Search Documents

By S. A. McGhee

Introduction ASARCO's Ray Operations include an open-pit copper mine in the Mineral Creek Mining District of Pinel County. The district is located in east central Arizona, 132 km (82 miles) southeast of Phoenix, AZ, and 126 km (78 miles) north of Tucson, AZ. The mine lies 8 km (5 miles) north of the Gila River in Mineral Creek Valley, between the Tortilla Mountains to the west and the Dripping Springs Range to the east. The rich copper deposits of the Mineral Creek mining district were first noted by a US Army Officer in 1847. The Ray Copper Company was the first major operation in the area. The company was named after the Ray mining claim, which was one of the earliest recorded claims. After decades of sporadic and unsuccessful mining ventures, the Ray Consolidated Mining Company was formed in 1910. The company introduced one of the first successful block caving operations in the world. In 1933, the Kennecott Copper Corporation acquired the Ray Consolidated Mining Company and continued operation of the mine under the same name until 1943, when the property was renamed the Ray Mines Division of Kennecott. Underground mining continued until 1955, when the mine was converted to an open pit operation. In November 1986, ASARCO Inc. purchased the Ray Mines Division and related facilities from Kennecott. The purchase also included the Hayden concentrator and the Ray Smelter, located approximately 32 km (20 miles) from the Ray Mine. This paper summarizes the 54,400 tpd (60,000 stpd) in-pit crusher and overland-conveying system and the 24,200 tpd (30.000 stpd) copper SAG concentrator and tailings disposal system constructed at ASARCO's Ray Complex - Ray Operations. General description of facilities The Ray concentrator includes a sulfide SAG concentrator, a "relocatable" in-pit primary-crushing plant and overland-conveyor system, a concentrator tailings-disposal system and plant ancillary facilities, The major elements of the project include: • A relocatable Fuller-Traylor in-pit 1524-mm (60-in) x 2261-mm (89-in) primary gyratory crusher at the 442 m (1450 ft) mine elevation. The crushing plant has a nominal capacity of 54,400 tpd (60,000 stpd) of sulfide ore. • A 1524-mm (60-in) wide x 1253-m (4110-ft) long overland belt conveyor, which runs from the in-pit crushing facility to a transfer station serving both the Ray Concentrator and the existing Hayden concentrator railroad load-out facility. • A 1524-mm (60-in) wide x 152-m (500-ft) long stackerbelt conveyor, which delivers a nominal 27,200 tpd (30,000 stpd) of ore from the transfer station to a 23,600 t (26,000 st) live-capacity coarse-ore stockpile serving the Ray Concentrator. • A nominal 27,200-tpd (30,000-stpd) concentrator, including semiautogenous grinding, flotation, copper concentrate filtration and associated plant ancillary facilities. • A tailings disposal system. Flotation tailings are pumped from the Ray Concentrator to a 122-m (400-ft) diam. thickener, located 4.8 km (3 miles) southeast of the Ray Concentrator site. The thickener overflow is pumped to two 76.2-m (250-ft.) diam. concrete process-water reservoirs. The thickener underflow, at 45% solids, is pumped to a new tailings disposal site located at Elder Gulch. • An HDPE-lined temporary-containment area to collect material from Ray Concentrator plant upsets and local storm-water run-off from a 100-year, 24-hour rain event. •A reclaim-water system from the Elder Gulch tailing pond area to the Ray Concentrator. • A 610-mm (24-in.) diam. x 31.9-km (19.2 mile) long fresh-water pipeline from the Hayden fresh-water-well field system to the Ray Concentrator. The overall process design criteria for the new Ray Concentrator is based on a nominal throughput of 27,200 tpd (30,000 stpd) of ore at 90% plant availability. However, based on the maximum performance capacity of the installed grinding equipment, it may be possible to achieve a sustained operating level in excess of 36,300 tpd (40,000 stpd) when processing soft ores. The balance of this paper will cover the major process systems including:

