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By J. F. Hutwelker

A pilot plant was constructed and operated to investigate the column flotation of 20 x 200 mesh North Carolina phosphate ore, using high throughput, high solids operating conditions developed at the NCSU Minerals Research Laboratory. Flotation was performed at 45% solids in a 9.5 cm (3.75 in.) diameter by 2.26 m (7.4 ft.) tall column at throughputs of 19.1 t/hr/m2 (2.0 stph/ft2) and 31.7 t/hr/m2 (3.3 stph/ft2). Recoveries in excess of 98% of the phosphate value were obtained at the lower throughput -- while obtaining concentrate grades containing over 28% P205 (61.2% BPL) at that recovery. Recoveries of about 95% of the phosphate value were obtained at the higher throughput, while making a concentrate averaging 27.6% P209 (60.3% BPL). In addition, a better understanding of the variables governing the column flotation of coarse nonmetallic minerals was gained. Low air flow rates adversely affected concentrate grade at the lower throughput. At the higher throughput, phosphate recovery decreased at an elevated air flow rate. An unexpected result of the study was the effect that frother type had upon phosphate metallurgy. Use of Nottingham Econofroth 925 provided better flotation selectivity than American Cyanamid F-65 at the low throughput. This is significant since the high' throughput tests were conducted with F-65 exclusively. It is reasonable to expect further improvement in high throughput performance when the optimal frother type and dosage are determined.

Jan 1, 1993

By R. S. Dennen

A ground penetrating synthetic pulse radar system has been used by the Bureau of Mines to probe into a coal pillar to locate hidden structures or anomalies. Two types of velocity tomographic reconstruction methods, direct matrix inversion and iterative, were used to obtain a velocity image of the interior of the pillar. The reconstructed image showed the existence and location of a relatively low velocity material within the pillar. Core samples were taken from the pillar in a region surrounding the low velocity material. Analysis of the cores showed the presence of a clay vein coinciding with the low velocity material imaged in the tomogram.

Jan 1, 1989

By Jürgen F. Brune

The Fourth Industrial Revolution, that of digital technologies and their application, is rapidly impacting the mining industry, as it is manufacturing, transportation, agriculture, trade, and most other industries. Mining is about 40,000 years old and has its origins in Africa. Since its earliest days, it has experienced four distinct “revolutions” that each resulted in significant improvements in production, productivity, and safety and health: The First Revolution in the fifteenth through eighteenth centuries brought technologies that improved miners’ lives and health, including pumps, forced and mechanical ventilation with wind catchers and bellows, the wire rope and black powder, to name a few. Many simple, muscle- or water-driven machines have been pictured and described in great detail by Agricola who wrote De Re Metallica in 1556. Agricola was familiar with, and concerned about, accidents where miners fell off rotten, wooden ladders, acrid smoke, and dust that caused respiratory illnesses and diseases. He also knew the dangers of fatigue and recommended that miners should sing aloud to prevent them from falling asleep.

By Paul H. Johnson

The CH Leaching process is a new, more sophisticated, form of gold, silver, uranium and sulfide copper heap leaching wherein each layer of a multi-layered heap is divided into a number of independent cells, each of which are successively formed and leached in the top layer of the heap to their maximum economic recoveries, and then rinsed and sealed from further leaching. Triangular earth berms form the outside walls of the heap and a gridwork of rock-filled berms on top of the bottom pad form independent under- heap solution storage zones. The high degree of solution recirculation and staging that occurs in this process produces a relatively small volume of very rich pregnant solution. The cellular heap design and its mode of operation result in a uniform, intensive, long-term leach for all of the ore particles in the heap. Besides improved metal recoveries, the process appears to have several cost and operating advantages. In the CR2MR process, sulfuric acid and a soluble sulfide are added to a gold and/or silver pregnant leach liquor to precipitate most of the contained silver, mercury, copper, etc. as sulfides at a pH below 2.5. The other product of the reaction is solubilized HCN. Following a liquid-solid separation step, cyanide is regenerated in the supernatant solution by raising the pH to a level above 9.0. This process regenerates a portion of the cyanide used in the leaching step, removes contaminant ion species (silver, copper, mercury, etc.) from the leach solution and, in a subsequent step, recovers the gold in an enriched form. It is believed that substantial cost savings may be experienced by the use of this process in some gold and/or silver leach systems.

