Search Documents

By S J. Brace

About 180 000 tons of explosives are used annually underground in South Africa. Most is loaded into holes less than 50mm in diameter. 75% is consumed in the gold and platinum mines where holes are between 25 and 4omm in diameter and no more than 3.0m in length. The small amount of explosives per hole with extreme conditions of heat, humidity and seismic activity, make the choice of explosive on safety and technical grounds very important to the success of a blasting operation. Taken together with the fact that many underground precious metal operations are now marginal then the choice of an explosive, when its price is also considered, becomes critical to the very viability of some mines.

Jan 1, 1994

By Axel Studeny

Geomechanical-numerical methods are an established tool for planning of underground excavations worldwide. By describing the interaction between heterogeneous layered strata and support elements it is possible to determine their suitability. The German hard coal mining industry has more than twenty years experience in investigation and using these parameters to carry out numerical calculations. Today, nearly all excavations (shafts, pit bottoms areas, bunkers, coal faces, development drivages, gate roads etc.) are calculated by geomechanical-numerical tools in combination with empirical planning methods. A high accuracy of planning results, which is a special requirement in the German coal industry with its deep-level longwalls, bedded and weak surrounding strata and multiple seam mining layouts, depends on the extensive calibration of the numerical models, which is achieved by: 1) Taking a large number of underground measurements with empirical evaluation. 2) Carrying out physical modeling. 3) Using the characteristic features of the installed support elements. This paper compares the planning approach used for multiple and single seam mining and presents the advantages of this planning tool. The main focus is on the feasibility of rockbolting as the sole means of roadway support for multiple seam mining operations, though the paper will also look at how the costs can be improved by using a low bolting density in single seam layouts.

Jan 1, 2007

By Richard E. Gray

Subsidence due to coal mining is poorly understood by non-specialists. This has led to numerous misconceptions and myths based on limited observations and lack of knowledge. The three most common are: 1. Mine maps are inaccurate. 2. Deep mines are not a problem. 3. If no subsidence has occurred for many years after mining, there is no risk of future subsidence. Maps are important during mining and most are carefully prepared. Future use to evaluate conditions at mine level often includes drilling to confirm what the map shows. Usually, little or no effort is made to tie the surface survey of the property to the mine survey, to conduct a well designed drilling program to confirm the mine map, or to drill test borings vertically. When a mine entry is encountered rather than a coal pillar, or vice versa, and conditions at mine level appear different than anticipated, the first reaction is the mine map is inaccurate. The idea of a safe depth from subsidence is often based on the false premise that mining results in sufficient breakup of the overlying rock strata that bulking compensates for the coal extracted. The safe depth idea first appeared in the literature about 1880 and remained prevalent well into this century. Sadly, it is still encountered. The modern understanding of fragmentation of the immediate mine roof with the overlying beds sagging down on the broken roof rock was first described in 1900. With full extraction mining, either longwall or retreat room and pillar, surface subsidence occurs regardless of the depth of the mine. Subsidence over longwall mines at depths of 2000 feet can be 90 percent of the mined seam thickness. Numerous studies of undermined sites conclude that mining occurred many years ago and since no subsidence has occurred, there is no risk of future movement. This is true if sufficient coal pillars have been left to support the overlying strata. However, every year subsidence occurs over mines that have been closed for 100 years or more. In a study of subsidence incidents over the Pittsburgh Coal, the senior authors found that 50 percent of the incidents occurred above mines that had been closed for at least 50 years and 10 percent over mines closed for at least 80 years.

