Ownership IGO 30% (AngloGold Ashanti: 70% and manager).
Location 330km ENE of Kalgoorlie.
Tropicana is located on the western edge of the Great Victoria Desert of which the traditional owners and custodians emanate from the Wongatha and Spinifex peoples.
Figure – Location of Tropicana Gold Mine tenure
IGO targeted and pegged the area containing the current gold reserves in 2001. AngloGold Ashanti farmed into the project in 2002, discovering Tropicana, Havana and Boston Shaker Gold Deposits respectively in 2005, 2006 and 2010. The gold deposits occur over a 5km strike length with gold mineralisation intersected over 1km vertically beneath the natural surface.
The decision by the Joint Venture partners to develop the Tropicana gold mine was announced to the market in November 2010 following a positive Bankable Feasibility Study. In early 2011, construction of the 220km access road commenced, followed by development of site infrastructure including an aerodrome, accommodation village, borefields and processing plant. Mining of the Havana deposit commenced in 2012 with the first gold was poured in September 2013. In October 2015, the Tropicana gold mine achieved its 1-million-ounce milestone.
The Tropicana and Salt Creek joint venture concession packages comprise approximately 3,200km2 and 2,300km2 of tenements respectively stretching over more than 250 kilometres in strike length along the Yilgarn Craton and Fraser Range Mobile Belt Collision Zone.
Tropicana lies to the west of a major tectonic suture between the Yilgarn Craton and the Proterozoic Albany-Fraser Province that stretches over 550km. The majority of the project covers tectonically reworked Archean rocks which form the eastern margin of the Yilgarn Craton. The regional geology is dominated by granitoid rocks, felsic to mafic paragneiss and orthogneiss, and felsic to ultramafic intrusive and volcano-sedimentary rocks. Tropicana is a rare example of a large gold deposit within high grade metamorphic rocks that have undergone widespread recrystallisation and melting.
The Tropicana gold mine comprises an open pit mining operation with production from up to four contiguous pits extending some five kilometres in strike length. Mining is carried out by Macmahon Holdings Limited under an alliance contract using a fleet of three Caterpillar excavators and fifteen 793 Caterpillar trucks and other support equipment. Mining is undertaken on 10m benches. Ore is hauled directly by truck either to the primary crusher or to ore stockpiles.
In FY17, a CAT 6060 (600t class) hydraulic shovel was successfully introduced to the open pit mining operation which has resulted in overall improvement in mining efficiencies. The shovel has delivered higher productivities and lower unit costs. It is capable of mining higher benches that are currently employed at Tropicana and work is underway to optimise bench heights in both ore and waste.
Photo - Tropicana Gold Mine
The original designed nameplate capacity of the processing plant of 5.8Mtpa was achieved in March 2014 and comprises crushing, High Pressure Grinding Rolls, one stage grinding and CIL recovery. In 2016 and early 2017, the processing plant went through a redesign and optimisation project to increase the throughput capacity to 7.5Mtpa, a rate at which Tropicana was able to demonstrate in the second half of FY17.
Photo - Tropicana Gold Mine gold room
Tropicana gold production for FY17 was slightly above guidance at 431,625oz (on a 100% basis) and cash costs and All-in-Sustaining Costs (AISC) were $817/oz produced and $1,162/oz sold respectively.
During the year, a total of 33.7M bank cubic metres of material were mined and hauled ex-pit. This material comprised of 7.9Mt of full grade ore (>0.6g/t), 1.0Mt of marginal ore (grading between 0.4 & 0.6g/t Au) and 73.2Mt of waste material. Full grade ore sources were the Havana Pit (3.91Mt), the Boston Shaker Pit (1.58Mt) and Tropicana (2.41Mt) with the average run-of-mine grade for full grade ore (>0.6g/t Au) being 2.05g/t Au for the year.
The reduction in gold production for the year compared to the FY16 (448,116oz) is a result of lower grade milled following the cessation of grade streaming in mid-FY16. This was partially offset by an increase in ore milled for the year, a total of 7.3Mt, which was up 12% on the prior year as a result of the processing plant optimisation work, while grade milled was 2.07g/t. Average metallurgical recovery was 89% for 431,625oz of gold produced.
IGO's attributable gold production during FY17 was 129,487oz and IGO's attributable share of gold refined and sold was 128,601oz. IGO's attributable average cash costs for FY17 were $817/oz Au produced and AISC were $1,162/oz Au refined.
Attributable gold production during FY18 to IGO’s account is expected to be in the range of 132,000oz to 147,000oz with cash costs plus royalties in the range of $680 to $750/oz and all-in sustaining costs in the range of $1,060 to $1,170/oz. IGO’s share of sustaining and exploration capital is expected to be in the range of $3 to $5 million and $4 to $5 million respectively.
Long Island Study
Work continued during FY17 on the Long Island Study, which is investigating cutbacks to the Boston Shaker, Havana and Havana South open pits. The mining strategy includes using the completed Tropicana pit as a void into which waste will be backfilled, significantly reducing waste haulage costs.
As noted previously, this approach considers a strip mining technique more commonly used in the coal mining industry that has the effect of reducing waste haulage distance by backfilling areas previously mined and hence lowering the mining cost. The study is expected to be completed in the December 2017 quarter.
Figure – Proposed gas pipeline construction (in red)
In 2014, AngloGold Ashanti, on behalf of the Joint Venture, entered into agreements with APA Group (APA) for the transportation of natural gas to Tropicana. Under the agreements APA would construct a new 292km gas pipeline which will connect Tropicana with APA’s Goldfields Gas Pipeline and Murrin Murrin lateral. The gas pipeline project including the installation of the gas fired generators is complete with the commissioning of the 17 gas fired generating units. Further cost savings resulting from this project will be achieved as site equipment requiring LNG as fuel is progressively upgraded to operate on natural gas.
A Resource extension drilling program continued during the first half of FY17 to form the basis of the Mineral Resource for the Long Island Study, based on a strip mining strategy designed to significantly reduce waste mining costs. Mineralisation remains open with high-grade ore shoots defined at both Boston Shaker and Havana South. Additional drilling will be completed in FY18 to test the down plunge extensions on these shoots as part of an underground mining study.
Regional exploration continues to identify and test numerous prospects away from the immediate mine area. AngloGold Ashanti have prioritised geological and structural targets in prospective domains and rock packages to ensure targeted exploration. The extent of the exploration tenure is such that any discoveries made by regional exploration will be within trucking distance of the Tropicana Mine.
Figure - Tropicana Joint Venture tenure (IGO – 30%)