Jan 1, 1995

By Harry M. Conger

Thirty years ago, the U.S. gold mining industry was hanging on by its fingernails. Save for one great mine, the Homestake, most production was coming from copper smelters such as Kennecott and Magma. Even Homestake itself was under great pressure from rising costs and a fixed price for gold. The outlook was dim, to say the least. Today, as it has for most of the past decade, the American gold mining industry stands among the world leaders in production, and in the development of mining and mineral processing technology. What caused this dramatic change? Obviously, the freeing of the gold price was a major factor, as was the decline in South African production, but these events alone could not have created the U.S. strength we see today. It was technology, investment, and the determination of miners to build an entirely new industry that were the indispensable ingredients. The U.S. Bureau of Mines, with great foresight, had begun the research that led to heap leaching before the gold price began to rise, and Newmont had committed to build a small mill at Carlin, a move then considered quite risky. From that point, the U.S. gold mining industry was placed on lower-grade ores then being found in Nevada and elsewhere, but it was soon apparent that we would have to develop new technologies to deal with more refractory ores, carbonaceous as well as sulfide-bearing. This is now being done with considerable success. Despite its success, or perhaps because of it, the gold mining industry has come under pressure from various groups who characterize their activities as motivated by "public interest." The public interest they refer to properly include the health and safety workers and impacted communities, as well as protection of the environment, and with these concerns we miners have relatively little argument. In fact, we consider health, safety and the environment among our highest priorities, and not just because regulations may require us to do so. The argument, however, is not about the regulation of a viable mining industry, it is about a well-organized movement to attack and condemn mining in the media and to misrepresent its importance to the Nation and its willingness to accept responsible regulation. Once largely local or regional, the interest groups to which I refer are now quite large, national in scope, and even becoming international. This trend, taken together with finances raised from their dues and contributions, would make the interest groups formidable adversaries for mining, but their grip on the media enormously magnifies their influence. Unfortunately, it also makes possible the wide dissemination of incomplete, incorrect or slanted information. I am not here to "bash" the interest groups. On the whole, I believe that many of them have made positive contributions to society. As conservationists, however, I question their authority to make, or foster, decisions about which American industries and communities live and which die. To illustrate, I would like to present for your consideration the problem of cyanide, one of the issues over which the gold mining industry is most threatened. CYANIDE-POISON OR MIRACLE SOLVENT? Let me get this out of the way right up front: cyanide in most of its chemical forms is toxic. In some forms it is also listed as a carcinogen. These are adverse characteristics cyanide shares with a considerable number of industrial chemicals, including some that are widely used without the stringent regulations already in place for the mining uses of cyanide. In these uses, by the way, the risk to humans comes from direct ingestion of cyanide or cyanide-bearing solutions, or from the accidental acidification of solutions leading to release of hydrocyanic acid gas. That these risks are under control in mining can be seen from the fact that, in modern U.S. practice, there has never been a documented fatality attributed to cyanide! Because of its toxicity, cyanide cannot enter and be accumulated in the food chain. It can, however, be a threat to birds and animals that ingest cyanide-bearing solutions. Protection against this is, quite properly, a responsibility of individual mining operations, and considerable sums are spent each year to prevent or reduce bird and animal exposures. It should be evident, though, that many human activities, including highway traffic, windmills, use of pesticides and the like, result in bird and animal losses. Mining's use of cyanide, and the measures taken to protect birds and animals, should be considered in context. Cyanide must be kept out of surface streams and groundwater, and existing regulations mandate this. Any cyanide residues left in leach heaps, waste dumps and disused facilities must be eliminated, and we have proven technologies to do this now, just as we have means to detoxify tailings prior to disposal. The gold mining industry decries those rare instances when irresponsible operators fail to deal with contamination, and agrees that they should be held responsible. We do not agree, however, that the great majority of responsible companies should be punished, in advance, for accidents that have never happened. So much for the poison, what about the "miracle solvent?" Is that an overstatement? Well, consider the fact that gold has been called "noble" from earliest times, because it does not oxidize under atmospheric exposure, and that it appeared to the ancients to be utterly insoluble. Later generations of scientists did discover that it could be dissolved, but only by a combination of acids so potent that it became known as aqua Regia. Later still, it was found that chlorine would also dissolve gold, and attempts were made to base commercial processes on this, without a great deal of success. It remained

