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By Mike Wardell-Johnson, Chris Campbell-Hicks, Craig Bitmead

Faster, simpler, cheaper and more accurate cyanide ex­tractable gold procedures are now available for grade control assay. Cyanide 'bulk leach extractable gold' or BLEG assays have previously been seen as desirable, due to the large sample size that can be treated, but not in common use due to the 24hr total assay time required. Sample sizes from 50g to several kilos can now be accurately assayed in less than 4 hours total time with the larger sample size increasing accuracy, without loss of precision, while greatly reducing the 'nugget effect' or coarse gold bias. Typical assay size is 200g, equivalent to 4 x 50g Fire Assays or 10 x 20g Aqua Regia Assays. Ongoing modifications and refinement of the procedures and reagents used also indicate applicability to the treatment of coarse gravity gold where substantial savings in both capital and operating costs for these circuits are possible. The successful use of this cyanide assay at the Bannockburn and Windine Well operations are cited to-gether with a compre­hensive comparative testwork program by Newcrest. Testwork at Gidgee and Lynas Gold operations is currently being initiated. Other operations using the method include Red Dome and Kidston; with Placer(Granny Smith) and PMA's Palm Springs operations to commence shortly.

Jan 1, 1995

By I R. F MacCulloch, K Jones

Pintail Systems, Inc, a Colorado USA based company has developed and commercially applied bioremediation processes for biological detoxification of cyanide compounds in mine waste. Site-specific microorganisms are isolated from spent ore, tailings or process solutions and augmented in the laboratory for cyanide oxidation, denitrification and metal biomineralisation. Biological processes typically treat complex contaminants (cyanide compounds, soluble metals and nitrates) in a fraction of the time of conventional remediation processes. Cyanide is used in microbial metabolic processes as a carbon or a nitrogen source. Biological detoxification processes applied at the end of mine life can end long-term liability and perpetual monitoring and containment. Case studies from commercial application and demonstration programs for the US Environmental Protection Agency will be presented in this paper.

Jan 1, 2004

By R J. Beazley, M C. Woods

"The International Cyanide Management Code (the Code) is a voluntary industry program for gold miners and associated cyanide transporters and cyanide producers. By becoming a signatory, a company commits to follow the CodeÆs principles and implement its standards of practice.Signatories are required to undergo an initial certification audit within three years and a recertification audit every subsequent three years. Recertification audits evaluate compliance over the preceding three-year period. This approach presents a number of challenges. Golder Associates has undertaken in excess of 75 initial certification audits and 25 recertification audits; more than any other audit firm. This paper outlines some of the challenges identified and lessons learnt from the recertification audit process. Central to the process is the challenge for organisations to maintain commitment to compliance over the full three-year period and effectively address deficiencies or non-conformances that may have occurred during that period in a prompt manner.The International Cyanide Management Institute (ICMI) provides guidance in evaluating deficiencies or non-conformances, which requires consideration of the æcauseÆ, ædurationÆ and æongoing compliance effortsÆ and an assessment of the concept of ægood faithÆ in response actions. Golder AssociatesÆ experience with the recertification process highlights some common deficiencies with Code compliance programs, such as: system breakdowns (leading to ineffective communication between departments or loss of information) exceedance of discharge limits inadequate inspections, maintenance activities and associated record-keeping.Such deficiencies can be attributed to: personnel changes organisational changes or structures management systems (eg integrated or standalone) awareness and interpretation of Code requirements transparency of management decisions with Code implications.We have identified that ongoing programed assessment is an effective strategy in maintaining Code compliance.CITATION:Beazley, R J and Woods, M C, 2013. Cyanide code recertification - the three-year challenge, in Proceedings World Gold 2013, pp 247-254 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Sep 26, 2013