Jan 1, 1984

By J. W. Rains

Arizona Portland Cement Company's limestone deposit (called Twin Peaks) is approximately 4 miles southeast of the cement plant. The pant is adjacent to both the Southern Pacific Railroad and Interstate 10, about 17 miles northwest of Tucson. Placer claims were filed on the Twin Peaks deposits in 1923. From that time until the present, geologic data have been accumulated and evaluated to define more closely the quantity and quality of the limestones. The cement plant at Rillito was originally constructed as a one-kiln plant in 1949. Capacity was increased in 1952 and 1956, bringing the plant to an annual capacity of 44,000 tons of cement. In 1972 anther expansion program was completed, bringing annual cement capacity to 1.1 million tons. Geologically, the Twin Peaks contain formations ranging from the Precambrian Pinal Schist to the Pennsylvanian Naco Formation. Within this sequence, other exposed formations include the Cambrian Bolsa Quartzite and Abrigo Formation, Devonian Martin Limestone, Mississippian Escabrosa Limestone, and Pennsylvanian Naco Formation. Generally, the Escabrosa, Naco, and Martin Formation are the primary sources of limestone for manufacturing cement. The Martin Formation is basically a dolomite with bands of limestone, quartzite, and siltstone. These limestones are blended with outside source materials (clay and iron ore) to make a raw mix that will make specification cements. Several drilling programs were initiated between June 1946 and March 1982. Information derived from these programs provided the means to develop cross sections, geologic blocks, and grade blocks. The configurations of the geologic and grade blocks are the same. Block boundaries delineate the various formations on any particular level. Cursory inspection of the structure would indicate a broad syncline elevated on the west side. A more detailed examination shows that the structure has been complicated by several periods of faulting and intrusion of igneous rocks.

Jan 1, 1987

By C. O. Petter

This paper, in its first part, compares the profile and economic weight in the extraction of industrial minerals and aggregates to the so called conventional mining activities (metals, coal, gas and oil extraction) in Brazil. In its second part, a descriptive analysis of the present situation of the education in Brazil is made, emphasizing the graduation and post-graduation formation especially in engineering. The curricular structure of the schools that prepare the mining workforce is discussed and the presence of specific subjects in industrial minerals is evaluated. Finally, considerations are made on the actions being taken in the main universities and companies, aiming to improve the formation of the specialized workforce. The Brazilian mining production, comparing 2010 to 2011 showed an expansion of more than 3% (IBGE, 2012). Not bad, but nothing to do with the 13% growth between 2010 and 2009 (influenced by a recovery effect from the 2008 commodities? nightmare). The commodities that had a rising behavior were titanium, gypsum, nickel, graphite, bauxite, phosphate, chrome and chrysotile. All of them were eclipsed by the impressive growth of iron ore production. Some decreases could be noticed, eg. in zinc, kaolin, magnesite and salt production (DNPM, 2012). In fact, the mining activities followed the positive growth of the country these last 5 years. The commercial balance (exports against imports) was not spectacular (positive in US$ 30 billion in 2010). It is important to notice that the mineral commodities balance was US$ 35 billion, representing 27.4% of the total exports and 15.6% of the total imports of Brazil (DNPM, 2012). In this positive environment, the workforce in Brazil showed progress in number of formal jobs and average revenues.

Feb 23, 2014

By William G. Doepken

After 15 years of production, 91 Mt (100 million st) of ore mined and nearly 227 kt (500 million lb) of molybdenum produced, Climax Molybdenum Co.'s Henderson Mine and Mill are being modernized as a new mining level is brought on line. The $40 million investment in mine development and plant modernization positions the Henderson complex as one of the largest, low-cost primary molybdenum producers for the next 15 years. Henderson history The Henderson Mine and Mill facilities are located on the east and west flanks of the Continental Divide about 80 km (50 miles) west of Denver, CO. The underground mine and surface mill sites are linked by 16 km (10 mile) of railroad tunnel and 8 km (5 mile) of surface trackage. The mine, railroad and mill were built between 1968 and 1976 at a cost of $500 million. Each has operated at various levels of production over the past 15 years. The Henderson Mine was originally developed using a highly mechanized, panel caving mining system. Over the past 10 years, mining methods, equipment and railroad operations have been improved to position Henderson as one of the most productive and lowest cost underground mining operations. At the same time, the mill and concentrator facilities were upgraded to reduce costs and improve product quality. During this time, manpower was reduced from 2000 to 560 employees. These 560 people increased productivity to 54 t (60 st) per total manshift. They reduced operating costs by 50%. And they dramatically improved safety performance. However, as the 1990s approached, the modernization of the Henderson mining and milling complex and the development of the new 7700 mining level became the primary goals to guide Henderson into the 21st century.

