Hidden Valley open pit gold-silver mine is located in Morobe Province of Papua New Guinea. Image courtesy of Slawojar.
The gold-silver mine started commercial production in September 2010. Image courtesy of Alchemist-hp.
Komatsu fleet at the Hidden Valley mine. Image courtesy of Btr.

Hidden Valley

Hidden Valley is an open pit gold-silver mine located in Morobe Province of Papua New Guinea. Newcrest and Harmony Gold Mining of South Africa own the mine through a 50/50 joint-venture (JV) called Hidden Valley JV (HVJV), which is one of three JVs between Newcrest Mining and Harmony Gold, collectively known as the Morobe Mining JVs (MMJV).

Construction of the mine started in 2007 and commercial production began in September 2010. The mine has an initial life estimate of 14 years and currently has approximately 2,000 employees.

Mine location, geology and reserves

Hidden Valley mine lies approximately 300km north-west of Port Moresby. The mine is located at an altitude of approximately 2,100m-2,800m above sea level.

The Simberi gold mine is located on the Simberi Island in the Tabar Islands Group, New Ireland Province of Papua New Guinea.

The deposit is made up of two structural zones, Hidden Valley Zone (HVZ) and the Kaveroi Creek Zone (KCZ). Both zones are classified as a low-sulphidation epithermal gold-silver system. The mine is bounded and structurally controlled by a series of north-west to north-north-west striking faults in Morobe Granodiorite and the basal contact of Kaindi Metamorphics.

Mineralisation is associated with coarse-grained pyrite-hematite-magnetite-quartz fracture fill veins with sericite alteration.

Hidden Valley mine comprises two main pits, located approximately 5km apart, exploiting three main ore bodies named Hamata, Hidden Valley and Kaveroi. The smaller pit exploits the Hamata ore body, whereas the larger pit exploits Hidden Valley and Kaveroi gold and silver ore bodies.

The mine is estimated to contain proven and probable reserves of 29.5Mt at a grade of 1.7g/t Au, containing 50,000kg of gold. The mine is also estimated to contain 29.5Mt of gold equivalent silver ore containing 15,000kg of silver.

Mining and processing of ore

Conventional drill and blast method of mining followed by load and haul is applied at the mine. Ore from the mine is processed at the Hamata and Hidden Valley crusher stations. The crushed ore is delivered to the primary stockpile via a 4.5km overland conveyor with a capacity of more than 5Mtpa.

The overland conveyor stretches and winds from the Hidden Valley Kaveroi pit down to the processing plant adjacent to the Hamata pit.

“Construction of the mine started in 2007 and commercial production began in September 2010.”

The mining fleet comprises PC2000 and PC1250 Komatsu excavators, HD785 Komatsu trucks, ECM 720 Production drills, WA900 Komatsu front end loaders and Komatsu dozers and graders.

With a processing capacity of 4.6Mtpa, the processing plant is estimated to produce 250,000oz of gold and four million ounces of silver. The plant includes conventional gravity and carbon-in-leach circuits for gold, and a Merill Crowe circuit for silver. The plant uses two jaw crushers to prepare the ore for transportation and feeding to the semi-autogenous grinding (SAG) mill, which has a nominal processing capacity of 4.2Mtpa of ore.

During 2013, the mine milled 1.84Mt of ore and produced 2,644kg of gold with a grade of 1.43g/t Au. Gold and silver doré produced at the mine are transported to the Western Australia Mint in Perth (the Perth Mint) to be refined.

Construction works and infrastructure facilities

Major construction works involved the mine infrastructure and a 4.5km overhead conveyor. The mine is accessible by road from the city of Lae. Workers are accommodated at the on-site camp and in the city of Lae.

Power supplied to the mine is provided by the Yonki power station under the Yonki Hydro scheme. Tailings from the processing plant are treated and permanently stored in the engineered tailings storage facility, the only one of its kind in Papua New Guinea.

The mine uses recycled treated surface water from the tailings storage facility for its operations.

Contractors involved with Hidden Valley

UMW was awarded the fleet maintenance contract from the beginning of mining operations to June 2012. The fleet is currently maintained in-house.

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