Search Documents

By J. E. Brownhill

After being closed for three years, Specialty Minerals Inc.'s Port Inland limestone facility reopened in the spring of 1992 as a commercial limestone producer. In 1990, Specialty Minerals, a division of Pfizer Inc., bought Port Inland's reserves and equipment from Inland Steel because of the strategic value of the limestone for the production of precipitated calcium carbonate (PCC). Specialty Minerals' project team faced many challenges in reconstructing the Port Inland facility. Many traditions and norms had to be overturned to achieve the productivity, flexibility and cost necessary to survive in today's competitive minerals environment. Port Inland's history Inland Steel built Port Inland in 1930. It was operated as a captive source of metallurgical grade limestone for the steel industry until its closure in 1989. The facility is located in the Upper Pen¬insula of Michigan on the north edge of Lake Michigan. Operations consist of a deep water port facility with crushing, screening and stockpile storage for 453 kt (500,000 st) of finished product at the port. Ninety-nine percent of the stone is shipped by lake boat to ports within the Great Lakes. The operation is unique in that both metallurgical dolomite and limestone are produced on site.

Jan 1, 1994

By D. R. Forshey

Although the United States has the world's largest coal reserves, most of those reserves will require underground mining. Unless underground injury and fatality rates are reduced, the number of disabling injuries and accidental deaths will grow as coal production increases. The Bureau's Mining Research Program, designed to reduce the exposure of workers to hazards while improving productivity, is described. Major program thrusts are 1) re- moving the hazards or removing miners from the areas in which hazards exist, 2) developing ways to improve management decisions and mining skills so as to reduce the incidence of situations requiring human involvement in hazardous, emergency, or corrective tasks, and 3) improving, or at least maintaining, productivity so that both the tangible (dollar) and intangible (human) costs are reduced. In these ways, projected demands for coal can be met using resources without an increase in human suffering.

Jan 1, 1987

By Trevor A. Moss

Installation of equipment and structures at mines often requires mine planners to evaluate unique loading and operating conditions. Consideration of these unusual features is required throughout design and construction and into operation. Most planners understand the necessity of employing sound civil, structural and mechanical engineering techniques to design these structures and equipment. However, the influence of geotechnical factors on the overall progress of construction and operation is less appreciated. Mine operators routinely perform exploratory drilling to define ore deposits. These exploration activities can be extensive and often include provisions for assessment of subsurface conditions as they relate to the mining operation - requirements for ground support. All of these factors are important to the economics of the mine and are well justified. Surface facilities are provided to access and service the mine, and they play an important role in the successful development and operation of a project. Headframes, hoist foundations and shaft collars, in particular, are examples of unique installations encountered at underground mine sites. The design and above-surface behavior of these facilities can be analyzed with the usual fundamental engineering practices employed throughout the engineering professions. However, near surface exploration for the purposes of assessing soil and rock conditions for foundations is often given a reduced priority and less consideration. This article provides an outline of the benefits and importance of performing such exploration. References here relate particularly to shaft headframes, hoists and shaft collars. But the issues raised apply equally to other installations of a similar nature, including milling equipment.

Jan 1, 1992

By Caren Caldwell, Leslie Thompson

1.1 Biological Process Description Pintail Systems, Inc. (PSI) has developed and in partnership with their clients in the mining industry has applied biological remediation processes for detoxification of spent ore and process solutions from heap leach operations. Contaminants that are treated to mine closure levels or drinking water standards include cyanides (weak acid dissociable and total cyanides), thiocyanate, nitrates and heavy metals. Biological processes are both site-specific and ore-specific processes. PSI specializes in isolating indigenous microorgan­isms from spent ore and process solutions and augments them in the laboratory for enhanced bio-detoxification in the field. Bioaugmentation in the lab is a key to successful heap bio-detox in the field. In PSI's bioaugmentation processes native microorganisms are isolated from the spent ore environment and are tested for contaminant remediation capacity. A majority of the indigenous microbes will be tolerant of the spent ore environment but will not contribute to contaminant metabolism. Indigenous enrichment or biostimulation of these non-working microbes by adding trace nutrients can competitively inhibit the working microbes. For this reason PSI focuses on the bioaugmentation process where non-working microbes are discarded and the working population is enhanced through stress, mutation and exogenous enrichment before it is re-introduced to the heap and process solutions.