Jan 1, 1991

By John F. Shea

When Dick Robbins asked me to give a keynote address, I felt it might be in order to review some of the practices and techniques used in tunneling and work up to some of the concepts now used to mine and construct tunnels. Needless to say, there have been many changes in tunneling technology and also many changes in the Safety Codes controling them. An example of this latter change was the fact that in 1931, my father excavated the Owyhee Tunnel No.5 with gas locomotives. He was able to do it because there was no natural gas in the rock and the ventilation system was designed to free the tunnel atmosphere from powder and exhaust fumes. Today OSHA rules would never permit gas locomotives underground, although there were no incidents on this particular project. One of my first tunnels, as Project Manager, was the Clear Creek Tunnel for the Bureau of Reclamation. Our method of handling muck was the Conway Muckers. This unit was a valuable improvement to the hand mucking of previous generations. The Conway was also used in our Navajo Project, in New Mexico. Unlike the Clear Creek project, where water was one of our main problems - up to 7,200 gallons per minute, at a pressure of 395 pounds per square inch - in the Navajo Tunnel, we had a mixed face which caused a major problem with our support system. In one of the Navajo Tunnels, there was a major cave-in, when the squeezing shale came in during an attempt to strengthen the support system. Although moving shale was not a constant problem, there were areas where the shale was five to six feet above the spring line.

Jan 1, 1976

By G. S. Walker, W. van Bronswijk

The accurate determination of free cyanide and metal cyanide complexes is of increasing interest to Carbon-in-Pulp (CIP) gold extraction operations as cyanide consumption is an important economic factor in the processing of complex ores. Characteristically complex ores are high cyanide consumers and these ores usually contain a range of sulfide minerals e.g. covellite (CuS), digenite (Cu1,S), chalcocite (Cu, S), Pyrrhotite (Feci-x)S), marcasite (FeS2), arsenic and antimony sulfides and zinc sulfide. These minerals can consume significant quantities of cyanide, e.g. various copper(!) cyanide complexes such as CuCN, Cu(CN)2·, Cu(CN)/ and Cu(CN)/ can form, depending on the cyanide to copper ratio in solution. Measurement of free and complexed cyanide is thus a prerequisite for efficient cyanide dosage control. Free cyanide can be determined potentiometrically or amperometrically but the methods are prone to error and are laborious [1]. Metal cyanide complexes can be determined by reverse phase HPLC, however, the species ofa single cation (e.g. Cu(CN)i-, Cu(CN);2 and Cu(CN)/) elute as one species [2]. Additionally the high amount of suspended matter in CIP leach solutions tends to introduce errors. Raman spectroscopy has the potential to be used as an in­line or on-line method of analysis. Free cyanide and the cyanides of gold, silver, copper and iron have been studied in aqueous alkaline solutions with a view to developing such a method. Spectra were obtained with a Bruker RFSl00 FT-Raman spectrometer using a 1064 nm laser delivering 800 mW of power at the sample. Depending on the solution, 250, 1000 or 4000 scans at 4 cm-1 resolution were accumulated. The cyanide stretches observed were relatively narrow (10 15 cm-1 full width at half height) and well resolved (Figure 1 ).

