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By J. R. Dartez

The use of CCD (counter current decantat.io;1) thickeners, or; clarifiers, in the gold mining industry is quite common. Although there are a number of technologies in the industry which utilize these types of tanks, the fundamental requirement is to settle leach tailings and eventually separate gold and silver "values" from the "barren" (no values) solution. The thickener separation process varies depending upon the raw ores found in any specific mine. In mines where rudimentary, rocky ores are most common the settling process is fairly straight-forward and uncomplicated. But, for those mines with complex carbonaceous ores, usually identified by high silting, clay components, the ability to monitor and control the settled materials is quite laborious and costly. The task of monitoring and maintaining control of settled residue in clarifiers and thickeners, of any design, is difficult in any industry, but due to the added desire in the gold mining industry of leaching the values from the liquid slurry, the problem is multiplied. Other common activities taking place in the thickeners are exaggerated internal flow rates, settleable solids activity due to rake movement, and the settling activity generated by flocculents being added to the liquid medium. All of this action within the liquid column causes the continual monitoring of the interfaces within the tank close to impossible.

Jan 1, 1993

By Karl P. Norrena, Clayton V. Deutsch

Ore and waste cannot always be visually separated. The distinction between ore and waste may need to be made on the basis of blasthole sampling. Hand drawn dig limits or computer-generated contour lines do not account for uncertainty, economics or equipment. Geometric methods for interpreting grade information such as the polygonal or triangulation methods share the same limitations as contouring. Geostatistical techniques exist for the realistic modeling of grade variations and uncertainty. Decision analysis techniques exist for the binary classification of ore, and waste blocks in the presence of this uncertainty. Block-by-block classification is not enough; mining equipment cannot exercise free selection of blocks. There is a need for procedures to determine optimal dig limits that account for (1) the uncertainty in the grades, (2) the economics of risk-qualified decision-making, and (3) the ability of the mining equipment to dig to specific limits. This paper presents a procedure for optimal determination of dig limits that account for these constraints. Simulated annealing (SA) is used with modest computational requirements because the number of variables is relatively small. The solution of the optimization problem is dig limits that maximize profit under multiple constraints. The method is illustrated with different constraints and tested against hand drawn dig limits in a "Dig Limit Challenge," which illustrates the efficacy of the new method.

Jan 1, 2002

By Joseph K. Cavey

To accommodate the new Pier A expansion at BWI airport, a 1.8 m (6.0 ft)diameter stormwater pipe was constructed below active Runway 15R-33L. The jacked tunnel alignment runs east/west below the runway, and the depth the crown was 6.1 m(20 ft). Soil conditions consisted of very loose to medium sand and gravel, with some medium stiff clay and silt. Super Jet Grouting was selected as the ground treatment system, creating large diameter columns. All work was performed from the surface of the runway between the hours of 12 am and 6 am. Monitoring points along the tunnel in the grout zone indicated zero settlement during tunneling. Tunneling operations in front of and beyond the treatment zone experienced significant settlement. Super Jet Grouting in the treatment zone provided a low permeability continuous stable soilcrete that was readily mined while the runway remained in service.

Jan 1, 2003

By S. K. Mishra, S. B. Kanungo, D. Biswal

An attempt was made to beneficiate low-grade, high-phosphorus manganese ores of the Garividi-Garbham region of Andhra Pradesh, India, by using wet high-intensity magnetic separation (WHIMS). The distribution behavior of both mass and chemical constituents in different size fractions of a typical highly weathered ore sample was studied to obtain information about the liberation characteristics of various chemical constituents. Magnetic separation indicated that in the +208-µm size fractions, P and acid insolubles were concentrated in the magnetic fractions. However, in the -208-µm size fractions, P and acid insolubles were concentrated in the nonmagnetic fraction because of a lower recovery of the magnetic fraction. Variations in field intensity between 1.3 and 1.75 T had little effect on the recovery and the grade of concentrate. The results also demonstrated that phosphorus was associated with all three major constituent phases, namely, oxides of Mn and Fe and aluminosilicate gangue minerals.

