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By R. K. Amankwah, E. K. Asiam

Changes in the thermal-oxidation behavior and other properties of gold-bearing waste activated carbon when milled in both a ball mill and a vibratory mill were investigated. It was found that significant changes occurred in the oxidation temperature of the vibration-milled waste carbon as a result of increases in surface area and mechano-chemical activation. The mechano-chemical action brought about modifications in the crystal structure of the waste carbon. As a result, the vibration-milled sample was completely oxidized at a temperature of 450°C. Thus, the study established that vibration milling is a better way of lowering the temperature of oxidation of the waste carbon. Furthermore, the gold was found to be concentrated in the ash and, when leached with cyanide for 20 hrs, the gold recoveries from a sample having a head grade of 2 kg/t was 99.5% for the vibration-milled sample and 82% for the ball-milled sample. The lower gold recovery for the ball-milled sample was attributed to sintering of the ash, which was caused by the higher temperature required for its oxidation.

Jan 1, 1997

By Robert N. Evans, Delon Hampton

During construction of the Washington Metropolitan Area Transit System, the hand-mining of a mixed-face condition was anticipated on a portion of tunnel located in the downtown area of Washington, D.C. The Section, consisting of two circular tubes, extends from Station 12+80, heading in a westerly direction, traverses along a curve under Lafayette Square, and ends in a northwesterly direction at Station 37+62 (see Fig. 1a). It was near the northernmost portion of the section that the mixed-face condition was encountered. Decomposed rock was first encountered in the invert at Station 31+00. From this point the rock gradually increased in height until it intersected the springline at Station 37+62, the project limit. Summarized within this paper are measurements of the soil load on a horseshoe-shaped portion of tunnel located in the mixed face condition. These measured loads are compared to the soil load on tunnels as determined by current design methods. The paper also discusses rib and surface movements associated with the post loading process. Comments will be made on how the presence of a mixed face condition might help or hender the tunnel design and construction procedures.

Jan 1, 1974

By Leo Wagner

In relation with the construction of the Sölk power station in Steiermark, Austria, tenders were called in October, 1976, for the construction of the 12-km "Donnersbach collector tunnel" by "Steirische Wasserkraftund Elektrizitäts AG". The specified showed both conventional blast tunneling as well as mechanical excavation with a tunneling machine, diameter 3.55 m. Total construction time from the date of the invitation to tender was given as 4 years. Part of the project was the construction of a concrete circular tunnel lining 20 cm thick. In 1977 the contract was awarded to "Arbeitsgemeinschaft Donnersbach", a joint venture formed by two companies, G. Hinteregger & Söhne, Salzburg, and G. Hinteregger, Bregenz. It provided for the project to be carried out with a tunnel boring machine. GEOLOGICAL DATA The entire tunnel was to be bored through a complex of the garnet mica schist group of the Wölz schists formations. These range from highly quartz-bearing to quartzitic mica schists, with thick, discordantly interstratified beds of marble and dolomite. In the western sector the axis of the collector tunnel intersects the bedding at an angle of 30° to 40°, in the eastern sector the bedding is about

Jan 1, 1979

By A. L. DeVegt, H. G. Bayer, C. J. Buisman

During the last ten years, Paques Inc. has been engaged in the development and installation of treatment systems to remove sulfur compounds from water and gaseous streams using biotechnological processes. Metal and sulfate can be removed from mine waters in two biological steps. In the first step, sulfate-reducing bacteria converts sulfate to hydrogen sulfide (H2S). The HS reacts with the dissolved metals to form insoluble metal sulfide precipitates. In the second step, sulfide-oxidizing bacteria convert excess H2S to elemental sulfur. The Budelco Zinc Refinery in The Netherlands installed a groundwater treatment system to remove metals and sulfate using the biological steps described above. The system has been operating since May 1992 and has been treating 5,000 m3/d (180 thousand cu ft/day). A pilot plant began operation in November 1995 at Kennecott's Bingham Canyon Utah copper mine to develop processes for metal and sulfate removal from groundwater and for the selective copper recovery from leach water. The principle of the biotechnological methods, the full-scale experience and an overview of the test program at the mine are presented

