Search Documents

By Verya Nasria, William Bent, William Hogan

"The South Hartford Conveyance and Storage Tunnel (SHCST) project is a significant component of the Hartford Metropolitan District’s (MDC) long-term control plan (LTCP), which is overseen by the Connecticut Department of Energy and Environmental Protection (CTDEEP). This project will address a portion of the MDC’s Clean Water Project (CWP), which will reduce combined sewer overflows (CSOs), eliminate sanitary sewer overflows (SSOs), and reduce nitrogen released into the Connecticut River. The purpose of the SHCST project is to eliminate West Hartford and Newington SSOs, eliminate Franklin area CSOs discharging to Wethersfield Cove and minimize CSO discharges to the South Branch Park River. The locations of each overflow are shown in Fig. 1. In 2010, the district prepared a preliminary design report (PDR) for the SHCST project, which included relief of the Folly Brook trunk sewer and proposed to keep the tunnel boring machine (TBM) retrieval shaft within the city limits of Hartford. Figure 1 shows the 2010 PDR recommended tunnel route. Subsequent to the PDR, the objectives of the SHCST have slightly shifted. In accordance with ongoing revisions to the LTCP, relief of the Folly Brook Trunk Sewer is no longer necessary. Additionally, the MDC has decided to perform less sewer separation in the Franklin Avenue drainage area. To replace the sewer separation, new relief points are proposed within the Franklin area and will be diverted to the SHCST. Figure 1 also shows the current recommended tunnel route (Alignment F). During 2012, the MDC conducted an evaluation of the potential of connecting the proposed North Tunnel (originally proposed as an independent tunnel with its own pump station) into the South Hartford Conveyance and Storage Tunnel. This evaluation concluded that the two proposed tunnels could reasonably be connected together and operated as a single tunnel system utilizing the tunnel pump station at the eastern terminus of the South Hartford Tunnel (Fig. 2). It also was concluded that this alternative was less costly than two independent tunnel systems."

Jan 1, 2014

By F. W. De Vries

A review as of the date of this meeting will cover the writer's perception of eachof the areas indicated in the charts. Changes in many are occurring with enough frequency that a detailed summary would be inaccurate within a few days of writing; for this reason, only an outline is appropriate for advanced preparation.

