IM-Mining - Spotlight Feature Article |

Newmont’s Nevada

Loading ore at Twin Creeks

Newmont has been pouring gold in Nevada for nearly 50 years along a 161 km section of highway in the northern part of the state. The company owns or controls some 1.8 million acres, but mining/processing only occurs on about 53,000 acres of this total.

Overall, in 2010 Newmont’s Nevada operations produced 1.735 Moz of attributable gold for the company, and at La Herradura in Mexico, the figure was 174,000 oz. Of the company total in 2010, including all the other global assets, Nevada’s 1.735 Moz accounted for about 32% of 5.391 Moz. These summary results had only just been released at the time of press.

Newmont’s third quarter 2010 production results (the last to have been fully released), show that Nevada produced 453,000 oz of gold at costs applicable to sales of US$575 /oz. Gold production decreased 7% from the 2009 quarter due to lower leach tonnes placed at Twin Creeks and Carlin, lower levels of Gold Quarry ore feed to Mill 5 due to a late 2009 slope failure and the completion of underground mining at Deep Post in 2009.

The gold that is mined at Newmont’s Nevada operations, aside with some high grade underground exceptions, tends to be sub-microscopic in particle dimensions, and has been described as comparable to smoke particles. The bulk of final production is in the form of gold dore bars that are poured by Newmont itself and contain approximately 90% gold, 8% silver and 2% trace material. These are shipped for further refinement.

Rather than operating as standalone mines, the Nevada properties – which include both surface and underground assets – operate as an integrated unit, and together, they boast the widest variety of processing methods of any gold mining complex in the world – from flotation to roasting and pressure oxidation to heap leaching.

In general, the oxide ore is processed by Carlin Mill 5, the Midas mill and the Twin Creeks mill.  Refractory ore passes through the Carlin Mill 6 roasting circuit and the Twin Creeks autoclave, as well as the Carlin bio-leaching operation. Then there are further separate heap leaching operations.

Mining started with open pit operations only in 1965, some of which have been extended underground since the early 1990s.  Operations now include 14 open pits, four underground mines and 14 processing facilities in all.

The main underground operations are Leeville and Chukar at Carlin, with Deep Post recently closing. Most, including Leeville and the Carlin open pit complex, are on the socalled Carlin Trend west of Elko, however, the Twin Creeks and the now winding down Lone Tree operations are in the Winnemucca area further west, while the Phoenix gold/copper mine is near Battle Mountain. The Midas underground mine is east of Twin Peaks and northwest of Carlin.

In addition to these operations is the Turquoise Ridge underground mine, which is 70 km northeast of Winnemuccaa and is a joint venture with Barrick, with Barrick as majority owner (75 %) and operator. It uses the processing plant at Twin Creeks.

Newmont also has the 100 5-owned Hope Bay project in the Canadian Arctic.  Development there on the Doris North underground mine is underway and will be the subject of a future article. Like Turquoise Ridge, Herradura in Mexico is also a joint venture, majority owned and operated by Fresnillo (56 %).

Production highlights for Newmont in Nevada over the years include the commencement of production at the Carlin Gold Quarry in 1985: the peaking of annual production at 3 Moz in 2000, and in 2008, when the combined Nevada operations (which include the former Santa Fe Pacific Gold, Normandy, Franco-Nevada and Battle Mountain Gold properties), had produced more than 50 Moz since start-up of the first Carlin Trend operation. Last year, 2010, was the company’s 45th year of producing gold in the region. It is also worth pointing out that considerable volumes of copper and silver are produced by Newmont’s mines, particularly at Phoenix.Water sampling at James Creek north of Carlin, Nevada

At end-2009, Newmont’s total Nevada proven and probable gold reserves were calculated to be 30.29 Moz. Of this figure, the Carlin open pits account for 11.4 Moz, and the Carlin underground mines 2.99 Moz. The Phoenix mine accounts for 5.67 Moz and Twin Creeks 3.85 Moz. Midas made up 300,000 oz of the total, with stockpiles accounting for another 2.21 Moz.

