Vince, here's a description of Newmont's ore processing facility in Nevada-interesting.
Processing Facilities
Oxide ore is amenable to gold extraction through the use of size-reduction processes, such as crushing and grinding, and the dissolution of the gold in such ore using conventional cyanidation treatment techniques. Refractory ore at Carlin contains minerals which require pre-treatment, such as roasting, to optimize recovery of gold from high grade refractory ore using conventional cyanidation processes. Approximately 73% of NGC's proven and probable gold
reserves on the Carlin Trend are refractory and the balance are oxide.
NGC currently has three operating oxide mills on the Carlin Trend (Mill No. 4, Mill No. 5 and Mill No. 3). Mill No. 3 is currently being operated on a batch basis, having operated for four months in 1996 and being scheduled to operate for two months in 1997.
Processing at NGC's oxide leaching operations includes crushing ore at two plants and leaching ore at four heap leach facilities using cyanidation for gold recovery.
In the fall of 1994, NGC completed construction of a refractory ore treatment plant, or roaster, known as Mill No. 6, to treat high-grade refractory ores that contain either sulfides or active carbon. Partial operation was achieved in October 1994, but because of a mechanical problem and a fire in a component of the Mill, final start-up was delayed until the end of December 1994. Ore processed through the plant yielded approximately 354,400 ounces of gold in 1995 and approximately 540,000 ounces of gold in 1996. This plant is
expected to account for approximately 40% of NGC's Carlin gold production in 1997. To finance the facility, the plant was sold to a third party and leased back to NGC in September 1994 pursuant to a 21-year lease. For a discussion of the financing of the refractory ore treatment plant, see page 50.
In 1996, operation of NGC's large-scale bioleach demonstration facility for processing low-grade refractory ores at Gold Quarry resulted in the production of approximately 28,000 ounces of gold at a processing cost of $207 per ounce. This demonstration facility will operate through 1997 to pretreat a third batch of ore using NGC's patented bacterial oxidization process. After bio-oxidation,
these ores will be leached with either cyanide or ammonium thiosulfate.
Additionally, NGC is using a direct ammonium thiosulfate treatment without bio-oxidation on some ore types.
A feasibility study completed in 1996 has resulted in a plan to commence construction on an 8 million ton per year commercial refractory bioleach facility near the Gold Quarry open-pit mine. Following receipt of environmental permits which are expected in the fourth quarter of 1997, the leaching process will commence in 1998 with full production anticipated in 1999. The facility is
expected to process in excess of 100 million tons of low-grade refractory ore from the Gold Quarry deposit and to produce approximately 3 million ounces of gold over the 13 year project life. |
