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By Mike Jahraus

The topic I would like to throw out for discussion this morning concerns the metallurgical solution management of operating a valley fill leach facility where ore depths approach 250 feet and deeper. We are currently beginning to experience solution transport times through our heaps on the order of 60 to 70 days as our heaps approach 250 feet. Incorporating a two-stage leach scenario, or solution enrichment, these times are nearly doubled. Concurrent with the increased solution transport times, the solution tenors being produced by our heaps are being diluted slightly as percolation occurs through the lower lifts. I feel the best way to handle these situations is to closely monitor solution application rates, and carefully manage ore stacking. Also, as heaps become deeper, metallurgical and hydrologic characteristics of the ore become inter-related, i.e. if channeling or preferential flow is taking place, lowering cross-sectional flow rates to older leach panels with help re­institute capillary flow while helping to prevent solution tenor dilution.

Jan 1, 1999

By Joe Hudson

The successful heap leaching of tailings as illustrated in the two photographs below, requires special provision. These will be enumerated in the presentation. The two illustrations show the project as it evolved. Note the bermed pads and the conveyor materials handling system which provides for agglomeration of the feed material.

Jan 1, 1998

By Tim Q. Haldane

The ability to efficiently process low grade gold ores has allowed the Gold Fields Mesquite Mine in Imperial County, California to expand from a 2.1 million tonne per year rate in 1986 to its present 7.3 million tonne per year processing rate. Increased tonnage demands led to the 1989 construction and start-up of a dump leach pad to supplement the existing heap leach operation, resulting in an excellent opportunity to compare the two processes at the same operation. Additional operating costs associated with the crushed ore heaps are justified through enhanced recoveries, even at very low ore grades. An overview of current operating practices at Mesquite is presented along with metallurgical and economic comparisons between the crushed and run-of-mine ore heaps.

Jan 1, 1990

By Tim Q. Haldane

The ability to efficiently process lowgrade ores has allowed the Gold Fields Mesquite Mine in Imperial County, CA to expand from a 2.1 Mt/a (2.3 million stpy) rate in 1986 to its present 7.3 Mt/ a (8 million stpy) processing rate. Increased tonnage demands led to the 1989 construction and startup of a dump leach pad to supplement the existing heap leach operation. This resulted in an excellent opportunity to compare the two processes at the same operation. Additional operating costs associated with the crushed ore heaps are justified through enhanced recoveries, even at very low ore grades. Gold Fields' Mesquite Mine is a gold heap leach facility located about 55 km (35 miles) east of Brawley in southeastern California. Five open-pit mines will be developed over the projected life of the property, covering a total area extending to a maximum of 5.5 km (3.4 miles) to the east and west, and 2.4 kin (1.5 miles) to the north and south. Mesquite will process 7.3 Mt (8 million st) of ore and produce more than 6.2 t (200 000 oz) of gold in 1990.

Jan 1, 1990

By Charles B. Escapule

The first successful heap leach of silver ores in the State of Arizona has been under continuous operation since early 1976 at the State of Maine Mine, two miles southwest of Tombstone, Arizona. The silver produced from leaching old mine dumps at this property vas the first in the Tombstone mining district to achieve a 999+ purity. While cyanide leaching of silver and gold ores is a time-proven accepted practice, a relatively new method of treatment called "heap" leaching was employed. Heap leaching is a comparatively inexpensive fast way to recover precious metals from low grade material.

Jan 1, 1981

By M. Irish

This paper describes the emergency water control measures used at Pegasus Gold's Zortman Landusky mine during the September 1986 flood. The amount of solution stored increased by approximately 78 165 m3 due to receiving 0.2134 m of rain in a 24 hour period. Three methods of water disposal will be discussed including continuous chlorination, batch chlorination, and reverse osmosis. A water management program will also be discussed.

Jan 1, 1988

By Harry R. Dahlberg

Heap leaching is discussed as a unit process. Five factors are identified as the principal elements that can be measured and/or controlled. These are: 1. Material Size 2. Volume of solution 3. Tonnage of heap 4. Time 5. Solution concentretion. The Rate of Extraction Curves obtained from an actual heap or column tests describes the economic viability of the unit process. By analysis of these curves and the five factors end their inter-relationship it is possible to determine how the extraction rate can be increased. The practice of leach and rest used by many operators is analyzed and shown on a hypothetical rate of extraction curve. The influence of the driving force of the hydrogen ion and ferric Lon as Lixivants and its effect on the rate of extraction curve is discussed.