Jan 1, 1999

By L. B. Hales

The advent of the process control computer with its capabilities of monitoring, storage, and real-time control has revolutionized control technology in the mineral industry. Initial efforts to introduce the computer into process control began in the early 1960's. However, it wasn't until the last decade with the introduction of integrated circuits and minicomputers that truly successful applications became visible. Computer hardware and real-time operating software have improved to the point that they rarely provide major problems in the implementation of successful control systems. At this time the most prevalent problems and obstacles affecting the successful implementation of a control system are as follows: (1) reliable and representative sampling systems; (2) rugged and reliable process sensors; (3) the availability of well-defined control strategies; (4) the willingness of plant management to provide the continuous support necessary to acquire and/or train appropriate personnel in the operation and maintenance of advanced control systems. Discussion of these problems and of the instrumentation required for the successful application of computers in minerals processing plants follows. In order to enhance this discussion the remainder of this subsection is broken up into individual mineral processing categories.

Jan 1, 1979

By Allen M. Newcome

The Ohio valley division of consolidation coal company has incorporated two new aspects within its coal mining concern. A new communication system, thru the cooperation of the c. & p. Telephone company, has been established in each of our mines with its central control in the general office building. In conjunction with this system, a Texas instruments 960 a computer has been incorporated into the system. The purpose for our computer is to provide modernization and improvement to our safety, production and maintenance programs. Thru proper use, the computer will help eliminate inaccuracies and inefficiences that have previously caused inaccurate analysis of problems. Due to federal requirements for more reliable communications in underground mines, Ohio valley division is making a concentrated effort to improve its communication systems. Systems such as the magneto phone and trolley phone have been looked at more critically. It was found that these systems are being used well beyond their limits. With these facts in mind, division personnel started looking for a system that would have these built in advantages: ease of maintenance and installation, increased reliability, low cost, and an inherent ability as a multiple use system.

Jan 1, 1975

By F. L. Wilke

In the german hard-coal mining industry the mechanization of longwall faces and the machinery used for the extraction process have reached such an extent, that an extensive increase in productivity and face performance is not likely to be expected. At present, the greatest amount of man-shifts is needed for operations such as tunneling, transportation and haulage (fig. 1.). The most restrictive parameter, especially considering the possible ad- [ ] vance rate of faces, is the comparatively low advance rate achieved in drifting operations. Therefore improvements in productivity and advance rates of drifting operations will have considerable influence onto the extraction rate of the faces. The importance of drifting operations - and especially the so-called "conventional drifting by drilling and blasting" within the scope of long- term planning strategy of the german hard-coal mining industry is reflected by the development factor. This factor is given by the ratio: cubic meters of rock excavated in drifting per 1.000 tons saleable coal produced. In 1973, which is considered to be the beginning of the oil-crisis, this factor was determined to be 17.7 m3/ 1.000 tons sale- able coal.

Jan 1, 1982

One of the largest mining shows in the world is set take place April 15-18 in Santiago, Chile. Expomin 2008 is expected to attract more than 60,000 professionals from around the world who are involved in all aspects of the mining industry. Expomin has become an important place for mining leaders to meet, organizers said, ?with great expectations for the development of new business in international markets.? This is the 10th Expomin. The event, held every two years, is expected to at-tract exhibitors from more than 25 countries, representing nearly 1,000 companies and more than 3,000 brands related to the mining industry, organizers said. Most all of the world?s largest equipment manufacturers and suppliers ? surface and underground ? will be represented. The importance of the event to the Chilean and international mining industry can be seen by the increase in size of the exhibition ? 13 percent more surface space in 2008, compared with the 2006 Expomin. The exhibit will be broken down into four pavilions, covering 34,054 m2 (355,570 sq ft). An outdoor area for the large mining equipment will cover 16,120 m2 (173,520 sq ft).

Jan 1, 2008

By F. P. Schwarz, A. J. Erickson, S. M. Weber

The Mount Hope stockwork molybdenum exposit, Eureka County, Nevada, occurs in a small igneous cauldron complex 32 to 38 mybp in age. The deposit is characterized by alteration zones and mineralized shells symmetrically distributed around multiple intrusives. For samples from the 25 000 meters of 1981-82 drilling, an appraisal of error in in-house sample preparation and in commercial assaying has been made. After splitting, drill core is crushed and reduced in volume (8:1 at 10-mesh, 8:1 at 70-mesh, 6:1 at 200-mesh) to supply 25 grams of 200-mesh pulp for replicate analyses. A 0.5 g portion of the pulp is used for dissolution and atomic absorption analyses. Factors which initially generated unacceptable data variances have been minimized by planning, repeat analyses, introduction of standards, and routine monitoring. Assuming that error between replicate assays defines a Gaussian distribution with its average ideally equal to zero, precision (from preparation including core splitting and analysis of 8400 pairs of molybdenum samples) is on the order of + 25%. The error distribution is not biased. Accuracy is approximately 4% lower than absolute as determined by replicate assays of commercially prepared samples.

