The Tropicana processing plant capacity was now upgraded from 5.8mtpa to 7.5mtpa.
By Elizabeth Fabri
DECEMBER is a big month at Tropicana. On the back of a major expansion and drilling program, the WA project will see the rewards of an upgraded 7.5 million tonnes per annum run rate, and its first reserves review that could extend mine life out to 2030.
THE Tropicana joint venture between AngloGold Ashanti (70 per cent) and Independence Group (30 per cent) has been producing gold since September 2013.
The project was the first significant Australian greenfields gold discovery to come online in more than 10 years, and has been closely watched by the industry since.
Its three gold deposits, Tropicana, Havana and Boston Shaker, and 3000sqkm of tenements along the Yilgarn Craton and Fraser Range Mobile Belt Collision Zone make it a profitable venture for both partners.
While Independence Group (IGO) was not involved in the direct management of operations, the miner took great pride in the project’s performance.
“Even though we only own 30 per cent of Tropicana it is very important to us,” IGO managing director and chief executive Peter Bradford said.
“We take a highly active interest in the day-to-day, month-to-month, and quarter-to-quarter results that AngloGold Ashanti deliver and we’re actively involved in the project by way of the joint venture committees and mechanisms that we have.
“Overall, the 2016 financial year was a good year; at a high level it was not as good as the two previous years but that’s a reality of the mining scheduling, as in those first two years of operations the project did benefit from what we call grade streaming.”
The grade streaming involved mining more material than needed for the processing plant; a strategic move to stockpile the low grade ore and put the high-grade gold through the processing plant to artificially improve results.
“The 2016 financial year didn’t get a full benefit from that but going forward we would expect to consistently deliver,” Mr Bradford said.
Despite the lower results, the financial year saw a number of achievements, as the gold mine celebrated its 1 millionth ounce in October 2015 just two years after first gold was poured.
Since June 2015 the Tropicana team has drilled more than 10,000m as part of an aggressive exploration program, particularly at Havana South, which returned high-grade gold mineralisation from a new ore shoot outside the existing mineral resource.
Tropicana’s expansion project was also completed with a 7.5 million tonnes per annum (mtpa) annualised processing throughput rate expected from the December quarter.
In the three months ending September, the mine processed a total of 1.69mt of ore at an average grade of 2.06 grams per tonne.
“At Tropicana our investments to expand the processing capacity and to extend the mine life are well advanced and we expect to realise the benefits of this in the December 2016 quarter,” Mr Bradford said.
Processing plant expansion
Completed late September, the processing plant optimisation work to upgrade name plate capacity to 7.5mtpa marked one of the most significant milestones at Tropicana to date.
The plant previously had a capacity of 5.8mtpa and was made up of crushing, high pressure grinding rolls, and one stage grinding and Carbon in Leach (CIL) recovery.
The upgrade saw commissioning of two addition CIL tanks, to increase throughput rate while maintaining the same level of gold recovery at 90 per cent.
“The expansion was started about mid 2015, so about 12 months program of work, and it was really a debottlenecking exercise to leverage off the existing major pieces of equipment that were there and to make sure that all of the bits in between that were slowing down the overall process were upgraded,” Mr Bradford said.
“We changed our pumps, we improved conveyors and then the one big piece of capital expenditure was adding two new CIL tanks.”
Updated mine life
Tropicana’s Long Island study running in parallel to the processing plant expansion was also nearing completion.
The study aimed to unlock the full potential of the mine through the 100km framework drilling; the adoption of a strip mining approach; and in pit dumping of waste.
“The first part of the project was drilling off resources underneath the existing pit so that we had the resource information as a basis for the project,” Mr Bradford said.
“We incorporated some of that work into our resource statement as of 30 June and we’re continuing to do work on the technical side which will result in a further announcement later this year, most likely in December when we update our reserves for the project and provide some new guidance on the mine life at Tropicana.”
Based on current reserves, Tropicana has a mine life through to about 2023/2024, which the joint venture partners hoped to extend to 2030.
“Now whether we get there in December or not is still unknown at this stage and it may be that we get to 2030 or beyond in instalments,” he said.
“The first updated reserves in December may not fully capture all of the drilling that we have done so far and there may be a component of the drilling work, what we call Havana South which is not fully captured in the reserve update, and that may follow in 2017.
“It’s certainly been the most active year of drilling at Tropicana in the life of the project.”
In the September quarter $1.7m was spent on exploration at Tropicana out of the $6-8m exploration budget for FY17.
The spend went towards two exploration streams, the resource extension work underneath and along strike of the existing pits, along with regional exploration in the broader Tropicana tenement package to discover ‘the next Tropicana’.
“A large part of that work over the last couple of years has been focused on understanding what’s the prospective ground and what’s the less prospective ground,” Mr Bradford said.
“By developing the understanding we’ve been able to significantly reduce the tenement area around Tropicana [which has] come down from about 12,000sqkm to 3000sqkm.”
As a result of that work, the joint venture leveraged off its increased understanding of the regional mineralisation to push it towards the next discovery.
Mr Bradford said that in 2017 the program would be focused even further, and given the reduced land area and more targeted search, the companies were on the right track to discovery success.
As the 2016 calendar year comes to an end, IGO and AngloGold Ashanti looked forward to continued excellence at Tropicana.
“We’re expecting Tropicana to deliver a fairly consistent production rate going forward because we’re expecting that consistent plant throughput rate of 7.5 million tonnes per annum,” Mr Bradford said.
Guidance for FY17 was expected to reach between 390,000oz and 430,000oz, a slight slump from the 448,116oz produced in FY16.
But the mine was off to a solid start after producing 100,038oz in the first quarter, with second quarter results due at the end of January.
Results from the Long Island study were also expected to advance through 2017.
“We are approaching a very exciting time for IGO with a number of major value catalysts ahead,” he said.
“The orebody itself at Tropicana is very consistent at an average grade of two grams per tonne so based on that we expect gold production year on year to average just over 400,000oz per annum.”