Jan 1, 1995

By Steven Hart, Graeme Hill

Boddington Gold Mine is situated 130km South-east of Perth, WA. The operation is managed by Worsley Alumina Pty Ltd. The Direct Leach plant was commissioned in mid 1986 at a rate of 3 million tonnes per annum. The plant was upgraded to 4.5 mtpa in 1988 and almost immediately to 6mtpa in 1989. Subsequent debottlenecking resulted in further increases in throughput up to 7mtpa by 1991. The SupergenelBasement Plant was constructed in 1990 and commissioned in early 1991. It was designed to process both copper-gold-silver anomalies within the laterite gold orebody and future hard rock ores. The Supergene plant incorporated control potential s­ulphidisation (CPS) and flotation ahead of CIL to remove a host of copper minerals. It operated in that configuration for 2 years at rates up to 350,000 tpa and average grades of 6.0 git gold and 1.2% copper. Gold recovery averaged 90.7% and copper recovery averaged 80.0% before the flotation circuit was decommissioned in March 1993. Quartz hosted high grade, free milling oxide and basement ores were discovered at the northern end of the orebody in 1990 and now comprise the major feed source to the basement plant. Oxide ores are currently milled at a rate of 550,000 tpa, while basement ores are milled at a 420,000 tpa rate. Metallurgical testwork during the feasibility stages indicated that up to 30% of gold in plant feed could be recovered by gravity separation methods. It was also highlighted that signifi­cant improvements in overall plant recovery and reduced operating costs would be achieved by maximising gravity gold recovery ahead of cyanidation. To achieve this, rec;iesign and upgrade of the gravity circuit was necessary.

Jan 1, 1995

By Satid Therdkiattikul, Donald A. Dahlstrom

Many gold ores are known to be refractory so that conventional cyanide processing will result in serious losses of gold and silver values. A significant percentage of these refractory ores contain aresenopyrite and the gold and silver is usually encapsulated within this matrix as well as the pyrite matrix. Normally the values can be recovered as flotation concentrates because of the sulfide compounds with recoveries of over 90% and at very good grades. In order to free the gold and silver, the sulfide matrix must be destroyed. This can presently be achieved by (1) pressure­temperature leaching (2) roasting and (3) bacterial leaching. All of them have advantages and disadvantages as well as an obviously increased cost for the each processing method. However, the increased gold and silver recovery should and must more than offset this cost. It is believed that gold recovery should be well over 90% from the concentrate so that overall recovery from the ore should be in the 90-95% region. All three processes must consider pollution control of both sulfur and arsenic to prevent contamination of air, water or land through improper waste disposal. This paper will concern only bacterial leaching and its necessary control of effluents and solids. Sulfur does not appear to be a problem as the element is oxidized to sulfate and is precipitated with an acceptable solubility. Other important improvements that must be controlled are arsenic and iron which are present as significant values (1-12 g/1 of arsenic, 20-40 g/1 of iron). In addition much smaller values of base metals, aluminum and magnesium can be present as well as other elements depending on the ore and these must be low enough after treatment to meet EPA regulations.

Jan 1, 1993

By Tom McDonald

Test work and plant operation confirmed that semiautogenous (SAG) milling is a viable option for Inco's milling rationalization project at Sudbury only if pebble crushing is included. Throughput increases more than 50% with pebble crushing incorporated into the comminution process. The finer product of high-speed pebble crushing provides further energy savings. The unconventional approach of pumping the pebble crusher product, while simplifying plant layout, has produced challenging wear problems. Inco Ltd.'s Sudbury operations are located in northeastern Ontario, Canada, about 400 km (250 miles) north of Toronto. Inco has 11 operating mines around the rim of the Sudbury basin. The mines currently produce about 11 Mt/a (12 million stpy) of ore. This ore contains pentlandite, pyrrhotite and chalcopyrite in mafic host rocks. The milling facilities are designed to produce 108.8 kt/a (240 million lbs/ year) of nickel as concentrate. This concentrate is further processed through Inco's smelting and refining facilities to produce nickel, copper and several other metals. Before 1991, -200 mm (-8 in.) ore was shipped to two primary mills. The Clarabelle mill had a design capacity of 29 kt/d (32,000 stpd). Frood-Stobie had a capacity of 16.3 kt/d (18,000 stpd). The flowsheets of these mills were similar. Two stages of open-circuit crushing were followed by rod milling and closed-circuit ball milling. The product from the comminution circuit, at 12% +250 mm (+65 mesh), was first passed through magnetic separators to recover magnetic pyrrhotite. It was then sent through a four-stage flotation process. The first two stages produced a high-grade copper-nickel concentrate. The final two scavenger stages produced a low-grade copper-nickel concentrate containing nonmagnetic pyrrhotite.

