WafiGolpu is a complex, multiphase mineralised system, comprising:- Golpu porphyry coppergold deposit;- Wafi epithermal gold deposit;- Nambonga porphyry goldcopper deposit.The upper portions of the porphyry systems were overprinted by the high-sulphidation epithermal mineralisation at Wafi. GolpuThe Golpu deposit extends over about 800 m northsouth by 500 m westeast, and was drill tested to more than 2,000 m depth. Porphyry-style veins are preserved within the clay alteration at the top of the Golpu deposit. These veins have had the copperiron sulphides removed, leaving only a skeleton of quartz. Irregular molybdenite veins are preserved stable remnants of the porphyry mineralising event. The dominant coppergold-bearing sulphide species vary laterally and vertically within the deposit from an inner bornite (plus chalcopyrite) core, to chalcopyrite as the dominant copper sulphide, and grading out to a pyrite-only shell on the mineralisation margin.The proportion, by volume, of disseminated copperiron sulphides varies from trace to as much as 10%. Pyrite increases from near absent in the core to 10% on the margin in a reverse relationship to chalcopyrite. Disseminated sulphides are typically located at the site of relict iron-bearing phases including primary phenocrystic hornblende and hydrothermal alteration-derived biotite magnetite.The Hornblende Porphyry (Livana Porphyry) is the main mineralised porphyry. Other porphyries act either as weak mineralisers (e.g., Golpu Porphyry) or as benign hosts (wall rock) from adjacent mineralising porphyries. The mineralisation style in benign (wall rock) porphyries can change due to rheological contrast and chemical variations. Quartz vein stockworks occur on the intrusive margin in sedimentary rocks. Significant zones of quartz flooding may be present. The porphyry system is mineralised with gold, copper, silver and molybdenum:- Gold, copper and silver trend from highest grade in the Hornblende Porphyry (Livana) core to background levels at the mineralised edge;- Molybdenum content is low in the gold and copper maxima, but increases outwards to a maximum at the copper margin and declines to background beyond the copper mineralisation limits. WafiThe Wafi deposit has a surface area of approximately 1,100 m x 800 m and was drill tested to about 600 m below surface. A number of zones, including the A, B, NRG and Link Zones, were defined. The NRG Zone is the nonrefractory portion of the A Zone, and the Link Zone is a more discrete, higher-grade zone characterised by both high sulphidation and low sulphidation mineralisation. It is unclear if the high sulphidation and intermediate sulphidation events at Wafi are independent, or are a continuum of a single event.The high sulphidation gold event alteration overprints the Golpu porphyry-style alteration and mineralisation, with the diatreme carrying fragments of the earlier porphyry alteration. The high sulphidation event was interpreted to have remobilised pre-existing porphyry-related copper from the phyllicargillic-altered upper porphyry and deposited this as zoned enargitetennantite covellitechalcopyrite mineralisation. Most of the gold in the high sulphidation overprint was introduced in association with pyrite.The low sulphidation Link Zone, which occurs on the diatreme margin, between and below the Zones A and B high sulphidation gold mineralisation, is characterised by pyrite with lesser quartz (quartzsulphidegold style) veins, which are overprinted by more than one generation of pyrite sphaleritegalenacarbonate veins (carbonatebase metalgold style). Selective sampling shows the gold in this zone is related to the arsenian pyrite of the quartzsulphide-style veins, while the multi-stage lowarsenic carbonatebase metal veins are not well gold-mineralised.Advanced argillic alteration contains primary copper mineralisation as chalcocite, but gold occurs within pyrite or as electrum associated with pyriteenargitetetrahedrite. Mineralisation appears to broadly follow the metasedimentary and volcanic host rocks stratigraphy (i.e., 4050 to the east, and northeast), and is often sub-parallel to bedding. The coppergold-bearing lenses occur in kaolinitechalcocitepyrite and vuggy quartz covellite enargite bands that may reach 20 m in thickness. Nambonga The stock is a low-grade copper and gold mineralised system, and extends over an area of approximately 200 m x 200 m and to a vertical extent of at least 800 m.Much of the mineralisation is associated with silicification, either pervasive or as veins. Quartz stockwork veins that may be as wide as 10 mm and stockworks overprint the porphyry, especially in the upper levels.Mineralisation consists of disseminated and vein-style coppergold mineralisation and structurally-controlled base metal mineralisation in steeply-dipping lodes. Chalcopyrite is the dominant copper sulphide mineral. Chalcopyrite and pyrite form anhedral grains ranging that can reach 0.2 mm in width, and tend to occur as centrelines to quartz veins. Magnetite forms anhedral grains that can be 0.4 mm wide, and is generally present in the margins of the quartz veins or in the wall rock adjacent to quartz veins. Minor magnetite, pyrite and chalcopyrite are disseminated through the host rock.