The combined power requirements of Newmont’s Nevada operations led to the development of the TS Power Plant, which was commissioned in 2008. This is a 242 MW coal fired plant with a 385 ft stack that serves a number of the Newmont properties. Newmont contracted with Fluor for engineering, procurement, construction and commissioning of the plant, which is supplied with coal from Wyoming via a 130-car train. In addition to the plant itself, Fluor worked on the delivery of a 100 acre evaporation pond; a five mile railway spur; a five mile electricity transmission line to connect to the grid; a three mile raw water pipeline and a railway switchyard. The completed plant has reduced Newmont’s annual electrical power costs by approximately US$70 million.

Blending and integration in Nevada

Blending of material ahead of processing is not a new concept. For Newmont, the segregation of ore by grade range (high, medium, low) has been a common practice aimed at maintaining reasonably constant head grade to the mill. However, with the introduction of the refractory ore treatment plant (the roaster) on the Carlin Trend in the mid 1990s, additional segregation and blending requirements were imposed to maintain sulphur and carbon levels within tight tolerances. Similarly, the autoclaves at the Twin Creeks and Lone Tree mines required consistencies and limits on the chemical properties of feed material. Today, blending gets even more attention as mill throughput is increasingly modelled as a function of hardness and grindability. The key objective in these cases is to identify the optimal material blends that maximise the value over time from the mill.

For example, the Sage autoclave at the Twin Creeks mine competes with the roaster in Carlin for concentrates from the Carlin flotation plant. The flotation tailings from the plant are treated through the CIL circuit and then discharged to the tailings impoundment. Satisfying these conditions demands more sophisticated modelling with the ability to split process stream tonnages as they propagate through a circuit.

A major reason for the integrated approach is that Newmont built up its Nevada operations through a combination of greenfield development and the mentioned acquisitions. Each processing facility, when constructed, was designed to address the needs of its host deposit but once these mines were connected through common ownership, Newmont’s technical staff identified value in the cross-shipment of ores between sites. This value is derived from the consideration of the combined set of ore types and available processes across this ‘theatre’ of operations and the application of methods to determine the optimal sequencing and material routings.

Mining overview – surface

Open pit mining still accounts for the bulk of production, and is dominated by fleets of Caterpillar 793 trucks, with loading conducted by Hitachi EX5500/EX3600/EX5500 hydraulic excavators and large Caterpillar wheel loaders, though Twin Creeks also has a P&H 2800 rope shovel. Drilling mainly uses Atlas Copco and former Ingersoll Rand models.

Mining rates for the Carlin surface operations are approximately 250,000 t/d, with the largest pit, Gold Quarry in the south Carlin area, having mined 23.5 Moz, with an estimated 7.7 Moz remaining. The Carlin total surface operations’ proven and probable reserves of 11.4 Moz point to a current mine life to 2028 and mill life to 2030. The northern area pits include North Lantern, Pete and Carlin. In addition, there are four other pits in the northern area that are scheduled for future mining.

Carlin also has a bio-leaching pad, which from the ground up consists of compacted clay, 80 mm synthetic liner, a natural cushion to protect the liner from damage, and a drainage layer that allows the pregnant solution to flow down into the ponds. The overall leaching system at Carlin is a 12,700 gal/min circuit, pumping 18.28 Mgal/d. There are three 1,250 hp barren pumps and eight pregnant solution pumps at various ponds ranging in size from 200 hp up to 900 hp. There are also 18 carbon columns with 7,000 lbs of carbon in each. The Carlin south area alone has approximately 25 Mft2 of leach pads. It currently has over 244 Mt of ore under leach pads and has produced over 3.395 Moz to date at a current rate of 485 oz/d.

Newmont has also recently upgraded to microwave radio systems at the Carlin surface operations to increase bandwidth while maintaining round-the-clock uptime on its wireless network. For many of its operations around the world, including Carlin, Newmont uses Caterpillar’s Minestar for fleet management/dispatch.  Each of the approximately 150 pieces of equipment at the mine has a radio on board. These radios connect to a network backbone that carries information between the equipment and the mine’s operations centre. When traffic began to bog down on the existing network, Newmont upgraded to Exalt microwave backhaul systems to carry dispatch, inventory and control information throughout its operation.

