The Pumpkin Hollow Project is a high-grade iron-oxide copper-gold deposit located approximately eight miles south-east of Yerington, Nevada, US.
The mine was discovered by US steel in 1960 and 275,000m of drilling has so far been completed.
Nevada Copper acquired the property in 2005 and the company filed a technical report in January 2019.
Exploration has outlined five separate deposits so far. Two high-grade deposits, designated East and E-2, are underground, while the remaining three, North, South and South-East are open-pit deposits.
All state and country level permits to begin the development of underground access were granted in April 2011. The mine started underground production in December 2019 and has a mine life of 13.5 years.
The underground project has been budgeted at $250m and the open-pit project at $650m.
Pumpkin Hollow copper mine development
Development of the project is being carried out in two phases. The first phase was a 6,500tpd underground operation, which included an advanced exploration programme and the sinking of two shafts to access the underground deposits.
The second stage will involve a 70,000tpd open-pit mining and milling operation by including a high-grade supplemental mill feed from the East and E2 underground deposits.
The mine is expected to annually produce 285 million pounds (Mlb) of copper, 45,000oz of gold and 1.1 million ounces (Moz) of silver for the first five years.
Reserves at Pumpkin Hollow
The proven and probable reserves at Pumpkin Hollow Mine as of January 2019 were estimated to be 3,590Mlb of copper, 21,266koz of gold and 617oz of silver.
The measured and indicated resources were estimated to be 5.9 billion pounds of copper, 1.6Moz of gold, and 42Moz of silver. Inferred resources were estimated to be 3.7 billion pounds of copper, 716,000oz of gold, and 21.8Moz of silver.
Geology at Pumpkin Hollow mine
The deposit lies within the Walker Lane mineralised belt, along the flanks of the Jurassic-aged Yerington batholith.
Granodiorite and diorite rocks from the batholith cut the limestone belonging to the Triassic Mason Valley Formation and the calcareous argillites, siliceous shales, siltstones and limestone of the Gardnerville Formation. The intrusion is accompanied by the development of large zones of skarn and related copper and magnetite mineralisation.
A hornfels halo and un-mineralised skarn represent the only near-surface expression at the deposit. Local folding, Cretaceous plutonism and the concentration of a thick complex of Oligocene-aged ignimbrites are among the geologic events that have occurred post mineralisation.
Exploration at the property began in the 1960s. US Steel carried out 180,000m of drilling between 1960 and 2001. Up to 2010, 211 holes extending 275,000m and more than 65,000 assays had been completed.
Further exploration of new Tedeboy targets and possible near-mine expansion to the underground mine is planned under the 2020 drilling programme.
Construction and infrastructure
Construction of shaft and hoist, and pre-collaring of underground shaft in the East deposit area began in February 2012. The hoist and head frame construction was completed in May 2013.
Power supply to the mine is provided from the newly upgraded 25kV line from the NV Energy grid.
The company completed the pre-works phase and moved onto the construction works by 2018. The development works primarily included the underground mine and the processing facility.
The underground mine development works included the sinking of the east/south main shaft to 2,770ft and then to 2,850ft. Fully mechanised mining was achieved on the 2,850 level which is about to reach the bottom of EN vent shaft.
The processing facility development works comprise construction of ore and waste stacking conveyance system and installation of electrical, instrumentation and communications equipment. Construction of administrative buildings and maintenance facilities was also undertaken.
The feasibility study for the open-pit project is planned to be completed in 2020.