By G. Piegols, J. A. Lombardi

Substantial volumes of cyanide are consumed in precious metals mining due to the purposeful destruction of base metal cyanide complexes and free cyanide to meet surface discharge regulations. This destruction of cyanide resource runs counter to the prevailing social ethic of resource conservation wherein cyanide recovery-and-reuse is considered a more socially responsible cyanide use pattern than systematic cyanide destruction. HW Process Technologies, Inc. (HWPT) has developed membrane based methods for the recovery of cyanide from barren solution as a means to reduce cyanide waste. The HWPT Engineered Membrane Separation (EMS™) system uses state-of-the-art spiral wound membrane elements that are engineered specifically for the treatment of high pH cyanide process solutions. The membranes fully reject WAD CN, SAD CN and most minor metals, and partially reject SCN, Free CN and precious metal cyanide from a high clarity barren solution feed to a small volume EMS™ “concentrate” stream. The EMS™ “concentrate” stream is returned to the process. The large percentage of the EMS™ process feed exits the system as cyanide lean EMS™ “permeate.” The EMS™ permeate, after residual cyanide destruction, polishing, and pH adjustment, is, thereafter, typically suitable for discharge. Separately, the HWPT EMS™-PLS method of cyanide recycling is an internal plant cyanide recovery step that removes base metal cyanides from a pregnant leach solution to a small volume EMSTM concentrate stream. The concentrate stream is then typically processed further for the recovery of metals and recovery-recycling of cyanide. The method makes it economically practical to recover gold from Merrill-Crowe or car-bon plant “fouling” solutions, e.g., those with greater than 400 ppm Cu, as might result from the use of the EMS™ method wherein EMS™ concentrate is constantly thrown back into the mine leach solution pool as part of the free cyanide recycle process, or as might result from the single-pass leach treatment of high copper content ores or concentrates. The EMS™ cyanide recovery method for barren solution treatment is shown to be “economic” for the treatment of clear solutions at the approximately 200 ppm total cyanide level (CNT), and for slurries at the approximately 400 ppm total cyanide level, where economic is defined as a 2 year EMS™ plant payback. The EMS™ plant payback calculation includes the beneficial monetary impacts of gold and free cyanide recycling and the avoided operating cost of cyanide destruction.• The cyanide recovery plant payback period is reduced further when the avoided capital costs for cyanide destruction (EMS™ permeate “clear solution CN destruction polish” only required) and/or metals precipitation are considered.

Jan 1, 2004

By B. J. Vorster

AngloGold South Africa region currently consists of twelve gold plants. These plants use a combined total of $20 million of cyanide per annum. Of this, the major portion (60%) is consumed at two Ergo dump retreatment plants. Historically the primary motivation for cyanide control at Ergo has been one of leach/cost optimization. However, more recently, with the increased public awareness of cyanide in the environment, a secondary but increasingly important motivation for control has been to ensure that only the minimum amount of cyanide is added to the process whilst not compromising leach performance. Following a brief overview of the Ergo process, the methodology in determining the amount of cyanide to be added is described. The paper then traces the developments in cyanide control from very basic manual systems to the current automated control system. In line with the increasingly sophisticated control systems, developments also took place in regards to the method of cyanide analysis. The development of these analysers is also discussed. Whilst cyanide is one of the major drivers, if not the major driver of gold dissolution, it cannot be viewed in isolation particularly with respect to the relationship between cyanide and oxygen as ascertained from the Elsner?s well-known equation. Consequently, in order to control cyanide addition, knowledge of the relative cyanide/oxygen profiles is necessary. Various means investigated at Ergo for pulp oxygenation have therefore been included for the sake of completeness. Finally a comparison is made of the control achieved from the current system compared to the original manual system. The knowledge and experience gained at Ergo is now being used to draw up guidelines for the installation and optimization work at the other AngloGold plants. The net effect of this will be reduced cyanide consumption for the region, which also, apart from the obvious economic benefit, translates into a reduced environ-mental risk.

Jan 1, 2001

By B. J. Vorster

AngloGold South Africa region currently consists of 12 Gold Plants. These plants use a combined total of $20 million of cyanide per annum. Of this, the .major portion (60%) is consumed at two Ergo dump retreatment plants. Historically the primary motivation for cyanide control at Ergo has been one of leachlcost optimisation. However, more recently, with the increased public awareness of cyanide in the environment, a secondary but increasingly important motivation for control has been to ensure that only the minimum amount of cyanide is added to the process whilst not compromising leach performance. Following a brief overview of the Ergo process, the methodology in detennining the amount of cyanide to be added is described. The paper then traces the developments in cyanide control from very basic? manual systems to the current automated control system. In line with the increasingly sophisticated control systems, developments also took place in regards to the method of cyanide analysis. The development of these analysers is also discussed. Whilst cyanide is one of the major drivers, if not the major driver of gold dissolution, it cannot be viewed in. isolation particularly with respect to the relationship between cyanide and oxygen as ascertained from the Elsner's well known equation. Consequently, in order to control cyanide addition, knowledge of the relative cyanide/oxygen profiles is necessary. Various means investigated at Ergo for pulp oxygenation have therefore been included for the sake of completeness. Finally a comparison is made of the control achieved from the current system compared to the? original manual system. The knowledge and experience gained at Ergo is now being used to draw up guidelines for the installation and optimisation work at the other AngloGold plants. The net effect of this will be reduced cyanide consumption for the region, which also, apart from the obvious economic benefit, translates into a reduced environmental; risk.