Jan 1, 1996

By J. R. Kyte, L. A. Rapoport

The material balance equation for partiai or complete 1:trter-drivc reser1,oir.s been re-arranged to include a pressure irrferferencr ternr. This pressure interfernce term was ohtained from the theory established hy Morinda. A .successful progranl deissed to solve the resrclritlg c,qrration in a few hours on a nleelitr .sizeti, digital compuier. No prior knowdelge of the properties of the eqrrifer is required in the solution. 7' ri~rl calculations areatle using various assumed con!binuiions of value of the constant expretsing the qquifer properties correspoinds to the best fit ohtained between observed and calculated field history. Details of the method of calculaion are illus trated by an example. INTKCDUCTICN A method 01' calculating the material balance equation for a partial water-drive reservoir completed in an aquifer has been described in the literature." Pressure interference i'rc,m other pools iocated in the same nquiucr is not taken into account in this solution. When present, the pres- sure interference effect must be included in order to make a complete performance analysis. A correction for this effect has been developed using the theory cstahlished by Mor-tada.' Manual calculation of the material balance for water-drive reservoirs is a formidable task. Such manual ca1culation when interference eflects are includcd would be impossible to completc in any reasonable time period. However, a medium-sized stored program, digltal conlputer can he used satisfactorily. The method is described in the following sections. THECKETICAL CONSIDEKATIOhS The material balance equation for a reservoir producing by partial or total water drive, as proposed by Van Everdingen, This relationship is linear for Z/a from which thc slopc, Z, and the intercept, N, can be obtained by the least-squares method from the data points. It is not necessary lo know the aquifer properties to uktain oplimum values tor 2nd IV. Various assumptions are made tor At,,: where 11 is production time, seconds (oilfield between the equal successive time intervals into which the history is divided. t,, h It, times the number of equal time periods from i.e.. the total dimen-sionless time interval from It is noted that the dinlensionless time interval, At,,, involves all the relevant aquifer properties. Accordingly, any assunlption of is an assumption of the combined aquifer properties which pertain to the solution of the equation. Deviations of the data points from a straight line arc calculated for each assumption of and the value of A, correspond ing to the minimunl deviation is chosen as the optimum solution. This method is described in Ref. 1 and 2. Thc material balance solution is usually made with an initial assumption that the reservoir being studied is located in an infinite aquifer from which there are no other withdrawals. Deviation of the points by amounts greater than can be attributed to inaccuracies in field data may be the result of: (1) boundary effects of a limited aquifer, (2) pressure interference from othcr pools completed in the .sarne aquifer, and (3) a combination of these effects. Differentiation of these effects can be made only on the basis of geologic data. Pressure interference from other fields will result in a pressure drop at the original oil-water boundary having an interference component, The measured instantaneous pressure drops at the oil-water

The mineralogy of nickel slags from the flash smelter of Western Mining Corporation Ltd. at Kalgoorlie was studied. Residual magnesium silicates in the sulphide concentrates raise the melting point of the slag and result in the formation of magnesium-rich olivines. Addition of lime lowered the melting point, and, in slowly cooled slags, resulted in the formation of a pyroxene.Magnetite and sulphides were also present in all slags.The converter slags contained an olivine near fayalite in composition, together with wiistite, magnetite, and a little sulphide.Accretions from the hearth of the flash furnace were largely composed of magnetite with subsidiary olivine similar in composition to those of the flash furnace slags.Wall deposits, however, were largely composed of nickel ferrite and nickel-iron olivines.

Jan 1, 1976

By Paul J. Lewis

Estimation of the axial side shear resistance of drilled shaft rock sockets is directly related to the unconfined compressive strength of the bedrock. Commonly, the mean unconfined compressive strength value is calculated from a range of laboratory test results and is used to estimate the side shear of the bedrock. This paper presents the results from a full scale axial load test performed on an 8.5-feet-diameter drilled shaft rock socket, and compares measured side shear values to estimated values for two different rock strata. Measured side shear values correlated well with the design value calculated for the "strong" rock stratum, but did not correlate well with the design value calculated for the "weak" rock stratum. The mean unconfined compressive strength was used to calculate the side shear in both strata, but review of the laboratory data indicates that this value may not have been appropriate for the weak stratum due to a large variation in the laboratory test results. Also included in this paper is a discussion of the subsurface conditions, the laboratory test results, and the methodology used to design the drilled shaft rock sockets for axial and lateral resistance.