Jan 1, 2000

By Tomb. T. F., R. A. Haney

During the past several years, the Mine Safety and Health Administration (MSHA) has conducted studies in underground mining operations to obtain information on occupational exposures to diesel particulate (DP), mine environmental DP levels and on the effectiveness of methodologies used to control DP. The studies conducted were representative of four coal mines and 10 metal mines. The metal mines included two lead-zinc mines, one limestone mine, two potash mines, one zinc mine and four salt mines. Three of the four coal mines were using disposable diesel exhaust filters to remove particulate from the exhaust and one was using a reusable wire mesh filter. Results of these studies indicate that average DP levels in coal mines not using exhaust filters range from 0.9 to 2.1 mg/m3, The use of exhaust filtration devices reduced these levels by about 50% to 90%. Studies conducted in metal and nonmetal mines showed average DP levels ranging from 0.3 to 1.6 mg/m3.

Jan 1, 1996

By Talaat A. B. Lawendy, Guerry H. McClellan

Batch laboratory-scale flotation tests were conducted on some carbonate-containing sedimentary phosphate ores to obtain concentrates suitable for chemical processing. The phosphate samples tested contained both calcite and dolomite. The calcitic phosphate ore was from Israel and the dolomitic ores were from China, India, Egypt, and Pakistan. The phosphate sample from Pakistan also contained a significant amount of silica. Several flotation techniques that have been proposed for upgrading carbonate -containing phosphate ores and concentrates were tested. Two processes gave better results compared with the other processes tested: a modified IMC anionic process and a. phosphoric acid depression process. At the best flotation conditions tested, phosphate concentrates assaying 32.5%-36.5% P205, 44.0%-51.0% CaO, and 0.6%-1.0% MgO were obtained at 69%-76% overall P205 recoveries from run-of-mine (ROM) ores containing 16.0%-25.0% P205, 40.0%-52.0% CaO, and 1.0%-11.6% MgO.

Jan 1, 1993

By R. Hemp

This paper describes work carried out to obtain a heat balance in the B3 shaft longwall stope at Blyvooruitzicht gold mine. Recordings were made of the temperature of the air and chilled water entering and leaving the section during three periods, August 1 September 1977, November 1 December 1977 and March 1978. These recordings, together with numerous other measurements were used to determine the rate at which heat was being removed from the section by the various fluids flowing through the section. The rate at which heat was entering the section was then calculated, by considering each source in turn. These two sets of figures made it possible to draw up a heat balance, and also obviously gave vital information on the magnitudes of the various heat sources and on the methods used to remove heat. In general reasonable heat balances were obtained, the errors being in the range -6 per cent to +22 per cent.

Jan 1, 1980

By Rudy Rogers

Gas hydrates have unique properties of storing selective gases. As much as 180 volumes of gas (standard conditions) per volume of hydrates may be stored. Recognizing the need for natural gas storage near electrical power plants for peak load use, DOE funded our laboratory to investigate gas hydrates as an economically viable storage means. Our developed process forms hydrates and self-packs the hydrates by only maintaining the gas pressure above a surfactant/water solution while hydrates form and self-pack. The laboratory process was scaled-up and demonstrated storage of 5300 scf of natural gas in hydrates. Subsequent to the demonstration, we discovered preparation procedures whereby laboratory gas hydrates could be stored at 1-atm with less than 1% decomposition over multiple days. The paper will discuss how these two advancements offer potential ways to recover vent gases as well as released hydrate gases from the seafloor. Keywords: gas hydrates, methane storage, surfactants, hydrate stability

Jan 1, 2008

By J. Patrick Powers, Joel Miller, Arthur B. Corwin

A combination of a slurry trench with dewatering successfully controlled groundwater for a large sloped excavation immediately adjacent to the Arkansas River. The Murray Hydro Electric Project required excavation through sand and gravel to bedrock, 85 feet below high water in the River. The perimeter system of deep wells pumping up to 25,000 GPM (1,600 1/sec) lowered the water level to 15 feet (4.6 m) above bedrock. A short soil/bentonite slurry trench near the toe of the slope cut off the residual head. The method cut six weeks from the critical path. Design of the slopes and the dewatering system demanded high safety factors because of risk to existing Lock and Dam No. 7. A localized pocket of soft organic clay was supported by a rock filled bolster. A major flood event was successfully withstood. The method can be applied to large civil excavations and open pit mines.

