A short series of lectures prepared for the

Fourth year of Geology, Tanta University

2014- 2015

by

Hassan Z. Harraz

hharraz2006@yahoo.com

This material is intended for use in lectures, presentations and as handouts to students, and is provided in Power point format so as to allow customization for the individual needs of course instructors. Permission of the author and publisher is required for any other usage. Please see hharraz2006@yahoo.com for contact details.

Topic 5: Underground Mining Methods Shrinkage stoping Vertical Crater Retreat stoping

Prof. Dr. H.Z. Harraz Presentation

Shrinkage & VCR stoping

1

Outline of Topic 5: Shrinkage stoping

Ascending method of mining

Advantages and Disadvantages

Vertical Crater Retreat stoping

Introduction

Application

Developmental sequence of stopes

Production

How Cratering Works

Prof. Dr. H.Z. Harraz Presentation

Shrinkage & VCR stoping

2

We will explore all of the above in Topic 5.

Method stopes

configuration in which the

ore is removed at horizontal

slices from bottom to top.

Of the ore is left detonated

accumulated until the stope

is completely mined. The

fragmented ore is then totally removed.

Shrinkage stoping

3

Shrinkage

4

Shrinkage

5

Ascending method of mining The ore is dismantled temporarily used as filler to support the walls

of the stope and working platform for the miners.

Overall the drilling is done on the ore disassembled using hand

drills (jacklegs).

The ore dismantled remains within the block until it reaches its

upper limit. Because of blistering, 30-40% should be removed by

kicking or drawpoints to make room for the next disassemble.

The space between the ceiling and ore dismantled dismantling is

1.8m to 2.2 m.

The Shrinkage is typically used in vertical or subvertical bodies

with a thickness between 2 and 20 m. The bodies of higher power,

the blocks can be arranged transversely.

The entries are made for miners from side to block chimneys.

Depending on the mechanical properties of the rock, the distance

between levels ranging from 30 to 90 m 30-100 m between side

pillars. The drawpoints are arranged every 7-10 m.

Prof. Dr. H.Z. Harraz Presentation Shrinkage stoping

6

Advantages: Allows plowing narrow bodies.

Low cost of development

Simple equipment for drilling and loading.

Disadvantages: Ore disassembled remains the filler.

The control of ore grade can be difficult.

It is a method for high production.

Security problems of staff working within the stope.

Prof. Dr. H.Z. Harraz Presentation Shrinkage stoping

7

6) Vertical Crater Retreat (VCR) stoping

8

VCR - Vertical Crater Retreat

Vertical Crater Retreat (VCR) or Vertical Retreat Stoping:

configuration method in stopes where drilling large diameter is used to

detonate horizontal slices of ore, leading them to the base of the block

being mined. The method progresses vertically, as successive slices

of ore are detonated.

Vertical Crater Retreat (VCR) uses parallel, vertical, descending and

spherical concentrated loads to fragment the ore (disassemble by

cratering) drilling;

The advance of the stope is disassemble from the bottom up;

The ore is recovered at the bottom of the block;

Part of the mineral remains in walk through serving as stope support.;

Introduction

Prof. Dr. H.Z. Harraz Presentation VCR stoping

10

Application Sharp dip in bodies (same conditions as those

considered for Sublevel Stoping method). Requires less stability of the host rock; Stopes may receive the backfill after extraction.

Developmental sequence of stopes... Galleries transport are dug along the ore body

at the level of drawpoints; Arrangement drawpoints is created in the

lower portion of the stope; Stope is highlighted (undercut); Top Access (overcut) is excavated to allow

drilling and loading of explosives.

11 Prof. Dr. H.Z. Harraz Presentation

VCR stoping

Production Drilling from the top level.

The detonation dismantle slices upward from the bottom of the block.

It is enough removed to make room for the next disassemble ore.

Geometry of the explosive charge:

L: D ≤ 6: 1 (length: diameter)

Drilling is large diameter (DTH or top hammer - 100 to 165mm) and preferably vertical;

The method enables a reduction in development compared to SLS

do not need to slot the initial stope

Longer drilling

The charge ratio fragmentation of ore and are larger than the blasthole stoping

12

High production rates; good recovery.

Appropriate mechanization.

Safe method with good ventilation.

Advantages

Prof. Dr. H.Z. Harraz Presentation VCR stoping

The technique of vertical cratering (VCR) might be used to: Create initial slot in SLS; Fabricate raises; recover pillars

13 Prof. Dr. H.Z. Harraz Presentation

VCR stoping

VCR - How It Works

Uses cratering theory: Developed by Livingston 1962 Charges 1 to 6 x hole diameter Placed at optimum distance from surface

Loaded from top of hole Gravity moves rock down:

Away from hole Providing a new face

Holes drilled form development heading(s) down to development Large diameter Accurate

Blasting progresses upwards in layers

14 Prof. Dr. H.Z. Harraz Presentation

VCR stoping

How Cratering Works

N = E W1/3

Where: N is the critical distance

(maximum for cratering); E is a constant for a given

explosive-rock combination; W is the weight of the explosive

charge.

15 Prof. Dr. H.Z. Harraz Presentation

VCR stoping

Best Efficiency at 0.58 N.

16 Prof. Dr. H.Z. Harraz Presentation

VCR stoping

Loading

• Lower plug and tie off

• Drop rock to seal plug

• Sand stemming

• Load explosive

• Sand stemming above

Drops out of hole after blast

• Alternate use water above

17 Prof. Dr. H.Z. Harraz Presentation

VCR stoping

Luosavaara Mine Example

165 mm Holes 100 m depth max deviation 1m.

ANFO 3.3 x 4 m staggered pattern

Max size required 0.75 m ; K50 12-14 cm

18 Prof. Dr. H.Z. Harraz Presentation

VCR stoping

Luossavaara Tests

19 Prof. Dr. H.Z. Harraz Presentation VCR stoping