Jan 1, 2005

By Burns W. G, Muceniekas E, Whitcher I. G, Hughes F. E

No iron ore deposits were reported before 1961 from the Hamersley Ranges, Western Australia, although low-grade bedded iron formations, associated with ferruginous jaspers and cherts, were known to occur in the local Nullagine Series of Precambrian age.In January-March 1961 preliminary investigations in the area drained by the Turner River, Duck Creek and Serpentine Creek revealed the presence of over 1000 million tons of dense botryoidal or pisolitic limonite, forming flat-lying orebodies with 50-57 per cent iron.Large bedded hematitic orebodies were also discovered in the same area in August-October 1961. These have a porous, biscuity texture and an iron content of 60-61 per cent. They occur at a welldefined stratigraphic level (Brockman Iron Formation), normally in synclines where they have been upgraded by circulating meteoric waters during an old cycle erosion.In 1962 systematic geological studies and mapping, together with sampling and scout drilling, indicated larger reserves of biscuity hematitic ore and led to the discovery of massive hematite deposits at Mt. Tom Price. These were extensively drilled in 1963, proving the persistence of' high-grade mineralisation to a depth of 200 ft and over.To date the total indicated reserves of the Hamersley deposits, within the area held by Hamersley Iron Pty. Limited, are of the order of 4960 million tons and thus rank among the more important of the world. The reserves are composed of 600 million tons of bedded dense hematite ore with 64-66 per cent iron, 2900 million tons of bedded biscuity hematite-limonite with 60-61 per cent iron, 1360 million tons of limonite (goethite) ranging in grade from 50 to 57 per cent, and 100 million tons of canga (conglomerate) iron ore containing 53-63 per cent iron. In all cases harmful impurities are comparatively low.

Jan 1, 1964

By Tuan V. Nguyen, Louis Mittoni, Murray Rudman, CSIRO Minerals, Jean D. Swift, John B. Farrow, Phillip D. Fawell

"Research projects towards developing a sound understanding of the factors controlling the performance of gravity thickeners have been conducted by the AJ Parker Cooperative Research Centre for Hydrometallurgy since 1988 through AMIRA International. The current phase of this work, the three year P266D “Improving Thickener Technology” project, has 27 sponsors comprising mineral processing companies, reagent suppliers and thickener manufacturers.These projects have resulted in the development of a range of tools and techniques to address flocculation, thickening and associated dewatering issues. A number of Computational Fluid Dynamics (CFD) models have been developed to predict likely full-scale thickener performance under various process conditions, based upon a knowledge of thickener design, plant flows and assessment of the flocculation behaviour of the feed slurry. At the same time, various laboratory and plant studies have been used to quantify important thickener processes, and to provide validation of the CFD models. These numerical and experimental capabilities have been applied to various thickener issues across a broad range of mineral processing operations, leading to significant process improvements and substantial financial benefits.This paper presents an overview of the work conducted during these projects, focussing on the research tools, the nature of the information that has been gained and the implications for thickener performance."