Jan 1, 1998

By Adrian Smith

14.1 INTRODUCTION From the time the last recoverable gold is extracted from ore on a heap leach, the ore - now spent ore - changes from being the resource, indeed the raison d'etre of the operator, to a potential liability. The spent ore contains process chemicals and constituents leached from the ore both in the interstitial pore water in the heap and on the surfaces of spent ore. If these chemical species were released to the environment, it could have a potential impact on the quality of both surface water and groundwater resources. Accordingly, the spent ore must be left in a condition where it does not present a potential environmental liability. This can be accomplished either on a decommissioned pad or, if the heap leach is operated as a load/unload scheme, in a waste facility. In general, the residual cyanide level in the spent ore is the perceived controlling factor when determining whether the leached material is suitable for abandonment. Regulatory authorities set permit conditions for heap leach abandonment in terms of residual cyanide levels, for example, Smith and Struhsacker (1987). This chapter discusses cyanide degradation and methods for detoxifying a heap leach in order to meet regulatory limits/permit conditions for abandonment. Cyanide degradation and detoxification by "natural" processes are described initially, based on the chemistry and geochemistry discussed in Chapter 13. This leads to a review of chemical treatment processes for detoxification of spent ore. The advantages and apparent disadvantages are then appraised. 14.2 NATURAL DEGRADATION AND DETOXIFICATION For the purposes of discussion, "natural" detoxification processes can be divided into two alternatives: • Passive abandonment (the so-called "do nothing" option); and • Water In the first alternative, the spent ore is merely left on the leach pad to age; the second alternative involves the flushing of the spent ore with water.

Jan 1, 1988

By P. J. Arps

Cyanide (CN) is used to recover gold from its ores in many locations worldwide. In spite of the established history of gold mining in Alaska, modern cyanidation methods have been used at only one location, the Ryan Lode Mine at Ester Dome, near Fairbanks. Ore was processed by heap leaching between 1987 and 1989, when permitting issues caused operations to be terminated. Those issues have since been resolved, and plans to reopen the mine are currently being discussed. Plans are also proceeding to develop several other ore deposits in the state, all of which include the use of cyanide for gold recovery [6]. Since tailings and effluent water produced from these mines will require treatment, it is important to develop detoxification methods suitable for the Arctic and sub-Arctic conditions found in Alaska. Several methods exist for removing cyanide from mining wastewater. However, most industrial users prefer chemical treatment systems, and typically use sodium hypochlorite, hydrogen peroxide, or sulfur dioxide/air/copper to oxidize free and complexed cyanides [9]. Biological treatment has been used successfully at two sites in the United States [30,32] and field tested at several others [20,27,28]. In addition, one mine uses "natural processes", which include natural oxidation, photodegradation, and degradation by naturally occurring bacteria [33].

Jan 1, 1994

By C. J. Edmonds

Of the gold mined in Canada over 90 percent is extracted from the ore by the process of "cyanidation". In this process crushed ore is treated with lime to provide "protective alkalinity" and cyanide, usually in the form of sodium cyanide. The gold is dissolved in the cyanide solution, which after further treatments for clarification, is precipitated by the addition of zinc dust. Wastes from the process consist of tailings which will contain cyanides. Water consumption, mill size, effluent quantity and quality are depicted in transparency (1). It should be noted that as far as the wastes are concerned it has been impossible to postulate a typical situation. Variation from the above data will occur. A summary of data from tailings pond effluents is presented in transparency (2). The figures in parentheses indicate the usual range of values for the parameter.