Jan 1, 1979

By Rex L. Outzen

Houston International Minerals Borealis Project is an open pit heap leach operation. The operation uses open pit mining, two stage crushing, agglomeration, heap leaching, zinc precipitation and induction refining to produce approximately 50,000 ounces of gold per year. Due to the ore being extremely ameanable to heap leach processing techniques, low manpower requirements and efficient management, the operation is one of the lowest cost gold producing operations in the United States.

Jan 1, 1984

By Menne D. M, Ladyman R

Camel Creek Mine operated by Lynch Mining Pty Ltd is located 65 km west of inghain and 160 kin north west of Townsville in North Queensland. (Figure 1). The Camel Creek gold mineralisation was discovered in mid-1987 in an area previously known for its tin workings. Mining commenced in January 1989 after an oxide reserve of 1.2 million tonnes @ 2.1 g/t gold had been delineated. The first gold pour was in May 1989. The mine developed into a medium sized open cut operation, with full site facilities. The initial mining rate was 500 000 tpa utilising run-of-mine (ROM) heap leaching to recover the gold. By the end of 1990 the wider orehodies were mined and efforts were focused on the narrow orebodies, of width typically less than three metres. Smaller earth moving equipment was employed to selectively mine the narrow orehodies leading to a decrease in the mining rate to 200 000 tpa. The Red Gold deposit (80 000 tonnes « 3.0 g/t to 18 in vertical) was mined in mid-1990 and ore was hauled approximately 8 kin to the Camel Creek heap leach operation. The ore was hauled in a dedicated campaign after being stockpiled. The cost of dedicated ore haulage ensured that only the more exceptional of the remote orebodies could be mined in this manner. The Golden Cup orebody, some 20 km from Camel Creek, was too distant to permit ore haulage. However, this prospect contained sufficient gold (initially 90 000 tonnes @ 3.0 g/t) to warrant the installation of a small mobile adsorption facility. Construction of the second heap leach operation commenced in late-1990. Gold production commenced in early April 1991. Mining of several smaller orebodies remote to the second heap leach facility has been undertaken and further mining is planned. This paper outlines heap leaching practice at Camel Creek Mine and summarises the success of the Golden Cup heap leach.

Jan 1, 1994

By T. D. Maki

FMC Gold's Paradise Peak Mine, located 13 km (8 miles) south of Gabbs, Nevada, became operational in April of 1986. Shortly thereafter heap leach testwork began on sub mill grade ore. Presently, testwork continues in combination with production size heaps that account for approximately 6% of total gold production at Paradise Peak.

Jan 1, 1989

By D. Scott Barr

The Zarafshan/Newmont Joint Venture operates the Muruntau heap leach project, located in the Kyzylkum desert of central Uzbekistan. The mine produces more than 12.4 t/a (400,000 oz/year) of gold from low-grade oxide ore stockpiles adjacent to the Muruntau open pit. It is op¬erated by the Navoi Mining and Metallurgical Combine and is one of the largest gold resources known (Fig. 1). Since commissioning in 1995, total heap leach production has exceeded 21 t (675,000 oz). The joint venture uses four-stage crushing and screening to produce a final product for heap leaching, Merrill-Crowe processing and local refining.

Jan 1, 1998

By Arthur Miller

Most of the production of copper in the United States comes from a few large companies. Often overlooked, however, are the more numerous small mining operations, which collectively produce a significant portion of the nation's copper. The objective of this paper is to describe the operations of a small mining company - Ranchers Exploration and Development Corporation - how it views its place in this industry of giants, how it exploits the advantages offered by its relatively small size, and how it protects itself from the hazards being small introduces. Environment is, of course, a critical factor for such a company because it does not have the resources which help large companies weather periods of financial stress. Ideally, this environment is characterized by a heal thy economy, strong product demand, relatively stable prices , adequate grades and tonnages of ore commensurate with depth and over-burden, ready access to utilities, a dependable labor pool, and suitable technical "know how". When the environment is right, properties which were previously uneconomical to operate attract the attention of companies whose primary interest is a return on investment commensurate with risk over a reasonable period of time. Naturally, the amount of the investment and the duration of operation determines the size of the company which would be interested in such a venture. Such is the case with Ranchers Bluebird Mine at Miami, Arizona - a small property operated by a small company in a favorable economic environment.