Jan 1, 1992

By Mark W. Johns

The design or optimization of a carbon-in-pulp (CIP) plant requires the determination and setting of a number of parameters to ensure optimum economic performance. A number of these parameters are either fixed, a function of the pulp, interdepen­dent, affect other parameters or outputs, so only a limited number of degrees of freedom exist from a metallurgical point of view. The traditional CIP contactor employs a low carbon concen­tration, a low agitation intensity and a reasonably long pulp residence time. The pump cell contactor employs a high carbon concentration, a high agitation intensity and a reasonably short pulp residence time. The two philosophies are dipolar in nature and the question arises as to which configuration is the optimum configuration for a CIP plant. The carbon particle size is shown to have a small effect on the capital cost of a CIP plant. A decrease in the pulp residence time, an increase in the pulp density, an increase in the carbon residence time, an increase in the agitation intensity and an increase in the number of stages are shown to have a positive effect on the capital cost of a CIP plant. The pulp residence time, the pulp density and carbon particle size are shown to have a small effect on the operating cost of a CIP plant. An increase in the carbon residence time, a decrease in the agitation intensity and an increase in the number of stages are shown to have a positive effect on the operating cost of a CIP plant. The optimum CIP plant, therefore, employs a short pulp residence time, the traditional pulp density, a long carbon residence time, the traditional carbon particle size, the traditional agitation intensity, and the traditional number of stages. Neither the pump cell configuration nor the traditional CIP configurations match the optimum configuration.

Jan 1, 1995

By John Wilson

HARRY HINDS: Our first speaker today is Dr. John Wilson. Dr. Wilson is chair and Union Pacific/Rocky Mountain Energy Professor in mining engineering at the University of Missouri-Rolla. He has previously held senior management positions with Trans- African Mining Ltd., Anglo American Corporation, Consolidation Coal Company, Smith International Inc., Adams Resources Inc., and Golder Associates. John started his mining career as a coal miner in the coal fields of northern England. Dr. Wilson received his bachelor of science degree from the University of Durham, his master's degree from the University of Newcastle Upon Tyne, and his doctorate from the University of Witwatersrand, all in mining engineering. Today, Dr. Wilson is going to address the subject "Hiring Recent College Graduates Versus Hiring Experienced Mining Engineers." Please welcome Dr. Wilson. DR. JOHN WILSON: The advantages and disadvantages of hiring engineers directly out of school or those with some experience are often discussed among mining company managers. The choice is essentially dependent on the culture of each company, the company's maturity and strategic direction, and the growth or phaseout plans in vogue at the time of the decision. Generally, major, established mining companies employ entry-level college graduates and train them, introduce them to company culture, include them in a succession plan to replace retirees, fill vacancies, and provide management to direct future growth of the company. However, some large companies take a different approach. During restructuring, down-sizing, etc., some companies do not hire college graduates directly from school. Rather, they tend to recruit from other companies or absorb valuable personnel available following acquisitions or mergers. While this is a logical approach, it seldom provides for the future management and leadership needs of the company. A clear example of this failure is found when reviewing the hiring practices, or lack thereof, in the coal industry of the 1950s.

