PRECONCENTRATION
25 mm fines which bypasses the sorter. The
plant feed grade uplift, coupled with
significantly reduced tonnage delivered to the
processing plant, results in strong forecast cash
flow generation for this project and pre-tax
return on capital (IRR) estimated to be 144%
over a three year life. The forecast capital
payback period is approximately six months.
The financial modelling makes a strong case for
further test work and a potential commercial
operation if stockpile grades of 0.7–0.8 g/t or
higher are confirmed (either through bulk
mining or selective reclaim of the stockpile).”
In another Parry-authored paper, with Kai
Bartram, Business Development Manager
Mining, Steinert Elektromagnetbau and Luis
Loaiza Ampuero of Volcan Compaňia Minera,
Upgrading of low grade silver-lead-zinc ore
stockpiles at Volcan Compa ň ia Minera SAA’s
base metals operations in Peru, using sensor-
based ore sorting, the bulk ore sorting test work
undertaken on material from low grade Volcan
open pit stockpiles is reviewed.
They conclude that “initial ore sorting test
work and subsequent bulk sorting trials have
provided data to indicate that the Cerro de
Pasco low grade stockpile is amenable to
upgrade using XRT ore sorting. Although there
are additional significant losses to waste in the
ore sorting process, the financial analysis
confirms that the major reduction in total feed
tonnages to the concentrator and the lift in
metal value per tonne of feed achieved by
introducing ore sorting transforms what would
be a marginal project into a highly profitable
project. The indicated capital payback is
approximately six months and the ore sorting
project generates a forecast IRR of 207%, while
achieving a significant reduction in wet tailings
tonnages and environmental impact. This
suggests that the company’s decision to build and
commission the ore sorting plant is a sound one.”
There is a lot of this ore sorting test work
going on in Australia. EganStreet Resources
announces that it has identified an opportunity
to optimise and significantly enhance the
financial outcomes of its 100%-owned Rothsay
Gold Project, located 300 km north-east of Perth
in Western Australia, through the application of
state-of-the-art ore sorting technology. The
Company has received highly favourable initial
results from ore sorting testwork completed on
a low-grade stockpile from the historical
underground mine at Rothsay, with the key
outcome that the use of a Steinert Multi-Sensor
Ore Sorter provides an opportunity to increase
underground mine production (being fed to a
similar-sized process plant), reduce the impact
of dilution from the main ore-hosting structure
at Rothsay, reduce life-of-mine processing costs
and substantially enhance project economics.
34 International Mining | MAY 2018
“Ore sorting technology is
increasingly being adopted
across the gold mining
industry in Western
Australia, with highly
encouraging results.
Representative samples
collected from the low-grade
stockpile located adjacent to
the portal of the historical
Rothsay Gold Mine returned
an average stockpile grade
of 2.5g/t Au. This compares
favourably with previous
sampling of this stockpile in
2013, which returned results ranging from 2.7 –
4.1g/t Au. More importantly, the results
demonstrated that the Steinert Multi-Sensor
Ore Sorter was able to successfully reject the
barren ultramafic material located in the
hanging wall of Woodley’s Shear.”
TOMRA introduced its innovative multi-
channel laser sorting technology at AIMEX last
August. It said then that this new laser sorting
technology “will enable quartz and gold
processes to achieve higher recovery, better
quality and more consistent sorting of quartz
material than can be secured using other sensor
technologies. More detail on this was included
in IM’s annual gold recovery article in the
August 2017 issue.
In the diamond sector, a TOMRA X-Ray
Transmission machine has been commissioned
at its mine by Australia's Merlin Diamonds. By
using this technology, it is expected that larger
diamonds will be recovered than previously
possible, as well as recovering low luminescing
diamonds. It replaces the conventional
concentrator and detects all diamonds including
coated and low-luminescent as well as
preventing the crushing of larger diamonds. The
Ector kimberlite pipe will be processed using
the TOMRA XRT machine initially due to its high
proportion of large diamonds.
At this year’s SME conference, K. Heiskanen
et al (colleagues from Outotec and IMA
Engineering) presented Developing real grade-
recovery curves for sorting noting that “sorting
technology has advanced rapidly recently. Of the
two possibilities particle sorting has advanced
especially in introducing new sensors and the
use of multiple sensors. The analysing and
computing lead times have also shortened. This
has made it a viable technology option for many
applications but not for the most important
sorting task at a mine; the ROM ore. Bulk
sorting, however, has advanced in smaller steps,
even if the technology has the capability to
tackle the ROM ore and offers a high potential
to bring mines substantial economic benefits.
The sensors, which are useful, are restricted by
IMA Engineering Fast Conveyor Analyser (FCA)
used in sensing coarse primary crushed and/or
fine crushed ore before it enters the grinding
mills and concentrator. It fast tracks ore grade
and type for optimum processing by delivering
immediate feedback
the difficult operating conditions or by ore
characteristics. One of the important features of
ROM sorting technology is the major material
handling infrastructure required. The capital
expenditure can be substantial requiring good
understanding of the sortability curve (grade-
recovery curve) behaviour of the ore.”
The paper discusses one industrial case,
where substantial amount of data measured
from the ore feed belt has been obtained. This
data was then analysed for the grade recovery
curves obtainable from that ore with sorting.
The XRF measurement used was the FCA
device from IMA Engineering. It is a specially
built version of XRF designed to operate with
coarse material. The measurement was taken at
the main belt conveyor taking ore from the
primary crusher to the stockpile. The crushed
ore was about 80% -300 mm at a capacity of
1,100-1,200 t/h. Measurement times were varied
from 30 seconds to a minute. Measurements
were obtained over several months.
The authors conclude that “the measured
grade recovery curves between ore types and
blasted block locations had different signatures.
Waste rock could always be detected from both
high- and low-grade ores. High-grade ores
benefited from sorting but some disseminated
low-grade ores were not amenable for sorting.
The results clearly point towards the benefits of
measuring the coarse mill feed for longer
periods of time at high sampling frequency
before the final technical and economic
assessment of sorting can be made at any mine.
In the studied case there is a possibility to
increase the metal stream to the products up to
2-3%. It may well be, that the measurement
alone without sorting can give substantial
operational improvements by enabling better
control and optimisation of the plant.”