Pumpkin Hollow Project, United States of America
The Pumpkin Hollow Project is a high grade iron-oxide copper-gold deposit located approximately eight miles south-east of the Yerington in Nevada, US.
The mine was discovered in 1960 by US steel. To date 275,000m of drilling has been completed.
Nevada Copper acquired the property in 2005. The company initiated a feasibility study in November 2010 and completed it in December 2012.
Exploration has outlined five separate deposits so far. Two, designated East and E-2, are underground. The remaining three, designated North, South and Southeast, are open pit deposits. The underground deposits are being developed first.
All state and country level permits to begin the development of underground access were granted in the first week of April 2011. The underground project has been budgeted at $250m and the open pit project at $650m.
Pumpkin Hollow copper mine development
Development of the project will be carried out in two phases. The first phase will be a 6,500tpd underground operation, which will include an advanced exploration programme and the sinking of two shafts to access the underground deposits. Production from the phase 1 is expected to commence in 2015.
The second phase will comprise of a 70,000tpd open pit mining and milling operation. Permits for the construction and operation are expected to be obtained in 2014, while production is expected to commence in 2016.
The mine is expected to produce 285 million pounds of copper, 45,000Oz of gold, and 1.1 million ounce (MOz) of silver annually for the first five years.
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The proven and probable reserves at Pumpkin Hollow Mine as of October 2010 are estimated to be 4.29 billion pounds of copper, 952,000Oz of gold, and 27.3MOz of silver.
The measured and indicated resources are estimated to be 5.9 billion pounds of copper, 1.6MOz of gold, and 42MOz of silver. Inferred resources are estimated to be 3.7 billion pounds of copper, 716,000Oz of gold, and 21.8MOz of silver.
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.
Mineralisation at the Pumpking Hollow mine
Mineralisation occurs as manto-like ore structures within skarn-banded hornfels hosted mainly in the middle-to-lower sections of the Gardnerville formation and within the marble and skarn formation at the upper section of the Mason Valley formation. It is also found within the intrusive endoskan-metamorphosed granitoid.
Copper mineralisation is widely distributed and controlled by fractures, with high-grade copper found as fracture fillings in skarn breccias. Copper skarn mineralisation occurs along the contact of a large granodiorite sill containing endoskarn within the Mason Valley Limestone.
Marble in the underlying calcic endoskarn is replaced by fine grain magnetite mineralisation that continues to a depth of hundreds of feet. Throughout the magnetite, sulphides are disseminated. Concentrated sulphides are hosted within zones of strata-bound skarn-breccia at the endoskarn-marble contact and at the replacement front between magnetite and marble.
The entire system is overprinted by regional late stage talc and abundant chlorite-calcite-pyrite veining. Strong calcic alteration of the main stage granodiorite is widespread. Secondary albite and potassium feldspar occurs along with the same skarn assemblage found in the sedimentary host rocks.
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.
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 power line from the NV Energy grid.
In March 2013, Nevada Copper secured $200m senior secured loan facility from MF Investment Holding along with a copper concentrate off-take agreement.
A $24m equipment finance arrangement was also made with Caterpillar Financial Services Corporation.
Contractors involved with the Pumpkin Hollow mine development
The contract for the project's preconstruction works was awarded to Merit Consultants International in April 2011. The works will involve preparations for shaft sinking and headframe construction.