Jan 1, 1998

By Richard E. Ray

INTRODUCTION Main mine fan installations at underground coal mines must be designed to comply with the requirements outlined in 30 CFR (Code of Federal Regulations) Part 75. However, very little emphasis is typically placed on the aerodynamic optimization of shaft collar designs, ductwork configurations, and the selection of a fan isolation, or "closing door," system. Field testing has shown that poorly designed systems may produce large pressure losses between the shaft and fan inlet, as well as air turbulence problems which adversely impact fan efficiency and sometimes fan structural integrity. This paper analyzes each component of a surface exhaust fan system for an underground coal mine: • The shaft collar arrangement, • The 45 or 90-degree turning duct that isolates the fan motor from the return airstream, • Alternative ductwork arrangements for parallel fan installations, • The self-closing doors or dampers that are required for multiple fans, and • Horizontal and vertical evas6 arrangements on the discharge side of the fan. While discussion is limited to axial fan installations at shaft mines, most of the recommendations would also apply to centrifugal fan installations and to main mine fans for drift mines. FEDERAL REGULATIONS The mandatory safety standards for underground coal mines that apply to the installation of main mine fans are listed in 30 CFR Part 75.310. Stipulations which impact the design of the fan sys- tem arrangement are contained in paragraphs (a)(l), (a)(5), (a)(6),(d), and (1) of 75.31 0: • Each main mine fan shall be installed on the surface in an incombustible housing; • Each main mine fan shall be protected by weak walls or explosion doors in direct line with possible explosive forces; • Explosion doors or weak walls shall have a cross-sectional area at least equal to the area of the return air shaft or drift opening through which the pressure from an underground explosion would be relieved; • Each main mine fan shall be offset by at least 4.57 m (15 feet) from the nearest side of the mine or shaft opening; • Automatic closing doors shall be provided to prevent possible air reversals through the fans in mines ventilated by multiple main mine fans. The installation of main mine fans underground is prohibited by 30 CFR Part 75.310, (a)(l). Providing explosion doors or weak walls in line with a possible underground explosion and offsetting the fan 4.57 m (1 5 feet) from the edge of the shaft preclude the installation of the fan directly over the shaft. In addition, 30 CFR Part 75.507-1 specifies that all electrical equipment used in return air courses be permissible, which requires locating the fan motor outside of the airstream exhausted through the fan. To comply with the Part 75.310 regulations, explosion doors are typically located directly over the shaft as part of the shaft cover or 'bonnet." A sufficiently long section of ductwork placed between the shaft enclosure and fan, equipped with a 45 or 90- degree turn, enables the fan to be offset at least 4.57 m (1 5 feet) from the shaft and the motor to be isolated from the airstream. The need for the turn in the ductwork can be eliminated by driving the fan from the discharge side, instead of from the inlet side, and providing for a 90-degree bend in the evas6. For multiple main mine fan systems, self-closing doors can be located on the inlet or discharge side of the fan. FAN SYSTEM COMPONENTS A poorly designed exhaust fan arrangement will produce turbulent conditions at the fan inlet and significant pressure losses between the shaft and fan. Field tests have shown that pressure losses through inlet ductwork at some installations may constitute as much as 30 percent of the total mine head. Unfavorable flow conditions may cause a change in the operating point on the fan performance curve, resulting in reduced fan efficiency and pres- sure generation capability. In some instances, poor airflow distribution through the fan may create mechanical stresses that lead to fan blade or fan housing fatigue failures. The objective in designing an air duct arrangement for a fan system is to provide a low cost duct that will move the air from the shaft to the fan in a uniform air distribution and with minimum energy requirements. The optimum solution is a compromise between technical and economic factors. Aerodynamic design considerations for the shaft collar and cover, fan inlet ductwork for both single and parallel fans, self-closing doors, and evas6 are discussed in the sections below. Shaft Collar/Cover To prevent excessive turbulence and non-uniform air distribution through the fan, a smooth transition for the change in direction of airflow at the top of the shaft must be provided. However, the concrete lining of the shaft is abruptly terminated at the surface at many coal mine installations (see Figure I), creating a sharp 90-degree bend. The airflow exiting the shaft becomes heavily concentrated in the upper portion of the horizontal fan in-

Jan 1, 1997

By Bruce K. Cantrell, Stephen W. Stein, Kenneth L. Williams, David Hassel, Harvey Patashnick

In June 1992, the Mine Safety and Health Administration (MSHA) published the 'Report of the Coal Mine Respirable Dust Task Group; Review of the Program to Control Respirable Coal Mine Dust in the United States." As one of its recommendations, the report called for the accelerated development of two mine dust monitors: (1) a fixed-site monitor capable of providing continuous information on dust levels to the miner, mine operator, and to MSHA, if necessary, and (2) a personal sampling device capable of providing both a short-term personal exposure measurement as well as a full-shift measurement. In response to this recommendation, the National Institute for Occupational Safety and Health (NIOSH), Pittsburgh Research Center, initiated the development of a fixed-site machine-mounted continuous respirable dust monitor. The technology chosen for monitor development is the Rupprecht and Patashnick Co., Inc. tapered element oscillating microbalance. Laboratory and in- mine tests have indicated that, with modification, this sensor can meet the humidity and vibration requirements for underground coal mine use. NIOSH is continuing that effort by developing prototypes of a continuous dust monitor based on this technology. These prototypes are being evaluated in underground coal mines as they become available. This effort, conducted as a joint venture with MSHA, is nearing completion with every promise of success. The immediate benefit of this effort will be to researchers, regulatory personnel, and mine personnel, by permitting evaluation of specific mining practices to see which expose mine workers to excessive dust levels. Using this information, mine personnel can optimize mining procedures to reduce dust exposure. MSHA and the operators will also be able to use the dust concentration data to judge whether dust plan parameters are adequate to continuously maintaining environmental dust levels below the applicable standard. The second development recommended by the Dust Task Group was a person-wearable version of the continuous dust monitor. It will be a monitoring system designed to provide a measurement of worker exposure to respirable dust, both during and at the end of the shift.