Jan 1, 1992

By G. Pan

A geostatistical approach is proposed for the design of infill drilling programs. The method consists of the following four major steps: developing geological favorability models, delineating mineralization and ore envelopes, classifying resource potentials, and designing infill drilling patterns. Geological modeling develops the permissible geological zones in which infill drilling is designed. Modeling mineralization and ore envelopes establishes criteria on the potential blocks to be drilled. The blocks that are included within the ore envelopes are considered in the infill drilling. The following four types of resource potentials are used in this analysis: measured, indicated, possible and barren. Blocks in the indicated category are the top targets to be confirmed in infill drilling. Blocks of possible resources may be considered exploration targets. The algorithms involved in the analysis include indicator favorability analysis, indicator kriging and ordinary kriging. A case study on a gold deposit of the Carlin type is presented to demonstrate the methodology. The deposit was originally delineated by a sparse drilling program with about 230ft of average spacing. The infill drilling design, based on the new method, suggests a significant reduction on the number of holes from a regular-grid infill drilling pattern.

Jan 1, 1996

By A. A. El-Midany, R. M. Farag, A. M. Salem, S. E. El-Mofty

Bentonite represents one of the main players in the stability of the drilling mud. Its particle size and particle size distribution affect the physical properties of the drilling mud especially the rheological properties. Therefore, a specific particle size distribution was recommended by American Petroleum Institute (API) for use in drilling mud. To clarify the effect of individual size and size distribution, in this study, the bentonite sample was classified into different size fractions. Each size fraction was tested separately in terms of controlling properties such as filtration loss, plastic viscosity, gel strength, cake thickness, and packing density. The effect of each size fraction on the rheological properties of the suspension was correlated to the behavior of the whole particle size distribution in the bentonite sample. The results indicate that the coarser the particles, the higher the rheological properties; in this case, the API mixture is the highest. The filtration loss and cake thickness for the API mixture are lower than that of the individual size fractions due to its wider size distribution due to the filling of voids between larger particles with smaller ones, which lead to bed compaction and consequently lower fluid loss and cake thickness.

By Nai-piu Tong, Huaren Dou, Sui-shun Poon, Leslie H. Swann

This paper mainly presents geotechnical aspects of a vehicular underpass that was built across under one of the busiest highway in Hong Kong. The underpass, in a section comprising an upper arch and invert slab, is approximately 6.2 m high at crown and 15 m wide at the base level with 40 m in length. The construction inevitably requires the underpass to be built using tunneling techniques to keep the overheadroad traffic uninterrupted. The paper will describe the design of temporary support for the tunnel excavation that was provided by an arch formed with horizontal pipes, which were installed using the pipe ramming method. The pipes arch was then supported by steel ribs founded on rock or mass concrete. Permanent lining design consideration was also discussed. Results of numerical modeling of the soil-structure interaction using the 2-D computer code FLAC will be presented. The predictions have been compared to the monitored results during construction, which indicates the prediction is in reasonable agreement with the measurement in the light of ground movement. The construction challenges will also be discussed in the paper.