Jan 1, 1997

By Melvin E. Poad

INTRODUCTION The placement of concrete by means of pumping is one of the fastest growing practices in the construction industry and is widely used in mining applications. In¬troduced in the United States in 1933, this method has been adapted to many aspects of the industry, especially where space for equipment is either limited or inaccessi¬ble. Concrete pumping offers many advantages over other methods of placement. Using pumping equipment, the concrete mixture can be transported in a single operation from a central mixing site to numerous forms in many remote locations, eliminating the need for rehandling the mixture and reducing the labor costs to a minimum. Pressurized pumping provides an extra mix¬ing and blending step, resulting in concrete of improved uniformity and greater density. In turn, this produces high compressive strength and increased durability. Various placement defects can be reduced or pre¬vented by pumping. The steady and even flow of the concrete minimizes the form distortion and delays caused by vibration problems that are common to fast dumping of the concrete mixes. Segregation, planes of weakness, bleeding, and surface faults are diminished considerably. Perhaps the greatest advantages of concrete pump¬ing are the distances and volumes that can be handled. Depending upon the equipment used, pumping rates of from 8 to 115 m'j/h (10 to 150 cu yd per hr) can be achieved, with a horizontal range of up to 460 m (1500 ft) and a vertical range of up to 140 m (450 ft). Theoretically, almost any concrete mixture could be pumped. However, consistency is an important consid¬eration for efficient operation. Mixes that are too wet, too dry, too hard, or poorly graded can cause difficulties that increase the costs. Similarly, mixes containing aggregate material that is over the maximum size or that is porous and highly absorptive can also result in diffi¬culties and increased costs. For the best efficiency, the mix formulation must have a well-graded sand and aggregate combination, with enough fines to provide flowability. If additional water is required for pumping, additional cement must be used to meet the design criteria of the structure. Each pump manufacturer can provide recommended mix formulations for the specific equipment furnished. Since the 1950s, many improvements have been made in pumping technology. Originally, only rigid steel pipe of 168 to 245 mm (6.625 to 9.625 in.) diam was used; today, both rigid steel pipe and flexible conduit are available in diameters of from 76 to 203 mm (3.0 to 8.0 in.). Improved pumps have been developed, and the introduction of power-coordinated booms has in¬creased the versatility of concrete pumping. The older and more conventional placement methods can no longer compete with the flexibility, efficiency, and econ¬omy of the pumping method, and continued research and development can only improve the system and expand its use throughout the mining industry. PUMPING EQUIPMENT The three major types of concrete pumping units currently available are the piston pumps, the pneumatic pumps, and the squeeze-type pumps. Table I provides a comparison of capacities, horizontal ranges, and vertical ranges for pumps of all three types. Piston Pumps The simplest of all concrete pumps are the piston¬type pumps; they are available from many manufac¬turers. As shown in Fig. 1, each unit consists of a

Jan 1, 1982

By J. W. C. Wong, S. D. Miller, J. J. Jeffery

Pre-mining identification of acid forming mine and waste materials is of concern to the mining industry because of the potential for the generation of acid mine drainage, acid rock drainage, and soil acidity problems. Accurate identification of acid forming material is essential for developing appropriate waste management strategies to reduce environmental problems related to acid generation from sulphide containing wastes. The acid-base accounting procedure, in its various forms , is commonly used for pre-mining screening of mine and mine waste materials. The procedure is generally effective when used and applied correctly but is prone to incorrect interpretation of results which can have significant financial and environmental implications. This paper examines the acid-base accounting Procedure and the possibility of misuse of this method with special emphasis on the sampling method, the sulphide forms, the acid neutralization capacity, and the interpretation of results. Data from numerous coal, base metal, and gold mining operations are used to illustrate the application of the acid-base account. The data base indicates that overall, approximately 1/3 of all waste generated by mining and mineral processing is potentially acid forming indicating the need for correct identification and management. Problems associated with simple application of 'absolute' acid-base criteria for classifying acid forming material are highlighted and the need for developing site specific or 'relative' criteria is discussed and illustrated by case study.