Jan 1, 1997

By Barry T. Kilbourn

Yttrium Oxide is versatile; it is essential for television phosphors, for microwave garnets, for laser crystals and for high-performance ceramics, to name but a few advanced applications. When produced commercially, the material must satisfy not only stringent specifications regarding chemical purity but, increasingly, also meet closely defined physical parameters. The techniques needed for its production range from solvent extraction to carefully controlled precipitation and calcination. The processing steps from mineral concentrate to pure oxide will be described and related to the final oxide. The simple word "material" has complex connotations; it means, to paraphrase "Alice", exactly what we want it to mean. Throw in the label "advanced" and the picture darkens further! Just what is an advanced material and how does it differ from a common-or-garden material?

Jan 1, 1990

By John W. Greene

ennec?tt's Bameys Canyon Mine personnel developed an mnovahve process to extract gold from a small (1.8 million tons) sulfide ore zone in an oxidized ore body located at the Bameys Canyon Mine. This approach consists of extracting the sulfides from the ore via flotation, shipping the concentrate to Kennecott's new smelter, and mixing the flotation tailings with the oxide ore, agglomerating the mixture, and stacking the resultin tailings/oxide ore combination on the heaps. Conventional heap leaching technology is utilized to recover the gold from the mixed materials. Overall, the total gold recovery from the sulfide ore is esti­mated to be 90%. This approximation is based on a smelter gold recovery of 98% from the concentrate and an 88% recovery from the tailings during heap leaching

Jan 1, 1996

By C. W. Schultz

The distribution of material passing a screen, or a set of screens, is described by the equation [ ] where p = the probability that a single particle will pass the screen on a single presentation k = number of layers of screen cloth n = distance from head of screen expressed as number of screen openings. This model can be used to predict the performance of conventional screening operations (i.e., k = 1) as well as the so-called "statistical screening" operations. Using this technique, in which multiple identical layers of screen cloth are employed, screening can be carried out at a finer size than is possible with conventional techniques with no loss of separation efficiency.

Jan 1, 1969

By J. van der Walt

The Meikle Mine is located in the northeastern part of Nevada in the gold-rich Carlin Trend. First discovered in 1989, Meikle is being developed into a 2.2-kt/d (2,500-stpd) underground mine that will open during the second half of 1996. Work has already been completed on the mine’s cooling plant, a necessary item due to the high rock temperature and the hot ground water. In North American mines, there has been little need for refrigerated cooling. Therefore, Barrick needed to draw on experience from elsewhere in the world — particularly South Africa — to meet these requirements. The history of cooling mines using mechanical refrigeration dates back to the 1920s at Morro Velho in Brazil and 1936 at Ooregum in India (Dobson,1940 and Biccard, 1946). From 1940 to 1960, several cooling plants were installed on the deep level gold mines on the Witwatersrand in South Africa. These were followed by similar installations on the mines in the Klerksdorp, Welkom, Evander, Rustenburg and Thabazimbi areas. The first mine cooling plant in Germany was built during 1976.

Jan 1, 1996

By Harold J. Bennett

The Minerals Availability Program is a Bureau of Mines Program to systematically measure and classify identified worldwide nonfuel mineral resources according to their respective extraction technology, economics, and commercial availability. The program is designed to identify, collect, compile, and evaluate information on worldwide active mines as well as on developed and explored mineral deposits, and on mineral processing plants. Objectives are to classify domestic and foreign resources, to identify by cost evaluations resources that are reserves, and to prepare analyses of the availability of these resources for 34 commodities and secondary minerals. Availability analyses consider such factors as geographic location, the type of producible material, the technology and time required to produce a marketable product, and the productive capacity and unit cost for each deposit. These factors, reflected in the aggregated tabular and graphical data in the study for each commodity, are developed for consideration in the formulation of both domestic and foreign mineral policy. To date, the data have been collected for the 34 commodities and the availability analyses are in various stages of completion; expected first cycle completion date for all 34 is early 1986. Raw and aggregated data are available to the public in the form of computer-generated listings, tapes, and maps as well as in published reports. Also, systems developed to assist in performing the engineering and economic c analyses, including the computerized economic evaluation program (MINSIM) and the cost estimating system (CES), are available.