Jan 1, 1998

By Richard Switalski, Thomas Scotese, James Morrison, Randall Essex

OVERVIEW Like many older metropolitan areas across the U.S., the Greater Cleveland area is served by a combination of separate sanitary sewers and combined sanitary-stormwater sewers. In 1966, a Master Plan was implemented by the Northeast Ohio Regional Sewer District (District) to minimize pollutant overflows into adjoining Lake Erie and its tributary rivers and streams, that would occur during wet weather events. One component of the Master Plan was to reduce the load on combined sewers by constructing new conveyances to intercept separate sanitary flows and convey them to upgraded regional waste water treatment plants for priority treatment. As part of a 15-year program to construct 74 km (46 miles) of new interceptors, the West Leg Interceptor (WLI) Project intercepts flows from four decommissioned waste water treatment plants (WWTPs), and conveys those flows to the new Southwest Interceptor (SWI), which conveys the flows to the Southerly Treatment Plant, a tertiary level treatment facility. The WLI Project was built in sections to permit decommissioning of the WWTPs as each segment of the interceptor system was completed and put into service. Flows from the first of the four WWTPs was converted to the WLI in November, 1992; the final connection was achieved in July 1994. The WLI comprises 9.1 km (5.7 miles) of 21 to 29 m (70 to 95 ft) deep mainline interceptor tunnel, four vortex drop structures, approximately 2 km (1.3 miles) of shallow tunneled connector sewer to the mainline, approximately 2.9 km (1.8 miles) of open cut connector sewers, five construction work shafts (not including one work shaft constructed under SWI Contract 6 at the north end of the WLI), and 15 access shafts.

Jan 1, 1995

The Mining Foundation of the Southwest will hold its 15th annual American Mining Hall of Fame Awards banquet on Saturday, Dec. 6,1997 in Tucson, AZ, preceeding the Arizona Conference of SME. The Mining Foundation's Hall of Fame, located in Tucson, recognizes outstanding contributions to the mining industry by individuals and industry partners. A permanent display of honoree vitae is located at the Arizona Historical Society at 949 E. Second St. in Tucson. Each year, one living award recipient and up to two honorees from mining history are chosen by the Hall of Fame committee and the board of governors of the Mining Foundation. In 1989, the Mining Foundation also initiated a Medal of Merit to recognize outstanding individual technical and professional contributions to the mineral industry. And in 1995, an award was instituted to recognize contributions made by companies and organizations in partnership with the mining industry. This year's inductee is James R. Moffett, chairman and chief executive officer of Freeport-McMoRan Copper and Gold Inc. He will be present as guest of honor and featured speaker. The Hall of Fame will induct John V. Dorr, metallurgist and chemical engineer. Also inducted will be Frederick L. Ransome, a geologist. Medals of Merit will be awarded to Hugo T. Dummett, senior vice president, Exploration BHP Minerals, and Spencer R. Titley, professor in the Department of Geosciences at the University of Arizona. An Industry Partnership Award will be presented to the Colorado School of Mines for its continued support to the mining industry through education and research. The banquet will be held at the The Westin LaPaloma in Tucson beginning with cocktails at 6:30 p.m. Tickets are available from Clare A. Roscoe, manager, Mining Foundation of the Southwest, telephone 520-577-7519, fax 520-577-7073.

Jan 1, 1997

By P. M. Fozzard

The Chaucha porphyry copper/molybdenum deposit was discovered by a United Nations team of geologists working with a ?counter- part" team of staff of the Ecuadorian government's General Directorate of Geology and Mines (DDGM) in July 1968. The exploration program formed the latter part of phase I work plan of a two-phased exploration project financed by the United Nations Development Programme and initiated in late 1964. The author was a team geologist during the period 1965-1967 and subsequently project manager for the period 1968-1972. The Chaucha property lies some 10 km (6 miles) east of the north- south-running western boundary of what was known as Operation Area No. 5. This area of some 10 500 km2(4050 sq miles) is a square truncated to the southeast and centered on the city of Cuenca, the major provincial capital (Azuay Province) of southern Ecuador. The eastern half of the exploration area is dominated by the Cretaceous- Tertiary sedimentary valley (basin) of Cuenca (Caar-Azuay) and its related drainage area. The western half, in which Chaucha lies, is dominated by the high Cordillera Occidental volcanic plateau and the western erosional valleys of the Andes draining to the Pacific. The valley that dominates the eastern part of the area [I500 m (4920 ft) above sea level] is transected by the Pan-American Highway. Because of increased agricultural activity associated with the Cuenca Valley, the area is reasonably well covered by a road network of varying quality. The high western area up to 4000 m (13,120 ft) in altitude is largely barren and completely inaccessible by vehicle. The geological reconnaissance map of the region is shown in Fig. 1.