Jan 1, 2003

By T. M. Klemetti, T. J. Batchler, T. J. Matthews

How representative are partial-panel screen tests of the in situ response of screen to roof and rib deterioration and displacements? Can a more representative procedure that tests up to two full screen panels improve the utilization and effectiveness of screen as a roof and rib support? This paper details a new full-panel screen test procedure and the initial results. The full-panel test frame was designed to test a 2.4 by 3.6-meter screened area with bolt spacing as small as 0.3-meter increments. The initial design included up to 6 screen pull points, but additional locations can be added to produce a more uniform loading. The test frame was developed to capitalize on the capabilities of the Mine Roof Simulator (MRS) at the Pittsburgh Mining Research Division (PMRD) of the National Institute for Occupational Safety and Health (NIOSH). The initial tests included a baseline test of a partial panel (1.22 by 1.22-m screen section) using the original 1.52 by 1.52-meter test frame, a 1.22 by 1.22-meter screen section test in the new full-panel test frame, and two tests of 2.4 by 3.6-meter screened area in the full-panel test frame. The 1.22 by 1.22-meter screen section tests in the full-panel test frame produced a peak load 6% higher and a yield load 30% lower than the partial-panel (original) test frame. The multiple pull points of the full-panel frame produced variable yield, peak, and intermediate loads, but on average were lower than the single pull-point tests. INTRODUCTION Roof and rib surface support has become a major component of the stability and safety of underground coal openings in the past 15 years. The use of screen, either metal or synthetic, has proven to decrease the injuries of underground coal miners. By 2005, there were 466 injuries in the United States caused by roof skin failures, with numerous mines not employing roof screen. In contrast, in 2015 there were 175 injuries caused by roof skin failures, with at least some of the reduction due to the increased use of roof screen. A continued effort to increase the utilization of screen in areas of underground coal mines where workers are traveling and working can reduce these injuries even further. To aid in this effort, the testing of various screen types under various loading and attachment conditions is required. Past testing efforts have primarily consisted of partial-panel testing in a laboratory setting. Laboratory testing of roof screen, both metal and composite, has been conducted in several ways by researchers, manufacturers, and other entities. The primary focus on the testing has been evaluating weld integrity of 1.22 by 1.22-meter screen section tests of various screen types utilized in mining (Dolinar, 2006; Dolinar, 2009; Tannant, 2001). There have also been several efforts at numerical simulation of the screen and screen/rock interactions (Murali et al., 2006; Shan et al., 2014). A few full-panel tests were performed with one pull or loading point in the center of the screen panel (Shan et al., 2014). As most previous efforts have mentioned, the only true way to evaluate the capabilities of screen is to conduct full-panel testing. Single wire strand, weld, and partial-panel (1.22 x 1.22-m) tests as well as numerical modeling only provide insight into the actual response of full-panel screen. A new test frame and procedure have been developed at PMRD to conduct various loading, anchoring, and material testing.

Jan 1, 2019

By Ting Ren, Lihai Tan, Alex Remennikov, Xiaohan Yang, Xueqiu He

"Due to recent coal bursts in Australian coalmines, research of coal bursts has attracted intensive interest from mining researchers and engineers worldwide. Previous research has shown that the sudden drop of fractal dimension may be a precursor of catastrophic failure of rock. This paper examines the fractal characteristics of temporal-spatial distribution of acoustic emission signals released during the compression loading process of coal. This research suggests the possibility of coal burst forecasting based on acoustic emission data. The concept and calculation equation of fractal dimension is introduced in this paper. Additionally, uniaxial compression experiments of Australian coal samples are conducted, and the acoustic emission waveform and 3D location are recorded simultaneously by eight sensors Express-8 AE monitoring equipment in the loading process. The experimental results indicate that the continued slowdown of fractal dimension in time sequence can be used as a precursory signal of coal sample brittle failure. The fractal dimension of the spatial distribution of acoustic emission events decreases with the evolution of coal fracturing.INTRODUCTIONCoal bursts refer to the catastrophic failure of overstressed coal subject to the dynamic and static loads. In recent years, coal bursts have occurred in major coal mining countries and this phenomenon has attracted the research interests of international mining and geotechnical scholars. A total of five coal burst accidents happened in Australian coalmines since 2014. On October 20, 2018, a coal burst occurred at Longyun Coalmine in China’s Shandong province, which led to 21 fatalities. Unfortunately, even after decades of research, it seems neither more accurate forecasting methods nor comprehensive controlling measures put forward by researchers have solved the problems posed by coal bursts.As an instantons energy releasing process, coal bursts are always associated with energy dissipation in the forms of acoustic emission, micro seismicity, and electromagnetic radiation (Yamada, Masuda, and Mizutani, 1989). It is believed by many researchers that the frequency–magnitude relationship of micro seismicity induced by rock failure satisfies Gutenberg-Richer relationship as well (Feng et al., 2017). Hence, based on the principal and theory of earthquake source locating, micro-seismicity monitoring equipment has been adopted in many coalmines to locate seismic event origins associated with coal and rock failure in an attempt to better forecast coal and rock bursts. Although many parameters such as b value (parameter of Gutenberg and Richter’s law) (Lu et al., 2015) have been adopted as indicators of risk, the forecasting of coal bursts is still of low accuracy. The same is true with earthquake prediction, as it remains as a worldwide problem even after decades of research and practice. Acoustic emission (AE) methods are now widely adopted to detect rock failure processes under an applied stress for application predicting the abrupt failure of rock in the laboratory (Li et al., 2017). Previous studies have found that significant overlap exists between research regarding AE and micro seismicity with respect to generation process (both are concerned with the generation and propagation of elastic wave) and event origin location, as geophysical signals of both are same (Lockner, 1993). That is, the frequency–magnitude relationship and early-warning indicators found by AE research in the laboratory have a potential applicability to in-field micro seismic monitoring of coal bursts. Through experimental study, Feng and Seto found that the temporal distribution of acoustic emission counts of rock have distinct fractal structures during load-increase processes (Feng and Seto, 1999). Landis and Lucie found good correlation between fracture energy and AE energy during testing of mortar specimens as well (Landis and Lucie, 2002). Based on preliminary experimental study, many schol"