An evaluation of potential mining methods included consideration of block caving, sub-level caving (SLC), sub-level open stoping (SLOS), and open pit methods. Block caving was selected for the following reasons:-Orebody geometry and geotechnical conditions;-High productivity, low operating cost mining method;-Higher-value material located at depth can be accessed earlier in the mine plan.The proposed mine plan uses technology conventional to block cave operations, including mine design and equipment. Due to high surface ambient temperatures and humidity, and the depth of the mine, considerable ventilation and cooling capacity will be required to be installed to ensure the health and safety of mine workers.The proposed mining method is block caving at three distinct elevations:- The BC44 extraction level is planned at 4400 mRL, to extract a total of approximately 67 Mt of material over a seven-year period at a peak annualised 16.84 Mt/a production rate. During caving operations, ore from the block cave drawpoints will be delivered by diesel loadhauldump vehicles (LHDs) to either of two underground gyratory crushers then conveyed to the Watut process plant on surface by an inclined conveyor system;- The BC42 extraction level is planned at 4200 mRL, to extract a total of approximately 93 Mt of material over a nine-year period at a peak annualised 16.84 Mt/a production rate. Materials handling from drawpoint to the Watut process plant is identical to that proposed for BC44;- The BC40 extraction level is planned at 4000 mRL, to extract a total of approximately 240 Mt of material over a 16-year period at a peak annualised 16.84 Mt/a production rate. Materials handling from drawpoint to the Watut process plant will be identical to that proposed for BC44.Access to the mine workings will be via the Watut and Nambonga declines, with each generating waste rock that will either be used in construction activities, processed or deposited within the waste rock storage facilities (WRSFs). Block cave mining will not result in the production of waste rock because all material extracted from the block cave will be fed to the Watut process plant. Block cave mining will cause a subsidence zone of fractured rock to develop that will propagate to surface.During the development of the block caving infrastructure, ore grade material will be temporarily stockpiled on the process plant terrace for later use during commissioning and initial production from the process plant. During caving operations, ore from the block cave drawpoints will be delivered by LHD vehicles to an underground crusher. The crushed ore will then be conveyed to the surface. The ore conveyor emerging at the Watut declines portal terrace will continue overland for approximately 600 m to deliver crushed ore to a coarse ore stockpile adjacent to the Watut process plant for processing.The mine is planned to operate 24 hours per day, every day of the year, apart from scheduled and unscheduled shutdowns.
