Tag Archives: block cave mining

New Gold heads towards New Afton’s B3 Zone

New Gold is set to soon start ore extraction activities at New Afton’s B3 Zone in British Columbia, Canada, after receiving its Mines Act Permit from the Ministry of Energy, Mines and Low Carbon Innovation.

The gold-copper mine has recently been focused on development of the B3 and C-Zones, which are likely to represent the major production sources over the next decade.

Current production is coming from the B1 and B2 Zones (Lift 1) where there are two panel caves (west and east) in operation. The B3 Cave is 160 m below and immediately to the west of Lift 1. Ore from B3 will be hauled by truck to the existing gyratory crusher, with production continuing until at least late 2024.

The C-Zone block cave zone is around 550 m below Lift 1. Development towards the C-zone is underway with production planned to commence with the first of 143 planned drawbells in the second half of 2023.

On the permit award, Renaud Adams, President & CEO of New Gold, said: “This is a significant milestone for the New Afton Mine. With the receipt of the B3 permit, ore extraction activities will begin this quarter and ramp-up over the year.

“C-Zone development continues to advance with C-Zone extraction expected to begin in the second half of 2023.”

The C-Zone permitting process was initiated during the March quarter of this year with the submission of the pre-application package to the Ministry of Energy, Mines and Low Carbon Innovation, Ministry of Environment and Climate Change Strategy and Indigenous groups.

Newcrest leverages Eriez HydroFloat tech to help boost Cadia output

Having installed the first full-scale HydroFloat™ cells for the recovery of coarse composited copper and gold at Newcrest’s Cadia Valley operation in New South Wales, Australia, in 2018, Eriez is about to help the miner boost output at the operation.

Today, the Newcrest Board approved two projects moving to the execution phase, being Stage 2 of the Cadia Expansion project and the Lihir Front End Recovery project, in PNG.

The Stage 2 Cadia Expansion project primarily comprises the addition of a second coarse ore flotation circuit in Concentrator 1 (graphic above), using Eriez’s HydroFloat technology, and equipment upgrades in Concentrator 2.

These changes are expected to see plant capacity go from 33 Mt/y to 35 Mt/y, while life of mine gold and copper recoveries could increase by 3.5% and 2.7%, respectively. Alongside this, the company was expecting a A$22/oz ($16/oz) drop in its all-in sustaining costs.

An increase in throughput capacity in Concentrator 2 from 7 Mt/y to 9 Mt/y will be achieved through crushing, grinding, cyclone, pumps and flotation upgrades; while the installation of the second Coarse Ore Flotation circuit on Concentrator 1 and additional upgrades to Concentrator 1 will facilitate an increase in throughput capacity to up to 26 Mt/y, the company said.

“Stage 1, which is already in execution, was designed to maintain production continuity at Cadia through the development of PC2-3 (the next cave development) and increase the processing capacity to 33 Mt/y,” Newcrest said. “Stage 1 comprises an upgrade to the materials handling system and debottlenecking of the Concentrator 1 comminution circuit.”

The rate of ore mined from Cadia is expected to vary over time according to draw rates, cave maturity and cave interaction as further caves are developed, according to Newcrest. From the 2027 financial year onwards, life of mine Cadia mining rates are generally expected to be in the range of 33-35 Mt/y, with an average of 34 Mt/y used for financial evaluation purposes, the company said. Higher mine production rates may be possible, subject to further studies.

At throughput rates of 34 Mt/y, gold recovery improvements from Stages 1 and 2 are expected to achieve LOM gold recoveries of 80.3% and LOM copper recoveries of 85.2% compared to Stage 1 baselines of 76.8% for gold and 82.5% for copper.

The estimated capital cost for Stage 2 is A$175 million, A$5 million lower than the October 2019 estimate, according to Newcrest, which added that timing for delivery remains on schedule, with completion expected late in its 2022 financial year.

The Lihir Front End Recovery project, meanwhile, primarily comprises the installation of flash flotation and additional cyclone capacity, as well as cyclone efficiency upgrades, to improve grinding classification and reduce gold losses through the flotation circuits, Newcrest said.

The flash flotation and cyclone upgrades target the following process improvements:

  • Implement flash flotation to reduce mineral fines generated from overgrinding and send the higher-grade concentrate stream to the autoclaves; and
  • Improve cyclone efficiency to achieve a reduction in unliberated coarse mineral particles entering the cyclone overflow, which are not recovered in conventional flotation.