Jan 1, 2019

By D. Carr, C. Anderson, M. Deal, C. Larson

"Construction of the OceanaGold Haile operation’s process plant in Kershaw, South Carolina is currently under way, with ore through the mill expected in late 2016 and commercial production expected in early 2017. The process is designed to treat 6,350 tonnes per day with minor upgrades required to achieve 8,270 tonnes per day. Plant optimization during detailed engineering, combined with a focus on de-risking the process, has resulted in numerous process changes since the initial design. This paper describes the plant optimization and de-risking, it also presents a proven commissioning strategy modelled after OceanaGold’s Didipio operation, whilst identifying potential expansion opportunities. INTRODUCTION Haile Gold Mine is located in Kershaw, South Carolina, approximately 50 miles south of Charlotte, North Carolina. Gold was first discovered at the site in 1827, and the property has been through several operating periods since. The last operation employed heap leaching from 1985 through 1992. Since then, the property has been closed and fully reclaimed. Romarco Minerals acquired the property in 2007, and began an exploration program that delineated 2.02Moz. of gold in reserve at an overall grade of 2.06 g/t. OceanaGold acquired Romarco Minerals and the Haile Operation in October of 2015. OceanaGold operates under a risk management philosophy in all aspects of operation, both corporately and at each individual business unit, and has implemented numerous process changes to eliminate or mitigate risks identified in the initial design of the processing circuit, and provided increased opportunity for optimization and expansion. This paper describes the plant optimization and de-risking, it also presents a proven commissioning strategy modelled after OceanaGold’s Didipio Operation, and identifies potential expansion opportunities. INITIAL PROCESSING CIRCUIT DESIGN An extensive metallurgical test work program was undertaken by Romarco Minerals and third party laboratories during the initial design phase of the Haile project [1]. This preliminary test work provided the technical information as a basis of plant design. The initial flow sheet for the Haile processing circuit is shown in Figure 1 (see APPENDIX). The plant is designed to process 6,350 tpd (7,000 stpd) on an annualized basis. The process begins with a jaw crusher followed by a SAG and ball mill grinding circuit to reduce particle size to P80 74 µm. A flash flotation cell treats 50% of the cyclone underflow in the ball mill circuit. Grinding circuit product is sent to a rougher flotation circuit to recover gold-bearing pyrite. The flotation concentrates from flash and rougher flotation are reground to P80 13 µm using stirred media detritors (SMD’s). The rougher flotation tail is pumped to the carbon-in-leach (CIL) circuit for gold recovery. The reground concentrate is pre-aerated prior to being pumped to the CIL circuit. The CIL circuit is a hybrid circuit with eight tanks. Tank 1 leaches the pre-aerated concentrate only, and tanks 2 through 8 leach the combined flotation tailing and tank 1 discharge. The carbon strip circuit is a standard pressure Zadra system, followed by electrowinning, and refining using an induction furnace. CIL tailing passes through a cyanide recovery thickener prior cyanide destruction and then pumped to the tailing storage facility (TSF)."