Jan 1, 1995

By C. J. Webb

Abandoned uranium mines in the southern Black Hills of South Dakota were sampled for uranium, radium, and rare earth elements during 1992 and 1993. Analyses of water samples from several shallow ponds in the mine pits showed pH values between 3 and 4 with uranium concentrations between 1600 and 2600 ppb. Rare earth elements and their respective isotopes were analyzed with an inductively coupled plasma mass spectrometer and were referenced to a shale normalization pattern. All samples showed an enrichment in the middle rare earth elements. Rare earth levels often were greater than 0.2 ppm. At one site, the concentrations of lanthanides were 150,000 times above background levels. While the southern Black Hills have long been known for rich uranium ore deposits, these analyses show that significant levels of rare earth elements also are present, indicating that the potential exist for future development.

Jan 1, 1995

By Ronald M. Fedrick

The microtunneling project for the State of Hawaii's Natural Energy Laboratory (NELH) facility in Kona, Hawaii, was awarded to Nova Group Inc., Napa, California. Nova has developed both microtunnel and deep pile cofferdam experience. Both of which would be required for this project. The project was designed by Makai Ocean Engineering of Honolulu as a continuation of the Ocean Thermal Energy Project (OTEC). The world's first OTEC plant has been successfully operational at NELH since 1982 netting approx 50 kw of usable electric power from a gross generation of 210 kw. A second plant designed to draw 39°F cold water from 3,000 ft below sea level and produce a gross output of 1 mw with a net 500 kw of usable power required 2 - 54 in. finished diameter pipelines. An ongoing problem with earlier offshore pipelines has been the damage to the near-shore pipes within the surf zone. The necessity for a deeper connection between the land based pipe and submerged sea pipeline was obvious. Earlier pipelines had been drilled and shot through the shoreline. This process was only practical at shallow depths. Makai Ocean Engineering and the NELH scientists looked at different methods to get the pipeline through the shoreline at a depth of 80 ft below sea level. Initially, the direction drilling method was proposed as the most potentially practical method. A contract was awarded and various attempts were made to complete a successful

Jan 1, 1995

By D. S. Bird

The Kennecott Utah Copper Modernization Project, initiated in 1986, was directed to provide an expansion and modernization of mining and process facilities at the property's Bingham Canyon Mine and ore concentrators. Major components in the project included installation of an in-pit ore crusher, transfer conveying system, and construction of a new copper ore concentrator with a design capacity basis of 70,000 tonnes/day. The Copperton Concentrator was commissioned in February 1988. A principal feature of the plant is the grinding circuit, comprised of three identical lines, each consisting of a 10.37 m (diameter) by 4.57 m (length) Semi-Autogenous Grinding (SAG) mill and two 5.54 m (diameter) by 8.62 m (length) ball mills. The SAG mills are driven by two variable-speed 9,000 kW DC motors coupled through a clutch-pinion gear-ring gear assembly. The ball mills are driven by 4,125 kW synchronous motors coupled through a typical clutch-pinion gear-ring gear system. The expansion and particularly the Copperton Concentrator performance was so successful that by early 1989, management began examining options to further expand production capacity. With regards to the concentrator, numerous alternatives were considered, ranging from installation of a grinding line similar to one of the existing lines, to a "super" line consisting of a 12.8 meter (diameter) SAG mill and a 20,000 kW motor with a capacity of 50,000 tonnes per day. The technical and economic analysis of the various scenarios indicated that one "large" 11.0 meter (diameter) by 4.88 meter (length) SAG mill with a production capacity of 32,000 tonnes per day and a 12,000 kW drive would be optimum. The key question to be answered in the project was whether to continue with the pinion-ring gear combination, or install a gearless drive. The following paper outlines many of the items that were evaluated in the mill selection process followed by actual plant performance, and a discussion of ongoing plant continuous improvement projects.