Jan 1, 1991

By William T. Folwell

INTRODUCTION - CURRENT RAISE BORING PRACTICES Raise boring is a comparatively new tool to the underground mining and construction industries. Underground raise boring, in this country, had its beginning in the early 1960's, in the iron mines of Michigan. These first raises were bored 40 in. and 48 in. in diameter with maximum lengths of approximately 200 ft. Since the late "sixties", the raise boring machine has been accepted by the mining industry as an important machine to increase excavation rates, provide adequate ventilation airways, improve safety, and reduce costs, to name a few of the benefits. The construction industry is now accepting raise boring techniques for hydro-electric power projects, water supply projects, tunnel projects, waste water projects, etc. Raise drills are now capable of boring raises to diameters as much as 12 ft, in the softer rock types. Raise lengths range from 200 ft to as long as 1700 ft. Bored raises, in general, are bored at dip angles ranging from 45º to 90º, depending on the requirement of the raise. The general practice is to drill the pilot hole down to an opening below and up ream the pilot hole to the required diameter. The pilot hole (9-7/8", 9", 11", or 12-1/4" diameter) is generally drilled with compressed air to remove the cuttings. In the event that ground water is encountered and removal of cuttings is impeded, a foaming agent is added to assist in lifting the cuttings. When excessive water is encountered, water is used as the circulation medium and the cuttings are removed by pumping. During the reaming cycle, the cuttings fall by gravity and are removed from the bottom of the raise by conventional methods.

Jan 1, 1997

By Edward H. Opitz

Much has been written recently about the Henderson Mine Project in Colorado being developed by American Metal Climax, Inc. To briefly recap the project, AMAX has an ore body, containing about 300 million tons of proven and probable molybdenum ore which is located under Red Mountain on the eastern slope of the Continental Divide. The mill, however, will be located on the western slope in the Williams Fork Valley where water and space for waste disposal are more available. AMAX will carry the ore by remote controlled trains from a gathering level underground at the mine, through a ten (10) mile tunnel under the Continental Divide and thence along a five (5) mile surface railroad to the mill site. One of the more challenging facets of the project is the western portion of the ten (10) mile tunnel being driven by Dravo Corporation through difficult ground conditions, downgrade, toward the Continental Divide. The tunnel is a 16'-6" wide by 15' high horseshoe, which runs in a straight line and drops at a constant three percent (3%) grade from the West Portal to the ore zone. Dravo's portion is anticipated to be about 6 1/2 miles long and includes permanent pumping stations located every 4,900 linear feet (lf) permanent rectifier stations every 12,5001f, and one (1) 1,560 ventilation shaft. The western portion of the tunnel lies in the Idaho Springs formation, a mixture of gneiss and schist with some granitic intrusions. Toward the Continental Divide a transition into Silver Plume Granite is expected to occur. Preconstruction geologic information indicated the Idaho Springs and Silver Plume formations to be basically competent with some faulted and altered areas. It

Jan 1, 1974

By J. L. González-Chávez, A. Ballester, M. L. Blázquez, F. González

In recent years, the bioleaching of sulfidic raw materials has been of great interest. However, the application of this biotechnology is now very limited for many different complex reasons. The mechanism of the chemical and electrochemical reactions taking part in the process is not well understood. The application of electrochemical techniques is useful in its elucidation. Among the common sulfides, galena has been studied very little with respect to its behavior during bioleaching. Therefore, the electrochemical evolution of massive electrodes of lead sulfide in the presence and absence of' a mixed culture of mesophilic microorganisms was investi¬gated by the application of potentiometry, anodic and ca¬thodic polarization and cyclic voltammetry. The agitation rate, the use of pH control and the composition of the nutrient mediums did not have any significant affects on the oxidation of galena. However, the temperature (25 'to 45 °C), the scan rate (4 to 100 mV/s) and the acid used to adjust the pH were significant variables that influenced sulfide oxidation. There¬fore, the peak (600 to 1,000 mV) corresponding to the oxida¬tion of sulfide ions from the mineral was only detected in the presence of a complexing anion of lead. In the presence of bacteria, the peaks corresponding to galena oxidation de¬creased and, at the same time, new peaks appeared both during the oxidation at -300 mV and during the reduction of the mineral surface at 150 and -300 mV. These signals were more important when the attack time increased. The rest potential of bioleached mineral increased with an increase in leaching time, which was related to the electrochemical transformation of the galena surface.

Jan 1, 2000