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By Joseph C. Rota, Charles E. Ekburg

Introduction The Gold Quarry gold deposit is the largest bulk tonnage epithermal gold deposit in northeastern Nevada to be developed by Newmont Gold Co., formerly known as Carlin Gold Mining Co. Exploration and development of the deposit extended over a period of nearly 50 years before bulk tonnage mining became economically feasible. Proven reserves at Gold Quarry are currently estimated at more than 255 t (8.2 million oz.) of gold, accounting for more than 40% of the total Carlin Trend mineable reserves for 1986. Milling began in late 1985; dump leaching of lower grade ores began in May of 1986. The mill has exceeded the initial design throughput rate of 6.3 kt/d (7000 stpd) and is now processing more than 8 kt/d (9000 stpd). The dump leach facility will process more than 7.3 Mt (8.1 million st) of lower grade ores in 1986. The Gold Quarry ore body is to be developed by an open pit that will eventually be 1830 m (6000 ft) long, 1220 m (4000 ft) wide and 300 m (1000 ft) deep. The mine currently produces 77 kt/d (85,000 stpd) on a 24-hour-a-day, seven-day workweek. Planned pit production will increase to nearly 168 kt/d (185,000 stpd) in 1988. Production equipment currently includes one Demag H-/285, three Komatsu PC-1500 hydraulic shovels, two Cat 992C loaders and 21 90 to 135 t (100 to 150 st) haul trucks. Mining is conducted on 8 m (20 ft) benches within the Paleozoic

Jan 4, 1988

By S. A. G. Poppen

The lining of a mine shaft is one of the most important considerations in the planning and operation of an underground mine. Generally, the function of a shaft lining is to preserve the shaft opening in a manner compatible with the expected mine life and -the other shaft operations. Where shafts are the only means of surface access in a mine, they also serve a critical function for the safety of the entire underground operation. Routine repairs and maintenance work on the shaft linings are only possible in stable strata with only minor interruptions to the shaft operations.

Jan 1, 1988

By J. Alvarez, S. H. Castro

The feasibility of chalcopyrite-pyrite separation in the flotation of a chalcopyritic copper ore, at reduced surface tensions regulated by methanol, was investigated. It was found that with methanol dosages from 0.5% to 1.5% v/ v, the chalcopyrite might be effectively separated from the pyrite, without use of other flotation reagents and pH regulators. However, under this simple condition, the chalcopyrite recovery was only around 50%, recommending the use of other reagents to reinforce the collector action. Low dosages of different collectors were tested, including SF-323 (Shell Float), S-6588 and S-7251 (Cytec), and S-701 (Molycop). Very promising results were obtained with low dosages of the collector S-701 and 1% v/v of methanol in the pulp, which evaluated against a reference test, gave similar copper recovery, higher Mo recovery and higher depression of pyrite. Consequently, this is an alternative process which does not require the use of lime to depress pyrite.

Jan 1, 1995

By R. Hogg, R. H. Weiland, P. Bunnaul

The dewatering of flocculated clay suspensions by compression in a centrifugal field was investigated. The results were analyzed with respect to the direct applicability of centrifugal dewatering (as in solid-bowl centrifuges) and indirect applications to gravity sedimentation systems. An important objective of the study was to evaluate the self-weight effect using centrifugal forces to simulate consolidation of deep sediments. Experiments were conducted in which the sediment mass and initial structure were maintained constant while the effective sediment weight was varied by centrifuging at different speeds. The relationship between the limiting sediment density and the applied consolidation stress was found to be the same for both gravity and centrifugal consolidation, indicating that small-scale laboratory tests can be used to predict consolidation in deep beds. The effects of the initial structure were also studied using controlled variations in flocculation conditions. The results imply that, for the flocculated suspensions studied, the longterm consolidation behavior is relatively insensitive to the actual extent of flocculation.