Coarse Ore StockpileCrushed ore will be conveyed to a single, conical, open stockpile which will have a live capacity of approximately 41.4 kt dry solids. The design basis average live residence time will be 20 hours, based on the Golpu flowsheet.Coarse ore will be reclaimed from the stockpile by four belt feeders. Each feeder will be designed to provide 33% of the full feed rate to the SAG mill to enable three feeders to achieve nameplate capacity. Each belt feeder will discharge onto the mill feed conveyor that will transport crushed ore to the SAG mill feed chute. Comminution Circuit The comminution circuit will consist of a single SAG mill in open circuit, followed by two ball mills, configured in parallel, operating in closed circuit with dedicated classification cyclones. However, the comminution circuit is configured as a single SAB combination for the LEAN flowsheet for the first three years.All three mills will share a common discharge sump. Scats/pebble return conveyors were incorporated into the circuit with a pebble crusher included, but deferred to the latter years of operation to accommodate harder ores at that time. Scats and pebbles will be recirculated via external conveyors to the SAG mill feed.The Golpu flowsheet will be commissioned in two stages with the additional ball mill circuit brought on later to match the increased tonnage profile, resulting in a SAG/ball mill configuration with the two ball mills operated in parallel. The Golpu pyrite circuit will be commissioned the following year.A pebble crusher is included in the scats/pebble circuit later in mine life when necessitated by the increased ore hardness of portions of BC40. The design caters for a possible future inclusion of a bifurcated chute and additional conveyors to return crushed pebbles to the ball mills in equal proportions should increase ore hardness towards the end of the LOM necessitate it.The SAG mill will be operated in open circuit while each ball mill will be configured in closed circuit with a dedicated classification cyclone cluster. Each ball mill will have a circulating load of 240%. The SAG and ball mill are designed for operating at 75% of critical speed. The specific energy values used were obtained from testwork and are 6. kWh/t for the SAG mill and 9.2 kWh/t for the ball mills. The total charge volume ranges between 2025% by volume in the SAG mill and 2534% by volume in the ball mill. The ball charge volume is adjusted according to the demand and operation of the mill. The in-mill density designed for is 67% by mass for the SAG mill and 70% by mass in the ball mills. The discharge of both SAG and ball mills will be via a trommel screen.Each ball mill will be operated in closed circuit with a classification cyclone cluster, the underflow will return to the mill while the cyclone overflow product will be routed across a 3 mm square aperture vibrating trash screen to protect downstream processes from ingress of oversize material in the event of the cyclones roping. Two standby cyclones are included in each classification cyclone cluster. The cyclone overflow product specification is a P80 of 106 m and a density of 36% solids by mass to allow for a nominal dilution from the downstream trash screen spray water while maintaining a flotation feed density of 35% solids by mass.Individual cyclone feed pumps will feed the separate cyclone clusters with cyclone underflow returning to the respective ball mill feed chutes. The mill feed conveyor will transfer ore (together with pebble/crushed pebble recycle) to the SAG mill feed chute. Steel grinding media will also be added to the mill feed hopper via an automated ball loading system.
The process plant will include the following:-Crushed ore stockpile and reclaim;-Single SAB milling circuit, with the ball mill operated in closed circuit with cyclones for operation at the lower design throughput of 8.42 Mt/a. This will be expanded to include a second ball mill, operating in parallel with the original ball mill circuit when the plant is expanded to a design capacity of 16.84 Mt/a. The target grind size is a P80 of 106 m;-A pebble crusher circuit is included. Pebbles are recirculated to the SAG mill during the 8.42 Mt/a LEAN and early years of the 16.84 Mt/a Golpu flowsheet with the pebble crusher included when necessitated by increased ore hardness in the later years of mine life;-Copper flotation comprising rougher flotation, copper rougher cleaner (single Jameson cell) which processes the first rougher concentrate, copper concentrate regrind, followed by a three-stage copper cleaner, and cleanerscavenger stage;-Additional copper ........
Metso will supply two complete grinding mills and related equipment to Newcrest Minings Cadia Valley gold mine, near Orange in New South Wales, Australia. The value of these two orders is over EUR16 million, and the delivery will be completed by June 2010. The orders comprise two grinding mills. The first is a ball mill that will be the most powerful ball mill supplied into Australia. The second is a vertical stirred mill and it is the first of this size to be installed in the world. The ball mill will be installed in the Newcrest Cadia concentrator and the vertical mill to the companys adjacent Ridgeway concentrator.
Cadia Holdings, a wholly owned subsidiary of Newcrest, received notice last month that planning approval had been granted for its proposed Cadia East project. The estimated capital cost of the project is expected to be nearly A$2 billion. Newcrest General Manager Cadia Valley Operations, Tony McPaul, said that receipt of planning approval was a critical next step in the project which was now expected to be considered by the Newcrest Board around the end of the first quarter in 2010 after remaining regulatory approvals have been finalised.