Jan 1, 1989

By M. Tokoglu

Accurate estimation of resources is one of the major challenges in mineral project evaluation. Contemporary mineral resource estimation practice calls for contribution from several disciplines and execution of several interdependent tasks. 3D estimation domain modelling is obviously one of the most essential components of such a substantial process which forms the basis of this research. The study constitutes a comparative analysis of four major domain modelling techniques; (i) explicit modelling, (ii) implicit modelling, (iii) indicator kriging, and (iv) conditional simulation. It involves comparison of outcomes for alternative scenarios to assess the implications of the modelling decision on resource estimates of a polymetallic massive sulfide deposit located in western Turkey. Thus, identical grade estimation method and parameters are considered to identify the discrepancies arising only from the choice of the domain modelling approach and underlying assumptions. Economic implications are demonstrated in the form of range of outcomes for the extends of the ultimate pit, ore tonnages (min:37.0 Mt, max: 46.7Mt), waste tonnages (min:201.2 Mt, max: 251.2 Mt), stripping ratios (min:5.18, max: 5.71), and total pit values (min: $1.05B, max: $1.45B). Examination of solid models as well as cross-sections revealed that major discrepancies are observed beyond outlying drillholes. Therefore, it has been proposed that assumptions regarding extrapolation distance is the main source of mentioned dissimilarities. Key words: Domain modelling, explicit modelling, implicit modelling, indicator kriging, conditional simulation INTRODUCTION Resource estimation is apparently a challenging process calling for extensive expertise and input from several sources, each of which introducing its related uncertainties. In the last decades, substantial role of quantitative analysis of several forms of risk and uncertainty in evaluating projects’ upside potential and downside risks has been realized. Studies indicated that mining companies have been severely impacted because of not meeting project expectations. As noted by Vallee (2000) “… in the first year of operation after start-up, 60% of mines surveyed had an average rate of production less than 70% of designed capacity”. Several other studies on mining projects also revealed that uncertainties related with the resource model are one of the major contributors of mentioned shortfalls. In this perspective, quantification of uncertainties associated with each component of estimation process is critical. 3D estimation domain models capturing major mineralization controls are the fundamental components of contemporary mineral resource estimation. Domain models are key guiding tools for estimation and are products of a complex process involving many unknowns and assumptions. There exists a number of 3D modelling alternatives which are distinct with respect to complexity, time and effort involved. Acknowledging potential influences on downstream mining practices and relavent economic implications, risks and uncertainties associated with 3D domain modelling are critical yet poorly studied aspects.

Jan 1, 2019

By M. O. Woodburne

The Mojave Desert province is comprised of a diverse group of mountains that range in elevation from about 2,000' (600 m) to 3,000' (900 m), separated by tracts of alluvial cover. The province is bounded on the southwest by the San Andreas fault, on the north by the Garlock fault, on the east by the Death Valley- Granite Mountains fault. Rocks preserved in the Mojave Desert Province collectively record a rich assemblage of Precambrian crystalline basement' ranging in age from ca. 1.8 to 1.35 Ga, upper Precambrian and Paleozoic Cordilleran miogeoclinal sediments and platform rocks, Mesozoic backarc and interarc shallow marine and continental sequences, locally emplaced Permian- Triassic syenitic plutons, extruded hypabyssal volcanic rocks of the ?Jurassic "Sidewinder Volcanic Series," and regionally intruded late Mesozoic granitoid batholithic rocks (Dokka et al., 1988). The Mojave block apparently was a high-standing element for much of the early Tertiary, with strata of Late Cretaceous or early Tertiary age preserved only on its margins. Beginning about in the late Oligocene an intense episode of regional north-south extension was developed in a roughly east- west trending belt that traversed the central part of the province. This extensional belt has been termed the Mojave Extensional Belt. The extensional regime lasted from about 22-17 Ma, and is generally divided into two phases. The first, from about 22-20 Ma records intense extension via the activity of crustal-scale, simple shear, low- angle normal faults, high-angle normal faults, and extensional fracturing, along with intrusion of intermediate to silicic volcanic rocks, including episodes of explosive volcanic activity. The Peach Springs Tuff, a major regional marker unit that extends across the Mojave from Arizona to about Barstow, forms an effective stratigraphic lid on the extensional interval, (i.e., is not rotated) and is dated isotopically at about 18.5 Ma. The extensional episode was followed by an interval of high- angle normal faulting and dike emplacement from about 19 to 17 Ma, and was accompanied by at least local uplift and volcanism. Most volcaniclastic and epiclastic sedimentary units of the central Mojave block post-date the interval of extension and normal faulting, and occur as a complex of marginal alluvial and more interior lacustrine facies that formed as recently as late Miocene (ca 13 Ma). Local sequences (e.g., Lava Mountains) record deposition up to about 8 Ma, but there appears to be a regional "gap" from then until at least local successions record Pleistocene deposition. Magnetic and isotopic age studies indicate a complex history of crustal rotations, distributed across a number of discrete domains, during the past 10 Ma. Some of the youngest volcanic and geomorphic features apparently developed at "holes" formed at the edges of rotated blocks.