Jan 1, 2017

By S. D. Bechtel

Bechtel Civil and Minerals, Inc., one of the Bechtel group of companies, is a large engineering and construction firm that services the mining industry, among others. The firm's head, S. D. Bechtel Jr., comments on how his E&C company is dealing with the recessionary economy. First, he offered a historical perspective. About a half century ago-in the middle of the Great Depression-W. A. Bechtel and several business partners drew up a fixed price bid to build the Hoover Dam. At that moment in history, the W. A. Bechtel Co. was a modest success, but the times were troubled and uncertain. Money was scarce and a lot of contractors across the country were one project ahead of bankruptcy. The bid for Hoover was a make-or-break proposition for Bechtel, and it turned out successfully. The Hoover Dam was a no-frills operation in an isolated and harsh environment. There was plenty of hard work, long hours, and not many amenities. Controlling costs was critical. Everyone knew what had to be done, and why and what the consequences were. Today's Challenge Bechtel is now a bigger, more complex organization whose management views the current economic recession as a challenge to be met in much the same way W. A. Bechtel met the challenge of the Hoover Dam: by pulling together with a sense of purpose and direction. In many respects, Bechtel's situation today has a number of parallels to that which faced my grandfather. The company is eminently successful, but times are tough and there are plenty of signs that they could get tougher. My grandfather bet on the Hoover Dam to insure the future health of his company and I think we can work together again in that same tradition, make some tough decisions together, and the company's future can be just as promising. The first and most important requirement is to make certain that everyone understands the situation. The Bechtel group of companies are in an excellent financial position now. Its workload hit an alltime high in 1982 and it is well positioned in its principal markets. But the next two years may be critical for the company. Traditionally, Bechtel's work load lags behind general developments in the economy. Although many of its clients continue to suffer serious business difficulties, Bechtel is only beginning to feel the impact. The worldwide market for basic metals remains soft; relatively low prices and abundant supplies of oil and gas have flattened the petroleum market and made once promising synfuels projects economically unattractive; utility clients are still caught in the vise between overregulation and escalating costs. And persistently high, long-term interest rates have made capital investments expensive and difficult to justify. The company maintained a healthy workload through 1982. In some areas it has had little new work and consequently has been forced to lay off some staff as projects have been canceled or concluded. In other areas new work has tided the company over and more people have been hired. But new work bookings have fallen off, creating some uncertainty for the near future. 1983 requirements are clear, although seemingly contradictory. Belt tightening and cost reduction are necessary for Bechtel to remain healthy and competitive, enabling it to handle a possible further downturn with a minimum of turmoil and dislocation. At the same time, we need to allocate resources and funds in areas that will keep us positioned for the turn-around marketplace.

Jan 2, 1983

By Frank Florez

INTRODUCTION The Magma mine, located at Superior, AZ, some 100 km (60 miles) east of Phoenix, was discovered in 1875, and was originally mined for silver. The property was acquired by W. B. Thompson who formed the Magma Copper Co. in 1910. Prior to 1965, square-set mining and cut-and-fill methods were used to mine steeply dipping veins at Magma. Ore was moved to the chute by gravity in the square-set stopes and by slusher in the cut-and-fill stopes. The stopes were gobbed with waste from the surface and development headings in the mine. The original square-set method of mining was modi¬fied in order to extract replacement ore bodies in limestones that dipped at 0.52 rad (30°) and varied in thick¬ness from 4.6 to 38 m (15 to 125 ft). Mining of these ore bodies was done by starting at the upper lateral ex¬tremities and retreating to the access openings. The timber square sets and cribbing were used as temporary support, the ground being allowed to cave as the mining retreated. It was found, however, that mining in such a manner was very inefficient; safety hazards increased be¬cause of the blocky and fractured characteristics of the ore and the weakness of the hanging wall. GENERAL DESCRIPTION The undercut-and-fill method of mining is now the primary stoping method used at Magma, and no pillars are left for later extraction. Four ore bodies are pres¬ently being mined. These ore bodies (see Fig. 1) dip conformably at 0.52 rad (30°) to the east with the host limestone and shale sediments, their average strike length is about 122 m (400 ft), and their thickness varies from 9 to 38 m (30 to 125 ft). The ore bodies are separated by varying thicknesses of barren rock. Three of them come together at various elevations primarily in the area of the main feeder fault, but there is an apparent horizontal displacement of about 23 m (75 ft) on the main feeder fault which complicates stope layout. The method as originally applied has been modified in order to mine more efficiently ore bodies that are 9 m (30 ft) or more in thickness. The modification was made to mine all the ore at a given elevation before dropping down for the cut below. The advantage of this is that mining is done on a horizontal plane and there¬fore muck removal can be mechanized. Also multiple faces are made available, thereby improving overall min¬ing efficiency. Another major change made was to carry a 6.7-m (22-ft) face when mining the top sill and a 6.4-m (21-ft) face when mining under fill rather than the former standard 3.35-m (11-ft) high face. This change lengthens the mining cycle and cuts mat prepa¬ration costs in half. Stopes are laid out (see Fig. 2) so that maximum mining panels are available and yet one stope crew will not tie up too much of the ore reserve. One stope might consist of as many as 20 panels, and these panels are divided evenly on opposite sides of the extraction cross¬cut. The stope layout is planned so that the maximum tramming distance to the orepass will not exceed 30.5 m (100 ft) on the crosscut and 38 m (125 ft) in the panel. Stope panel distances are sometimes exceeded when min¬ing to the extremity of the ore body. Tramming distance limits are determined by the efficiency of the com