If approved by the Board, the Cadia East project will be the largest underground mine in Australia and will secure our future in the region for at least the next 20 years. It will be Newcrests first panel cave, building on our expertise in underground mining.
In an updated feasibility study released mid-March 2018, Newcrest Mining has added almost US$170 million to the forecasted costs to develop the Wafi-Golpu copper-gold project in Papua New Guinea (PNG), bringing the cost estimate to US$2.82 billion.
Wafi-Golpu, a 50-50 joint venture between Newcrest and Harmony Gold, was previously expected to cost $US2.65 billion to build in a 2016 pre-feasibility study. Even though Newcrest has flagged the increase in development costs, it has lowered the life-of-project costs to $US5.3 billion from 2016s $US6.3 billion.
Newcrest Managing Director and Chief Executive Officer Sandeep Biswas said The improved business case set out in the updated Feasibility Study clearly demonstrates the world-class nature of this multi-decade project.
We are excited to have this tier 1 asset in our portfolio with an IRR of 18%, first quartile production costs and decades of operating life. We have a clear pathway forward for the project and together with our Joint Venture partner, we are committed to working with the Government and people of PNG to progress this world-class asset.
The project is estimated to generate free cashflow averaging around $0.9bn per annum in the first ten years post commercial production (including being over $1bn in five of these years) in line with the grade and recovery profile of the ore milled. Periods of lower annual free cash flow reflect lower grade and recovery of the ore milled generally towards the end of production from the first two caves, together with the capital expenditure required to develop additional block cave extraction levels.
It is proposed that the first block cave, BC44, be situated at 4,400mRL. This deeper block cave with a larger footprint, compared to prior studies, results in a net increase in mining capital expenditure of approximately $70m. The second block cave, BC42, will be situated at 4,200 mRL. These block caves are expected to be mined for 7 and 9 years respectively during the first 14 years of the mine life. The third block cave, BC40, proposed to be situated at 4,000 mRL, is expected to be mined for 16 years leading to a total mine life of 28 years from first production of the processing plant (excluding construction and closure phases).
Due to high surface ambient temperatures and humidity, and the depth of the mine, considerable ventilation and cooling capacity is expected to be installed to ensure the health and safety of mine workers.
The mine dewatering designs include the dewatering from the block caves to surface using a cascade pumping system. Emergency dewatering in the case of extreme rainfall entering the cave through the subsidence zone is also catered for. The extraction level is sloped away from the crusher chambers to provide emergency surge storage capacity. In addition, all pump stations and electrical equipment associated with dewatering are installed above the flood line, to ensure mine dewatering can still be achieved during and after a flood event.
The proposed Watut Process Plant is a compact copper concentrator that is progressively built to be capable of safely and efficiently processing 17Mtpa of crushed ore to produce a high-grade copper concentrate.
The facility comprises a semi-autogenous grinding mill, two ball mills and a recycle crushing configuration, flotation, thickening, concentrate pumping and tailings pumping systems. The facility is designed to recover copper and gold on average over Life of Mine at 95% and 68% respectively. Concentrate grade average over the Life of Mine is assessed to be 29% copper and 15g/t gold.
Three types of tailings management options have been considered during the various studies undertaken since 2012, those being various terrestrial tailings storage facilities, dry-stacking and DSTP, with DSTP being the preferred tailings management solution.
The ASIA Miner is a bimonthly magazine published in English and Chinese by SEMCO Publishing, providing extensive coverage to the mining industry and is essential reading for those serious about doing mining business in the Asia Pacific region. The ASIA Miner team in Melbourne, Orange and Jakarta not only scour the region for news but are often contacted by companies seeking information about the region or seeking referrals to related companies.