The Minestar system was initially deployed at the mine in 2004 using 900 MHz radios on the equipment with a 5.8 GHz network backbone to support them.  Over time, however, the network’s performance had begun to degrade.  Working with KNS Communications, Newmont selected Exalt microwave radio systems for a network backbone upgrade.  Exalt had previously been deployed at its operations in Australia, Indonesia and Ghana.

Exalt EX-11s radios using the licensed 11 GHz frequency band were used to avoid interference with an adjacent mine’s radio systems at the far end of the operation. These systems use split-mount configurations so that the radio system electronics can be located inside weather-proof enclosures.

All of the new microwave radio systems are configured for 200 Mbps of aggregate Ethernet data throughput, which is more than enough to support the Minestar system. Since the upgraded microwave systems were deployed in early 2009, they have provided a much faster and more reliable communications link between the mine’s managers and the mining equipment.

The current Twin Creeks mine began as two separate mines operated between 1984 and 1987 – Rabbit Creek and Chimney Creek. The two pits were merged in 1993 to form the socalled Mega Pit, which is 3 miles long, 1 mile wide and over 1,000 ft deep. The entire US$270 million Phoenix operation was commissioned in 2006 following Newmont’s merger with Battle Mountain Gold in 2001.  It currently employs 475 people between the mine and mill, primarily from Battle Mountain and Winnemucca. Phoenix has a remaining mine life of some 23 years.

Mining overview – underground

The Midas operations consist of a highly mechanised narrow vein underground mine near the town of Midas, where gold veins were first discovered over 100 years ago.  Unlike the disseminated mineralisation at other Newmont sites, Midas is a high grade operation, and 10 oz of silver are produced for every gold ounce produced. The mine has a portal and decline, is some 1,300 ft deep with a strike length of over 6,000 ft. Its fleet (the underground fleet listed in detail in the attached tables) includes 18 LHDs, five underground trucks and five jumbos.Drilling blast holes at Newmont’s Leeville underground mine

Leeville was Newmont’s first underground mine in Nevada to be accessed via a shaft. The mine plan saw ramps and drifts developed to mine three distinct deposits – West Leeville, Four Corners and Turf, all located approximately 1,400 to 2,100 ft below the surface. Development at Leeville commenced in 2002 with the beginning of an almost milelong drift from the Carlin underground mine, northward to the Leeville deposit. This drift serves as an exploration platform and as a secondary access route to Leeville. In early 2003, sinking of the ventilation shaft and the adjacent production shaft to an ultimate depth of 1,875 ft commenced.

The mine uses the long hole stoping and cut and fill mining methods. Cemented rock fill (CRF) is used as the backfill in the open stope.  CRF design includes the aggregate design, the ratio of cement and fly ash design, and strengths for the long-hole stope and cut-andfill. In the aggregate design, the particle size distribution is one of the most influential aggregate characteristics in determining how it will perform as a basic backfill material.  Gradation helps determine durability, porosity, cement and water requirements, strength, and shrinkage. To cut the backfill cost, fly ash usually is added into the binder to replace some of the cement. However, adding fly ash can also affect the strength of the backfill.  Based on the different mining methods, different backfills with different strengths are designed.

A systematic quality control procedure for aggregate and backfill is followed. After four years application, the CRF system in Leeville has achieved very good result according to the company.

The Chukar mine fleet is operated by local mining contractor, Small Mine Development (SMD). SMD started the portals at Newmont’s Chukar Mine in January 2002. The job was originally a three-month development with a small amount of long-hole open stoping. Nine years later, the contractor is still mining at Chukar. The mine is located under the Gold Quarry pit, and uses transverse long-hole open stoping with a lot of remote mucking. Primary stopes are filled with cemented rock fill.  Secondary or tertiary stopes may be filled with waste rock. A two-boom jumbo, a Sandvik Robolt, Sandvik and JCI 6 yd3 LHDs and a fleet of Caterpillar 30 t trucks make up the mining and development fleet. SMD also has a contract at Leeville, where its crews helped connect the Leeville shaft to Carlin East in 2005. Since that time, the company has been helping establish infrastructure, develop and mine the orebody. Daily activities can encompass any part of the mining cycle.