Jan 1, 1995

By R. A. Kirkland

The oxygen consumption method utilises an oxygen sensor to monitor the gas-phase oxygen concentrations in sealed chambers filled with reactive waste rock with subsequent confirmation of the oxygen content by gas chromatography. Results of experiments utilising low sulphide (<0.5w1%) waste rock yielded reproducible oxygen consumption rates on the order of 10-10 mol O2.kg-1. s-1. Petrographic analysis of the waste rock material indicated that the dominant sulphide mineral is pyrite (FeS2). Assuming a stoichiometry of 1.75 moles of O2 per mole of SO4 sulphate release rates were inferred to be between 6 and 18 mg SO4 kg-1 wk-1 Typically these results are 2 to 3 times greater than measured sulphate release rates from humidity cells. Our findings suggest that this techniques offers a rapid. cost efficient method for determining sulphate release rates in waste rock piles, even at low sulphide concentrations.

Jan 1, 2000

By Jan Walaszczyk

The paper concerns the calculation of stresses and displacements in working area of room-and-pillar mining system of cooper ore mines. A three-dimensional rock mass model based on the finite element method has been developed. The complete strain-stress characteristic for pillars has been applied, but for the purpose of modeling the curve has been approximated by three segments of lines: - the first represents a behavior of pillar before a failure, -the second corresponds to a progressive pillar failure phase, - the third represents the part of the curve, where the increase of strains do not cause the stress changes, and it is called the residual strength. The criterion of model stability has been derived, which can be useful for predicting rockmass stability. The programs have been built, which allow to calculate stresses in bar elements, displacements in plate nodes, and estimate the stability of the model, which consists of plate elements and one-dimensional elements with a segment strain-stress characteristic. The programs were used to consider two different problems, which are connected with mining design and the exploitation systems.

Jan 1, 1992

By J. Derwin King, Harrison R. Cooper

Applications of nuclear magnetic resonance (NMR) offer possibilities for on-line sensing of the concentrations of several elements in flowing sample streams. In addition to hydrogen, these elements, generally of low-order atomic number, include aluminum, phosphorus, fluorine, sodium, boron, and lithium contained in minerals having commercial importance. Many such elements have been difficult or impossible to successfully measure on-line using the more familiar X-ray fluorescence and neutron activation analysis techniques. The availability of practical on-stream analysis methods is essential to applying advanced controls to processes incorporating these elements. On-stream NMR instrumentation has been demonstrated in the past for several process applications including, as an example, coal flow and analysis; and the technology has recently been extended to the measurement of phosphorous BPL in Florida beneficiation plants. The technique involves simultaneous sensing of proton (hydrogen) and 31P intensities to provide data for continuous calculation of BPL in the phosphate through calibration to volume fractions of water and solids. Initial operating results are described using the PhospholyzerTM on-stream phosphorous analyzer designed for plant application.

Jan 1, 1990

By K. Irmscher

During the last years, using modular computer models on the software and distributed computer capacities on the hardware side has become quite common in the mining industry. When tackling real mining problems under the condition of heterogeneous systems, however, some problems become obvious: the incompatibility of the heterogeneous platforms in connection with the heterogeneously structured information and the necessity of interpreting the data. Knowledge based approaches are employed for solving different planning problems in the field of mining industry. The main problems here consist in the knowledge representation and data acquisition. Starting point of the investigation form classifications of mining planning problems and the corresponding models which can be transformed into information models for evaluation. With help of an expert system a practical solution is represented. Distributed systems with mobile computing and communication facilities for immediate access can be used as an additional support for planning and processing. On the base of public or private computer networks (including mobile networks) the foundation is given for a computer supported treatment of planning tasks. Additionally the use of teleworking scenarios in regions of mine planning and data collection in geological applications is prepared. Foundation forms a workflow system on an object-oriented distributed platform.

Jan 1, 1996

By J. D. Scott

This paper consists of a review of the development and application of spherical charge blasting at Inco Metals Company. Topics will include the Livingston Strain Equation, the field data required for its use in full scale operation, the type of ground in which mining has been carried out, explosives in use and their characteristics and finally, an overview of actual production applications. These applications include Primary Stope Mining, Secondary Mining Against Fill, Mining a Faulted Ore Zone and Drop Raise Blasting. INTRODUCTION Crater blasting in itself has been in use for over twenty years, but only recently has the technique been combined with a spherical size charge to form the Vertical Retreat Mining Method. This article endeavours to put the Livingston Strain Equation in a practical light, to describe several actual hard rock applications, and the results achieved in each case. THE LIVINGSTON STRAIN ENERGY EQUATION C.W. Livingston put forward the following equation as a standard means of determining the optimum burden required for full crater production blasting. The constant "E" is included in an attempt to recognize secondary breakage caused by strain waves.