Jan 1, 1984

One of the core tenets of Sustainable Development is transparency and information sharing, i.e., government and corporate reporting. Governments report on issues within their sphere of responsibility to the degree that their constituents demand that they do so. Firms undertake reporting for two reasons: they are required to do so by law, and doing so makes good business sense. In recent years, stakeholders have come to see themselves as having a right to information about government actions and business operations that have the potential to affect their lives, health, community and environment. As a result, disparate groups, including industry associations, non-profit groups, academics, and individual firms, attempted to lay out what governments and firms should report. There are many types of sustainability reporting. In this paper we focus on three of them that both governments and firms utilize. We discuss the benefits of each. We argue that while the goal of complete and perfect data is not achievable or feasible, sustainability reporting of all three types is necessary to ensure that sound public and private decisions are made.

Jan 1, 2007

By W. M. Ma, Daniel W. H. Su, K. Centofanti, Yi Luo, W. L. Zhong, Syd S. Peng

9.1 INTRODUCTION There are approximately 70,000 abandoned coal mines nation¬wide, which is about 35 times the number of underground coal mines presently operating. The US Bureau of Mines estimates that there are over 8 million acres of undermined land due to the extraction of coal, metals, and nonmetals. Subsidence has affected more than 2 million acres, and more than 99% of the subsidence is related to underground coal mining. There is reason to believe that some of the remaining 6 million acres of the undermined land have a high potential to subside. The expansion of housing, highways, commercial structures, and other facilities has required the use of many areas that are underlain by abandoned coal mines, and this growth will continue. Many subsidence problems are derived from the collapse of aban¬doned underground coal mines. There are numerous abandoned mine workings in the anthracite fields of northeastern Pennsylva¬nia, in the Appalachian bituminous fields, the Illinois Basin, the Rock Springs, Wyoming area, and other areas of the United States (Gray et al., 1976). Various room and pillar patterns of mining have been used in the dipping anthracite seams and the nearly flat-lying bituminous seams with considerable variation in the per¬centage of coal extracted. The progressive deterioration of pillars, mine floors, and mine roofs after long exposure to air and water may later result in the collapse of strata over the mine entries, the crushing of the remaining coal pillars, or the bearing failure of the mine floor beneath the coal pillars. Subsidence then results as the collapse reaches the ground surface in the form of differential strains, depressions, cracking of the ground, and sinkhole devel¬opment. Subsidence over active longwall mines, which occurs concurrently with mining or is completed within a short period following coal extraction, has been studied extensively over the past decade. On the other hand, subsidence over abandoned coal mines receives little attention by the researchers, mainly because it is difficult to predict and takes place decades after mining has ceased. The techniques of investigating the subsidence events over abandoned coal mines are similar to those employed for active mines except that at the outset, it is necessary to determine whether or not the subsidence events are mining-related (Chugh et al., 1986; Cummings and Singh, 1986; Peng and Hsiung, 1986). This calls for the identification and confirmation of abandoned mine workings under or near the affected surface structures. Gen¬erally old mine maps, if available, are acquired, the surface bore¬holes are drilled for confirmation of the accuracy of the mine maps and determination of the potential for continued subsidence. Sub¬sidence monuments are established and periodic surveys con¬ducted to determine the amount and trends of surface movement in and around the affected surface structures; surface boreholes are used to investigate the integrity of the underground structures (i.e., roof, coal pillars, and floor) by TV camera. They are also used for monitoring the vertical and horizontal movements of the subsur¬face strata by Sondex (FPBX) and inclinometer (PFBI), respec¬tively, for determining the continuity of the subsidence events. Tape extensometers, crackmeters, etc., are used to monitor the development trends of major cracks in the structures or on the ground. These data are used to identify the causes of the subsidence events. Finally, abatement methods are selected to stabilize the structures. It must be noted that most subsidence events over abandoned coal mines are reported after the fact, and investiga¬tions are begun some time after reporting, that the subsequent measured movements are generally much smaller than that at¬tained in the active mines, and that due to lack of knowledge about the damage conditions and the exact location of the abandoned mine workings with respect to the affected surface structures, the precise causes of surface subsidence or surface structural damages are in most cases very difficult to identify. 9.2 TYPES OF SURFACE SUBSIDENCE According to Gray et al. (1977), after examining 354 incidents of subsidence above abandoned mines in the Pittsburgh metropol¬itan area, the subsidence features have a mean diameter (i.e. the average of long and short dimensions) from less than 1 ft to 1600 ft, with 84% less than or equal to 15 ft; the subsidence features have a depth ranging from less than 1 ft to 48 ft, with 89% less than 25 ft; 66% of the subsidence features are deeper than they are broad. Nearly 59% of the subsidence features occur with overbur¬den less than 50 ft thick and 81% less than 100 ft thick. No subsidence features occur with overburden thicker than 450 ft (Fig. 9.1). Occurrence of subsidence incidents varies from imme¬diately to more than 100 years after mining (Fig. 9.2). In analyzing the characteristics of approximately 3000 chim¬ney subsidence features along the Colorado Front Range, Matheson and Eckert-Clift (1986) examined historical aerial photographs on 4- to 14-year intervals between 1937 and 1967 and found that the majority of observable surface subsidence features occurred within 30 to 40 years after mining. According to Gray et al. (1977), the most prevalent subsi¬dence features over abandoned mined land are sinkholes, with depths of more than 3 ft, and troughs or sags, usually less than 3 ft deep. Sinkholes are steep-sided pits, while troughs are shallow depressions much wider in area than sinkholes. A. SINKHOLE SUBSIDENCE A sinkhole is caused by the collapse of a mine roof that works its way upward. If it is not arrested during the process it will eventually reach the surface and emerge as a sinkhole. The process is governed by the thickness and character of the overburden, the width and height of the mine openings. Sinkholes are usually 3 to 20 ft deep and may be 2 to 40 ft in diameter, although most are fewer than 16 ft across (Gray et al., 1977; DuMontelle and Bauer, 1983). Newly formed sinkholes have steep sides with straight or bell-shaped walls. At times, they appear to be conical in profile with the apex upward. If the topsoil collapses, the top portion will widen to form an hour-glass shape. Sinkhole subsidence usually occurs over abandoned mines less than 165 ft deep (Hunt, 1979). Matheson and Eckert-Clift (1986) found that chimney sink¬holes are likely to occur when the ratio of overburden thickness to mining height (h/m) is less than 4 to 5. When h/m is between 5 and 10 to 11, the potential occurrence of chimney sinkholes decreases rapidly. When h/m is more than 10 to 11, less than 10% of the mine openings that collapse will induce sinkholes on the surface.