Jan 1, 1967

By Kerry Lahti, Bryan Ulrich

On Feb. 11, 2005, more than 20 mining professionals gathered in Elko, NV for a day-long round-table discussion on heap leaching. Attendees included project managers, operators and environmental professionals. They represented 10 mining organizations. Knight Piésold sponsored the special event. Its seven representatives included three staff members from the company’s Elko Operation, and one each from its Denver, Cajamarca (Peru) and Vancouver offices. The roundtable format was chosen to allow people from the mining industry to share ideas and experiences in an open forum. Rather than presenting prepared talks, spontaneity was encouraged. This resulted in a lively and enjoyable discussion.

Jan 1, 2005

By J. M. Mwase

The platinum group metal (PGM) industry is currently reliant on the crush-mill-float-smelt-refine route to process PGM ores. However, there are many instances where this route would not be feasible. An alternative process route has been developed which involves heap bioleaching to extract base metals followed by heap reclamation and a water wash step, leading into heap cyanide leaching to extract precious metals. This process was evaluated through test work on samples of Platreef ore using laboratory scale columns. After 304 days 75% Ni and 93% Cu were extracted in the bioleach experiment at 65°C, and after 60 days 58% Pt, 99% Pd and 90% Au in the follow-up cyanide leach experiment at 50°C. A preliminary process flow sheet has been developed around this. Analysis via a mineral liberation analyser showed that the remaining Pt was in the form of the mineral sperrylite, which appeared to be slow leaching in cyanide in comparison to the other mineral types. Analysis of cyanide effluent solution showed high levels of thiocyanate, which present an environmental risk for disposal and high consumption of cyanide. Further studies to develop the process for commercial application in the South African PGM industry are outlined.

Jan 1, 2014

The object of crushing and grinding for leaching is obviously to permit contact of the solvent and mineral and subsequent removal of pregnant solution in a reasonable time. Heap leaching is the leaching of ores that have been mined and transported to prepared, relatively impervious pads for leaching by sprinkling or ponding, and percolation of the lixiviate through the ore. Dump leaching is the leaching of dumps or low-grade ore or overburden without the use of prepared pads under them. Run-of-mine material, e. g., low -grade ore from open pit stripping operations, may be leached without crushing, and a fairly high recovery made by heap leaching. An alternate method for better grade gold/silver ores is to crush to 9 to 13 mm (318 to112 in. ) size for pad heap leaching, as used by Smoky Valley Mining Company at Round Mountain, Nevada, on gold ore, and to 38 rnrn (1 -1 12 in.), which will be done by Candelaria Partners, at Candelaria, Nevada, on silver ore. Heap leaching of copper probably began at Rio Tinto, Spain, about the year 1752. This was done by the leaching of weathering piles of ore in the open air followed by iron cementation of the liquor that drained off the heaps. Its application to the low -grade southwestern United States copper ores was overlooked for many years, and low- grade ores from Sacramento Hill at Bisbee, Arizona, were the first to be heap leached in 1923. Site preparation used a half century ago is the same today. "The need for some form of waterproofing of the pad was evident. Before leaching ore was piled, the site was cleared of cactus and brush. After clearing a gentle sloping area, it was then covered with a blanket of rolled and tamped clay or slime tailing. When heaps are built, a layer of coarse fragments may be put down first to assist drainage. A second method of leaching without grinding, usually for higher grade ores, is by vat or tank leaching of material crushed to 9 to 13 mm (318 to 112 in.) size. Such a plant is considerably more expensive than a heap leaching installation but much less costly than grinding for agitation leaching, and a recovery higher than that obtained by heap leaching is to be expected. Vat leaching has been widely used by the copper industry on higher grade copper ores but has been used in only a few small operations on that size gold or silver ores. However, such a plant should be considered for a modest tonnage of a few million tons, 3 to 7 g per mt (0.10 to 0.20 oz per st), of Carlin-type leachable ores crushed to 9 mm (318 in.).

Jan 1, 1981

By S. D. Hill, G. E. McClelland

To maximize productivity and improve minerals processing technology, the U. S. Department of the Interior, Bureau of Mines, is investigating a particle agglomeration technique as a means of increasing the percolation rate of leaching solutions through heaps of clayey or finely crushed, low- grade, gold-silver ores. Bench-scale and pilot-scale experiments conducted on different ores indicated that the percolation rate of cyanide leaching solution was enhanced markedly by mixing the ore with a binder, such as lime or portland cement, moistening the mixture, then mechanically agglomerating and aging the feed prior to heap building and leaching. In addition, the rate of silver and gold extraction markedly increased without sacrificing total recovery of values. The use of concentrated cyanide solution instead of water during the agglomeration procedure substantially decreased the leaching time required to obtain maximum recovery. Results from bench-scale and pilot-scale experiments using the particle agglomeration technique are discussed.