Jan 1, 1995

By Corale L. Brierley

Bacteria, algae and fungi react to heavy metals in their environment by immobilizing, mobilizing and/or transforming metals. Microorganisms carry out these changes by (1) precipitating metals outside of the microbial cell, (2) binding and complexing metals to the outside of the microbial cell's protective coating, (3) accumulating metals inside of the microbial cell, or (4) transforming metals by oxidation, reduction, methylation or demethylation. Most of these mechanisms are operative in constructed aerobic and anaerobic wetlands for metal's remediation. Several more advanced biotechnologies for metal's removal from aqueous streams have been introduced, but have not been widely accepted commercially.

Jan 1, 1995

By F. A. Renninger

Limestone and dolomite are the most common rock types mined and quarried as industrial minerals in the United States. In 1993 over 720 million tons of limestone and dolomite valued at over 3.1 billion dollars were extracted and consumed throughout the nation. While the greatest volume of this vast production is used as aggregate for construction purposes, few people realize how critical limestone and dolomite are to our food chain and our national goals of clean air and water. Limestone, including dolomite, can truly be called nature's gift to the environment. Without a reliable, economical source of limestone the quality of our environment would be severely comprised and the standard of living of our citizens dramatically reduced.

Jan 1, 1995

By J. A. Cole

The mill project at Lone Tree was commissioned in October, 1993, followed by the commissioning of the autoclave pressure oxidation circuit in February, 1994. Discussion of the first year of milling operations at Lone Tree is presented. The mill is currently operating above the design rate of 2,267 mt/d (2,500 st/d). Both phases of the start-up were essentially trouble free. The few problems that were encountered and the respective solutions are addressed.

Jan 1, 1995

By Richard P. Killmeyer, Carl P. Maronde, W. W. Wen, Peter J. Suardini

Under a cost-shared Department of Energy contract, awarded as part of the Coal Preparation Program&apos;s High Efficiency Preparation subprogram, Custom Coals International will be installing and testing a 227 kglhr micronized-magnetite cycloning circuit in PETC&apos;s Coal Preparation Process Research Facility. The project includes the design, construction, testing, and decommissioning of a fully integrated circuit complete with feed coal classification to remove the minus-30-micron material, dense-medium cycloning of the 300 by 30 micron feed coal using micronized magnetite (<10 microns), and medium recovery via drain & rinse screening and various stages and types of magnetic separation. This paper will describe the micronized-magnetite beneficiation technology and the scope of work for this project including an update on the status of the project, the circuit, and the proposed test plan.

Jan 1, 1995

By B. Nyman

A lot of work is in progress to improve copper recovery by leaching-solvent extraction-electrowinning (L-SX-EW). At Outokumpu the focus of attention is on SX equipment development as a result of which a new mixing-settling technology, the Vertical Smooth Flow (VSF) has been introduced. Using helical stirrers in the VSF mixers a more gentle and uniform contacting can be obtained than in the mixing compartments of the low-profile design. The benefits of Outokumpu&apos;s new approach are an essential decrease in organic losses and in aqueous in organic entrainments. Separate pumping using a smoothly pre-contacting "Dispersion Overflow Pump" (DOP) is a key feature of the VSF design. The scale-up of this pump as well as the VSF mixers are shown to follow simple mathematical relationships which also have been confirmed by full scale experiments.

Jan 1, 1995

By S. B. Patton, T. Novak

To fully utilize a ventilation simulator as a planning and production tool, the network database must keep pace with mining progress. By using AutoCAD&apos;s™ attribute-definition function, the branch data and node coordinates can be stored as part of the branch-diagram file and updated with the drawing. Attributes are drawing entities that contain text which can he extracted in a standard spreadsheet format or as an ASCII text file. The data can be subsequently loaded into a ventilation simulator. This paper presents the methodology for using AutoCAD&apos;s™ attribute feature in a ventilation simulation format.

Jan 1, 1995

By Samuel A. Rasmussen

Lead anodes are used in commercial copper electrowinning operations, yet there is no method to calculate anode life. To be discussed in this paper are operating characteristics of rolled plate (Pb,Sn,Ca) alloy anodes at Morenci&apos;s electrowinning tankhouse along with fundamental operating conditions and how the anode reacts to these conditions. These include anode maintenance, electrolyte temperature and viscosity, cobalt concentration, and manganese concentration. Also to be discussed are anode substrate characteristics under normal operating conditions and how the corrosion rate is affected by changes in operating conditions.