Jan 1, 1995

By G. J. Allen

Kennecott Copper Corporation's Nevada Mines Division initiated a program to stabilize the inactive portions of the tailings disposal area and perimeter dikes in 1946. To date, approximately 1,000 acres have been stabilized with vegetation and ground cover.

Jan 1, 1978

By Stephen B. Castor

The rare earth elements (REE) which include the 15 lanthanide elements (Z = 57 through 71) and yttrium (Z = 39) are so called because the elements were originally isolated in the late 18th and early 19th centuries as oxides from rare minerals. Most REE are not as uncommon in nature as the name implies. Cerium, the most abundant REE (Table 1), comprises more of the earth's crust than copper or lead. Many REE are more common than tin and molyb¬denum, and all but promethium are more common than silver or mercury (Taylor, 1964). Promethium (Z = 61) is best known as an artificial element, but has been reported in very minute quantities in natural materials. Lanthanide elements with low atomic numbers are generally more abundant in the earth's crust than those with high atomic numbers. In addition, lanthanide elements with even atomic numbers are two to seven times more abundant than adjacent lan¬thanides (Table 1) with odd atomic numbers. The lanthanide elements traditionally have been divided into two groups: the light rare earths (LREE), lanthanum through eu¬ropium (Z = 57 through 63); and the heavy rare earths (HREE), gadolinium through lutetium (Z = 64 through 71). Although yttrium is the lightest REE, it is usually grouped with the HREE to which it is chemically and physically similar. The REE are lithophile elements (elements enriched in the earth's crust) that invariably occur together naturally because all are trivalent (except for Ce+4 and Eu+2 in some environments) and have similar ionic radii. Increase in atomic number in the lanthanide group is accompanied by addition of electrons to an inner level rather than the outer shell. Consequently, there is no change in valence with change in atomic number, and the lanthanide elements all fall into the same cell of the periodic table. The chemical and physical differences that do exist within the REE group are caused by small differences in ionic radius, and generally result in segre¬gation of REE into deposits enriched in either light lanthanides or heavy lanthanides plus yttrium. The relative abundance of individual lanthanide elements has been found useful in the modelling of rock-forming processes. Comparisons are generally made using a logarithmic plot of lanthanide abundances normalized to abundances in chondritic (stony) meteorites. The use of this method eliminates the abundance vari¬ation between lanthanides of odd and even atomic number, and allows determination of the extent of fractionation between the lanthanides because such fractionation is not considered to have taken place during chondrite formation. The method is also useful because chondrites are thought to be compositionally similar to the original earth's mantle. Europium anomalies (positive or negative departures of europium from chondrite-normalized plots) have been found to be particularly effective for petrogenetic modelling. REE were originally produced in minor amounts from small deposits in granite pegmatite, the geologic environment in which they were discovered. During the second half of the 19th century and the first half of the 20th century, REE came mainly from placer deposits. With the exception of the most abundant lanthanide el¬ements (cerium, lanthanum, and neodymium), individual REE were not commercially available until the 1940s. Since 1965, most of the world's REE have come from two hard rock deposits: Mountain Pass, United States, and Bayan Obo, China. GEOGRAPHIC DISTRIBUTION OF REE DEPOSITS More than 70% of the world's REE raw materials come from three countries: China, the United States, and Australia. China emerged as a major producer of REE raw materials during the 1980s, while Australian and United States market share decreased dramatically (Fig. 1). Table 2 gives recent annual production figures along with estimated reserves by country, and Fig. 2 shows loca¬tions of significant REE mining. MINERALS THAT CONTAIN REE Although REE comprise significant amounts of many minerals, almost all production has come from less than ten minerals. Table 3 lists minerals that have yielded REE commercially or have po¬tential for production in the future. Extraction from a potentially economic REE resource is strongly dependant on its REE miner¬alogy. Minerals that are easily broken down, such as bastnasite, are more desirable than those that are difficult to dissociate, such as allanite. In general, producing deposits contain REE-bearing min¬erals that are relatively easy to concentrate because of coarse grain size or other attributes. For more thorough discussions of REE¬bearing minerals see Mariano (1989a) and Cesbron (1989).