Jan 1, 2003

By P. Rosten

US mine production of iron ore in 1984 showed some improvements compared to 1983. But reduced demand from the iron and steel industry caused temporary shutdowns of many iron ore mines and pelletizing plants. US raw steel production in 1984 was slightly above 1983, but still at a depressed level. Production was 83 Mt (92 million st), compared with 77 Mt (85 million st) in 1983 and 68 Mt (75 million st) in 1982. Two major production trends continued in 1984. They were the increased production from electric furnaces and the growing use of continuous casters. Electric furnace production included 33.2% of the steel poured in 1984, compared with 31.5% in 1983. Continuous casting was used for 39% of 1984 steel production, compared with 32.1% in 1983. Statistical Process Control Statistical Process Control (SPC) has taken on new proportions in the iron ore and steelmaking industries within the last year. This mathematical technique is used to monitor, control, evaluate, and analyze a manufacturing process. The technique charts variability of important quality parameters. Training and adaptation of SPC techniaues for process control have been initiated at Inland, Steel's Minorca, Pickands-Mather's Hibtac, Cleveland-Cliff's Empire and Sherman operations, and at Reserve Mining. One of these operations has requested its bentonite supplier provide SPC charts on quality specifications. Some of the steelmaking operations (Inland Steel, Bethlehem Steel, Dofasco, LTV Steel, National Steel, Stelco, Weirton Steel, and Wheeling-Pittsburgh) have set up SPC programs within their operations. And they also have insisted that some of their suppliers use SPC. Plant Shutdowns The permanent closure of Stelco's Griffith mine at Red Lake, Ontario, has been delayed by one year. This gives employees more time to adjust. The mine is now set to close in April 1986, instead of April 1985. Sidbec (Canadian government) and its other partners (including British Steel Corp., Quebec Cartier Mining, and US Steel) closed its iron mining operations at Gagnon, Quebec. The pellet plant has been leased to Quebec Cartier. New Iron Ore Operations The massive Carajas iron ore project in Brazil is scheduled to come onstream in Jan. 1986. It is to achieve full-scale commercial shipments by July of that year. The 66% iron crude ore requires only crushing and screening before shipment. The product consists of 83% sinter feed and 17% coarse ore. Annual production capacity will be 32 Mt (35 million st) when the project is completed. Principal customer for the ore is Nippon Carajas Iron Ore Co., a consortium of Japanese steel mills. The Arab Iron & Steel Co. (AISCO) has started up a $US300 million, 3.6 Mt/a (4 million stpy) iron ore pelletizing plant built by Kobe Steel Ltd., at Al Hidd-hide in Bahrain. By 1986, this grate-kiln-cooler plant will supply high quality iron ore pellets to feed direct reduction plants in the immediate Gulf area and Far East markets. Iron ore supplied from Brazil, Peru, India, and Mauritania provides the feed to the pellet plant. Hydrated lime (2%) is used as a burden.

Jan 5, 1985

By Francesco Vegliò, Luigi Toro, Francesca Pagnanelli

"Different hydrometallurgical processes have been studied in order to recover manganese(II) from oxidised minerals such as MnO2 (Vegliò and Toro, 1994). An innovative acid reductive leaching carried out in soft experimental conditions was here considered using agro-industrial wastes containing carbohydrates as reducing agents (Vegliò et al., 1998).The leaching process was investigated from a kinetic and equilibrium point of view in order to optimize the experimental conditions and obtain high purity and concentrated MnSO4 solutions.The overall leaching process (not considering the complex network of intermediate oxidation reactions of the carbohydrates in hot sulphuric acid medium (Vegliò and Toro, 1994)) can be described by the following reaction:24 MnO2 + C12H22O11 + 48 H 24 Mn2+ + 12 CO2 + 35 H2O (1)A Shrinking Core Model (SCM) was modified by a variable activation energy term to take into account both the variable reagent concentrations and the reaction rate change with respect to the manganese dioxide conversion. The influence of the particle size in the kinetic model is discussed with the support of SEM analysis and BET surface measurements before and after leaching.Manganese extraction yield was maximised (170-190 g/L) using appropriate carbohydrates and acid excesses, while impurity concentrations were kept low (Fe<10ppm and Ca<300ppm) pre-treating the ores, using hydroalcoholic leaching medium and different combinations of down-stream processes. In particular precipitation, solvent extraction and adsorption onto active carbon were tested to eliminate Fe and Ca from MnSO4 solutions."

Jan 1, 2003

An intensely sheared and mineralized zone occurs in the quartz dolerite greenstone (or younger greenstone) mass on the western limb of the Kalgoorlie syncline. This zone comprises the western part of the Golden Mile and has produced the greater part of the 33,000,000 oz of gold produced to date from the main mining belts. A study of the general geological and structural features suggests that the lode shear system will continue southward on a pitch similar to that of the main syncline. Although payable ore has been found recently further to the south, the expectation of large quantities extending southward from the present mining areas is problematical.INTRODUCTIONUntil the late 1930&apos;s the principal mining activities in the western lode system were centred on three major ore-shoots formed on the No. 4, No. 3 and to a lesser extent on the No. 2 lode shears (Fig. 1). With the gradual reduction of grade in depth on these main ore shoots, increasing attention was paid to the &quot;Minor Lode&quot; system of lode shears known to exist in the same area. A large quantity of payable ore was found on these &quot;Minor Lodes&quot; particularly in the central part of the mining area. In recent years more attention has been given to exploration in a southerly direction.ROCK TYPES AND STRUCTURESThe western system occurs on the western flank of a dragfolded, south pitching syncline. The rock succession consists of Black Flag sediments overlying the younger greenstone horizon which overlies the fine grained older greenstone horizon. The axis of the syncline is regarded as a tight infold of the overlying Black Flag sediments. This infold has been faulted and intruded by albite porphyry resulting in the formation of a composite body of slates...