This article was first published by Mining Magazine, 3 June 2017 and is reproduced here with permission of the writer and editor, Carly Leonida. I would also like to take this opportunity to acknowledge that these algorithms wouldnt be operational, if it wasnt for Newcrests world class achievement in partnering with a start-up to take a prototype solution (from Brisbane 2016 Unearthed Hackathon) into operations so quickly! Also a few pics have been added that dont appear in the full article:
Dr Penny Stewart, managing director and principal at PETRA Data Science, is a busy person. Nonetheless, in early May, between preparing her presentation for the upcoming Austmine 2017 conference, which will take place in Perth in late May, and catching a flight, she found a few minutes to speak to me from an airport departure lounge.
And the reason for our call? At the start of the year, the company achieved something rather special, perhaps even a world-first in mining: it has enabled Newcrest Minings Lihir operation to avoid overload events in its semi-autogenous grinding (SAG) mills (read: unplanned downtime) with the help of machine learning algorithms; something you, our readers, will want to know about.
Located on Aniolam Island in the New Ireland Province of Papua New Guinea, the gold deposit at Lihir is one of the largest in the world; since starting production in 1997, the mine has produced more than 10Moz of gold. Most of the ore is refractory and is treated using pressure oxidation before the gold is recovered by a conventional leach process.
We took part in the Unearthed Hackathon in Brisbane [Australia] in March 2016. The team from Newcrest was there. They saw what we were doing and arranged for us to talk to the reliability team at Cadia East, and that led to us working with them to minimise pump downtime at the operation.
Sometimes it can take quite a while to get it running again. Because the SAG mills at Lihir are critical pieces of production equipment, and theres no way of diverting material, it was really important to avoid these events wherever possible.
Stewart talked us through the algorithm development process. We take historical data going back a year or two, in this case it was one year, and we look at the critical signals or indicators related to overload events, she said.
There is a huge amount of data that comes off a SAG mill noise is recorded, power, speed, energy consumption and control parameters there are hundreds of measurements, usually taken at five-second intervals that need to be analysed.
We take all of that data and use the patterns and anomalies to predict whats going to happen next. There are leading indicators as to whats going to happen, and an algorithm is a mathematical equation that describes all of those signals. It either feeds that information back into the mines automated process control system or, in this case, it triggers a visual warning so that the operators can respond to the increasing probability of an overload event. At Lihir, the algorithm predicts the probability of an overload event in an hours time, which allows the mine to take appropriate action to prevent it.
Lihir has different levels of response that it deploys depending on the likelihood of an event occurring, and each of the three mills has its own algorithm. For each one, there werent many overload events recorded compared with normal operating data, Stewart explained, so it was difficult to identify that tipping point from normal operating conditions into an overload situation.
The algorithms effectively allow the mills to operate at maximum throughput with minimum risk of overload. The main challenge was the quantity of data based on failures compared to normal operating conditions, which made it difficult to predict when these events were going to happen, particularly an hour in advance.
Often, machine learning specialists use unsupervised machine learning in this type of scenario, but in this case, that wouldnt give the mine enough time to respond. Thats the advantage of using a supervised machine learning algorithm.
So what benefits has the project delivered? Stewart is rather modest: Obviously I cant give exact figures relating to this case, but I can say that preventing one or two downtimes paid off the cost of the project, she said. Lihir was having multiple overload events each year. And since implementing the algorithms in January this year, they havent experienced any overloads.
This success has led to further collaboration between the two companies. We have created other algorithms for Newcrest as well, and were also working on their big data mine-to-mill studies, Stewart added.
From what I can tell this hasnt really been done before; using live algorithms to predict downtime events in hard-rock mining. The same sorts of algorithms are being used in oil and gas, and were just about to partner with Woodside [an Australian oil and gas producer] on a similar project. Thats a big win for us.
She continued: Newcrest is one of the first in the world to implement live algorithms to prevent downtime, but as word gets out, I expect interest from the mining community will grow. After all, this is something that can be done on existing systems; you dont need to spend money on a new platform to deploy these algorithms, theyre platform agnostic.
With that, Stewart heads off to catch her plane. And just a few days later, PETRAs FORESTALL downtime prediction algorithms were named as a finalist in the Austmine 2017 Awards METS Innovation category.Get in Touch with Mechanic