Jan 1, 1981

By J. Libaude

The Changement mine in French Guyana has, since 1983, processed gold ore by classical gravity methods. A large part of the gold is in the form of very small, free or enclosed grains. Recovery by gravity methods is thus limited (25-30%) and the present plant produces about 40,000 t annually of auriferous waste assaying about 6 git. The company therefore decided to retreat the waste by heap cyanidation. After laboratory tests which showed the feasibility of the method, a pilot test was set up on site. An experimental 3000 t heap, composed of waste of 0-8 mm grain size, was laid out by bucket loader on an impermeable pad covered by PVC and geotextile cloth. The upper layer of the heap was reworked by mechanical shovel to break up the area that had been compacted by the passage of the loader so as to restore adequate permeability.

Jan 1, 1998

By Rod Samuels, Rupert Allen, Thomas Harper

"Viceroy Resource Corporation of Vancouver, B.C., has recently developed and brought into production the Brewery Creek Mine, an open-pit heap leach gold mine, located 55km east of Dawson City in Yukon, Canada. Mineable reserves are 15.2 million tonnes of ore grading 1.45 grams/tonne, containing 22 tonnes (707,315 oz) of gold. Ore processing employs the heap leach technology using run-of-mine ore. Highlights of 1996 activity included construction of a 158,000 m2 of leach pad, placing 1.9 million tonnes of ore at a grade of 1. 46 gpt to the leach pad, construction and successful commissioning of the ADR plant, and pouring of the first gold bar on November 15th.Permitting of this mine has drawn significant attention because of the innovated heap leach technology; although this technology has been proven in other jurisdictions, it has not been used at such extreme northern sites where winter temperatures routinely reach -45°C for extended periods.ABSTRACT ONLY"

Jan 1, 1997

By W. J. Witte, M. K. Witte

"The purpose of this report is to present a generalized preliminary design and cost estimates for a typical heap leach operation such as might be undertaken in Northern Ontario. This report should be of value to anyone in the mining industry planning, or contemplating, a heap leaching operation in Ontario, either on a large or small scale. While more detailed costing and design work will obviously be required for each specific project being contemplated, the data provided in this report should enable parties to make preliminary estimates of the costs of proposed projects and should identify most of the planning and design parameters that will need to be considered.Although heap leaching has been used extensively as a low cost gold recovery method in other parts of the world for many years, it has only recently become of interest to the Canadian mining industry.In order to investigate and demonstrate the feasibility of using heap leaching in Ontario, the Ontario Ministry of Natural Resources in 1982, undertook to locate a private sector proponent willing to undertake a 10,000 ton demonstration project. This project was to have been carried out at a production scale under normal northern Ontario field conditions. The Ministry was to have provided technical management and design for the designated project."

Jan 1, 1985

By Thorndycraftm R. B.

"PURPOSEThe purpose of this presentation to the Canadian Mineral Processors is to review gold heap leaching systems currently in use and discuss their applicability to Canadian ores. The author's experience with the development and operation of heap leaching spans the past four years at. Pinson, and visits to many ether heap leaches in the western United States.INTRODUCTIONBy way of introduction to the heap leaching system, I will describe in slight detail the method used at Pinson Mining in northern Nevada. This will be followed by a discussion of optional methods in use at other operations visited.The Pinson orebody is a finely disseminated, well-oxidized hydrothermal deposit. Gold particles are finer than 20- microns. The orezone hostrocks are metamorphosed and silici¬fied limestone and shale. Sulfides and carbonaceous materials are negligible.The Pinson open-pit mine has operated since June 1980. It produces 1500 tpd of C.I.P. mill feed averaging .10 oz gold per ton, and 1500 tpd of heap leach material averaging .025 oz gold per ton. Cutoff grades are 0.04 for mill feed, and 0.01 for heap leaching. Stripping ratio is 9 tons of waste and leach grade to 1 ton of mill feed.The project is located in northern Nevada at 4900 feet above sea level.,Winters are fairly severe, with freezing conditions affecting operations from early December through April. Although officially designated as ""high-mountain desert"" country, snow and/or freezing rain occur almost every week of the winter.To date, all Pinson production-scale heap leaching has treated run-90,000 tons of ore are stacked on 300 foot square clay leach pads. Cyanide leach solution is applied through ""wobbler"" sprinklers at .0025 gpm/sq ft for 60 to 90 days. The pregnant solution flows from the heap by gravity to plastic-lined ditches, into a collection sump and then through buried piping to the 2.2 million gallon pregnant solution pond."

Jan 1, 1984