Jan 1, 1973

By Malcolm Mudge

"One of the oldest mining areas in the World exist in Africa and the Middle East. This area is being exploited by foreign and local mining entities. Several large plants, both foreign and local as well as small operators, conduct their mining business on a scale which would be could be prohibited in any other part of the world. Relatively recent European disaster with tailing disposal and breakout has highlighted the problem.More important to the author is that the presence of foreign entities in zones which have not remedied the situation but has heightened the concern due to those entities using similar outrageous methods in treatment of waste. The abject misuse of technology cannot be permitted to continue and the lack of any metallurgical knowledge in the treatment of gold ores is considered deplorable for the majority of third world countries.The destruction of cyanide is simple and straightforward and requires no special skills. In South America, we developed a system that is modular, compact and can be operated in batch mode to cater for several clients, as required. Larger installations would require a separate module, as treatmentwould be on a continuous basis."

Jan 1, 2003

By A. G. Eccles

"INTRODUCTIONWestern Mines' copper-lead-zinc operations are located in Strathcona Provincial Park, near the geographic centre of Vancouver Island. This park includes Buttle Lake, which flows into the Campbell River water system. The latter provides domestic water for the Town of Campbell River, approximately fifty-eight miles from the mine site.Operation of the concentrator commenced in December 1966, at which time the tailings were discharged into a small tailings pond near the plant. On May 8, 1967 Permit No. 185 was granted to the company, allowing discharge of the tailings, through a submerged outfall, to the bottom of Buttle Lake.Needless to say, the concept of operating a mine within a park, and the discharge of tailings into Buttle Lake generated considerable controversy. However, this has all but been eliminated over the years by the proven effectiveness of Western Mines' pollution control program. In 1973 this program was further upgraded with the addition of an alkaline chlorination plant. Effluent treatment by this method became necessary as a result of process modifications, and has been effective in maintaining the levels of characteristics in the tailings within the ever increasing pollution control requirements imposed on the industry."

Jan 1, 1977

By N. Katsikaros, R. Agius, B. Adaszynski

"With stricter limits globally being imposed on cyanide discharge levels in plant tailings, having a reliable and well designed cyanide detoxification circuit is critical for any operation. The INCO SO2/Air method is most commonly used for cyanide detoxification where sulfur dioxide and oxygen combine to oxidize cyanide to the much less toxic cyanate. This paper discusses the steps involved with the development, from laboratory through to design, of a robust cyanide detoxification circuit. The goal is to produce a cyanide detox circuit that reliably meets discharge target with the lowest operating and capital cost.Design begins in the laboratory where continuous tests simulate full scale operation of a detoxification circuit. Detailed design relies on several design parameters, based on theory and experience, to ensure the reactor can satisfy requirements of the cyanide destruction reaction. Selection of the correct reagents and their supply to the reactor is important to an operable process with minimal operator workload. The operability of the system relies on correct process control strategies to maintain optimal reagent addition and chemical conditions in the reactor. These design factors are critical to providing a robust plant that will consistently meet cyanide discharge levels, ensuring uninterrupted production and plant profitability."

Jan 1, 2014

By James L. Hendrix, Michael R. Straka, Emil B. Milosavljevic, Ljiljana Solujic, Neil P. Gallagher

Analysts that utilize the classical distillation procedures for cyanide analysis are often frustrated by the poor reproducibility and repeatability of these techniques. Capital intensive business decisions and environmental management regulations are exas­perated by the fact that the EPA/ASTM approved cyanide deter­mination methods produce data of questionable quality. Reliable cyanide values are important in monitoring the effec­tiveness of the cyanide detoxification procedures. Efficiency and cost of gold and silver cyanidation recovery can also be improved by precise cyanide monitoring in the process itself.