Jan 1, 1994

By Patrick Corser, Mitch Usibelli

Introduction Coal mining in Alaska's interior, specifically in the Healy area, began as early as 1918 with the construction of the Alaska Railroad. Mining was originally limited to underground operations but has expanded to entirely surface operations. In 1943, the Usibelli Coal Mine was formed and started developing Alaska's first surface mine east of Suntrana (Usibelli Coal Miner, 1984). Production from the local coal deposits has steadily increased and, in 1978, surface mining of Poker Flats was initiated (Fig. 1). Currently, a 25-m3 (33-cu yd) walking dragline strips two coal seams, using an extended bench on the second pass. In addition, a fleet of trucks and shovels are used for coal removal and some limited overburden stripping. In 1984, a contract was signed between Usibelli Coal Mine and Sun Eel Shipping Co. in 1984. Since then, production has nearly doubled to more than 1.3 Mt/a (1.5 million stpy). This article will discuss geotechnical constraints on mining within the steeply dipping coal deposits that exist within the Poker Flats mining area. Specifically, the article will describe how the mining operation retriggered an historic landslide on the No. 5 coal seam (Fig. 2). And the article tells how a mine plan was developed that allowed the coal to be safely removed without inducing additional movement. Regional geology The coal-bearing group in the Nenana coal field is of Tertiary Age. It is overlain in some areas by several thousand feet of Tertiary gravels - the Nenana Gravels. In areas mined by surface methods, the Nenana Gravels have been eroded off, and up to 30 m (100 ft) of quaternary outwash gravels overlay the coal-bearing formations. The coal-bearing group is divided into five formations: Healy Creek, Sanctuary, Suntrana, Lignite, and Grubstake (Wahrhaftig, 1969). Lignite Creek lies on the north limb of a west plunging anticline. This has brought the Suntrana coal-hearing formations near enough to the surface to allow surface mining. Mining is presently in progress on the south side of Lignite Creek in the Poker Flats area. The coal-bearing formation is cut off to the south by a fault having perhaps several thousand feet of vertical displacement, with the upthrust side to the north. South of this fault, Nenana Gravels are exposed on the surface. The Suntrana Formation contain the minable reserves at Poker Flats. This formation is a repeated sequence of poorly consolidated pebbly sandstone near the bottom, grading through a silty fine sandstone to a footwall clay unit immediately below a coal seam cap. The footwall clays are high plasticity clays to silty clays. It has been reported that they contain 30% to 50% montmorillonite (Usibelli Coal Mine Inc., 1982). There are six coal seams in the Suntrana Formation, No. I (the lower seam) through No. 6. Only the top four seams are currently exposed. No. 3, No. 4, and No. 6 seams are the only mined seams. The No. 5 seam is very thin or not present. Portions of the undisturbed Suntrana Formation are overlain by up to 15 m (50 ft) of Quaternary outwash gravels or recent landslide rubble. The surface is overlain by a very thin layer of muskeg and isolated areas of permafrost. In many areas, the outwash gravels are found immediately below the surface muskeg. Numerous landslides have been documented along the north facing slopes of Lignite Creek (US Geological Survey, 1970, and Wahrhaftig, 1958). These appear to be surficial solifluction or skin flow types of landslides. In addition, deep-seated structurally controlled slides are also evident on both the north and south sides of Lignite Creek. Structural features Premining aerial photographs (Fig. 3) of the Lignite Creek slopes in the Poker Flats area indicate substantial evidence of deep-seated landsliding. The landslides noted in Fig. 3 are both inside and outside of the current mining area. Surface mapping and geologic exploration indicate that the coal seams are dipping out of the slopes within the noted slide areas. It is suspected that, historically, these landslides were triggered by undercutting of the toe of the slopes by Lignite Creek. And sliding it thought to have taken place on one or more of the clay beds underlying the coal seams (Golder, 1985). The slide areas are characterized by semicircular head scarps and slumped topography. Based on the premining photographs, these slides do not appear to have been recently active. However, they are expected to be in a state of only marginal stability. Extensive coal exploration indicates that the primary structural feature within the