Newmont crews finished underground mining in Carlin East in 2007. However, through further exploration and engineering, additional ore was found. A new portion of the deposit is called Full House. SMD drove an exploration drift there in 2008.   After a successful drilling campaign, SMD is now helping to develop the Full House deposit, as well as conducting some remnant mining in the old Carlin East workings.

After a decade of mining, Deep Post, one of Newmont Nevada’s high-grade underground mines, ceased production at the end of 2009. The mine has depleted all known economic ore and Newmont’s access agreement with Barrick expired. A number of Deep Post employees transferred to the nearby Leeville and Chukar mines, but a few remained onsite to maintain the mine and oversee exploration drilling.  Contractors provide support on shorterterm projects at Newmont and other mine locations. Entry through the Deep Star mine, where a mile-long cross cut was put in place to connect it with the Deep Post mine, will remain intact and could provide for access should additional economic ore be discovered.

Initial development started at Deep Post in 1999, when the first portal was excavated in the bottom of Barrick’s Betze-Post Pit and construction of the surface facilities and infrastructure began. Since that time, nearly 3 Moz of gold were removed.

Leeville – new efficiencies and mine control

In 2009, after being in production for three years, Leeville’s cost per unit metrics were not deemed to be comparable to similar-sized mines using similar mining methods. It was determined that significant improvements in production and costs should be targeted for improvement. Project goals were defined as the reduction of waste and to improve efficiency by 10%.  A Value Steam Mapping assessment was completed on both the mine and preventative maintenance cycles to determine areas of inefficiency or Non Value Add (NVA) activities. These included in order of importance areas such as first hour losses, the bolter breaking down at the face, too long being spent waiting for the shotcreting vehicle and too long waiting for the LHD, last hour losses, full skips and others. It was determined that in the mine cycle there was 39% of NVA activities and in the preventative maintenance cycle, 44%. A special project was implemented focussing on equipment availability, which saw the mine cycle reduce NVA by 13% and preventative maintenance by 22%. The company has estimated a three year net benefit of US$25 million.

Also at Leeville, the Mine Control Project Team has just commissioned a new Mine Control System (MCS) at the mine, following four years of intensive research, assessment of current and future needs, and evaluation and selection of various hardware and software components.

Safety was the primary driver behind the effort, and the new MCS offers a new level of support in the task of tracking miners and mobile equipment, while also providing detailed, real-time production data that is vital to maintaining efficient underground operations on a daily basis. One the major challenges underground is rounding up all employees in an emergency scenario. Prior to the new MCS going live, it could take up to an hour to account for all staff during an evacuation. Now each miner’s location can be seen precisely on a monitor by a dispatch team, and be directed within minutes to the nearest refuge chambers or other evacuation points. Dispatch can then track each miner’s progress towards shelters or exits and send assistance if needed. The MCS personnel tracking component uses a network of exciters (electronic devices that trigger a wireless transmitter to send a signal) and individual Wi-Fi tags attached to cap lamps or utility belts. When a miner wearing a tag passes by an exciter at the collar (top of the shaft), they are automatically “brassed out” by the system. Other exciters distributed throughout the mine help track the miner’s position during the shift prior to their return to the surface where they once again walk past the collar exciter and are brassed back in.  While the technology will not complete replace the conventional brass board (retained in case the automated system were to malfunction), it will expedite the verification of who is actually underground. This could be helpful if a miner forgot to brass in at the end of a shift.  Additionally, a remote controlled camera allows dispatch operators to visually verify the brass status of employees.

In operational applications, the MCS has a number of other useful features. It can automatically trigger different kinds of alerts such as those related to machine health and potential person/vehicle or vehicle/vehicle traffic conflicts. It can also be used to collect measurements of diesel particulates and other environmental data, optimise grade control, and feed equipment usage hours data into Mincom Ellipse or Maptek MineSuite. Through an interface an asset management application, the system would also be able to track a miner’s qualifications for operating various pieces of equipment and could even go as far as disabling a machine should an unqualified person attempt to operate it. Using portable, tablet computers, underground operators can pull up KPIs for their area, feed pre-shift inspection information about their vehicles directly to the shop to optimise preventative maintenance and repair schedules, and receive an updated cue of assignments in advance so they will know where to go after completing each task.