Jan 1, 1992

By Alfredo Menendez, Alberto Sarmentero

A B S T R A C T The Los Pijiguaos bauxite is one of the largest accumulations of trihydrate alumina ore recently discovered; it is a plateau type, with no overburden, relatively soft tertiary quartz-bearing bauxite developed on a pre-Cambrian Rapakivi Granite batholith. The deposits are found in the northwestern rim of the Guiana Shield, State of Bolivar, Venezuela, and were discovered in 1976 after a grass-roots exploration campaign. Target areas were mainly selected on the basis of geological and geo¬morpholigcal criteria, guided by correlation with known deposits elsewhere in the Guiana Shield. The vertical. lateritic profile consists of an upper concretionary zone, followed by a mottled zone, a palid zone and finally the weathered rock merging into fresh granite. The upper concretionary zone displays a cellular, pisolitic or spongy texture and contains the following minerals: gibbsite (60-90%),quartz (5-10%), hematite (5-10%), goethite (under 5%), boehmite (traces), kaolinite (traces). The gibbsite content decreases sharply downward from the lower limit of the concretionary zone and the kaolinite and quartz content increases in the underlying mottled zone. The mottled and palid zones display a pseudo rapakivi texture and quartz, kaolinite and mica are the. essential minerals.

Jan 1, 1984

By M. C. Roberts

The success of any industrial mineral project requires an accurate forecast of the demand for the material. This paper develops a general method of evaluating these needs and applies it to the case of graphite. The basic method is to explain graphite consumption in each of its major uses by the output and manufacturing technology of the using industry. Once these underlying factors are determined, they can be projected to establish future requirements. This demand forecast is critical to the evaluation of a new source of supply, such as the graphite resources of upper Michigan.