Jan 1, 1989

By Oscar Auerbach, Marvin Kuschner, Rosemarie Mick, Geno Saccomanno, Stephen Wood, Victor E. Archer, Marlene Egger

INTRODUCTION Excess bronchogenic carcinoma has been demonstrated among underground uranium miners in the United States, Czechoslovakia, and Canada (Archer 1981). This excess cancer is attributed largely to radiation from the alpha particles delivered to the tracheobronchial epithelium by the decay of short-lived daughters of radon. Interaction between the radiation and cigarette smoking has been demonstrated in production of the excess cancer (Archer 1973). The distribution of histologic types of bronchogenic cancer among uranium miners was established as different from that in other men in 1964 when an analysis of the first 51 cases among United States uranium miners was published (Saccomanno 1964). It was confirmed five years later by Yugoslavian studies (Horacek 1969). A later analysis, using a relative frequency method, indicated that oat cell and other small cell undifferentiated carcinomas increased markedly with increasing exposure to radiation in uranium mines (Saccomanno 1971). A subsequent analysis used only cases from an epidemiological study so as to enable calculation of expected numbers. It showed that there was an elevation in incidence of epidermoid, adenocarcinomas, and possibly other types, as well as small cell undifferentiated carcinomas (Archer 1974). At that time, it was felt that the histological distribution of cancer among uranium miners was well established. However, one of the authors (GS) has noted that fewer oat cell carcinomas were appearing among uranium miners in recent years. In his material the fraction of oat cell carcinoma, in successive 5 year periods between 1960 and 1980 was 59, 46, 37, and 22 percent. The association with calendar years is almost certainly spurious, reflecting some other factor associated with time. From the standpoint of tumor biology such a change must be important. This is a preliminary report which attempts to determine the cause of that change. POSSIBLE REASONS FOR OBSERVED CHANGE IN CELL TYPES 1) It might reflect a decrease in radiationinduced carcinomas, so that most of the ones being seen now are cigarette-induced. This appears to be a possibility because radiation levels in mines had been markedly reduced in the early 1970s, and because most of the uranium miners now developing carcinoma had quit mining during the 1965-1975 period. 2) It might represent a change in interpretation by the pathologists involved. 3) It might represent a real change in distribution as a result of increased latency, an aging population, cessation of smoking, increasing pack years of cigarettes, or other factors which have changed with time. Each of these possibilities is being checked. Dr. Waxweiler, later in this conference, is presenting an updated mortality analysis of United States underground uranium miners. His data indicate that lung cancer incidence among the Study Group of uranium miners is still quite high, but the ratio of observed to expected is falling somewhat. It is apparent that decreasing exposures in uranium mines is not yet reflected in normal lung cancer mortality rates. Reason #1 is therefore very unlikely. Thirty-five percent of the histologic types of carcinomas in this study were classified by a panel of three pathologists, 45% were classified by one of the panel members, and 20% were classified by a number of

Jan 1, 1981

By R. D. Rein

The Henderson mine is a large continuous panel caving operation in central Colorado. The orebody is roughly 760 m by 910 m and will be extracted from two production levels. Each level is divided into three north - south panels 244 m to 317 m wide. The general arrangement of a production level and its associated undercut drifts is shown in Figure 1. The production drifts (3.6 m by 3.7 m) are spaced 24 m apart center to center and have undercut drifts (3.4 m by 3.8 m) 17 m directly above them. The production drifts are interconnected with drawpoint crosscuts (4 m by 4.3 m) driven on 12 m centers. Drawpoint crosscuts receive substantial brow steel and concrete support prior to undercutting. The brow steel is a 15 cm by 46 cm wide flange beam with a 2.5 cm wear plate to box in the 'cave' side of the beam. The concrete is a minimum of 0.3 m thick and the batch design results in 27 500 kPa strength. The finished drawpoint opening is 3.7 m by 3.2 m with a choke area of 3.7 m by 2.4 m. (Figure la) Undercutting and bell formation is accomplished by blasting rings of 7.6 cm holes drilled from the undercut drifts. The rings have a burden of 2.0 m and six rings develop one complete bell.