Jan 1, 1995

By Gilbert A. Bonforte, Hugh P. Caspe, Tracy K. Lundin

The Narragansett Bay Commission (NBC) Combined Sewer Overflow Abatement Program is a major effort to address and mitigate discharges from combined sewer overflows in the Providence, Rhode Island area. The proposed system consists of three deep rock tunnel segments totaling 17.8 km (11.1 miles) in length that will provide 860,000 cu m (227 million gal) of storage at depths up to 99m (325 ft). This paper discusses 13.5 km (8.4 miles) of 6.64m (21.8 ft) finished diameter tunnel, four construction shafts, 19 dropshafts and one large diameter pump station shaft tapered from 1 5.2m (50 ft) at the surface to 27.4m (90 ft) at depth. All facilities are in preliminary design.

Jan 1, 1995

By Terrence Chatwin, Michael Sweeney, Steve Accardo

Sutter Gold Venture excavated an exploration decline into a mineralized zone in the Sutter Creek gold mining district. Delays in obtaining the conditional-use permit resulted in 7 to 10 million gallons of water accumulation in the decline containing elevated dissolved arsenic. Sutter received a permit to land apply the water after reducing the arsenic concentration to 0.05 mg/L. Initially the water was treated by co- precipitation arsenic with ferric hydroxide. Operational difficulties of this treatment system resulted in Sutter pursuing alternative treatment methods. The activated alumina adsorpting was selected due to its flexibility and ease of operation. Operating and maintenance data and costs will be presented.

Jan 1, 1995

By Barry Cloutt

Western Mining Corporation Limited owns and operates the St Ives Gold Plant located near Kambalda, approximately 90 kilometres south of Kalgoorlie in Western Australia. Production commenced in March 1988 at a design capacity of approxi­mately two million tonnes per year. The plant was quickly expanded as a result of new ore discoveries in the district and has been processing ore since 1993 at the rate of three million tonnes per year. The plant has recovered over 50 tonnes of gold since the operation began, The plant was able to maintain acceptable recoveries throughout the plant expansion phases. Further gains in recovery were possible since there was still free gold in the tailings after approximately 24 hours of leaching. Testwork carried out on prospective orebodies showed that some contained considerable quantities of free visible gold, while others were seen to be semi­refractory using a conventional grind - leach circuit. Alternative treatment techniques were considered because a substantial amount of revenue was lost with the treatment of these ore bodies using conventional milling techniquies. The basis for all the investigations was to maximise the gold recovery from each orebody while minimising the effective cost per ounce of gold produced,

Jan 1, 1995

By K. R. Weller

In recent years, a variety of new or substantially modified grinding machines have been offered to the mining industry with claims of improved performance relative to standard grinding machines especially rod and ball mills. The incentive for developing such new machines is high, because costs associated with grinding are a very substantial part of the total costs of processing run-of-mine ore, and gold ores are no exception in this regard. The incentive is also high because of the very low conversion of input energy to comminution energy in most tumbling mills. If the most energy-efficient means of mechanical size reduction is slow compression of single particles, then this energy amounts to only about 3% of that used in tumbling mills. It would seem, therefore, that there is a huge potential to do better. This paper examines three types of grinding machine for which claims of higher energy utilisation ( amongst other beneficial claims) have been made, namely the high pressure grinding rolls, the vibrating drum mill and various styles of stirred mill. It presents evidence concerning the claims, examines the range of particle size and particle size reduction over which benefits might reasonably be expected to accrue, discusses the major issues in contention and briefly describes the research the CSIRO Division of Minerals has in progress, both independently and collaboratively, the latter mainly with the Julius Kruttschnitt Mineral Research Centre (JKMRC) via the Cooperative Research Centre for Mining Technology and Equipment (CMTE) and the Australian Mineral Industries Research Association (AMIRA). There are many criteria which may be chosen to assess relative performance of grinding machines. Those used below are:

