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, which is due for completion by the third quarter of 2011.
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 will be 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.
Development of the project will be carried out over three phases. The first phase, which will commence by the last quarter of 2011, will include an advanced exploration programme and the sinking of two shafts to access the underground deposits.
The construction of a mill and mine production to support an 8,000t / day operation will begin in the second phase, which is scheduled to start by late 2013.
In the third phase, the permitting process will begin for a 60,000t / day open pit mine operation, and construction of a second mill.
The combined measured and indicated resources at the mine, estimated at a cut-off grade of 0.3% copper, amount to 3.5 billion tons grading at 0.71% copper. Inferred resources at the same cut-off grade have been estimated at 2.2 billion tons grading at 0.52% copper.
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 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.
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.