Jan 1, 1996

By F. Qunfei, W. Laijun, X. Lyu, A. Cosmos, L Huijuan, Z. Jinggang, G. Yao

In this paper, four cyanide-utilising bacteria strains were isolated from a gold mine tailings pond, in the Hexi gold mine (Shandong), China. Based on the analysis of 16S rRNA gene sequence, four strains were identified as Aeromonas hydrophila strain C1, Bacillus mojavensis strain C3, Shewanella oneidensis strain C2, and Aeromonas media strain C4. Based on the cyanide detoxification efficiencies results of the four strains, Bacillus mojavensis C3 had the highest detoxification rate and was selected to assess its efficiency to detoxify cyanide in gold mine tailings at different pH (9.5, 10.5, and 11.6) using cyanide as the sole carbon and nitrogen sources. Strain C3 was capable of detoxifying 46.5mg/L of cyanide-containing gold mine tailings at all tested pH ranges at 30oC, 196 rpm after 15 d. The amounts of cyanide detoxified were 87.5%, 84.1%, and 73.5% at initial pH 9.5, 10.5, and 11.6, respectively. The highest cyanide detoxification was observed at pH 9.5. The viable cells growths in the samples were 5.7E+09CFU/mL, 4.9E+09CFU/mL, and 2.7E+09CFU/mL at pH 9.5, 10.5, and 11.6, respectively. Free ammonia concentrations were observed as a byproduct of the biodetoxification process. The residual ammonia concentration in the sample was observed at 0.35 mg/L, 0.33 mg/L, and 0.62 mg/L at pH 9.5, 10.5, and 11.6, respectively. The highest residual ammonia concentration was noticed at pH 11.6. The amount of cyanide removed by mixed culture strains C3 and C4 was 94.6% and showed a residual free ammonia concentration of 2.6mg/L, as biodetoxification byproduct after 120 h. The pure culture Bacillus mojavensis strain C3 and its mixed culture strains exhibited higher potential to detoxify cyanide-containing gold mine tailings at alkaline pH values and could be cultivated to detoxify gold mine effluents at large-scale. Keywords: Bacteria strain, cyanide, detoxification efficiency, gold mine tailings

Jan 1, 2020

By Val Cachic, Harry M. Castrantas, Craig McKenzie

In April 1986, FMC- Paradise Peak Corporation began milling at the Paradise Peak Mine, which is located eight miles southeast of Gabbs, Nevada. The mill processes about 4DOO tons per day of ore through the mill and cyanide leaching circuit. Gold and silver are recovered via the Merrill-Crowe zinc precipitation process. Tailings are routed to a tailings pond located about one half mile southeast of the mill facility. The pond, lined with 60 mil MDPE, was 25 acres at the start of the cyanide detoxification, covers 90 acres and will ultimately cover 180 acres. Solution is reclaimed from the pond and circulated back to the mill.

Jan 1, 1998

By W. J. C. Meynink

In drier regions of the world, total containment of cyanide liquors for rainfalls less than a specific design value is often required by government regulation. For example, in Queensland total containment is required for rainfalls up to 'the 1% annual exceedence probability. In equatorial regions, where rainfall greatly exceeds evaporation, a total containment requirement is unrealistic and this is recognized by regulatory authorities. Regulatory constraints typically require that cyanide concentrations at an agreed downstream compliance point not exceed a specific value more than a specified fraction of the time. While the excessive rainfall prevents total containment, it does provide substantial dilution. This paper outlines a methodology for assessing the distribution of cyanide concentrations at a downstream compliance point in an equatorial region with limited hydrometeorological data. Consider the hypothetical mine environs depicted in Figure 1. The mine is located near the catchment divide and draws its water supply via a gravity line. Tailings from the process plant are piped to a tailings dam on a sub-catchment below the plant site. The objective is to determine the distributions of cyanide species concentrations at a compliance point just upstream of a major settlement to ensure they do not exceed regulatory limits.

Jan 1, 1991

By B Rosemberg, F Lemos, A J. B Dutra

The chemistry of cyanide solutions is complex, this complexity being responsible for the ability to act as complex-forming agents in metal dissolution processes, among them gold and silver. Such ionic species are used in hydrometallurgical processes, in particular in gold extraction and electro-plating. Due to the high toxicity of cyanide, the discard of effluent from processes and/or industries demands rigorous treatment so as to minimise its concentration. Among the conventional chemical treatment of such effluents one can mention SO2/air; biological degradation; oxidation by using hydrogen peroxide; oxidation by sodium hypochlorite, etc. However, the electrolytic recycling process is also promising for cyanide recovery and offers the possibility of recycling it to the aforementioned industrial processes. Such a process does not use additional chemicals but enables direct re-utilisation to the main process aiming at adjusting the cyanide concentration.