Jan 1, 1985

By F. Feichtinger, M. Riess, A. Lammer

Introduction This article discusses the unique range of properties of platinum and its applications as a high technology metal. World reserves of this strategic and precious metal are confined mostly to South Africa and, to a far lesser extent, the Soviet Union. An analysis is given of past trends in world platinum output. The timepath is computed for the world platinum output rate, covering a period of more than 350 years. This is based on the postulate that the industrial conversion of a virgin resource progresses according to a Sigmoid curve. This computation is performed by means of a nonlinear, three-stage optimization model employing a multiform Sigmoid function. Finally, the price dynamics are examined. Platinum is the most important of the group of the platinum metals to which it gives its name. Other platinum group metals are iridium, osmium, palladium, rhodium, and rhutenium. The metals occur in nature in close association and are chemically very similar to each other. Three members of the group - platinum, iridium, and osmium - are the heaviest metals known to man. Platinum's density is 11% heavier than gold and about twice the weight of the same volume of silver or lead. Properties Platinum is a typical grayish-white metal. Its special properties were known 1000 years ago to the American Indian craftsmen of what is now Ecuador and Colombia. From those distant beginnings, platinum is now firmly established as the most precious and distinctive metallic element known to mankind. It is shown in Table 1, platinum has a unique wide range of physical, chemical, and mechanical properties including high melting point, resistance to chemical attack, high catalytic activity, mechanical strength, and malleability. These properties make it indispensable for use in many industries. Application Platinum is first and foremost a high technology metal. During the last few decades, fertile scientific minds searched for and developed widespread cost-effective uses for this precious metal. Its unique properties render it irreplaceable in many key industrial processes. Important major fields of application include: • protection of man's natural environment (pollution control), • defense, • fuel production, • fertilizer manufacture, • glass and glass fiber manufacture, • pollution-free energy generation - replacement of nuclear and fuel operated power plants, • electronics, • dentistry, • medicine, and • jewelry. Besides these industrial markets, platinum is increasingly finding a place in investment portfolios around the world as investors switch from gold and silver holdings to this relatively scarce and strategic commodity. Platinum has a growing popularity among private investors. This is being accelerated by the predicted "big crash" of the US dollar and its associated weak currencies, which American financial analysts are expecting towards the end of the decade. Figure 1 shows the demand for platinum in various applications throughout the western world in 1986. The total demand amounted to 88.6 t (97.6 st) of which autocatalyst usage accounted for 32.8 t (36 st) or 37%, the biggest share. Catalytic converter technology is increasingly centered on rhodium-platinum three-way catalysts. These catalysts are able to deal with all three pollutants - carbon monoxide, hydrocarbons, and nitrogen oxides - in a single catalytic unit. The introduction of these three-way converters will result in a further steep rise in the platinum demand for autocatalysts. Among all the metals used in the antipollution devices for automobiles, platinum remains