Jan 1, 1964

By Christopher C. Woomer

Cyprus Shoshone Mine uses the longwall method to extract a deep, thick, pitching coal seam in the Hanna Basin of South Central Wyoming. The immediate, and main roof rock consists of weak, thinly-bedded, silty mudstones with weak, interbedded fine-to medium-grained sandstone. Tailgate ground control has been a critical factor impacting productivity at the mine. A gateroad condition mapping program for the 11 left longwall gateroads indicated potentially severe ground control problems for the tailgate. It was predicted that the existing, secondary support pattern of wood cribs would not provide adequate support capacity. As predicted, severe deterioration of the tailgate occurred in the form of a roof cutter, sloughing ribs, and failing wood cribs. Productivity was affected and additional support was required. Shoshone personnel evaluated several options for providing the additional support needed in the tailgate. The additional support system and placement method had to satisfy several requirements with respect to access, materials handling, placement method, set-up time and support capacity. Approximately 6,000-ft. of deteriorating tailgate had to be supported. The initial wood crib support system left a 6-ft. walkway for access and construction of the additional support. This access was further reduced as the roof loaded the wood cribs. This eliminated the possibility of mechanized material handling to the construction locations. All materials would have to be transported by hand. The additional support system had to be placed quickly to stay ahead of, and keep pace with, the required longwall advance rate. It had to incorporate the existing wood cribs and provide at least 500 tons of extra support capacity. And most critically, the system could not affect longwall ventilation. Longwall coordinators and engineers made the decision to use a low density, pumpable cement known to the industry as TeksealTM, to provide the system required. A 200 psi ultimate strength mix was decided on to provide the required load capacity. The existing cribs were formed with 1-in. by 6-in. boards and brattice cloth to provide the containment. To overcome the access limitations, three boreholes were drilled from the surface to the tailgate on 2,000-ft centers. A mobile pumping station was established on the surface and the TeksealTM was pumped 900-ft. down the boreholes through a 1.5-in. steel pipe, then as much as 1,800- ft. along the tailgate entry through 1.25-in. miner spray hose. The materials required for the TeksealTM supports could all be carried into the construction locations by hand. As a direct result of incorporating relatively new methods of pumping high yield, low density, cementitious grouts, the Shoshone Mine reduced downtime due to tailgate ground control problems by approximately 70% in comparison with previous Longwall panels. The longwall set three monthly production records while mining the 11 left longwall under the deepest cover, steepest pitch, and most extreme ground control conditions ever encountered at the mine.

Jan 1, 1995

By Tobias Hansson

The quality of Lime Cement (L/C) columns is to a great extent dependent on the installation procedure. At a site in the south of Sweden, the client reported problems with the installed columns. To evaluate the operator and equipment dependent part of the installation, Hercules Grundläggning AB was appointed as a competitor to the site contractor. The purpose was to install a number of L/C columns with equal installation parameters for both contractors. A total of 65 test columns were installed in June 1999. The geology is a typical Swedish organic soil profile with a top layer of peat overlying gyttja and clay. Two different binders were used in the comparison; blast furnace slag with cement and lime with cement. After installation, the quality of the columns was monitored by penetration tests and a column sampler for extracting whole columns. The column penetration test were performed 28 and 134 days after installation and extraction 134 days after installation. Inspection and tests of the extracted columns showed that by using a fully computer controlled procedure, the contractor produces columns of superior quality and homogeneity.