This is projected to result in LOM gold recoveries increasing by 1.2% and incremental LOM gold production increasing by 244,000 oz. It came with an estimated capital cost of A$61 million.

OZ Minerals eyes up block cave opportunities at Carrapateena underground mine

A prefeasibility study on an expansion of OZ Minerals’ Carrapateena copper-gold underground mine, in South Australia, has indicated a block cave conversion in the lower portion of the Carrapateena resource has the potential to almost double average production from 2026.

It is these results, plus the potential Block Cave 1 and Block Cave 2 expansion net present value of circa-A$770 million ($534 million) at final investment decision in 2023, that has seen the company confirm it will progress the plan to feasibility study stage, with the Carrapateena Block Cave Expansion Feasibility Study Stage 1 report expected before the end of 2021.

The PFS plan includes the potential to transition to dry-stacked tailings to reduce reliance on groundwater resources and a trial of electric light vehicles and establishment of a renewable energy hub – both of which are aligned with OZ Minerals’ strategy and aspirations, OZ Minerals Chief Executive Officer, Andrew Cole, said.

Carrapateena produced first concentrate in December 2019 following a three-year construction period and is targeting a 12-month ramp-up period to achieve a production rate of 4.25 Mt/y by the end of this year.

Currently an underground sub-level cave operation with an estimated mine life of 20 years, the latest study, which comes with a A$1.2-1.3 billion capital expenditure bill shows the potential for a future expansion of the bottom half of the operation into a series of block caves.

Cole said: “The prefeasibility study analysed the whole Carrapateena Province and determined that replacing the lower half of the current sub-level cave with a block cave and expanding the expected annual throughput rate from 4.7-5 Mt/y (currently planned from 2023) to 12 Mt/y, has the potential to create significantly more value than the sub-level cave alone.”

He said the block cave would leverage existing underground infrastructure, supported by expanded surface processing capability.

OZ Minerals added: “The proposed block cave is different from previous Carrapateena block cave studies as it targets a smaller, higher-grade footprint in BC1 (block cave one) with 600 m height of draw, followed by a lower-grade BC2 (block cave 2) with 400 m height of draw. The Carrapateena block cave builds on modern block caving experience, and aims to deliver an automated, electrified, data-driven mine with technology embedded in the design.”

The conversion to block cave operations enables a series of future add-on block caves, all of which were considered in the Life of Province scoping study, Cole added.

The plan could see annual production double to around 110,000–120,000 t of copper and 110,000–120,000 oz of gold from 2026, with life of mine all-in sustaining costs of some $0.75-0.85 c/lb ($1,654-1,874/t), he said.

Key upgrades to underground infrastructure include faster conveying systems with improved utilisation and a larger crusher station three for the block cave with increased capacity over that required for the sub-level cave.

An additional primary ventilation fan and circuit will be required for the transition period from sub-level cave to block cave before a reduction in the mine’s ventilation requirements for the life of mine, the company added.

The prefeasibility study currently recommends the process plant upgrade to 12 Mt/y via a parallel processing circuit to minimise brownfield interfaces and introduce energy load scheduling via the vertical roller mill as the primary surface crushing option, OZ Minerals said.

“The parallel process plant approach also allows both plants to be run independently, and for mine production to continue during plant shutdown periods,” the company said.

However, pivoting back to a traditional SAG/ball grinding circuit in the parallel process plant or tertiary crushing, to increase sub-level cave process plant throughput, will remain as options until final detailed design, OZ Minerals explained. This will not have a material impact on project value and allow time for optimisation of the current sub-level cave process plant before a final decision, it added.

PT-FI makes headway at Grasberg Block Cave underground copper-gold mine

Freeport McMoRan has confirmed that, during the second quarter of 2019, PT Freeport Indonesia (PT-FI) commenced extraction of ore from the Grasberg Block Cave underground mine, in Papua, Indonesia.

This is the same orebody historically mined from the surface in the open pit, Freeport noted.

Since its discovery in 1988, production from the Grasberg open pit has totalled approximately 27,000 MIb (12.25 Mt) of copper and 46 Moz of gold. Over its life, PT-FI expects to produce an additional 17,000 MIb of copper and 14 Moz of gold from the Grasberg Block Cave underground mine, making Grasberg one of the world’s largest copper and gold deposits.

In 2023, PT-FI expects to produce an average of 130,000 t/d of ore from five production blocks spanning 335,000 sq.m in the large-scale Grasberg Block Cave underground mine. At average reserve grades of 0.96% Cu and 0.72 g/t Au, this is expected to equate to production of 850 MIb of copper and 700,000 oz of gold per year.