Jan 1, 1991

By Peter J. Huck, Yoginder P. Chugh, M. Jennings

INTRODUCTION Large areas of the United States coal reserves have been undermined by room-and-pillar mining over the past century. These abandoned mines generally cause subsidence of the ground surface many decades after mining. Reports from England (1) where there is a longer history of room-and-pillar mining indicate that mines abandoned two centuries ago may still be causing subsidence, and causing surface destruction to urban areas or farm lands that have been developed in the interim. The devastation wrought by subsidence, both in terms of property loss and societal disruption is enormous. The authors discuss here the methods by which subsidence in abandoned mines may be controlled. Two distinctly different subsidence control technologies have been developed in the U.S. for abandoned coal mines. These are referred to as (1) Point Sup- port methods, and (2) Areal Backfilling. As the names imply, point support methods are used to protect individual structures, or even individual foundation elements of structures, whereas areas backfilling techniques may be applied to protect entire neighborhoods or urban districts hundreds of acres in extent. Both point support methods and areal backfilling have specific sub-categories of techniques that may be applied under different conditions as appropriate. POINT SUPPORT METHODS Point support methods are characteristically employed by civil engineers chartered with the design of a new structure or the protection of an existing structure. The subsidence control measures are only a part of a larger project, the safety of which must be assured to a degree of near certainty. The costs of point support methods involve a large number of bore-holes and the use of expensive materials in relatively small quantities. There exist several dozen point support methods, which operate either to support the underground cavities, controlling subsidence, or to isolate the structure from the effects of subsidence if it should occur. The latter methods usually involve deep foundations through the mine opening supporting the structure on the underlying strata. Our concern will be with the former method to support underground cavities to prevent subsidence. Gravel Columns and Associated Methods Gravel columns may be placed in the mine opening using the methods shown in [Figure 1]. Boreholes are drilled through the mine strata, and gravel poured down the borehole to form a pile on the mine floor. When the tip of the pile contacts the mine roof, it is rodded down to spread the pile, and permit additional gravel to be placed. The objective is to place as much gravel as possible in the mine opening, and to achieve firm contact with the mine roof. The gravel pile acts to reduce subsidence by three mechanisms. The filling of a significant fraction of the open mine volume reduces the amount of potential subsidence simply by killing open volume within the mine. In effect, the extraction ratio has been reduced by introducing the volume of gravel. The toe of the gravel pile abuts against nearby pillars, providing lateral support and protection against pillar deterioration. In effect, the height of the pillars has been slightly reduced by burying their lower portions. Finally, some direct support is provided to the roof strata, reducing the roof span and enhancing stability. The gravel column method may be used in a variety of applications, and with materials other than gravel. For example, gravel columns may be placed in a close line around the perimeter of the building to form a continuous gravel wall. The interior of the site may then be completely filled with sand, slurry or other material. Alternatively, a lean concrete may be used in place of gravel, so that the piles achieve significant structural capacity. The grout column, shown in [Figure 2], begins with the installation of a conventional gravel column which is placed around a grout pipe that extends through the borehole into the mine opening. When the gravel column is in place, portland cement grout is injected in stages. At each stage, sufficient grout is injected to fill the interstices in the gravel to build a column perhaps two meters in diameter and a meter tall. The group pipe is then raised one meter, and after the previously injected grout has set, the next stage of grout is injected. The process builds a column of grouted gravel to the

Jan 1, 1982

By Edmundo Tulcanaza

Increasing exploration costs and the need to reduce the time-frame from exploration to production presently demand formalized procedures to assist exploration planning and reserve analysis. Exploration planning is basically required to select the most cost-effective drilling/sampling program, and to flag the needs for data of greater relevance and reliability. Reserve analysis is necessary to determine the sensitivity of grade-tonnage relations, and to clarify the economic implications of mining when alternative technical choices are to be considered.

Jan 1, 1982

By Dennis Molvik, Omar Fulton, Chris D. Breeds, Don Gonzales

The Tolt Pipeline No. 2, West Snoqualmie Valley project, is part of a water supply project linking the Tolt reservoir in East King County to the City of Seattle through a nominal 2.13 m (7-ft) inside diameter conveyance. Receipt of the National, 2002Microtunnel Award provided recognition of the many challenges overcome by this project. Baseline conditions revealed in the Geotechnical Documentation included over-consolidated glacial deposits, landslide and alluvial deposits, artesian water, boulders up to 36-in in diameter, logs, heaving sands, and liquefiable soils beneath the river. Schedule constraints associated with setting the shafts in the floodplain of a salmon bearing river and the fickle performance of the river during those times it was not supposed to flood added to the challenge.