Jan 1, 1982

By Raymond W. Peterson

The practice of Countertrade and all of its variations has increased dramatically during the last five years in great part due to the worsening world economic situation and the Third World's increasing debt problems. Conventional wisdom has held that the goods finding their way into countertrade will tend to be manufactured goods of ever increasing value added. It is my contention that this has not been the case. The continued depression of most metals and minerals prices has conspired to keep a great number of metals and raw materials in the forefront of countertrade negotiations. The concept that if a country needs hard currency it will simply sell metals into world markets for cash has been significantly modified by countertrade which encourages subsidies for raw materials which are in turn funded by higher prices for the manufactured goods which the country must import. Countertrade is a term that is relatively new to most of us who have been involved in the international trade of metals and minerals, but it is one that we will continue to hear more of in the future. Countertrade as it is generally known today had its beginnings after the Second World War in Eastern Europe. As the shattered economies of Europe struggled to right themselves, a "cashless" system of trade developed. This system included such ancient concepts as barter as well as more modern ones like bilateral clearing agreements. For over 30 years countertrade was confined mainly to the COMECON nations and their various trade protocols with Third World nations. If metals and minerals were involved, there was little disruption of world markets by such examples as Cuba shipping ferronickel and sugar cane to the U.S.S.R. for a host of manufactured goods and oil. As the world's economy began to slow in the late 70's and the debt crisis began in earnest in the early 801s, this all began to change. As more and more nations which had previously been almost totally dependent upon their mineral wealth over-extended themselves in an attempt to industralize, they concurrently found their income from minerals falling, due to the decreased demand and subsequently lower prices available in the marketplace. At first these nations attempted to balance their payments by promoting the sales of their high value-added manufactured goods. We have all heard numerous examples of U.S. companies going to sell their high technology products in Rumania or Yugoslavia and being confronted with counterpurchase requirements for machine tools, shoes or drill bits. When faced with these demands, a number of companies chose not to sell into those markets while others merrily signed up the obligations without much intent to carry them out. The Performance Bonds required were generally minimal, especially when considered in light of the high margin inherent in high tech items; and the penalty clauses were equally small or nonexistent. A third group of companies actually tried to buy the machine tools or drill bits either for their own internal use or resale but found that due to poor quality and high prices, they were faced with a difficult if not impossible task. This is not to say that no one was able to fulfill a countertrade requirement, but the success ratio on these transactions was incredibly low. This was one of the major contributing factors to the reputation that countertrade has gained as a discipline ... "that it is mostly talk and very little action." As this situation slowly evolved, both the countries imposing the countertrade obligation and the exporters assuming the obligation began to realize that something