Because of the MCS real time data gathering capability, reporting will be more timely and flexible, making it an especially valuable tool for senior managers who may need the latest performance info for executive meetings. They can also have secure, remote access to the MCS from off site. Ultimately, the system could be accessible to the corporate team in Denver.

Formerly there was only one dispatcher per crew. But as the dispatch room has developed into a high-tech mine control centre, additional communication and control personnel have been added. The dispatcher position is transforming into a higher profile function known as mine controller, and those in this position require underground mining as well as computing experience. Using the new MCS, the shift coordinator is able to make impromptu production decisions that deliver desired results more quickly than post-mortem meeting room discussions.

Processing

Grinding mill at Phoenix plant

Higher-grade oxide ores are processed by conventional milling and cyanide leaching at Carlin Mill 5, Twin Creeks’ Juniper mill. Lowergrade material with suitable cyanide solubility is treated on heap leach pads at Carlin and Twin Creeks. Higher-grade refractory ores are processed through either a roaster at Carlin Mill 6 or the autoclaves at Twin Creeks (Sage mill) . Lower-grade refractory ores are processed by a bio-leaching/flotation or direct flotation at Carlin Mill 5. Ore from the Midas mine is processed by conventional milling and Merrill-Crowe zinc precipitation at Midas itself.  Activated carbon from the various leaching circuits is treated to produce gold ore at Carlin and Twin Creeks. All milling at the other main processing site, Lone Tree, was completed in 2007.

Overall, Nevada operations include some 21 major ore flows. The refractory mill grades are reliant on the level and grade of tonnes produced underground, with the surface refractory ore tonnes processed dependent on how much mill capacity is not used by underground ore.

The full range of processing equipment used at the key Newmont Nevada operations is listed in the attached tables. As stated, Carlin has two main processing operations, Mill 6 and Mill 5. At Mill 6, the annual ore throughput is some 3.2 Mt/y, containing over 700,000 oz of gold with the plant achieving an 88% recovery. Following primary gyratory and secondary cone crushing, the ore is milled in a large 560 t/h ball mill before passing to a 6,500 t fine ore bin. This ore is then conveyed via air slides to each of two identical roasting circuits (North and South), where the ore is heated at 350 °F in a circulating fluid bed (CFB) preheater before being conveyed to CFB roasters for roasting at 950 °F. It then passes through calcine coolers, quench tanks, neutralisation, thickening and enters the CIL and CIC processes for cyanide leaching.

At Mill 5, 15,000 t/d are processed with the plant achieving 94% availability and 70% overall gold recovery. Some 600 t/d of concentrate is produced. Following SAG and ball milling, the ore is floated, with the concentrate thickened and dewatered using a filter press.

Twin Creeks’ processing complex consists of two mills, Sage and Juniper. The Sage mill is huge, processing 3.6 Mt/y and with 520,000 oz of gold budgeted for production in 2010. It also handles concentrates from Carlin’s Mill 5.

Following SAG and ball milling, the ore is slurried and passed to the pressure oxidation autoclaves following preheating. The autoclave oxidises the ore by chemical reaction at 440°F and 460 psi. the slurry goes through flash vessels to recover heat for slurry pre-heating. The slurry is then neutralised and then leached by CIL.

The Juniper mill processes 1 Mt/y and was projected to produce 26,000oz in 2010. Its route consists of SAG and ball milling, with the slurry processed via neutralisation and CIL. Twin Creeks also has two active and two inactive leach pads.