During the June quarter, Freeport noted:

  • Undercutting in the Grasberg Block Cave underground mine exceeded 20,000 sq.m, over 20% above forecast. Inception to date, undercutting in the Grasberg Block Cave underground mine totals 48,000 sq.m;
  • Initiated drawbelling in two additional production blocks, bringing the active production blocks to three. Eighteen drawbells were opened, exceeding forecast. Open drawbells in inventory in the three active production blocks currently total 29;
  • Ore extraction ramped up from an average of 5,000 t/d in March quarter 2019 to an average of around 9,000 t/d in June 2019 and is expected to reach 15,000 t/d by the end of 2019, and;
  • The fully-autonomous, state-of-the-art underground rail system is supporting efficient transport of ore to the oreflow system for delivery to the mill processing facility.

Freeport said: “Monitoring data on cave propagation in the Grasberg Block Cave underground mine is providing increased confidence in growing production rates over time. As existing drawpoints mature and additional drawpoints are added, cave expansion is expected to accelerate production from an average of 30,000 t/d of ore per day in 2020 to 130,000 t/d in 2023.

The Deep Mill Level Zone (DMLZ) underground mine, located east of the Grasberg orebody and below the Deep Ore Zone (DOZ) underground mine, is expected to produce 8,000 MIb of copper and 8 Moz of gold over its life.

In 2022, PT-FI expects to produce from three production blocks in the DMLZ underground mine spanning 200,000 sq.m. At average reserve grades of 0.92% Cu and 0.76 g/t Au, 80,000 t/d of ore is expected to equate to production of 500 MIb/y of copper and 560,000 oz/y of gold.

During the quarter hydraulic fracturing operations at the DLMZ were ongoing and continue to be successful in conditioning the rock for large-scale mining, according to Freeport. Undercutting approached 4,000 sq.m, in-line with forecast (inception to date, undercutting totals 58,000 sq.m).

In June 2019, undercutting commenced on the second production block to establish two large production blocks in the DMLZ underground mine for ore extraction, while a total of four drawbells were opened, bringing total inventory of drawbells to 74.

Lastly at DMLZ, production ramped up from an average of 6,800 t/d of ore in the March quarter to an average of some 9,000 t/d in June. The DMLZ underground mine is expected to reach 11,000 t/d of ore by the end of 2019.

Ongoing hydraulic fracturing operations combined with continued undercutting and drawbell openings in the two production blocks are expected to expand the cave, supporting higher rates of production with an average of 28,000 t/d of ore estimated in 2020 and 80,000 t/d of ore in 2022.

Meanwhile, PT-FI continues to mine the final stages of the Grasberg open pit. During the most recent quarter, PT-FI opened an additional mining area to extend pit life options into the September quarter and potentially longer (previous estimates were based on mining through June 2019).

“The mine sequencing changes in the open pit delayed access to the high-grade material previously forecast to be produced during second-quarter (June quarter) 2019, resulting in lower copper and gold production from the open pit than the April 2019 estimates,” the company said.

Revised 2019 mine plans for the Grasberg open pit are expected to meet and provide an opportunity to exceed the April 2019 estimates for copper and gold production for the year 2019, Freeport noted. PT-FI will continue to monitor geotechnical conditions to determine the extent of mining in the open pit, with material not mined from the open pit available to be mined from the Grasberg Block Cave.

Major miners join Mining3 and SMI for Cave Mining 2040

Mining3 and the University of Queensland’s Sustainable Minerals Institute (SMI) have joined forces with Newcrest Mining, Vale, OZ Minerals, BHP and PT Merdeka Copper Gold to develop the Cave Mining 2040 initiative.

Cave Mining 2040 was originally proposed by Professor Gideon Chitombo (SMI) whose clear understanding of caving needs and his strong engagement with the mining industry was key to its successful formation, according to Mining3.

The international consortium will collaborate on projects aimed at developing new and improved cave mining methods that could help meet future demand for minerals, the company added.

Mining3’s CEO Paul Lever said: “Involving researchers, industry and government will accelerate the required innovations and information to transform cave mining, ensuring its longevity through viable and sustainable methods.”

Cave Mining 2040 aims to develop solutions to reduce lead times and capital investment while also improving viability, safety, cost, production, and societal and environmental acceptance, according to Mining 3.

SMI Director, Professor Neville Plint, said the agreement was important because it brings together two Queensland-based, world-class research organisations. “We are working collaboratively with industry to unlock complex orebodies that occur at depth and require advancements in cave mining technologies,” he said.