Jan 1, 1981

By Gordon M. Pugh, David G. Rasmussen

INTRODUCTION Shrinkage stope mining can be employed in steeply dipping veins where both the wall and the vein material are sufficiently strong to stand with only minimal ground support. Shrinkage stope mining takes advantage of the swell in volume produced in breaking in-place ore. This expanded volume of ore is allowed to occupy part of the mined-out vein, and in so doing provides ground sup¬port and a working surface for the miners. Only enough of the ore is drawn after each stoping cut to allow work¬ing room. Not until the entire mining block has been broken is the full amount of broken ore drawn from the stope. DEVELOPMENT PRACTICES FOR SHRINKAGE STOPING The vein is developed into stoping blocks, each of which is 76 to 91 m (250 to 300 ft) in length and 61 m (200 ft) between levels. Level development, described later, is either on the vein or parallel to it with crosscuts periodically driven over to the vein. There are usually two exits from each stope. The first entry is a raise at one end driven either conventionally by raise climber, or by a raised borehole. Present practice is that this raise, put in from level to level, is either a 2.1- x 2.1-m (7- x 7-ft) Alimak raise or a 1.2- to 1.8-m (4- to 6-ft) diam borehole. Either raise system will require pro¬visions for an ore chute carried with the stope to the haulage level or the scram drift. At 9- to 12-m (30- to 40-ft) vertical intervals, dogholes are developed from the raise so that when stoping breaks back into these dogholes, timber or steel sets and necessary service facilities can be installed. The second entry to the stope may be either a similar raise at the stope endline, or more economically, a cribbed raise carried with the stope. As previously stated, development of the ore block is achieved by either drifting on the vein or by paralleling the vein with a footwall lateral and then crosscutting over to the vein at specified intervals. In the following discussion, three basic cases are illustrated in Figs. 1, 2, and 3. In Fig. 1, development is in the footwall by a 3- x 3-m (10- x 10-ft) trackless lateral. A heading is also driven on the ore and taken either full width or driven a standard size and slabbed to the vein width. Approxi¬mately 9-m (30-ft) long crosscuts on 7.6-m (25-ft) cen¬ters are driven from the lateral to the vein. For ease in muck handling they are usually put in on a slant rather than at right angles. A single orepass, located off the lateral and in the center of one stope block, can serve not only that stope, but also one on either side, up to a tramming distance of not more than 137 m (450 ft). Raises are put at the stope endlines on 91-m (300-ft) centers. The back of the vein is shot down and just enough broken material is drawn off to permit access for men to work off the broken ore. Development in Fig. 2 progresses by driving a 3- x 3-m (10- x 10-ft) trackless heading on the footwall side of the vein. The ore block is delineated by raises on 91-m (300-ft) centers. Crosscuts are again driven on 7.6-m (25-ft) centers over to the vein. Approximately four rounds are then taken up to the vein and each round is successively belled out so that all the crosscuts (pockets, in this case) connect. In this development, as opposed to that in Fig. 1 where there were no belled