The Phoenix mill handles 33,600 t/d with a 92% availability. It produces 240,000 oz of gold and 22 Mlbs of copper per year as well as 900,000 oz of silver. The process includes primary and secondary crushing, SAG and ball milling, flotation and desliming, as well as the recent addition of a tank leaching circuit. The Phoenix process team came up with an innovative way to improve gold recovery by 28%. The team circulated a rough copper and gold concentrate, which was re-floated twice to produce a clean concentrate. They then recombined and processed the tails from each flotation circuit through a leach circuit, resulting in improved gold recovery. However, subsequent assays showed that tails from the cleaner flotation circuit contained approximately 30 times more gold than originally found in the rougher tails. As a result, more concentrated leaching of the cleaner tails (in a separate tank with longer retention time) increased the recovery from 28% to as much as 99 %, improving the overall recovery by 5 %. This higher recovery has generated about US$10 million in additional annual revenue for Phoenix within the first year that the new process was implemented.

Roasting and flotation plant efficiencies

The Newmont roasting plant at Mill 5 in Carlin commenced operating in December 1994.  Over the years, refractory ores and pyrite concentrates from different gold deposits constituted the feed to the facilities. Historical plant performance indicated that the roasting temperature was the main variable that affected the structural characteristics of the calcine which, in turn, affected the recovery of gold by cyanidation.

Gold recovery as a function of roaster temperature was then closely monitored since October 2000. The original design temperature was 550 oC but it was noted that lower roaster temperatures of around 500 oC resulted in a gold recovery increase by more than 6 %. This increase was directly related to an increase of the surface area of the calcine.  The implementation of an “intelligent” process control system helped significantly in achieving steady low roasting temperatures thus achieving high gold recoveries between 92 and 93%.

But high gold recoveries can be achieved at the lower roasting temperatures providing that the arsenic content of the roaster feed is low.  Plant data demonstrated that the specific surface area of the calcine product from the oxidising roasting of refractory gold ores containing arsenopyrite is strongly dependent upon the arsenic content. Results indicated a marked decrease of the surface area as arsenic content increased. The calcine with the lowest surface area corresponded to the highest arsenic content, which also corresponded to the lowest gold recovery.

Newmont uses a Scanning Electron Microscope (SEM) with a JKTech Mineral Liberation Analyzer (MLA). With the MLA software package, raw particle image and Xray data can be converted into particle mineral maps and bulk and liberation data can be calculated for minerals of interest. This type of quantitative mineralogical data can be used for a wide variety of applications including supporting existing operations or providing valuable mineralogy and liberation information during process development.

The company owns several properties in the Carlin Trend containing gold associated with fine-grained reactive sulphides that do not respond to conventional whole ore cyanidation for the recovery of their contained gold values.  These refractory ores and require pre-treatment to make them amenable to cyanidation. At Carlin’s Mill 5, flotation is used to preconcentrate some of these difficult and lower grade ores to produce a concentrate, which is blended into the whole ore feed to the CFB roasters.

These ores generally contain gold associated with pyrite, arsenopyrite and arsenian pyrite (pyrite enriched in arsenic). It is of interest from a flotation perspective to be able to study the floatability of pyrite, arsenopyrite and arsenian pyrite individually. Since these minerals have different quantities of gold associated with them (arsenian pyrite usually contains the majority of the gold), it is useful to be able to discern the effect of changing process conditions on the individual mineral flotation kinetics and recovery.

The ability to measure the mineral flotation kinetics of the gold-bearing minerals of Carlin Trend ores using this equipment was shown to be invaluable in order to successfully interpret metallurgical test results. Previously, through studying chemical analysis results, it could only be inferred that improved arsenian pyrite recovery was responsible for improvements realised in gold recovery.

The MLA takes samples from flotation tests using various Carlin ore types, using air or nitrogen as flotation gas, specifically to study the differences in floatability characteristics, which ultimately impacts overall gold recovery.

Twin Creeks magnetic separation projectMill at the Twin Creeks plant

Twin Creeks has optimised its Sage mill blend to increase gold recovery by limiting chemical variation within its various stockpiles. The team evaluated the existing recovery process to determine opportunities for improvement. Improved chemical control has led to a highergrade blend through the mill – an average of 7,200 oz of gold per year.

