rock

broken (cu.m).

The thermochemical energy (Q) is expressed in terms of calories per unit volume or weight of

an explosive. The absolute bulk strength (ABS) of a given explosive is the amount of

thermochemical heat energy expressed in terms of calories per cu.m. the absolute weight

strength (AWS) of a given explosive is the amount of thermochemical heat energy expressed in

terms of calories per gm. For ANFO AWS=832 ca./gm and density of 0.81 gm/cc., thus

ABS=AWS x density = 673.92. The ratio of ABS of an explosive to that of ANFO is the

relative bulk strength (RBS) of the explosives. The RBS is the measure of thermochemical

energy per unit of an explosive compared to an equal volume of bulk ANFO at the density of

0.81 gm/cc. It is calculated by dividing the ABS of an explosive by the ABS of bulk ANFO

multiplying the product by 100. Thus, Q=AWS x Wt. Of explosive in hole and EF=Q/Vol. of

rock. By obtaining the various energy factor (EF), charge distribution in a borehole can becalculated. Energy in boreholes or energy distribution per linear length of the boreholes is given

by: Qf (kcal/m)=0.7853 x De x Pe x AWS, where, Qf=explosive energy (kcal/m), De=length of

explosive column (cm), Pe=density (gm/cc), and AWS=absolute weight strength.

Based on the properties of cartridged explosives, the author had suggested following Energy

Factor values for different rock types. ENERGY FACTOR has been used as an useful tool in

selecting type of SMS explosives, since this has been achieved with cartridge explosives

without changing existing Burden and Spacing values.

Rock type Burden Spacing S:B

ratio

Maximum Energy

Factor(kcal/kg)

With 250mm dia drill hole, 12.5 m bench height

Steel Grey Hematite 6.0 7.0 1.17 900

Banded Grey Hematite 5.5 6.5 1.18 800

Banded hematite 6.0 7.0 1.17 700

Blue Dust 6.5 8.0 1.23 500

Laterite Ore 6.5 7.5 1.15 450

Shale 7.0 9.0 1.29 600

SMS Explosive of IBP had been used in 8 blasts, and the explosive charged had been selected

based on the Energy requirement of the strata. This has lead to –

A) Charging explosive combination giving Energy Factor as per cartridge use.




B) By reducing density of SMS at 0.7 and 0.8 gm/cc, the charge/M. has been restricted at

39Kg/M to 45Kg/M. Table states comparison between Site Mixed Emulsion explosive & Site

Mixed Slurry Explosives of IBP.

Comparison between Site Mixed Emulsion explosive & Site Mixed Slurry Explosives of IBP

(using Energy Factor as explosive selection criteria)

Parameters Manufacturer I Manufacturer II IBP

Rock Type Banded Hematite Qwuartzite & Lateriate Ore

Condition of holes All holes were dry and adequate care has been taken to

maintain the accuracy in drilling.

Rock Density 4.0 gm/cc

Bench Height M 11.0 11.60 12.00

Drilling pattern Hole Dia. 250mm IR drill

No. of holes 14 20 14

Av. Depth M 12 12.60 13.00Sub-grade M 1.0 1.00 1.00

No. of rows 2 2 2

Av. Burden M 5.80 5.07 6.00

Av. Spacing M 6.30 5.43 6.0

B: S ratio 1:1.1 1:

Av. Stemming ht M 5.25-5.55 5.50 4.5 to 5.00

Explosives

Type Emulsion Emulsion Slurry

Density 1.20 1.10* 0.70Quantity/hole Kgs 391 406.25 360.00

Charge/M, kgs 56.10 55.00 35.00

Cast booster/hole kgs 0.70 0.8375 0.70

Total expl. Kgs 5784.80 8141.75 5029.80

INITIATION 10gm Det. Cord and 50MS Cord Delay detonators used

BLAST RESULTS

In-situ Volume CuM 5627 6387 6048

Tonnage 22508.64 25548 24192

Powder factor T/kg 4.10 3.14 4.80Fragmentation Good Good As desired

Throw in M 10 Maxm. 8 8-10M

Back Break/Crack M 2.50 2.50 5.0M

• After 2 hrs of charging density attained in the hole was 1.10. All stemming of the holes

was stopped so as to allow the explosive in the column to attain this density from the

original pumped density of 1.30 gm/cc.




• In case of SMS of IBP, the cup-density was 0.70 gm/cc and all stemming completed

within 10 minutes of charging of the holes.

SAVINGS as reported by the mine management with the use of SMS explosive –

1) Saving in Quantity of explosives charge per M of hole – 30 to 63 kgs

2) Powder factor attained has been 4.80 with SMS as compared to 4.10 and 3.14 obtained

with explosives of Manufacturer I & II respectively.