“We look forward to developing further partnerships to enhance Queensland’s and Australia’s reputation as a leader in research, technology and innovation.”

After initial consultation with established and future mine owners, mining equipment and technology services, original equipment manufacturers, and a range of other organisations a number of cave mining challenges have been identified.

The first phase of Cave Mining 2040, Horizon 1, is now underway comprising eight research areas – total deposit knowledge, cave engineering, cave establishment, mine design for new and emerging technologies, high stresses and major seismicity, macro-block design and sequencing optimisation, sublevel caving and open automation platform.

Cave Mining 2040 is a cornerstone activity within the Transforming Cave Mining initiative – a partnership between Mining3 and the SMI.

Cullinan shines in Petra Diamonds’ first half results

The Cullinan diamond mine, in South Africa, led the way in Petra Diamonds’ first half fiscal year 2019 results, with run of mine (ROM) from the underground block cave up 30% year-on-year to 785,444 ct.

Petra’s overall group production rose 10% year-on-year to 2.02 Mct (1.84 Mct in H1 2018), while ROM output rose 13% to 1.9 Mct.

Cullinan’s ROM diamond production increased 30% to 785,444 ct, due to a 12% increase in ROM treated to almost 2 Mt, as well as a 16% increase in the ROM grade to 39.3 ct/ht. This increase in volume and grade was due to the continued ramp up of production from the C-Cut phase 1 and a reduction in ore mined from old areas with higher waste dilution, the company said.

During the period, production from the C-Cut phase 1 was largely concentrated in the south-western part of the footprint and, therefore, not representative of expected production associated with the full extent of the C-Cut phase 1 block cave, Petra said.

The third and final underground crusher was commissioned during December, delivering increased operational flexibility as mining progresses across the footprint of the cave, the company added. The new Cullinan plant is fully operational and meeting design parameters while normal optimisation is ongoing.

“Overall, Cullinan production increased by 37% to 832,026 ct (H1 FY 2018: 607,235 ct) with increased ROM production supplemented by the ramp-up of tailings production,” the company said.

The C-Cut phase 1 project is planned to contribute around 3 Mt this year, with a further 700,000 t to 1 Mt sourced predominantly from the CC1E mining area, as well as from other B Block tonnes. Steady state production of 4 Mt/y will be delivered from C-Cut phase 1 and CC1E from FY 2020 onwards, according to the company. At the same time as this, the ROM grade at Cullinan is expected to remain in the 38-42 ct/ht range from FY 2019 onwards. The company’s current mine plan has a life to 2030, but the major residual resources at the mine indicate that the actual LOM could extend beyond 2030.

Meanwhile, at the company’s Finsch mine (South Africa), ROM carat production was flat at 927,934 ct in the company’s first half. A planned winder upgrade was successfully completed during the period, which necessitated a planned shutdown from December 21 to January 4. Overall, Finsch production decreased by 9% to 947,424 ct due to the planned reduction in tailings production.

Koffiefontein’s (South Africa) ROM production in the half remained flat at 25,275 ct as the company was negatively impacted during the period from community unrest relating to municipal service delivery, operational challenges experienced relating to plant availability and a lower than planned grade recovered. Since the start of January, additional crushing capacity has been introduced to the plant, employee attendance has normalised and monthly production is expected to ramp up.

Williamson’s (Tanzania) diamond production increased 23% to 214,421 ct, mainly due to an 18% increase in the ROM grade recovered as well as a 4% increase in tonnes treated to 2.7 Mt. Petra said it remained in discussions with the Government of Tanzania and local advisers in relation to the overdue VAT receivables and a blocked diamond parcel.

Wafi-Golpu Memorandum of Understanding signed

Harmony Gold Mining Co and its Wafi-Golpu joint venture (WGJV) partner Newcrest Mining have signed a Memorandum of Understanding (MOU) with the Independent State of Papua New Guinea.

The MOU is an affirmation of the parties’ intent to proceed with the Wafi-Golpu project, subject to finalisation of the permitting process and Harmony and Newcrest board approvals. It establishes the framework for the parties to progress the permitting of Wafi-Golpu as quickly as practicable in accordance with applicable regulatory processes.

The MOU provides a framework of key terms to be included in the Mining Development Contract and other related agreements with the state, including provision for stability to underpin the significant long-term investment required to develop and operate the project.

The agreement also re-affirms the intention of the parties to complete the permitting process and achieve grant of a Special Mining Lease by 30 June, 2019.