As ore is processed in the Carlin Mill 6 roaster, a small portion of the gold it yields is trapped in “maghemite”, magnetic particles that prevent any gold encapsulated by them from being recovered downstream in Mill 6′s carbon-in-leach (CIL) circuit. The new Carlin Process facility seeks to recover some of this gold through a physical magnetic separation method. The mag sep system processes the Mill 6 carbon in pulp (CIP) tailings in six double drums with powerful rare earth (RE) magnets.  These magnets corral the gold-bearing maghemite particles into a rough concentrate, which may also contain a significant amount of non-gold bearing magnetic particles. This rough concentrate is then cleaned up by being exposed to a low-intensity, ceramic double drum magnet, which attracts mostly goldbearing maghemite and allows the non-gold material to pass. The cleaned-up concentrate moves downstream to be combined with the flotation concentrate in the Mill 5 flotation thickenener. The flotation product, which now includes gold-bearing maghemite, is then shipped offsite to be processed in the autoclave at Twin Creeks, while the flotation tailings will be processed as usual through the existing Mill 5 CIL.

Liberating the gold from the magnetic part of the Mill 6 CIP tailings has the potential to increase Mill 6 recovery by 1.5-2%, resulting in an additional 12,000-15,000oz annually. The detailed engineering for the mag sep facility was done by ICPE in Salt Lake City and the construction executed by TIC. The mag sep plant was started up and commissioned in September 2010 and placed into operation in October 2010. The total project cost is estimated at US$9.7 million.

Future projects

There are a series of future development projects in planning by Newmont for its Nevada operations.  Two of the most significant are centred around the existing Gold Quarry in Carlin, which is a world class asset having produced 25 Moz since 1982, but which in its existing design has a limited future. The most advanced is the so-called Gold Quarry West Wall, which would extend the existing pit and represents the main near mine exploration project. Some 60,000 m had been drilled from late 2009 through to April 2010 and an additional 60,000 m of drilling in 2010. Some 3.1 Moz of reserves have been added and the project, now in bankable feasibility stage, would add up to 10 years of life to the pit, within the currently permitted mining area.  However, the challenge is that the project would require additional waste and tailings dump storage, which comes under separate permitting.

Expected production would be 270-330,000 oz/y for the first five years. The first production would be expected in 2018-2019 and the initial capex is in the region of US$45-65 million.

Regional potential of Leeville area mineral exploration

A second and longer term project, known as the Greater Gold Quarry, is at a pre-Feasibility stage and will determine the potential for further expansion at Gold Quarry, leveraging off the results of the Gold Quarry West Wall work. No official reserves have yet been released but it could represent another 10-12 year extension for Gold Quarry beyond the additional mine life from the West Wall project. Newmont is currently working with the BLM and state agencies on preliminary permitting activities.

In underground mining, is the Greater Leeville/Turf project, which is at pre-feasibility. New exploration drill intercepts have expanded the known Leeville/Turf mineralisation. The 2009 drill program included 18 holes and 15,500 m, with 2010 expanding to almost 65,000 m of underground drilling, four access drifts totalling 4,300 m as well as 3,700 m of surface drilling. The main challenge at the mine is geohydrology.

Also, in the wider Greater Leeville/Turf area, new mineralisation is open to the north, east, west and at depth. This is also the target of an expanded exploration program of 20,000 m and 22 holes. It involves exploration distances from the shaft of 3,500 m north, 950 m east and 1,150 m west. Studies are ongoing to evaluate production capacity/infrastructure options. There are also new discoveries below the current water table.

Finally, there is the Eureka project. The deposit was discovered in 1996 as part of a program to extend mineralisation along the Castle Reef Fault northwest of the Lantern Pit.  It encompasses less than five acres of additional private land disturbance due to being mined underground. Some 45,747 ft of underground lateral drifting will generate 983,000 t of non-potentially acid generating (non-PAG) waste material. No additional dewatering or Waste Rock Disposal Facilities (WRDF) will be needed at Exodus, which will access some 1.78 Mt of ore. IM

This is the second in International Mining magazine’s six-part ‘Great Mines Series’ profiling Newmont Mining Corporation operations around the world.  To get all six, and the full benefit of the industry’s top global monthly magazine, Click here

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