Jan 1, 1982

By James Watson Baxter

Fluxes are used to promote pyrometallurgical processes that rely on adhesion (soldering or brazing) or fusion (gas and arc welding) to join metallic surfaces. In the adhesive processes, the metal surfaces to be joined are not melted; the join is formed using a filler metal with lower melting point than the base metal. Fusion welding involves use of heat in excess of the melting point of the base metal. The fused joint may be achieved either by simply fusing together metal surfaces brought in contact with each other or by introducing additional molten metal of similar composition to form a fused joint. ADHESIVE PROCESSES--SOLDERING AND BRAZING In order for molten filler metal, solder or braze, to spread in a manner that creates a successful join; the work surfaces on the base metal must be thoroughly cleansed. Fluxes remove stubborn oxide films and other surface contaminants, promote wetting of the work surfaces, add fluidity to the solder or braze, and enhance workability and ease of spreading. Brazing processes involve higher temperatures than those reached in soldering. Brazing fluxes, which must remain active and effective at the higher temperatures, differ from those employed in soldering. Some common fluxes used in adhesive processes are rosin for soldering tin and electrical connections, hydrochloric acid for use in soldering galvanized iron and other zinc surfaces, and borax for brazing. Soldering and brazing are similar processes, the primary difference being the temperature at which the joining operation is carried out. Soldered joints, produced with low-melting-point fillers (solders) that melt and flow at temperature less that 450°C (Althouse et al., 1988) can sustain loads of 1 to 1.7 MPa for extended periods of time (Anon., 1966). Brazing involves the use of filler materials with melting points commonly above 500°C and generally provides stronger joints than those obtained with solder. Both processes require local application of heat to melt and spread the filler so that the molten filler can wet (adhere to) the base metals by alloying and diffusion. Soldering Soldering is a means of joining metals by adhesion using a metallic bonding alloy as the filler, commonly a mixture of lead and tin. However, the adhesion of solder depends more on its ability to be keyed into minute surface irregularities than on alloying. The most familiar application is to provide and secure electrical connections. Soft solders can range from 1 to 70% tin with the remainder mostly lead. However, for general-purpose, soft-solder work, the alloy is commonly 50% lead-50% tin. Higher lead contents provide a wider range in the melting temperature and, for this reason, a 60% lead-40% tin alloy, which yields a mushy mixture, is used for wiped joints in lead sheet and pipe work. Conversely, 40% lead-60% tin alloys are used in soldering tin and other low- melting-point materials for which a narrower range of melting temperature is required. There are numerous other solder compositions such as tin-silver, 95% tin-5% silver and antimony-tin, 95% tin and 5% antimony (Carlin, Jr., 1992). Heat needed to melt and spread the solders is commonly provided by electrically heated, copper-tipped soldering irons or by means of torches; the solder is applied by hand, usually face-fed by means of wire. For wiped joints in plumbing and lead-cable splicing, the solder is manipulated with cloth pads. The molten solder wets the joint surfaces and is drawn, by surface tension, into minute fissures and capillary openings. Other applications involve use of induction heaters and furnaces with pre-shaped solder appropriately placed prior to fluxing and heating. In some processes, the joints are immersed in molten solder. Constituents and Role of Soldering Fluxes: Soldering fluxes generally fall into one of three categories: highly corrosive fluxes, intermediate fluxes, and noncorrosive fluxes. These same categories are sometimes designated inorganic, organic and rosin-based respectively (Althouse et al., 1988). Common constituents of each group are discussed briefly below. Corrosive Fluxes (Inorganic). Work with aluminum, magnesium, stainless steel, high alloy steel, aluminum bronzes, and silicon bronzes is carried out at temperatures in the upper portion of the range for solder operations. Soldering these materials requires use of highly active, corrosive fluxes to remove and prevent the formation of the especially stubborn, hard, oxide films that form on these materials upon exposure to the atmosphere. The corrosive fluxes consist of inorganic acids and salts that are applied either as pastes or dry. They are active at elevated temperatures and, since they remain active after the soldering is completed, must be completely removed. The main constituent of most corrosive fluxes is zinc chloride with a melting temperature well above the solidus temperature of most commercial tin-lead solders. It is made by the action of hydrochloric acid on zinc. When zinc chloride is used alone, un- melted particles of this corrosive salt get caught up in the joint and weaken it. For this reason, other inorganic salts such as ammonium chloride (NH4Cl) or sodium chloride (NaCl) may be added to lower the melting temperature. A mixture of zinc chloride and ammonium chloride is very effective because the excellent oxide reducing properties of ammonium chloride and the protective action of the molten zinc chloride combine to produce a fluxing action superior to that achieved when either is used alone. In addition to zinc chloride, ammonium chloride, and sodium chloride; common con-

Jan 1, 1994

By G. Labonte

The behavior of four different redox sensing electrodes (gold spiral, black platinum, chalcopyrite, and galena) during roughing and cleaning flotation is examined and related to the flotation response. Although it is difficult to provide unequivocal interpretations of the different potentials measured, the results indicate that the solution potential (as sensed by the black platinum electrode) is different from that of the pulp potential (gold spiral) and is only weakly related to the flotation response. On the other hand, the potentials exhibited by the gold spiral and the two mineral electrodes are related to the floatation response. The gold and mineral electrodes exhibit different transcient responses during the addition of flotation modifiers (e.g. NaCN, SO2). These responses appear to be related to the reactivity of the minerals and could indicate the conditioning time required to achieve flotation or depression of selected minerals.