3) ENERGY FACTOR in this case of SMS has been maintained at 650 Kcal/kg.

4) Back-break extended upto 5.0M, from the last vrow of holes and at the final blast

configuration the depression achieved has been 5 to 6 M, indicating the movement of the

entire back-break area. In the post-blast excavation the observations indicated, no

boulders, muck-pile has been uniform needing minimum of dozing, etc.

C) By varying percentage of Aluminium in the formulation, we could change quantity/hole.

D) Scope for Blast-hole Pattern expansion is there in this mine, which ultimately would lead to

the savings in cost of drilling. In the future blasts the author plans to conduct blasts on expanded

pattern, without changing powder factor, and only by changing the properties of explosive.

MOBILE SUPPORT UNIT

IBP installed its total manufacturing facilities at deposit 14 & 11C, by bringing in Mobile

Support Unit. This proto-type unit consists of boilers, mixing and agitator facilities in insulated

tanks, pumps and other machineries to mix guar-gum and other ingredients to manufacture hot

oxidizer solution. Hot oxidizer solution, along with trace ingredients (for gelling etc) and fuels

(like diesel, Aluminium powder and sulphur) are transferred into Pump Truck. At the site of

blasting out of over 20 formulations, three selected formulations are mixed and pumped into the

blast-holes.

Pattern Expansion with packaged Explosives

The author had conducted few blasts by using high energy packaged slurry/watergel explosives

of IBP make, and the results are presented in the following Table.

Table Showing Pattern expansion with use of High Energy Packaged Explosive of

IBP make

Sl. No. Parameters Existing Pattern with

Packaged Explosive

(normally in use)

New Pattern with

Packaged Explosive

with High Energy

Explosive




1 Blast location/Rock Type Blue Grey Hematite(Density of 4.10)

2. Bench height 12.00 13.0

3. Depth of holes (m) 14.00 15.0

4. No. Of Holes Assuming one hole 31

5. Average Burden (M) 5.50 6.20

6. Average Spacing (M) 6.5 6.77. No. Of Rows Drilled 2 2

8. Volume/Hole (Cu M) 429 540.02

9. Explosive type Indoboost +

Ing – 250 +

Ing- 210

Indoboost (HE) +

Ing – 270 +

Ing- 210

Energy available (kcal / kg) 600 980

Energy factor (kcal / Cu M) 538 868

10 Average charge per hole (kg) 475 478.23

11. Total booster (kg) 20% 3100

12. Total base (kg) 50% 7500

13. Total column 30% 4225

14. Total Explosives (kg) 100% 14825

15. Average Stemming (m) 5.0 5.2

16. Charge factor (kg/Cu M) 1.11 0.89

17. Cost of explosive / Cu M (Rs) 24.93 29.10

18. Drilling cost / m of hole (Rs) 9688 10380

19. Drilling cost / Cu M (Rs) 22.58 19.22

20. Total cost / Cu M (Rs / Cu M) 47.51 47.3321. Saving achieved / Cu M (Rs) - 0.19

Remarks Satisfactory

Conclusion:

Use of bulk Site Mixed Slurry explosive had not only improved fragmentation, loading machine

performance, reduction in no. of boulders generated etc. but also shown substantial

improvement in powder factor. By using low density explosives in the range of 0.65 to 0.70

gm/cc density, qty/m of explosive was also brought down by 15 to 18%. By reducing densitythe energy content in the explosive was not distributed, in turn higher percentage of solid fuel

like Aluminium Powder percentage was raised. Varying density in a large number of explosive

formulation could be possible only with SMS. In case of SME it cannot be brought down

1.10gm/cc.




It can be conducted that by using Energy factor substantial gain can be had in qty/m and

qty/hole. The one blast with expanded pattern using high-energy product showed scope in

pattern expansion to the tune of 15% over the existing explosive contribution.

Acknowledgement

The author is thankful to the management of IBP Co. Ltd for giving permission to present this

paper at ISEE International Conference. The views expressed are those of the Author and not of

the company of his association. The help extended by the mine management is duly

acknowledged.

Reference:

1.Kate, S.R(2000), Role of explosives energy in the improvement of drill productivity, Procc. of

Drill Blast 99, National Seminar on Drilling & Blasting for the Next Millenium, Bhubneshwar,17-18 January 2000. p 6-11.

2. Singh, R.D, and Ghose, A.K. (1980) Optimization of drilling and blasting sub-systems – A

Case study, Unpublished Report, Indian School of Mines.

Copyright © 2004 International Society of Explosives Engineers

24713877 Education Drilling and Blasting Docs11

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