Jan 1, 2003

By A. T. Iannacchione

Recent fatal injuries occurring during pillar retreat coal mining call for better identification of the hazards and recognition of risks. Ground control hazards associated with room-and-pillar retreat mining tend to intensify with depth, requiring extra precautions in the form of additional controls. In many locations these activities are further complicated by local complexities often associated with unique or novel circumstances, such as over-mining or under-mining. One technique recently studied by NIOSH, Major Hazard Risk Assessment (MHRA), may help mine operators to mitigate the risks associated with pillar recovery operations. The approach was trialed at two underground coal mines in southern West Virginia that are currently practicing pillar recovery. The first step in the MHRA process involved reviewing the segments or parts of the pillar extraction mining system and identifying associated hazards and threats to the operation. Some of the high risk hazards at these two sites included: ? Rock fall during pillar extraction covers equipment and injury occurs during recovery operations, ? Rock fall above the roof bolt horizon, potentially injuring ? workers and/or requiring recovery action, ? Rib fall under deep cover, potentially injuring workers, and; ? Strata instabilities associated with subsidence of the interburden due to simultaneously mining two seams in close vertical proximity to one another. The mines? risk assessment teams then considered each threat individually in order to systematically identify potential unwanted events. The top unwanted events were examined individually using structured risk analysis tools. The output from the process includes a list of priority existing controls for monitoring and auditing, and a second list of potential new controls. These controls consisted of: Examples of best practices, ? Enhanced communication, ? Implementing standard operating procedures (SOP), ? Protocols for emergency response actions, ? Effective layouts, ? Efficient monitoring, and; ? Successful audits. This paper documents the process as it unfolded at the two mines, and analyzes the strengths and weaknesses of the MHRA technique as it applies to pillar recovery operations. This work was part of a larger NIOSH research project. NIOSH was responsible for: 1) facilitating the risk assessment process known as Major Hazard Risk Assessment (MHRA), 2) documenting the risk assessment process, and 3) providing mine management with a written draft summary of the risk assessment process. The results of the risk assessment represent the thoughts and opinions of the individual risk assessment teams and should in no way be construed as an endorsement of the risk assessment output by NIOSH or the University of Pittsburgh.

Jan 1, 2009

By K. N. Santini

The evaporite deposit at Searles Lake consists of alternating brine-saturated saline beds and saline-bearing mud beds. Three major subsurface brine-saturated saline horizons have been identified by private companies and the U.S. Geological Survey. They have been termed, from bottom to top, the Mixed Layer, Lower Salt, and Upper Salt. The important water-soluble components (Na, K, Mg, CO3, HCO3 , SO4, Cl, and B407) are either in brines or have combined to form the following minerals: halite, hanksite, trona, nahcolite, burkeite, borax, thenardite, northupite, sulfohalite, glaserite, etc. Kerr-McGee Chemical Corp., the current operator at the lake, selectively pumps interstitial brines from each of the major horizons to feed its three chemical plants. As the pumping continues, brines are continuously replenished within the deposit by dissolution of the minerals through natural recharge or artificial fluid injection (solution mining). The brines are processed to produce a variety of chemical products, which include sodium carbonate and sulfate, potassium chloride and sulfate, sodium borate, and boric acid. The Anaconda Minerals Co. has been evalua¬ting potential domestic trona acquisition since 1981. We have evaluated various properties in the Green River, Wyoming trona district, and Owens Lake and Searles Lake in southern California. In 1983, we purchased with our joint-venture partner, Leslie Salt Co., the southern portion of Searles Lake from Occidental Petroleum Corp. Since mid-1983, Anaconda has been conduct¬ing a small exploration-drilling program at the property. The initial core holes were drilled along and adjacent to the existing access road. In 1984 we used an all-terrain drill rig to gain access to drill sites on the playa where no roads exist. The use of this equipment proved to be highly successful. The drill program consists of coring to an average depth of 450 feet and collecting brine samples from potentially commercial horizons. The brine samples are collected by setting a packer and swabbing the hole. The core is logged and split lengthwise; one-half is submitted to our Tucson Geoanalytical Laboratory for semi-quantitative mineralogy by X-ray diffraction and the following suite of chemical analyses: Na, K, Mg, C03, HCO3, SO4, Cl, B407, Li, H20 insolubles, and acid insolubles. Additional test work for selected core samples will include effective porosity and horizontal permeability determinations. The brine samples are subjected to the same suite of chemical analyses (minus insolubles) as the core samples. In addition, specific gravity is also determined. Both cross sections and isopach maps are being constructed. The hydrological characteristics of the potentially commercial horizons are also being investigated.