Jan 1, 2002

By H. E. Pawson

"COMMON METHODS OF ELIMINATION: The four methods most frequently used to dispose of cyanide wastes are:1. Oxidation2. Dilution with water or with cyanide free wastes3. Acidification and dilution of resulting gas with air4. Alkaline ChlorinationMost operators practice a combination of the first two methods, allowing oxidation and dilution of cyanide waste in tailings ponds. Then, pond effluent is introduced to a stream for further dilution andoxidation which is expected to take care of the cyanide. This method oftreatment does work to a certain degree. Atmospheric oxidation in tailings ponds and in receiving streams chemically breaks down the cyanide radical to form carbon dioxide and nitrogen.2(CN) + 202 2 CO2 + N2The monetary advantage to this method is obvious to the operator but too frequently though, climatic conditions are ignored. Length of winter, and reduced flow of the receiving stream in summer, adversely restricts the result of this combined method. For those of us who rely mainly on dilution it would be wise to remember that 70 million pounds of water are required to dispose of one pound of sodium cyanide (1).The third method outlined involves addition of acid in a closed vessel and venting resulting gas to atmosphere with or without air dilution by mechanical means. Cost, safety and some form of secondary treatment to complete destruction of cyanide remaining in the solution usually make this method prohibitive.The alkaline chlorination method is the one most commonly accepted for treating cyanide bearing wastes since it is felt that cyanide is completely eliminated in this manner."

Jan 1, 1973

By Adrian Smith, Debra W. Struhsacker

13.1 INTRODUCTION Cyanide is, a generic term indicating the presence of the cyanide ion (CN-). Cyanide is a very common, naturally occurring compound produced by many biochemical reactions. Many plant species synthesize organic compounds which contain cyanide in the form of cyanogenic glycosides (Knowles, 1976). For example, trace amounts of cyanide are present in the seeds and leaves of many members of the Rosaceae (rose) family (Kingsbury, 1964). Many common items such as lettuce, maize, sweet potatoes, kidney beans, (Oke, 1969) almonds, and cigarette smoke contain cyanide. As examples, a recent chemical analysis of chocolate-covered almonds measured a total cyanide content of about two ppm (Steffen Robertson and Kirsten, 1987); and the U.S. Surgeon General (U.S. Department of Health, 1964) has shown that cigarette smoke contains up to 1,600 ppm total cyanide. The chemistry of cyanide solutions is complicated because the cyanide ion forms compounds and complexes with many elements. Some cyanide species are highly toxic whereas others are relatively inert and harmless. Molecular hydrogen cyanide (HCN) is the most toxic form of cyanide. Under most conditions, HCN exists as a gas which readily dissipates or reacts with the environment to form less toxic or nontoxic forms of cyanide. Thus HCN is an ephemeral toxin, and many naturally occurring geochemical processes reduce the HCN concentration of a heap system with time. As discussed below, free cyanide includes the two species, ionic cyanide (CN-) and molecular hydrogen cyanide. Free-cyanide toxicity in man, mammal s, and aquatic species is we1 1 documented (Doudoroff, 1976; Ecological Analysts, 1979; Towill et al., 1978). The lethal doses reported for human adults vary with the type of exposure as follows: • One to three mg/kg body weight if ingested; • One hundred to 300 ppm if inhaled; and • One hundred mg/kg of body weight if absorbed. Acute toxicity of free cyanide to freshwater invertebrates ranges from 0.028 to 2.295 mg/l, depending on species and test conditions. Generally, free-cyanide concentrations greater than 0.1 mg/l are expected to kill sensitive species in freshwater or marine environments (Doudoroff, 1976;

Jan 1, 1988

By Adrian Smith, Debra W. Struhsacker

There is now overwhelming evidence that, despite concerns to the contrary, natural degradation of cyanide and cyanide attenuation by hydrogeochemical processes are capable of minimizing or eliminating potential water qua1ity impacts from heap leach systems. A1 though there was some recognition of these data by the regulatory authorities, for example the initial USEPA modification of cyanide standards to an advisory level, many states have codified standards inappropriate to the clearly site specific nature of heap leach operations. As an overview to this problem, this paper will integrate the theoretical chemical data on cyanide with the observed geochemical behavior of cyanide in the decommissioned heap leach environment. The cyanide species that are likely to exist within an abandoned heap leach system will be identified, and the relative toxicity and potential environment effect of these cyanide species will be discussed. These data will then be used to evaluate cyanide detoxification regulations for decommissioned heap leach projects in 14 states.

Jan 1, 1987