“This MOU is an important step in progressing the permitting of the Wafi-Golpu project. I wish to thank Prime Minister O’Neill and his government for the constructive manner in which they have worked with the WGJV partners and for the commitment demonstrated in advancing this important project in the best interests of the people of Papua New Guinea and shareholders,” said Peter Steenkamp, Chief Executive Officer of Harmony.

He added: “Our joint understanding of the terms and timeline that we are working towards as set out in the MOU is central to the commencement of the initial work programme. Harmony is committed to make a meaningful contribution to the social and economic development of Papua New Guinea and we look forward to continue working with the government and people of Papua New Guinea to complete the permitting process.”

As a result of entering into the MOU, the WGJV is completing approval processes to commence a substantial work programme, including the establishment of underground access for further drilling of the Golpu deposit and the construction of a bridge over the Markham River, which is an integral feature of the proposed new Northern Access road from the Highlands Highway to the mine site.

The MOU recognises that development of the Wafi-Golpu project will be of major economic significance to the people of Papua New Guinea, and encourages the development of the project in a way which will contribute to the advancement of the social and economic welfare of the people of Papua New Guinea, while also providing a viable and stable foundation for the long term development of the Project by the WGJV.

The Golpu deposit is located approximately 65 km southwest of Lae in the Morobe Province of PNG, which is the second largest city in PNG and will host the Wafi-Golpu export facilities. The proposed mine site sits at an elevation of some 200 m above sea level in moderately hilly terrain and is located near the Watut River about 30 km upstream from the confluence of the Watut and Markham rivers.

The feasibility study update was released in March 2018. Project economics set out in that demonstrate significant free cash flow generation. Once in production, the asset has the potential of being one of the lowest decile cost copper-gold producers.

The WGJV submitted an Environmental Impact Statement for the project to the relevant PNG regulatory authority, Conservation and Environment Protection Agency in June 2018. Consultation with the regulatory authority, community and other stakeholders is ongoing.

The project has mineral resources estimated to contain 26 Moz of gold, 8.8 Mt of copper and 48 Moz of silver. This includes ore reserves for the Golpu deposit estimated to contain 11 Moz of gold and 4.8 Mt of copper.

Currently, the Wafi-Golpu project includes the Golpu copper-gold porphyry deposit, the Nambonga copper-gold porphyry deposit and the Wafi high sulfidation epithermal gold deposit.

Exploration activity to date has shown that the Wafi-Golpu tenements host one of the highest grade porphyry copper systems in southeast Asia (the Golpu deposit).

The Golpu deposit is one of several porphyry ore bodies identified along the 25 km long Wafi-Transfer. Newcrest and its joint venture partner are actively exploring this highly prospective terrain for additional deposits.

The plan is to develop the Nambonga decline and twin underground access declines to access the orebody in which three block caves and associated services and infrastructure will be developed, including a portal terrace, the Watut process plant, power generation facilities, laydown areas, water treatment facilities, wastewater discharge and raw water make-up pipelines, raw water dam, sediment control structures, roads and accommodation facilities. Block caving is the proposed mining method.

The project area comprises three main areas of proposed activity:

  • Mine area – The proposed mine area is located on the northern side of the Owen Stanley Ranges of PNG, approximately 65 km from the Port of Lae, in the foothills of the Watut River catchment. The elevation of the Mine Area ranges from about 100 m above sea level (mASL) to 380 mASL. Most of the area is steep and mountainous, and is covered by dense tropical rainforest.
  • Infrastructure corridor – The proposed corridor is situated on the floodplains of the Watut and Markham rivers and includes the Mine Access Road. The proposed 32 km long Northern Access Road connects the Mine Access Road to the Highlands Highway. A concentrate pipeline extends from the Mine Area to the Coastal Area.
  • Coastal Area – This includes the proposed Port Facilities Area and the proposed Outfall Area. The proposed location of the filtration plant and associated materials handling and ship loading facility is the Port of Lae and the Outfall System comprising the mix/de-aeration tank and associated facilities is located some 6 km to the east of the port, in close proximity to the Markham River estuary on the Huon Gulf.

Harmony and Newcrest each currently own 50% of Wafi-Golpu through the WGJV. The State of PNG retains the right to purchase, at a pro rata share of accumulated exploration expenditure, up to 30% equity interest in any mineral discovery at Wafi-Golpu, at any time before the commencement of mining. If the State of PNG chooses to take-up its full 30% interest, the interest of each of Harmony and Newcrest will become 35%.