Jan 1, 1987

By T. P. Weldum, W. Conger

"The objective of the study conducted by the authors is to determine what media size(s) addition will maximize any given plant ball mill’s grinding efficiency (Fig. 1). The functional performance parameters “mill grinding rate through the size of interest,” and “cumulative mill grinding rates” from both plant and smallscale tests are applied to this task. A plant media sizing methodology, and industrial case studies, are provided.BackgroundA previous article (“Ball mill classification system optimization through functional performance modeling,” Nov. 17, McIvor et al., 2017, Mining Engineering) described circuit classification system efficiency (CSE), equal to the percentage of coarse (plus circuit P80 target size) material in the ball mill. It can be measured and then increased through pump and cyclone adjustments. By so transferring the application of ball mill power from fine (minus P80 product size) to coarse material, circuit efficiency is increased and overgrinding is decreased.The other factor that determines overall circuit efficiency is how well the power that is applied to the coarse material grinds it. This is affected by design and operating variables like the media sizing and mill percent solids. From circuit functional performance (McIvor et al., 1990):Circuit production rate of new fine material (t/h) = Power applied to coarse material (kW) x Mill grinding rate of coarse material (t/kWh) (1)The power applied to coarse material is the total mill power multiplied by the CSE. Therefore:Circuit production rate of new fine material (t/h) = Total mill power (kW) x CSE (%) x Mill grinding rate of coarse material (t/kWh) (2) Production rate, mill power and CSE can be measured during a plant circuit survey. The mill grinding rate of coarse material is then calculated. At the circuit target P80 size, this is the mill grinding rate (of coarse material) through the size of interest. The objective is to maximize this rate. The mill grinding efficiency can also be calculated by taking the ratio of the mill grinding rate over the material’s grindability as measured in the lab. Mill percent solids optimization has thusly been achieved (McIvor et al., 2000). For media sizing, maximizing the mill grinding rate on a given ore is equivalent to maximizing the mill grinding efficiency. Ores of different grindability will be part of the discussion."

Jan 11, 2018

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 Richard Jr. Ray, Richard Druesedow

The Virginia Operations of Consolidation Coal Co. include a diversity of mine fan configurations which have been tested to quantify pressure losses through the inlet ductwork. Airflow and pressure measurements were taken at four shaft sites to calculate losses for the 90-degree bend at the top of the shaft and the self-closing dampers or closing doors located between the shaft and fan. Velocity contours were then developed from the test data to determine flow patterns in each fan system component. In addition, yaw and pitch angles of airflow through the fan annulus were measured to evaluate turbulence levels created by various inlet ductwork designs. The test results indicate that proper design of the shaft collar and ductwork arrangement for main mine fans can substantially reduce system pressure losses and air turbulence. BY minimizing the pressure drop experienced on the surface, these design improvements enable the bulk of the total pressure developed by the fan(s) to be utilized in the mine.

Jan 1, 1995

By Gerhard Sauer, Heimo Gold

The main advantage of the New Austrian Tunneling Method over conventional drill and blast techniques, TBMs and shields is its outstanding flexibility. Many different support concepts help to cope with all but the most adverse conditions. A considerable variety of unique additional support measurements provide a functional tool when dealing with particularly difficult conditions or restricting requirements. The resulting adaptability of NATM with respect to geometric and geologic changes is a cornerstone to providing an economic design and to a safe and unhindered execution of the tunnel work. To take best advantage of this flexibility and to emphasize its cost-saving capacity, NATM explicitly extends the design period into the construction phase. In accordance with corresponding ground classes or other anticipated conditions, a number of basic support categories and an array of additional support measurements are established during the actual design phase. The decision for applying a particular support category at a specific location and for necessary additions to the given support scheme, however, is regularly made on site after each advance, and is determined by the key persons involved in the construction. Contract documents must reflect this approach to facilitate the execution of the work and to curtail construction costs. Biased distributions of risks, however, can adversely effect the envisioned benefits. Consequently, the respective responsibilities of engineer, contractor, and client need to be redefined.