Jan 1, 1989

By R. Woods

INTRODUCTION Gaudin (1), considered that "the mechanism of mineral collection is the central problem of flotation theory". From their work on adsorption phenomena in flotation for more than fifty years (2), Gaudin and his co-workers have made major contributions to the elucidation of this mechanism, a fact acknowledged by their contemporaries in the field (e.g. (3)). Their investigations in a number of areas, e.g. demonstrating that submonolayer quantities of adsorbed collector species can induce flotation, or identifying the influence of substances which can activate or depress (1), have helped to provide the basis for and the development of a theory to account for the interaction between mineral and collector. It was established in the late fifties (4) that the presence of oxygen is a prerequisite for the flotation of metal sulfides with thiol collectors. This fact rendered inadequate the concept of simple ion adsorption being responsible for rendering these minerals hydrophobic. The requirement for oxygen has been explained (1) in terms of this species being a component in chemical reactions between the sulfide surface and the collector. Gaudin has been instrumental in identifying the products of chemical reactions at sulfide minerals (1.5), a line of work which has been continued particularly by Finkelstein and co-workers in South Africa (6). In presenting a detailed mechanism of the mineral-collector- oxygen interaction, it has often been considered that the mineral surface - must first be oxidized to a metal oxy-sulfur species which

Jan 1, 1976

By D. M. Kjos

Large-diameter autogenous and semiautogenous grinding mills represent the primary thrust of the expanding grinding technology. In spite of initial difficulties, large autogenous and semiautogenous mills have reached an acceptable level of technology that provides the mineral engineer with a reliable, low cost means of ore comminution. A successful milling installation begins during the design stage of the grinding mill and the plant in which it is to be installed. This is particularly true in autogenous and semiautogenous mills. Critical mill and plant design factors should be considered while the mill and installation are still only "paper." Various current liner designs will be discussed ranging from lifter bar/plate to integral types. Modes of operation such as "high-low" will be considered. Liner maintenance procedures ranging from laydown area in plant design, proper mill shutdown methods, to installation and bolt tightening complete the equation to yield optimum performance possible for any particular grinding application. The objective of this paper is to discuss trends in wear materials, designs, and operating practices, and to provide some guidelines for good practice as we move through the 1980s. We will put together concepts that relate to the designs, materials, and applications so that higher performance can be obtained by the operator for his specific application. The concepts are shown as being in series became they are dependent on each other to achieve the desired performance: designs times materials times application results in higher performance (Arnson, Parks, and Kjos, 1983).

Jan 1, 1987

By Mingju Liu

The coal and gas outburst accident on May 20, 2007 at Sihe Coal Mine is unique in that there was no or very little soft coal in the coal seam and that the coal strength was very high. The outburst also showed that there was a very high gas content of 20-30 m3/t in the coal seam nearby the outburst site. Based on the field test and observations, together with laboratory experiments, detailed analysis was conducted on the controlling factors of coal and gas outburst potential at Sihe Coal Mine. Stress data available from Sihe Coal Mine, northern China, and other parts of the world, were also taken into account to facilitate the analysis. The results shows that the stress level was not abnormal compared to other coal fields in China prone to outbursts, and that gas contained in the coal seam was the main factor that triggered the outburst. All these factors were essentially controlled by the tectonic evolution features in Qinshui Coal Basin, to the Southeast of which Sihe coal field is located. Based on the analysis, assessment of coal seam outburst potential was carried out by measurements of coal seam gas contents, observation, and detection of soft coal layers in the coal seam. The results show that outbursts are limited to only a small part of the whole coal seam and that the eastern part of coal field is not prone to outbursts.

Jan 1, 2009

By James R. Arnold

With all of the publicity, criticism, and notoriety that the mining industry has received over migratory birds, it is diffi­cult to remember that six years ago no one even suspected that this issue would'emerge. After all, cyanide had been used in Nevada mining for 20 years without significant effects on wildlife. Although the mining industry has been buried in unjustified criti.cism for not having a clearer crystal ball, most of those critics forget that no one else predicted this problem either. In fact, the Nevada Department of Wildlife reviewed and had no objections to the Paradise Peak Plan of Operations before they began production. As we now know, Paradise Peak had one of the first and most severe avian mortality prob­lems in the State. It should also be noted that Paradise Peak has done more to research and solve the migratory bird problem than all of the rest of the Nevada mines put together. It is not possible to review all of the research and field work that has gone into investigation of the avian mortality problem over the past five years in this short paper, but a synopsis can be presented. In most instances we can say that we have solved the problem, We have learned what works and what does not. Let's start with what does not work. Unfortunately, the list is long and elaborate, but can easily be summed up in one word: hazing.