Jan 1, 1986

By Peter Joralemon

Introduction The Sierra Nevada Foothill Gold Belt in California extends from Mariposa north for more than 420 km (200 miles). It includes the Grass Valley and Alleghany districts in the zone of Northern Mines and the famous Mother Lode to the south. The gold belt has produced more than 3.1 kt (100 million oz) of gold since its discovery in 1848. This remarkable production, at the present gold price, would be valued at more than $40 billion. The Law of Gambler's Ruin supposes that averages are based on systematic rather than random variations. It emphasizes the vast differences between finite and infinite probability. By applying this Law to this figure, it can be seen that the belt has produced an average of 15.5 t (500,000 oz) of gold per running mile. Many geologists believe, with some justification, that less than half the gold in this belt has been mined. Sixty per cent of the past production has come from lode deposits, the balance from Tertiary and Recent placer gravels. This paper will concern itself with the developing lode mines along the Sierra Nevada Foothill Gold Belt. As a further and final note regarding placer mining along this belt, Mark Twain suggested that placer miners, having lost their senses, had contributed liberally to the population of California's insane asylums. After a 40-year lull with little or no gold production, the lode mines of this famous belt are showing signs of renewed activity. Two open pit mines, the Sonora (Jamestown) and Carson Hill, are now in operation at substantial scales. Two others, the Goldenbell (Pine Tree-Josephine) and the Royal-Mountain King, are being readied for production on equally impressive scales. All are in the southern part of the Mother Lode. Exploration farther north, at Sutter Creek, Drytown, and Georgetown, is showing encouraging results in developing deeper lode deposits. This new activity has been sponsored to a large extent by junior Canadian mining and exploration companies. Most of the established American mining companies have looked the other way, not participating in this important development. One major reason for domestic disinterest in this opportunity is there is little chance for heap leachable open pit ore in this belt, excluding Carson Hill. And heap leaching has become fashionable with American mining companies today. Also, this great old gold belt must have been worked out, for why else is there so little activity here - Catch 22 logic. Another reason is that if a new deposit of size and grade similar to the mines in the past was found, high costs would preclude a profitable operation. And, finally, California environmentalists would not permit mining, even if a rich deposit were found. These may all be pefectly valid reasons not to explore for gold along this belt. But a look at the history of gold mining in California may suggest that the future for exploration and development of the gold resources in the Sierra Nevada Foothills can be greater than the past. It was during the Depression of the 1930s that this gold belt saw its maximum activity, with more than 3000 mines in operation. Some were father and son operations producing only a few tons of ore a day. Other mines employed hundreds of miners to hoist more than 900 t/d (1000 stpd). Some ores were of marginal grade. Others, like the Sixteen to

Jan 7, 1987

By Richard R. Klimpel

INTRODUCTION Previous papers by this author have discussed some of the difficulties involved with optimizing the performance of industrial flotation circuits, e.g. Klimpel (1988, 1989). The two major problems seem to be: 1) the inherent "systems" nature of the froth flotation process which leads to a great deal of self-compensation among the various operating options available and 2) the inherent variations in mineralogy, water chemistry, etc. that always seem to be present in industrial operations. In particular, the influence of reagent dosage has been emphasized in the above referenced work including an industrial system interaction denoted as the R/K trade-off, Klimpel (1984, 1987). Using a simple two parameter model for fitting time - recovery data, Klimpel (1980): [ ] where r is cumulative recovery at time t or at the t th cell, R is the long-term equilibrium recovery and K is the first-order rate of mass removal from the cell (time ), the definition of the R/K trade-off with increasing reagent dosage can be given as follows: at low dosages both R and K increase, at intermediate dosages R continues to increase but K starts to level out, and at high dosages, R may flatten out or still continue to increase but K starts to decrease, sometimes rather quickly. An illustration of this effect in a batch laboratory flotation cell is given in Figure 1. The purpose of this paper is to give a detailed plant illustration of this R/K trade-off phenomena with changing collector dosage which shows just how highly interactive the grindinglflotation system in sulfide mineral processing really is. This is one of about 20 plant level case studies that are being presented and evaluated in an upcoming book, Klimpel (1990). The particular study given here was completed in late 1979 on a copper ore of head grade 0.93% Cu. The frother being used was Dowfroth* 250 at a constant dosage of 0.15 g for each ton of solids feed to the rougher bank and the slurry pH was 10.2. The motivation of the study was to better understand the relationship of changes in feed rate (hence in particle size and state of liberation) with variations in collector dosage (potassium amyl xanthate). The major concern was to determine how much extra economic benefit could be gained by better utilizing the existing grinding mills and rougher bank consisting of eight identical cells. The remainder of the flotation circuit was also studied, including regrinding of rougher tails, but did not prove as critical as the rougher bank operation itself. It appeared from an overall economic viewpoint, the battle was being won or lost in the manner in which the rougher bank was being operated. This was not to minimize the roles of the scavenging and cleaning circuits but those portions of this particular circuit could be rather obviously operated to achieve maximum benefit given the specific output of the rougher bank. A special attempt was made to maintain constant ore type throughout the entire test program. Eight specific test conditions were evaluated including three different feed rates (and hence three different size distributions) to flotation. Tables 1 and 2 summarize the eight test conditions and overall recovery results at the end of the rougher bank for each test. A single test consisted of at least three consecutive eight-hour shifts operating at steady-state with composite cell lip samples taken over the final eight-hour shift. "Trademark of The Dow Chemical Company

Jan 1, 1990