Jan 1, 1995

By Norbert Patzelt, Hans Knecht, Wolfgang Baum

Future ore reserves of major gold producers in North America and elsewhere will consist of refractory gold ores. About 60 % of the current U.S. gold production is mined in Nevada. Several of the large gold operations in this state indicate that 40 to 90 % of their future ore feeds will contain refractory gold. To compound problems, average head grades for refractory U.S. gold ores have fallen from 8 - 9 g/mt to about 4 g/mt by 1991. In Latin America, 52 % of the gold operations will require milling for optimal recovery. Deeper reserves are, like in North America, refractory. Particularly in hard, (semi)refractory sulfide ores, many operations may experience substantial decreases of gold recov­ery. For example, Martins et al. (1991) report that at an Austra­lian mine, sulfide ore treatment led to 4 - 10 % lower gold reco­veries as the work index increased from 8 kWh/t to 14 kWh/t and the grind coarsened. Many refractory ores should actually be classified as semirefractory since a fine sulfide fracturing and liberation would make 80 - 90 % of the gold cyanide leachable. However, conventional comminution is often prohibitively expensive for these ore types.

Jan 1, 1995

By Jacques Monette

Gold and silver cyanide complexes are presently desorbed from activated carbon by means of hot caustic elutions. These solutions may or may not contain additional sodium cyanide. There are several parameters which affect the rate of stripping. Some of these include pH, ionic strength, and tempera­ture. Stripping is conducted in recirculating (ZADRA) or once through (AARL) circuits. This paper describes the development of a new chemical eluant which increases the rate of stripping of both gold and silver cyanide complexes from carbon. Two case history applications are described.

Jan 1, 1995

By John Batty, Rennie Stallknecht, Dave Dew, Rennie Marais

GENCOR was contracted by Lonrho Plc of London to design a treatment plant for the benificiation of ores from the Amantaytau Goldfields in Uzbekistan (CIS). The testwork required for determining the design parameters was conducted at GENCOR Process Research in Randburg South Africa, on large bulk samples of ore shipped from the CIS. The initial milling and flotation testwork was designed to both optimise the conditions for maximum gold recovery, and to provide flotation concentrate for subsequent testwork. The concentrate produced was fed to a pilot scale BIOX® plant, and at the client's request a portion was shipped to specialists in roasting and pressure oxidation technology for comparison. Besides the testwork conducted at the GENCOR Process Research Laboratories in South Africa, the client also requested that the testwork be repeated at the Ingichki Research centre in Uzbekistan to demonstrate to their CIS joint venture partners that the results obtained in South Africa are reproducible and to demonstrate the ease of operation of a BIOX® plant. Pilot scale equipment was air freighted to Ingichki where the results of the testwork obtained in South Africa were successfully duplicated. BIOX® technology was shown to achieve higher gold recoveries than either roasting, whole ore roasting or pressure oxidation.

Jan 1, 1995

By David Martin Menne

In a small tank, slurry is passed through the high shear impeller zone with small time intervals, and a large proportion is regularly exposed to air at the surface, and at relatively high shear rates. This accounts for significant differences in the performance of large and small tanks. It is preferable to derive data where possible directly from an operating plant rather than applying data generated in small tanks where allowances must be estimated for the above differences [and where slurry aging and often substantial cooling compared to hot freshly milled ore further distorts results]. Various measurements have shown that many gold slurries can suffer extreme variability, as streamers of bypassing material or boules of hold-up periodically condstitute the instantaneous discharge from a tank - the relatively high Yield stress of slurries [around 1 to 10 Pa] causes very incomplete homogenization of slurry in any tank, the worse the larger the tank and the more viscous the slurry. To provide a background for this subject, this monograph presents leach and adsorption models based on the fundamental physics and chemistry of these processes, and includes quantitative discussions of factors which can lead to deviations on scale-up. The Throughflow model which avoids the need for such alowances is then presented, as well as a Computer Programme applying this model, and which allows direct calculation of the effects of:

Jan 1, 1995