Jan 1, 1990

By J. K. Mohanty, D. Panda, P. K. Sahoo, R. K. Paramguru, K. C. Nathsarma

Ferromanganese slag, a product of the manganese industry, was characterized mineralogically. The slag, which contains high Mn values, was characterized using optical microscopy, XRD analysis and electron microscopy. No separate Mn-bearing oxide mineral phase was found. The slag is amorphous, and no crystalline phase was identified in the hulk sample by XRD, However, in. fine fractions, quartz was identified. Scanning electron microscopy (SEM) revealed the presence of Mn, Si, Al and Ca in the matrix without the development of a mineral phase. Leaching experiments using H2SO4 were carried out to determine if Mn could be extracted from the slag. At room temperature, almost 100% of the manganese could be dissolved at a solid-liquid ratio o f 1:10 by leaching with dilute sulfuric acid. The impurities could be precipitated by pH adjustment to produce a manganese sulfate solution suitable for the production of MnO2 or electrolytic Mn metal. Based on the laboratory-scale experiments, a suitable process is proposed to recover manganese values from the, ferromanganese slag.

Jan 1, 1999

By M. Vesely

Abrasive grinding, leading to ultrafine product and "critical size" material build-up inside the mill, is proposed as the cause of high power consumption and low capacity in many fully autogenous grinding processes. Addition of steel balls (hence, semiautogenous grinding) or pebble removal and separate crushing have been used, with different efficiencies, to overcome the problem. Information and data for the conceptual analysis, basic design and operation of a pebble crusher at the Los Bronces semiautogenous grinding plant is presented along with data showing a production increase of 1000 mtpd and significant operating costs savings.

Jan 1, 1985

By G. L. Myers

The Fortitude skarn near Battle Mountain, NV is currently one of the largest producing gold skarns in the world. It contains about 11 Mt (12 million st) of minable ore grading 5.14 g/t (0.149 oz per st) and is the distal portion of a continuous skarn system in the Copper Canyon area centered on the Eocene Copper Canyon granodiorite porphyry. Calcsilicate compositions, opaque mineralogy, and the high gold grades are atypical of other base metal skarns (iron, Fe; copper, Cu; lead-zinc, Pb-Zn; or tungsten, W). The Copper Canyon skarn is systematically zoned from a garnet (AD 70-100) dominant, pyroxene (HD 20-45) subordinate zone, with major Cu mineralization, adjacent to the intrusive (West ore body), to a pyroxene (HD20-100) dominant, garnet (AD90-100 cores. AD 30-60 rims)subordinate assemblage, with major Au, near the distal marble front (Fortitude ore body). An extensive biotite ± diopsidic pyroxene ± kspar alteration halo surrounds the pyroxene > garnet gold-bearing skarn and represents the early stages of metasomatic alteration. Retrograde alteration is limited in areal extent and intensity, and consists of actinolite, chlorite, quartz, and prehnite. Economic gold mineralization begins in the pyroxene > garnet zone and continues to the marble front, a distance of 1 to 1.5 km (0.6 to 0.9 miles), respectively, from the plutonic contact. The opaque mineralogy in this gold zone includes pyrrhotite, arsenopyrite, marcasite, minor chalcopyrite, galena, sphalerite, argentite, hessite, hedleyite, volnyskite, and native bismuth and gold. The pyrite-pyrrhotite geothermometer yields temperatures that range from 450° C to 300°C (842° F to 582° F) and the electrum-argentite-sphalerite geothermometer yields temperatures which range from 290°C (554° F) at the marble front to about 420°C (788° F) more proximal to the intrusive. Log fS2 calculations from the sulfide assemblages yield values near - 10 with log fO2 values of about -30, in a solution of near neutral pH (5-6). Calculations of metal solubility suggest that the metals were transported as chloride complexes in the proximal skarn but that bisulfide complexes were predominant within the distal gold skarn. Relatively low oxidation states buffered by the carbonaceous to argilliceous, calcareous protolith and subsequent ferrous iron-rich skarn assemblages appear to have increased the gold carrying capacity of this large hydrothermal system.

Jan 1, 1991