Jan 1, 1989

By Cyril Heever

ROCKS outcropping in Elandsrand's lease area consist of quartzite, shale and lava of the Pretoria group and are underlain first by 1 300 metres of dolomite and then by the Black Reef series. This in turn rests unconformably on Ventersdorp and Witwatersrand rocks and truncates the basal member of the Ventersdorp Super group, the Ventersdorp Contact Reef (VCR), near the northern boundary of the lease. The Ventersdorp Super group is composed of lava and varies in thickness from nil in the north of the lease area to 1 000 metres in the south. The VCR, less than 100 cm thick, dips 210 to the south east and lies between 1 786 and 3 386 metres below datum. The Oberholzer dyke straddles the north-western corner of the property and separates the dewatered Oberholzer compartment, over which most of Elandsrand lies, from the as yet undewatered Turffontein compartment. As so much of the lease area is covered by thick impermeable rocks, the water-bearing capacity of the underlying dolomite was expected to be low. The man-material (MM) and rock hoisting ventilation (RU) shafts were sited well within and above a gravimetrically determined 200-metre 'safe-limit' contour of the northern slope of the Gatsrand. Two pre-cementstion holes were drilled and the cementation rigs were placed within a 15 metre annulus round each shaft to seal any likely water-bearing pockets in the proximity of the excavation during sinking through the first 300 metres of shales and the surface water-table.

Jan 1, 1981

By W. H. Pomroy

Spontaneous combustion fires in deep metal mines, through relatively infrequent, are nonetheless cause for considerable concern because they pose a direct threat to the safety of miners and are quite disruptive to mine operations. They often occur in remote, inactive, or abandoned sectors of a mine where access for firefighting is difficult or impossible. Over half of all noncoal mine fires that last more than 24 hours are caused by spontaneous combustion. The most common means of fire control for spontaneous combustion fires is sealing and/or Flooding the affected zone. This process is never easy, but it is made especially difficult (and hazardous) if the fire grows in size and intensity to the point where underground fire- fighting crews must wear self-contained breathing apparatus owing to mine air contamination. The Bureau of Mines has developed and in-mine tested a mineworthy fire detection system capable of sensing the earliest traces of spontaneous combustion, thus enabling mine personnel to initiate fire control operations before hazardous atmospheres are created. This paper discusses system design within the context of the harsh mine environment, and describes laboratory and in-mine performance tests of prototype equipment.

Jan 1, 1985

By R. Simon

Strain-burst phenomena are generally characterised by sudden releases of energy in a volume of highly stressed rock. Strain bursts are encountered in situations such as crown pillar bursts during cut-and-fill mining, face bursts at development headings cord floor bursts in deep shaft sinking. This paper describes a simple two-dimensional linear elastic FE modeling approach that leads to the calculation of the energy-release rate (ERR) and the total energy storage rate (TESR) in the rock-mass around the openings. The merits of using such energy parameters in the analysis of strain-burst problems for identifying areas of high energy release/storage are discussed through a case stud v. However, much site-specific back analyses are needed to better understand how strain bursts and energy parameters are interrelated.