Jan 1, 1989

By Rogério C. Guimarães, Antonio E. C. Peres

Arafertil&apos;s oxidized ore presents barite grades that oscillate between 5 and 12%. The barite separation plays a major role in the production of apatite concentrates for the manufacturing of phosphate fertilizers. The selectivity, via flotation, in the system barite-apatite is inherently difficult due to the similarity of the physical/chemical characteristics of these minerals. The evaluation of the relevant aspects of this separation was performed based on the determinations of the electrical surface charge of barite and apatite, the abstraction isotherms of cetyl-stearyl sodium sulfate and fatty acids soaps for barite and apatite, microflotation in a modified Hallimond tube, and flotation tests in a batch column. The results showed that the adsorption of cetyl- stearyl sodium sulfate occurs preferentially onto barite, in comparison with apatite. On the other hand, the rice bran oil soap presents similar adsorption levels onto both barite and apatite. The cetyl-stearyl sodium sulfate was selective as a barite collector in the presence of apatite, a fact that was not observed in the case of rice bran oil soap.

Jan 1, 1999

By James W. Cooksley

Through the early stages of metamorphism, when diffusion is the predominant mineral forming process. there is a tendency toward homogenization of rock units; but there is also zoning resulting from differing primary lithology and structure. Later stages of metamorphism, when infiltration occurs, tend to intensify zoning within the rock mass. The above concepts have been borne out in exploration of talc deposits and skarns. Initially, geologic mapping and soil sampling are directed to understanding mineralogy and petrology. Later, seismic methods are employed to further define lithology in the subsurface. Magnetometer surveys can also define some metamorphic units efficiently. Then, drilling must ensue to confirm lithology and determine extent of mineralization.

Jan 1, 1992

By W. Stahl, K. Keller

In addition to classifying bulk material, vibration screens are commonly used in dewatering. However, the lack of a comprehensive physical theory of dewatering often leads to difficulties in the design and operation of the vibration screens. First, in this report, the dewatering of bulk material are shown based on a physical model. Because of tile oscillatory motion of the liquid in the bulk, the inertial force of the accelerated liquid and the dripping of water out of the bulk or screen must be taken into special consideration. The physical model put forward shows the effect of the various operations parameters of dewatering screens. A comparison between dewatering theory and practice are shown by measurements using coal, limestone, etc. Dewatering measurements conducted on a vibration screen demonstrated that different vibration frequencies and rates of acceleration lead to different residual moistures. Finally, the possibility of improving vibration dewatering is described.

Jan 1, 1998

By Harry R. Price, Keith M. Swaffar

The Northeast Raw Water Tunnel transports untreated water to the Detroit Water and Sewerage Department&apos;s (DWSD) Northeast Water Plant where it is treated and distributed. The occurrence of a subsidence area which was attributed to the tunnel prompted the DWSD to have the tunnel investigated. After an extensive historical and geotechnical investigation, two access shafts were constructed along the alignment in the vicinity of the subsidence. Following completion of the shafts, the subsidence area was inspected in the wet prior to dewatering the tunnel. Upon the completion of dewatering, a dry inspection was performed. During the dry inspection, an area of significant distress was encountered where sand and silt were boiling into the tunnel along with large volumes of groundwater. This distressed area was located 800m (1/2 mile) north of the original subsidence area. The tunnel was immediately refilled with water and an emergency repair program was planned and implemented. As a result of the distressed nature of the secondary tunnel liner, dewatering of the tunnel could not be performed until the secondary liner and the surrounding soils were stabilized. This paper presents a case history of both the investigation and the repairs of the Northeast Raw Water Tunnel including the various grouting and unique tunnel stabilization methodologies which were utilized.

