"Heap Leaching Gold Recovery at Yangu Mine in Yuanshan, Nevada"

Overview of Tobacco Valley Gold Mine Operations

Tobacco Valley, situated near the Round Mountain gold mine in Nevada, approximately 96 kilometers north of Tonopah, has been a notable site for gold production since its establishment. The mining infrastructure, which required an investment of 18 million dollars, was completed and commenced operations in 1977. In its initial year, the facility produced 1.152 tons of gold, and by 1979, production was projected to increase to 1.71 tons of gold and 0.98 tons of silver, supported by a workforce of 140 employees.

Ore Reserves and Composition

The mine boasts an ore reserve of 12 million tons, with a gold cut-off grade set at 0.68 grams per ton. The ore is rich in precious metals, averaging 1.93 grams of gold and 2.18 grams of silver per ton. Utilizing cyanide heap leaching techniques, the operation achieves a gold recovery rate of 86%, making it an efficient method for extracting valuable minerals.

Mining and Processing Techniques

The mining method employed is open-pit mining, where ore is initially crushed to a size of 178 millimeters using a primary cone crusher. The crushed material is then transported via a belt conveyor to a secondary crusher, further reducing the size to -50 millimeters. A pair of short-head crushers then refine the ore to -9.5 millimeters, preparing it for heap leaching.

The heap leaching facility is designed as a rectangular area measuring 640 meters in length and 86 meters in width. The base of the heap leaching site consists of a 178-millimeter thick cushion, topped with a 50-millimeter water-resistant layer made from rubber sheets and asphalt. The transportation road, constructed from crushed ore, is elevated 660 millimeters above the asphalt surface. The leaching area is divided into five distinct fields, each sloped to facilitate the collection of leachate into a designated pool. Each field can accommodate approximately 45,000 tons of ore, with four fields dedicated to leaching and one for washing and loading.

Leaching Process

The leaching solution contains 0.045% sodium cyanide and 0.04% calcium oxide. It is distributed to each leaching pile through a network of four plastic pipes connected to a main supply line. Each pipe features a Baghdad swinging ejector every 12 meters, ensuring even distribution of the leachate. Each leaching pile is equipped with approximately 84 nozzles, allowing for a liquid flow rate of 2.7 to 3.4 milliliters per square meter per second, covering an area of 116 square meters, with a total hourly spray volume of around 1500 liters. The leaching process spans a duration of 27 days, during which daily samples of the leachate are taken. If the gold leaching rate falls below a predetermined threshold, the leachate is halted and the piles are washed with water for two days.

Waste Management

The waste rock generated during the leaching process is transported to a designated site using two ore loaders and five 45-ton trucks. Given the proximity of the waste rock site to the leaching area, transportation is efficient, typically taking around 28 hours. To protect the asphalt surface of the leaching site, a layer of waste rock, 200-250 millimeters thick, is placed at the base of the heap. To monitor potential contamination, a deep well is drilled in the lower section of the leaching field for periodic testing of the leachate.

Recovery of Precious Metals

The gold-laden leachate is pumped to a dedicated adsorption-desorption-activation facility via a turbo pump. Here, the solution passes through a series of five activated carbon adsorption tanks at a flow rate of 6056 liters per minute, yielding approximately 7.775 kilograms of gold per ton of processed ore. The process involves the reverse operation of leachate and carbon particles, with one ton of gold-loaded carbon being removed from the first tank daily and replaced by fresh carbon in the fifth tank. The depleted leachate is treated with sodium cyanide and lime before being recycled back into the leaching process.

The gold-rich carbon undergoes elution in a desorption tank at a temperature of 88 degrees Celsius using hot sodium hydroxide and sodium cyanide. The desorbed carbon is then sent back for recycling in the irotech kiln. The final product, a gold and silver-rich eluate, is collected in three electrolytic cells, where gold is recovered at the steel wool cathode.

Conclusion

The Tobacco Valley gold mine exemplifies a well-structured operation that effectively combines modern mining techniques with efficient waste management and recovery processes. With its significant ore reserves and advanced processing methods, the mine continues to play a crucial role in the region's gold production landscape.