Jan 1, 1999

By James R. Arnold

Gold Fields Mining Corporation started processing ore from it's Chimney Creek operation in northern Nevada in November, 1987. Since that time production has averaged about 200,000 ounces per year from the milling and dump leaching circuits combined. The events that led up to commissioning of the plant started in January of 1985 when the Gold Fields exploration team drilled their first hole in an area now known as Discovery Hill. The major orebody was located later in the year in what is currently the major focus of activity, the North Pit. Subsequent drilling since plant startup has found another 14 million tons of ore two miles south of the original orebody. This South Pit orebody is currently being stripped and metallurgical testing is underway. Engineering Engineering on the Chimney Creek plant started in earnest in May, 1986. Davy McKee Corporation from San Ramon, California, did both the engineering and the construction management. Before engineering began the entire senior staff of the Plant Department was hired and assigned to the project. Senior staff included the Plant Superintendent, Plant General Foreman, Maintenance General Foreman and Chief Metallurgist. Gold Fields does not employ an internal central engineering staff to design their plants. We feel that the people who design the plant should be the ones who will be required to run it once it has been commissioned. This philosophy affords a continuous accountability from start of design through commissioning and operations. All four of the senior staff spent the most critical phase of the engineering stage at Davy McKee, so the plant is truly a reflection of all four disciplines. In bringing on the Maintenance General Foreman from the start, there was a focus placed on ease of maintaining the plant. Another philosophy that was adopted from the start was that the plant be easy to work in and maintain for both operators and maintenance personnel. Numerous design criteria were given to Davy McKee to ensure this. For example, we required that every piece of equipment could be reached easily with a crane or fork lift. All conveyors were required to have walkways on both sides for ease of maintenance and a minimum of 30 inches of clearance under them for ease of cleanup. Visibility for operators was considered very important and the control rooms and general plant layout were designed with this in mind. A list of about 100 general rules were given to Davy McKee during the early layout meetings and these were held as the general design criteria throughout engineering and construction. While engineering was progressing in San Ramon, California, dump leach test work was being done at the site. Three 6 foot diameter fiberglass columns were constructed and filled to a 20 foot height with low grade ore. Leaching characteristics were determined and the dump leach design was based on information collected from these columns. Construction The major contractors on the project were The Industrial Company for the bulk of the piping and structural, EMKO on the electrical/ instrumentation and Hunewill for most of the earth work and leach pad construction. All plant operating and maintenance personnel were employed eight weeks before startup for intensive training. Instructors were Gold Fields personnel, including foremen, and Davy McKee engineers. On occasion, selected suppliers representatives were brought in to discuss major pieces of equipment. Project completion was targeted for January, 1988 at a projected cost of 78.9 million dollars. Actual startup was about 1 1/2 months ahead of schedule and slightly under budget. Full design capacity was achieved the first full month of operation. Crushing Run of mine ore is delivered to the crusher and dumped into a 90 ton hopper which is topped with a 30" X 30" opening stationary grizzly. Ore is fed to a 50" X 60" Telsmith jaw crusher with a 5' wide apron feeder. The closed size setting of the

Jan 1, 1989

By A. Ballester, F. Gonzalez, M. L. Blázquez

Pyrometallurgical process are usually used to recover valuable metals from metal sulphide concentrates. However, their use is diminishing as the cost of energy rises and pollution controls become strictes. An alternative method of treatment sulphides could be bacterial leaching due its simplicity and negligible contamination (1-2). This process is presently used commercially to re cover metals such as Cu and U from low grade ore concentrates. In spite of numerous researchs during recent years (3-5) there exists very little kinetic data concerning the speed of bioleaching process. The kinetic analysis of bacterial activity is related with the metabolism and growth of microox ganisms . This fundamental information permits ma- king the best utilization of bacterial oxidation and to suggest techniques which might increase the production of the products desired. However, bio- kinetic models are especially complicated due to the existence of many metabolic routes and parallel reactions which are important for the life of the bacteria. Microbiological oxidation of a mineral substrate is influenced by its own inicial concentration: This influence can be determined by means of a kinetic study. In a medium with sufficient concentration of nutrients (nitrogen, phosphorous and potassium) and an adequate supply of 0, and CO2, as the only & L source of carbon for the biochemical synthesis, the substrate concentration would remain the only limitation in the rate of leaching. In this case the Michaelis-Menten model could be applied (6). The model is based on an association of the enzyme (El with the substrate (S) with consequent decomposition of the latter into enzyme and products [ ] The rate of dissolution is defined by the equation : [ ] Were V is the rate of metal extraction (mg 1-1 1 h-1 ) ; S is the pulp density Mn is the maximum rate for metal extraction (mg 1-1 h-1) and K is the constant of Michaelis (concentration of substrate that yields Vm/2). This method is applicable only when the rate of bacterial growth is similar to the rate of metal extraction. It would therefore be sufficient to control the concentration of metal in the medium over the period of time. In the present work a systematic study of the kinetics of ZnS and CuFeS bioleaching in sphalerite and complex ore concengrates was carried out. The rate of dissolution of the Zn and Cu as function of the pulp density and temperature was determined. However, most oxidations of sulphide dissolution take place with a very slow kinetic; but, this can be accelerated considerably by the addition to the solution of suitable catalytic ions, as was Suggested many years ago by Bjorling (7). Such ions can exercise an important influence on the rate of the oxidation-reduction reactions, both homogenous and heterogenous, which take place during the leaching of sulphides; they also affect the nature of the reaction products. The action of catalytic ions has been fully developed in aqueous systems, but in the absence of bacteria (8 - 11) although the actual machanisms is not totally known. The mechanisms proposed as hypotheses in the literature (8) indicate that, in the case of ZnS, the catalyst ion act through an electrochemical mechanism according to the reactions: [ ]

Jan 1, 1989