Jan 1, 1987

By M. R. Peterson, C. R. Ferguson, T. H. Jeffers

The ability of microorganisms such as yeast, bacteria, and various aquatic flora to sorb metals from dilute aqueous solutions is well documented. Although microorganisms have significant potential in decontaminating waste waters, techniques and equipment suitable for bioassisted decontamination are limited. The Bureau of Mines has investigated the use of microorganisms immobilized in porous polysulfone beads for extracting toxic and heavy metals from dilute waste streams. The minus 8- plus 12-mesh beads were fabricated from high-density poly- sulfone dissolved in dimethylformamide (DMF). Dried, thermally killed yeast, algae, duckweed, xanthan gum, and alginates were blended into the polysulfone-DMF, and spherical beads were formed by injecting the mixture into water. Microscopic analysis revealed microorganisms immobilized within the bead pores. The beads had excellent handling characteristics and were tested in stirred reactors, fixed bed columns, and fluidized bed columns for their ability to remove metal contaminants from several waste waters. The effluents resulting from these waste waters met or exceeded the National Drinking Water Standards for cadmium, copper, manganese, and zinc. Other heavy metal contaminants readily sorbed by the beads included arsenic and mercury. Elution of metal values from the beads was accomplished using dilute nitric acid or sodium carbonate.

Jan 1, 1989

By H. H. Murray

In the past thirty years, there have been a large number of ownership changes in the industrial minerals arena and many medium to large companies have made industrial mineral acquisitions. Industrial minerals are exceedingly important to the achievement and maintenance of a high standard of living in the United States and in other developed countries. In the developed countries of the world the value of industrial minerals exceeds the values of the metallic minerals. In the U.S., the value of our industrial minerals is some 2 112 times that of the value of our metallic minerals. Almost every single thing we use or touch in our daily lives can be related to an industrial mineral. Examples are the construction industry, agriculture, ceramics, paper, paint, plastics, electronics, glass, petroleum, and many more in which an industrial mineral or minerals playa functional role. Industrial minerals are exceedingly diverse in their values, properties, and applications. Sand and gravel is an example of an essential industrial mineral commodity which has a low price but moves in very high volumes. Geographic location of this commodity is critical because of transportation costs. High calcium limestone or marble has a moderately high price particularly if it is white enough for use as a pigment or extender. This moves in moderately high tonnages and location is not as critical be-cause it can be shipped for considerable distances and still be competitive. Some specialty industrial minerals such as a white tale or white bentonite sells at a high price at low volumes and geographic location is not a major factor in marketing. Prices of industrial minerals do not tend to be cyclic and generally keep up with inflationary increases. Because of the diversity of industrial minerals very careful analyses of acquisitions or divestitures must be undertaken by buyers and/or sellers in order to prevent serious mistakes.

