Process Of Gold Mining And Gold Mining Production In Cortez Mine Nevada

The Cortez gold mine is located 100 kilometers southwest of Elko, Nevada in Lander County. The Cortez Pipeline property is 11 kilometers northwest and the Cortez Pediment property (which includes the Cortez Hills deposit) is four kilometers southeast of the original Cortez milling complex. The Pipeline and South Pipeline deposits are mined by conventional open-pit methods. The Cortez property covers approximately 2,800 square kilometers on one of the world’s most highly prospective mineral trends.

Process of gold mining in Cortez  Nevada United States of America

Conventional open-pit mining methods are used for the Pipeline and South Pipeline deposits, scheduled in nine stages. From 2001 to 2005, production averaged 70Mt/y. Mining is carried out with electric shovels, a hydraulic shovel and haul trucks. A fleet of miscellaneous equipment includes rotary/hammer blasthole drills, wheel loaders, bulldozers, graders and water trucks.

A pit dewatering system including 40 wells helps to prevent water inflows, the water being transported from the pit to a series of shallow infiltration ponds for recycling.
The original Cortez concentrator was placed on care-and-maintenance in late 1999, following the change from milling ore to heap-leaching ore from the Pipeline pit. Consisting of crushing, dry grinding, circulating fluid bed roasting, wet grinding and carbon-in-leach gold recovery facilities, it may be re-opened to treat suitable ore towards the end of the mine’s life.

The Pipeline concentrator has a throughput of 8,650t/d, having been designed to handle various types of oxide ore from the Pipeline and South Pipeline orebodies. Its flowsheet consists of primary crushing, autogenous/ball mill (AG) grinding, carbon-in-leach and carbon-in-column gold recovery systems, together with carbon stripping, reactivation and gold refining facilities. Low-grade, run-of-mine oxide ore is heap-leached, with gold-bearing carbon from this section being returned to the main concentrator for gold recovery.

Run-of-mine oxide ore is crushed and stockpiled before grinding in an autogenous mill and a ball mill. Discharge from the AG mill is screened, with screen oversize being conveyed to a cone crusher and recycled to the AG mill. Screen undersize and ball mill discharge are sized in hydrocyclones, the overflow being thickened to provide feed for the carbon-in-column (CIC) and carbon-in-leach (CIL) circuits.

The CIL circuit consists of eight CIL tanks, 16 screens and eight carbon-forwarding pumps. Retention time at the 9300t/d throughput rate is 44 hours, increasing to 54 hours when milling South Pipeline ore at 7500t/d. The CIC circuit consists of six carbon columns with a retention time of 18 minutes. After stripping the carbon using a pressurised Zadra process, the gold is recovered by electrowinning on to stainless steel wool cathodes. The filter cake is dried, melted in an induction furnace and poured into dorĂ© bars assaying approximately 90–94% gold and 3–6% silver for shipping to commercial refineries.

Gold mining production process Cortez  Nevada United States of America

The mine produced 902,000 ounces of gold in 2014 at all-in sustaining costs of $706 per ounce1. In 2015, production is expected to be 825,000-900,000 ounces at all-in sustaining costs of $760-$835 per ounce.

Proven and probable mineral reserves as at December 31, 2014, were 9.85 million ounces of gold.

Production began at Cortez in 1969 with the Pipeline deposits, where mining is now centred, being discovered subsequently. "Proven and probable reserves in January 2005 totalled 234Mt grading 1.4g/t gold, equivalent to 7.8Moz of gold at 74% recovery."

The Pipeline deposit is situated along the Cortez/Battle Mountain trend in the north-central Nevada basin-and-range province. Submicroscopic gold particles are evenly distributed throughout carbonate host rocks. The two principal lithological units are a sheared and altered thinly-bedded calcareous siltstone and quaternary alluvium varying from chert, argillite, siltstone, limestone and quartzite to fine sands and silts.

Proven and probable reserves in January 2005 totalled 234Mt grading 1.4g/t gold, equivalent to 7.8Moz of gold at 74% recovery. In September 2005, the joint venture approved the development of the nearby Cortez Hills deposit, discovered in 2003, where proven and probable reserves of 64.7Mt at a grade of 1.8g/t gold contain a further 5.5Moz.

A prefeasibility study for underground mining at Cortez below currently permitted levels will be completed in late 2015. Mineralization in this zone is primarily oxide and higher grade compared to the current underground mine, which is sulfide in nature. The limits of the Lower Zone have not yet been defined, and drilling has indicated the potential for new targets at depth. The exploration drift has been extended to the south, enabling additional step-out drilling, which is anticipated to begin in June. Drill results to date include 36.6 meters at 31.5 grams per tonne and 27.4 meters at 20.9 grams per tonne, both oxide in nature, which compare favorably with the average grade of 13.8 grams per tonne in refractory ore above the 3,800 foot level.