Jan 2, 1988

By Steven J. Kirk

In the past decade, many hardrock surface miners have revegetated dumps and tailings ponds to allow those waste disposal areas to blend more easily with the surrounding landscapes. Efforts have also been made to more creatively use the flat land resulting from the disposal of overburden and tailings. However, the mines which serve the best post-mining land uses are those that have been preplanned to incorporate such end uses. To more fully explore such a philosophy, interdisciplinary team from The University of Arizona conducted a study during 1974 and 1975 of six open pit copper mines in the Santa Cruz River Basin south of Tucson, Arizona for the purpose of investigating both interim and end-use possibilities for mine waste disposal areas. Among other reasons for the study, it was felt that alternatives for such waste areas would be more socially acceptable than barren dumps or tailings ponds. The team, known as the Mines Project Group, consisted of architects, engineers, and hydrologists. As it would have been economically infeasible to move the existing waste rock dumps or tailings ponds, preplanning was limited to the disposal of waste generated after the inception of the project. To better present their concepts, architecture professors Kenneth Clark and Fred Matter constructed a large-scale cardboard relief model of the mines and the surrounding Santa Cruz River Valley (1). The model was built at a scale of 1:12 000 (1 in = 1000 ft) with 30.48 m (100 ft) contour intervals and covered an area of 40.23 km by 32.18 km (25 miles by 20 miles) in scaled area. The mines being studied were cut into the model, but the proposed waste dumps and tailings ponds were built separately so different disposal configurations could be evaluated.

Jan 1, 1980

By Jess W. Smith

The carbonaceous Monkemeyer sandstone member of the Creede Formation on Bachelor Mountain hosts alteration and mineralization which contrasts with other silver deposits of the Amethyst system. More than 20 million ounces of silver are contained in disseminated mineralization in the volcaniclastic conglomerates and sandstones. Hydrothermal fluids entered the Creede Formation directly from the Amethyst fault system and mixed with flowing meteoric ground waters trapped beneath the Monkemeyer sandstone. Portions of the basal rocks of the Creede Formation were argillically altered by more dense acidic fluids generated by boiling. The carbonaceous base of the Monkemeyer and much of the conglomerates below were mineralized and well silicified. Deposition of the mineralization resulted from two processes: (1) reduction by carbon in the Monkemeyer, and (2) fluid mixing in the conglomerates. Monkemeyer mineralization is confined to the carbonaceous basal material and silver content is relatively consistent. Silver is contained in acanthite which is commonly associated with traces of galena, chalcocite, covellite and sphalerite. Fluid mixing and mineral deposition in the poorly sorted conglomerates was controlled by the highly variable porosity and permeability. Anomalous silver contents are dispersed throughout a large volume of conglomerates but zones of higher silver content reflect the crude layering of the conglomerates. Acanthite is finely disseminated in pore spaces and partly replaces some detrital magnetite. other metallic minerals are rare in the main zone of mineralization.

Jan 1, 2013

By Mona M. Fawzy, Ahmed A. Eliwa, Ebrahim A. Gawad, Ahmed H. Orabi, Amal E. Mubark

The growing demand for rare earth elements (REEs) has led to numerous recent studies to recover these elements from various bearing ores and wastes. Therefore, the recovery of REEs from Ras Baroud polymetallic concentrate has been investigated in the current study. Physical beneficiation for the Ras Baroud pegmatite sample was carried out, yielding a concentrate for euxenite (Y), fergusonite (Y), xenotime (Y), monazite (Ce), allanite, thorite, uranothorite and Hf-zircon, which resulted in raising the concentrations of REEs, Th, Zr, U and Ti in the sample. Fusion digestion processes with sodium hydroxide were studied using the conceived predictive diagonal (CPD) technique. The three experimental digestion groups proved the dissolution of 99.9, 95.6, 99.9, 52.5 and 0.47 percent for REEs, Th, U, Ti and Zr, respectively, under fusion conditions of 723 K, 120 min, 1/1.5 ore-to-alkali ratio, and smaller than 100-μm particle sizes. Fusion kinetics, isotherms and thermodynamics were investigated using several suggested models, namely, pseudo reversible first order, uptake general model and shrinking core model, which matched well with the experimental digestion results. Selective recovery of actinide content from the REE content of the digested concentrate chloride solutions was accomplished using solvent extraction with di-2-ethyl hexyl phosphoric acid. About 99.9, 99.9 and 4.2 percent extraction efficiencies for Th, U and REEs were realized, respectively, using 0.3 mol/L solvent concentration in kerosene as a diluent, 1/2 organic-to-aqueous ratio, aqueous pH of 0.2 and contact time of 15 min. Thorium and uranium ions were stripped with 2.5 mol/L sulfuric acid solution with 94 and 98 percent stripping efficiency, respectively. A highly purified REE precipitate was obtained from the raffinate solutions. Zircon mineralization tailings were obtained as a byproduct through the alkaline digestion process.

Oct 1, 2024