Pumpkin Hollow copper project is a high-grade iron oxide copper gold (IOCG) deposit located in Nevada, US.
Nevada Copper owns and will operate the $1.67bn Pumpkin Hollow project, which involves the development of an underground mine and an open-pit mine.
The integrated feasibility study of the underground and open-pit mining project, which is expected to have a life of 23 years, was completed in April 2015.
The pre-feasibility study (PFS) for the stand-alone underground mine was completed in November 2017 and was further updated in January 2018. The PFS of the open-pit mine was completed in February 2019.
Construction of the underground project began in 2018 and first production is expected to be made at the end of 2019. Construction on the open-pit project is expected to be started in 2021, with ramp up to production expected in 2023.
Pumpkin Hollow project location, geology, and mineralization
The Pumpkin Hollow copper project is spread over 17,500 acres of contiguous mineral rights near Yerington, Nevada, 12.8km south-east from Yerington in Lyon County.
The project falls within the Yerington copper porphyry district in the Walker Lane mineral belt, Nevada.
The mining area comprises two adjacent distinguished mineral deposits namely the Eastern Area Deposits and the Western Area Deposits, at a distance of approximately 3.2km.
The main focus of the underground mine is on the development of the Eastern Area deposits, while the open-pit mine is focused on the Western Area Deposits.
The iron oxide-copper-gold (IOCG) mineralization at Pumpkin Hollow is made up of high-grade skarn, which is a lime-bearing siliceous rock. The skarn is associated with copper and magnetite mineralization along with silver and gold.
As of April 2019, the Pumpkin Hollow open-pit mine was expected to contain proven and probable reserves of 386Mt of ore grading 0.47% Cu, 0.002oz/t Au, and 0.055oz/t Ag. It is estimated to contain 3.6 billion pounds of copper, 617,000 ounces (oz) of gold, and 21.3 million ounces (Moz) of silver.
The underground project is expected to contain reserves of 23.9Mt, grading 1.59% of copper, 0.006oz/t of gold, and 0.139oz/t of silver.
Mining and ore processing at Pumpkin Hollow copper project
The Pumpkin Hollow underground mine is located on the Eastern Area of Pumpkin Hollow property and is expected to produce 5,000 short tons a day (stpd).
Mechanized transverse long-hole mining method will be applied at the underground mine. All primary and some secondary stopes will be backfilled using cemented paste fill (CPF), while the remaining secondary stopes will be back-filled using un-cemented paste fill (UPF).
The project will feature a single production/service shaft supported by three ventilation/emergency egress shafts.
The open-pit mine will be developed in two phases, with the first phase having a production capacity of 37,000stpd and the second phase 70,000stpd.
The first phase will include a throughput concentrator to produce a filtered concentrate from the run-of-mine (ROM) ore. The second phase is expected to include a process circuit for milling and flotation to produce unfiltered concentrate and filtered tailings.
The open-pit mine is further divided into two mining areas namely the North Pit and the South Pit. Initial mining will be commenced at the high-grade North Pit, followed by the lower grade South Pit.
Ore processing at Pumpkin Hollow
The underground processing plant will have a capacity to process 5,000stpd of copper ore. The estimated recovery rates are expected to be 92% Cu, 78% gold, and 70% silver.
The plant will feature a coarse ore storage facility, a semi-autogenous grinding (SAG) mill, a SAG ball mill crusher (SABC) comminution circuit, a regrind circuit, rougher flotation and cleaner flotation units.
The produced flotation concentrate will be thickened, filtered, and forwarded to the concentrate load-out facility for further transport/shipping.
Open-pit ore will be processed at a single processing facility consisting of a crushing station and overland conveyor, a comminution circuit, and a flotation circuit.
The resultant flotation concentrate will be thickened, filtered, and stored in concentrate containers for subsequent transport/shipping.
The Pumpkin Hollow copper-gold -silver project is accessible via sealed public roads.
Water supply for the project will be made by the on-site water wells or through a 10km-long pipeline connected to the water supply system of the City of Yerington.
For the power supply, a new 120kV transmission line will be constructed from an existing service point operated by Nevada Energy Systems. The project will also feature a new 120kV switchyard, while the substation will feature a 30MVA electrical transformer.
Financing for Pumpkin Hollow copper project
Nevada Copper secured $115m credit facility from KfW IPEX Bank for the development of the Pumpkin Hollow Underground project, in May 2019.
Nevada Copper and Triple Flag Mining Finance Bermuda signed a metals sales and purchase agreement in December 2017, under which the latter agreed to provide $70m financing for the project. Triple Flag will receive gold and silver produced during the life of the underground project.
Further, in December 2017, Nevada Copper secured a $378m construction financing and recapitalization package from a group of financers including Triple Flag, Pala Investments, Red Kite Mine Finance, and Concord Resources.
Nevada Copper also secured a $35m working capital facility from Concord Resources in May 2019, with regard to the underground project.
MF Investment, an affiliate of Orion Resource Partners and RK Mine Finance entered an off-take agreement with Nevada Copper, in March 2013.
Nevada Copper also entered off-take agreements with Concord, Aurubis, and Aurubis Bulgaria.
Contractors involved in the Pumpkin Hollow project
Sedgman Canada, a part of CIMIC, was awarded the engineering, procurement, and construction contract, worth $118m, for the construction of Pumpkin Hollow surface plant and a copper concentrator plant, in August 2018.
Cementation USA is responsible for the construction of the shaft sinking and underground mine at Pumpkin Hollow.
Merit Consultants prepared the pre-construction reviews and project scheduling activities, between 2011 and 2012.
Sedgman Canada and Mining Plus Canada Consulting were selected for the pre-feasibility study of the underground mining project in 2017, while Golder Associates and Sedgman prepared the pre-feasibility study of open-pit mining project.
Tetra Tech conducted the PEA metallurgical test work for the project, while Caterpillar and Epiroc provided underground mining equipment.