St Barbara
A refusal to accept the status quo and a willingness to adopt innovative techniques will see the life of the historic Gwalia mine extended to 2031 and beyond, according to St Barbara managing director and chief executive Bob Vassie.
AS part of its bid to extend mine life at Gwalia, in the WA Goldfields, St Barbara will complete a $100 million expansion (GEP) over the next 12 months, while also investigating a change to mining and haulage methods, called the Gwalia Mass Extraction (GMX).
According to St Barbara’s Bob Vassie, the GEP was about 50 per cent complete, on schedule, and on budget, with planned completion expected at the end of 2019.
He said the GEP would improve production by addressing existing ventilation constraints.
“We are currently ventilation constrained at Gwalia, which limits how many activities we can do at one time, including trucking,” Mr Vassie told The Australian Mining Review.
“Further, much of the waste rock we generate must be trucked to the surface, which displaces ore capacity.
“The GEP solves this by upgrading the ventilation capacity and installing paste aggregate fill (PAF) equipment underground.”
Mr Vassie said PAF would enable St Barbara to combine crushed waste rock from underground development with cemented paste from the surface to use for stope fill.
“Having this set up underground will allow us to fill stopes faster and increase productivity and trucking efficiency,” Mr Vassie said.
“Increasing the ventilation, along with upgrading power and cooling, will enable Gwalia to be mined to 2000 metres below surface.”
Mr Vassie said St Barbara had also identified further chilling and fan upgrades to mine down to 2200 metres below surface.
“This, along with the GMX results in a life of mine plan out to FY31,” he said.
The PAF component was the faster of the two areas and was due to be finished in the March quarter of 2019.
When turned on it would not only be able to dispose of the waste rock underground, but also be able to deal with the waste rock chippings generated by the ventilation raise-boring.
Mr Vassie said this would immediately improve ore trucking capacity.
“When we commission the new ventilation and chilling at the end of 2019, that is when we can well and truly liberate the mine,” he said.
Exploring New Methods
While implementation of the GMX was still a while away, the feasibility study was progressing well, having been expanded to consider alternative designs for hydraulic hoisting.
The feasibility study was due in March 2019.
“GMX is an innovative solution we’ve been studying that allows us to maintain gold production, in a deepening mine with lower grades, by changing mining and hauling methods to double ore tonnage production,” Mr Vassie said.
St Barbara announced the results of the pre-feasibility study in February 2018, highlighting the use of either continued truck haulage or hydraulic hoisting.
Hydraulic hoisting involves crushing and potentially grinding ore underground and pumping it to surface, then to the plant.
According to Mr Vassie, St Barbara would also change mining methods in some areas for economic extraction of thinner lodes.
GMX scenarios have 280,000 to 300,000 ounces per annum (ozpa) produced in the initial years, which were expected to be FY21 and FY22.
Production would then be maintained above 200,000ozpa until FY29.
Despite being an innovative solution, Mr Vassie said the crushing and pumping technologies St Barbara was exploring had been proven within other applications.
“It’s a little bit of horses for courses,” he said.
“Other deep mines would generally have a haulage shaft, so they would not need to consider pumping; that is why there are not many examples of vertical pumping of ore.
“In St Barbara’s case we seek to innovate to maintain margins as Gwalia gets deeper.
“Both the GEP and GMX are examples of not accepting the status quo and adopting innovative techniques.”
Drilling Further
Beyond the GEP and GMX, St Barbara also hoped to extend mine life through exploration success according to Mr Vassie, who said the miner had already had good results from the Gwalia Deeps drilling during the September quarter, with high expectations for the future.
Drilling at Gwalia Deeps returned significant intersections including 18.6 metre grading at 10.3 grams per tonne (g/t) of gold and 6 metre grading at 12.2g/t of gold.
Both results were from two daughter holes, which tested the southern extension of the ore body.
Mr Vassie said the most pleasing thing about the results was the grades and thickness of the lodes, which were both similar to what St Barbara was currently mining 250 metres above.
He said St Barbara had increased the Leonora region’s exploration budget for FY19 by $3 million, largely based on the results of that drilling.
“We have drilled a further two daughter holes since the September quarter was released and we’re waiting on assays,” Mr Vassie said.
“Other greater Gwalia exploration includes a drill hole to test a third seismic target located further south of the previous two.
“In the Leonora region we’ve also completed a reverse circulation program at Horse-Paddock as well and are waiting on results.”
Mr Vassie said St Barbara would be doing a lot more on the large regional tenement package it held north of Leonora.
“This ground is along trend from Gwalia for about 60km and has not been explored by modern techniques,” he said.
“Previous exploration was shallow drilling decades ago.
“The long-term outlook for Gwalia looks very promising, with the work we’ve completed to date on the GMX indicating a mine life to FY31; if we factor in exploration success both at Gwalia and within trucking distance, the mine could operate for many years beyond FY31.”
In addition to its drilling around Gwalia, St Barbara has also entered into a joint venture agreement with Australian Potash at the Lake Wells gold project, 180km north east of Laverton.
Under the $7 million agreement, St Barbara will pay Australian Potash $1.25 million in cash and a minimum exploration spend of $1.75 million during the initial 12-month earn-in period.
After the first-year earn-in period, St Barbara could elect to earn a 70 per cent interest in the tenements by spending a further $3.5 million on exploration over a 24-month period and reimburse Australian Potash $500,000 in costs previously spent on exploration.
Mr Vassie said St Barbara viewed these types of investments as another form of exploration and part of its growth pipeline.
“The investments are targeted on areas and regions we view as highly prospective, but also have teams who are genuinely putting the money into the ground,” Mr Vassie said.
“The size of our investment allows for accelerated exploration and also gives us options should they have success.”
Performing Strongly
Exploration and extensions aside, Gwalia has already proven itself to be a strong performer for St Barbara, pouring its 2 millionth ounce of gold in October.
“It is a high-grade underground mine, but also the deepest trucking mine in the world and getting deeper each year,” Mr Vassie said.
“When the mine restarted in 2008, the initial target was producing around 185,000ozpa, which the company achieved in FY12 and FY13.
“Since then, new records for annual production have been set almost every year, with FY18 producing a new record of 268,000ozpa.”
Mr Vassie said while St Barbara was benefitting from production moving through a very-high grade portion of the orebody, much of the success since FY12 was due to increased tonnage productivity.
“The success has been driven through a focus on business improvement by our team on site,” he said.
“Reducing waste haulage, introducing ore passes and adoption of remote bogging have all contributed to productivity and efficiency.”
“Both the GEP and GMX are examples of not accepting the status quo and adopting innovative techniques.”