Jan 1, 1994

By W. E. L. Minter

Discussion by R.W. Hutchinson Minter&apos;s excellent recent paper (1990) on the great paleoplacer gold deposits of the Witwatersrand and its subsequent discussion (Cheney, 1991) and reply (Minter, 1991) provide an informative, interesting and up-to-date review of the geology of these unique ores and some long enigmatic questions regarding their origin. Clearly summarized by Minter (1990) are the compelling sedimentologic and stratigraphic relationships indicating that the Central Rand Group conglomerates are ancient placers and documenting the fluvio-deltaic conditions of their transport and deposition. As Minter (1991) indicates, Cheney&apos;s discussion broadens Minter&apos;s 1990 coverage of the subject by considering higher and lower stratigraphic units and by adding detailed comments concerning recently published information about metamorphic and age relationships. Cheney&apos;s discussion and Minter&apos;s reply also readdress the old controversy of epigenetic hydrothermal vs. syndepositional placer origin for these deposits. This controversy has been resurrected by: • recent recognition of hydrothermally-altered granites (HAGS) in the older Archean basement rocks that lie unconformably beneath the Dominion Group rocks north and west of the Witwatersrand depository; • recognition of greenschist metamorphic assemblages in the Witwatersrand strata; and • the presence of interpreted epigenetic mineral assemblages and textures in some of the deposits. These relationships are briefly discussed by Cheney who suggests they may result from later, superimposed metamorphism and deformation and do not prove that the gold was introduced by epigenetic/metamorphogenic processes. In his paper, Minter (1990) cited the 1986 abstract of a subsequently published paper by Hutchinson and Viljoen (1988) who also considered many of these aspects and attempted to integrate them all in abroad genetic hypothesis. In addition, they emphasized the additional important problem of determining the source for the Witwatersrand gold. Although this issue was partially addressed by Reimer (1984), Mossman and Dyer (1985) and Reimer and Mossman (1990), the question has been generally under emphasized in earlier work and was, therefore, not stressed by Minter and Cheney. Reimer (1985) also emphasized the importance of weathering of the basin&apos;s Archean hinterland and its affects on Witwatersrand sedimentation. Since the epigenetic hydrothermal hypothesis was essentially discarded in favor of placerist origin, the gold source for these great deposits has generally been attributed to the weathering of lodes in greenstones or granites of the uplifted, older Archean hinterland to the north and west. However, Hutchinson & Viljoen (1988) present evidence that this explanation is inadequate, as well as data in support of an alternative explanation. They suggest that the gold and accompanying abundant, clearly detrital and auriferous pyrite in the conglomerate reefs were derived by erosional degradation of auriferous-pyritic exhalite previously deposited, by shallow marine discharge of hydrothermal fluids, along the fault-bound northwestern margins of the Witwatersrand depository. The auriferous-pyritic exhalites were generated by fluid-rock reactions in the subsurface, particularly in the highly-altered lavas of the Dominion Group but also in adjacent basement granitic rocks. The process envisaged is comparable to that observed in sea floor hydrothermal systems today, although, in this case, it occurred at the margin of a rapidly subsiding, shallow marine or continental basin. Important evidence for this explanation is the anomalous gold content of the ferruginous, shaley strata occurring throughout the Witwatersrand Supergroup and including the distinctive contorted bed that is an iron formation. These layers have been interpreted (Hutchinson and Viljoen, 1988 and 1990) to represent the more distal, finer-grained, mixed chemical/clastic sedimentary strata. Thus, they are the basinal equivalents of the proximal, auriferous-pyritic exhalites that were deposited along the basin&apos;s margin and subsequently reworked by sedimentary processes. This gold source explanation resolves many of the enigmatic questions regarding Witwatersrand geology and the reawakened controversy between proponents of hydrothermal and placerist genetic hypotheses. The theory invokes a hydrothermal origin for the gold in the basin-margin pyritic exhalites, thus explaining the visible hydrothermal characteristics (Figs. 1 and 2). It also provides compelling evidence for placer origin by encompassing all of the fluvio-deltaic processes of clastic sedimentary transport and deposition that are clearly summarized by Minter. These characteristics result from the degradational reworking of the pyritic exhalites along the depository&apos;s margins. Fluvial reworking, transport and deltaic redeposition of this detritus, along with additional detritus carried into the depository from the hinterland, then formed the conglomerate reefs. Other enigmatic aspects of Witwatersrand geology include: • the rarity of magnetite and ilmenite (the two most common heavy minerals in placer deposits) and the contrary abundance of leucoxene in the conglomerate reefs; • the presence of differing varieties of pyrite (authigenic, allogenic, compact and porous) all of which are auriferous; and • the presence of well-rounded pebbles, even cobbles, of pyrite that, in view of the brittleness of the mineral, could not have been transported great distances from a hinterland.

Jan 1, 1993

By H. E. Bonner

The recovery of fine coal has historically had limited success due to the intimate clay association on the surfaces of the coal particles. This clay presence has detrimentally affected conventional beneficiation techniques resulting in a recovered product containing unacceptably high concentrations of ash and moisture. An ultrasonically activated tray that operates in a continuous fashion has been developed that separates the clay film from each particle&apos;s surfaces. This separation is of sufficient duration to allow conventional beneficiation techniques to be utilized more efficiently.

Jan 1, 1989