Gold Fields Results
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9
maintenance programs on mechanised mobile equipment. The
percentage of employees exposed to >85dB (A) increased from 52.4
per cent in the June quarter to 55.6 per cent in the September
quarter. This measurement is without hearing protection, which is
currently provided and almost universally used. (We do comply with
the milestone on equipment but employees without hearing
protection devices are over exposed. If all our employees wear their
hearing protective devices correctly at all times in high noise zones
none of them will be over exposed.)
The Group continues to pursue best practice in the area of dust
control in accordance with the MHSC. In order to improve upon dust
exposure targets, the following core initiatives are ongoing:
· Equipping the water blasts with flow control valves. Flow control
valves were installed to minimise water wastage. The blasts can
now be manually activated to water down the work area and
control the water flow ;
· Real time dust monitoring;
· Foggers/water mist spray systems at dust sources;
· Dust allaying at internal tips; and
· Footwall dust allaying.
West Africa region
Tarkwa
BPR initiatives are ongoing. The major BPR projects for 2013
include:
·
Extending life of heavy mining equipment, including tyre life,
through improved haul road conditions;
·
Increasing CIL throughput through the installation of a tipper car
on the North heap leach crusher conveyor to supplement the CIL
feed rate. The current circuit is limited by the feeding equipment
capacity into the primary crusher. The cross over from the North
heap leach crusher will assist in maintaining and increasing the
ore stockpile levels for feeding into the primary crusher and
increase the CIL milling rate from 1,460 tonnes per hour to 1,500
tonnes per hour. On an annualised basis this equates to an
increase in the milling rate from 11.9 million tonnes per annum to
12.3 million tonnes per annum;
·
Acceleration of waste strip through the implementation of a
larger sized load and haul fleet. The improved flexibility is also
designed to ensure a continuous ore supply to the plant. This
project has the potential to increase the annual mining volume
by an estimated 10 per cent; and
·
The purchase of an additional front end loader to improve loader
availability in the optimisation of crusher throughput from ore
rehandled from the ROM-pad.
The tipper car on the North heap leach crusher conveyor to
supplement the CIL feed rate was commissioned in May 2013.
Since inception of the haul road improvement campaign, average
tyre-life has increased from 4,250 hours in the March quarter to
5,200 hours in the June quarter and to 5,427 hours in the September
quarter.
Damang
BPR initiatives are ongoing. The major BPR projects for 2013
include:
·
Continued savings from owner mining and maintenance
initiatives implemented in early 2011;
·
Optimisation of the plant circuit to achieve the maximum
recovery rate of 89 per cent under current blend conditions
which include:
·
Installation and commissioning of the intensive leach reactor
(ILR) which was completed in the December 2012 quarter.
The unit is performing as expected with higher recovery
rates being achieved on the gravity concentrate. The ILR
replaced the Gemini shaking table used for treating gravity
concentrate from the Knelson concentrators. The use of
intensive cyanidation as applied in the ILR unit increased the
recovery of gold from gravity concentrate from 70 per cent
(using a gravity shaking table) up to 98 per cent. This
reduced the circulation of gold into the circuit from gravity
concentrate tailings and improved overall plant gold
recovery;
·
Commissioning of the pre-leach thickener (PLT) project to
improve control of the circuit water balance and optimise
gravity circuit feed rates was completed in July 2013. The
PLT increases the leach feed density from an average 45
per cent solids to above 50 per cent solids by removing
excess water content from the slurry. Leaching reagents are
added based on ideal solution concentration. As a result of
the PLT operation there is now less solution in the leach
feed thereby reducing the reagent requirement to maintain
the optimal concentration for leaching. The actual cost
saving will be measured in the December quarter;
·
The milling circuit has two installed gravity concentrators
which recovers course gold from the mill circulating load and
adds excessive solution as part of the gravity gold recovery
process. In absence of the PLT it was not possible to run
both concentrators as excess solution contributed to an
inefficient mill circuit density and circulating load. With the
commissioning of the PLT the operation now has the ability
to remove excess water added by the gravity units. As a
result both units can now be operated with the associated
increase in gravity gold recovery complemented by the
operation of the ILR.
·
With the PLT removing excess water from the leach feed
slurry the opportunity arises to re-circulate the removed
solution back into the milling circuit. This improves internal
water circulation and reduces water consumption in the
plant. In the absence of the PLT the solution circulated via
the TSF pond at additional overland pumping cost; and
·
An additional CIL leach tank to take the number of leach
tanks from 7 to 8, is being added to the circuit to improve the
residence time and recoveries and circuit reliability. At the
end of the September quarter the 8th
tank was 40 per cent
complete.
Australasia region
St Ives
BPR initiatives are ongoing. The major BPR projects for 2013
include:
·
Cyanide optimasation project: cyanide is a significant contributor
to site costs. The intent of the cyanide optimisation project was
to improve the management of excess cyanide in the leach
process, optimise consumption and reduce cost. The project
involved establishing a loop system to measure excess free
cyanide in the final stage of the leaching process and using that
information to control and improve cyanide dosage in the first
stage of leaching. The project has resulted in approximately 20
per cent reduction in cyanide used per milled tonne of ore. A
further phase of the project involves optimising dosage across
the first two stages of leaching to further improve control and
reduce waste;
·
Focus on the drill and blast function in open pits. As the Open
pit mines get deeper and harder through 2013, there is a greater
demand on drill and blast performance. In response to
increased demand, several drill and blast improvement projects
were carried out through the quarter. Projects included reducing
non-productive time for drills, work flow reorganisation between
operations and maintenance, reconfiguring work crews,
establishing visual daily targets and short interval tracking for
drill and blast crews. The improvement activities have resulted
in a 10 per cent improvement in drill utilisation hours per shift, an
improvement in blasting performance and increased broken
stock availability;
·
The open pits ramp-up project was initiated to manage the
significant increase in production in the open pits from 2013 to
2014. A range of productivity improvement areas across the
mining value chain are being targeted in preparation for the
transition. These include improving excavator and truck
productivities and utilisation and establishing daily crew targets
and short interval control boards;
·
Underground mining operations require a slot or box hole within
stoping blocks to provide void space for the stope to be blasted.
This activity has a significant cost and time impact for the
Underground Mining department. Cave Rocks underground
mine is currently trialing an alternative method – using pipe
jacking methodology combined with boxhole boring in a self-
contained mobile unit called a ‘vertical miner’ – for boxhole
boring to improve the efficiency and cost of the activity.
Indications from the trial show a potential improvement in drilling