GOLD EXTRACTION_proof 19/07/2016 14:52 Page 1
GOLD EXTRACTION
Au-some
John Chadwick reports on
some innovative mining
and processing methods
likely to see more
widespread use soon
et us start this year’s examination of better
ways to extract gold by reviewing some of
the innovative ore extraction techniques
and how these are advancing.
AngloGold Ashanti is making progress with its
innovative reef-boring system. One MK IV
prototype machine has been deployed at the
TauTona mine test site in South Africa. It extracts
only the gold ore before backfilling. The backfill
is not conventional but a specially developed
ultra-high strength backfill (UHSB) to fill the
void.
AngloGold Ashanti CEO Srinivasan
Venkatakrishnan commenting recently on the
pillars left after mining said “we’ve left 40% of
the gold behind.” One of the aims of the reef
boring development is to exploit these pillar
gold resources.
Venkatakrishnan said the system would not
replace conventional mining, nor was it a form
of mechanisation. But it would give South
Africa’s gold mines the ability to recover what
was previously inaccessible.
AngloGold Ashanti started testing the reef
boring system in 2013, producing about 3,000
oz during the initial test phase at TauTona mine.
Last year the system at TauTona produced about
13,000 oz and AngloGold aims to increase this
to about 20,000 oz this year.
Venkatakrishnan said the company had
invested more than $100 million in the project
and the results were finally showing, especially
because TauTona produces the highest grades.
However, he warned that “it is a tough
technology to roll out on a large scale.”
L
Looking down an AngloGold Ashanti reef boring
hole
66 International Mining | AUGUST 2016
“We see this as a potential game-changer
and potentially something which could arrest
the rate of decline in gold production, but not
enough to completely transform it,”
Venkatakrishnan said.
Orebody knowledge and exploration plays a
critical part in the mine design for any orebody.
Enhanced geological information will improve
current planning practices and will be essential
in the application of mechanical reef mining. In
order to mine the different reef packages
optimally, the location of the reef terraces,
structural information and time to analyse
geological information is essential for the
success of mechanical mining methods. RC
drilling is being developed to replace
conventional geological drilling techniques.
The reef-boring technology is being
developed to extract gold-bearing reef using
mechanical boring techniques, with the aim of
creating an explosive-free, and, therefore,
continuous mining operation. At the core of this
initiative is the need to remove people from risk
while creating a continuous-mining environment
AngloGold Ashanti is well advanced on a reef
boring project to cut mining costs and reduce
waste extraction
where only the reef is extracted - without
diluting the orebody by up to 200% and more,
as is the case with the current mining methods.
Three MK III prototype reef boring machines
were deployed in 2015 at TauTona 97 Level in
the Carbon Leader Reef prototype sites. The MK
IV was deployed in the extended test site.
Reef boring cycle times have improved to 82
hours per hole, from roughly 160 hours per hole.
One MK III prototype reef boring machine was
also deployed in 2016 at TT 67 Level in the
Ventersdorp contact reef prototype site.
The USHB needs to be a support medium that
is stronger than conventional backfill. The
development has focused on a cost effective,
UHSB ‘recipe’, which on curing will attain 170200 MPa strength (as hard as the country rock).
Due to its density, this product needs a
special delivery system to transport the USHB
for in-hole placement as quickly as possible at a