Jan 1, 2000

By Trevor Yeomans, David Yaschyshyn

"Placer Dome (CLA) operates the 90-year-old Dome Mine, in South Porcupine, Ontario.The milling operation currently processes 5 million tons of ore per year, from both the underground and Open pit mining operations, producing 320 000 ounces. The milling process is conventional crushing and grinding, with gold recovery by gravity followed by leach/CIP.Cyanide tailings are impounded in a large (325 ha) tailings area where cyanide is allowed to degrade naturally. Effluent is discharged seasonally during the summer and early fall months to maintain site water balance. Pond water is reclaimed for sole use within the mill process.In 1995, an Effluent Treatment Plant (ETP) was constructed for the purpose of removing dissolved metals and suspended solids. In 1997, an INCO S02/Air cyanide destruction module was added.During this time period, the treated effluent often failed toxicity tests required by the Ontario MISA Regulation, even though effluent chemical parameters were below permit limits. Two studies identified ammonia as the toxicant to Rainbow Trout, and free copper as the toxicant to Daphnia magna.From a literature study, and contacts within the Ontario Mining Association, the use of chelation as a final end of pipe treatment step to render any remaining free copper and metal fractions biologically unavailable was considered. Lab and plant scale tests followed.During the 1999 ETP operating season, the addition of the chelant EDTA (ethylene-diamine-tetraacetic-acid) commenced. To date discharged effluent has passed all toxicity tests.The paper will review the effluent treatment history, current effluent treatment plant operation, and detail the use of EDTA for successful toxicity control.History of Tailings Deposition, and Effluent Treatment From 1910 to 1995Over it’s ninety years of operation, the Dome Mine milling circuit has changed from the original 1910 stamp-mill mercury plant, to today’s modem 14 000 ton per day automated gravity and Carbon in Pulp based plant.By the 19803, a modern mill was operating on mainly underground mined ore. The plant was operating at some 3 800 tons per day, using fairly conventional processing routes.The number 4 tailings dam was being used for tailing’s deposition.All effluent treatment was by natural degradation of cyanide. Discharge was from decanting type structures during the summer months only, maximizing the use of natural degradation no tailings effluent was recycled for Mill use."

Jan 1, 2001

During the last 125 years, the steel industry has witnessed revolutionary changes in the process of steelmaking. The Bessemer process was the predominant steel production technology during the last two decades of the 19th century. The open hearth process accounted for the lion&apos;s share of world steel production for six decades from 1910 to 1970. With the appearance of the LD process on the industrial stage in 1952, the importance of open hearth process declined and currently the basic oxygen processes are contributing more than 60 per cent of the world steel production. The LD process also led to the development of several other oxygen blown processes such as LDAC, OLP, OBM, QBOP, EOF, Clc.

Jan 1, 1999

By D. J. Duck

INTRODUCTION Construction of the 3,600,000 kilowatt Third Powerplant at Grand Coulee Dam started in late summer 1967 approximately one year after authorization by Congress. The project was made possible by a treaty with Canada providing for cooperative development of the Columbia River which was signed in 1961 and ratified in 1964. Description of the Work The existing Grand Coulee power complex consisted of a dam and two powerplants with a switchyard serving each plant, one on each bank of the river. See Fig. 1. The switching facilities were connected to transformers at the powerplants by overhead 230-kilovolt and 115-kilovolt tie circuit conductors. [ ]

Jan 1, 1997

By Horst Peter Wölfel

The goal of biodynamic models is to simulate the vibration behaviour of the human body. In combination with experimental studies biodynamical models can be a powerful tool for the analysis of the effects of vibration exposure on health [1] and comfort. This paper gives an overview of the state of the art of biodynamic whole-body vibration models of humans, addressing both numerical models and hardware dummies. Method Two approaches are distinguished, the phenomenological and the anatomical, as illustrated in Figure 1. [ ] Phenomenological models aim to reproduce the vibration behaviour of humans with respect to particular physical quantities, chiefly the driving-point impedance at the interface to the seat, and partly with respect to other transfer functions. Discrete systems of masses, springs, and dampers with several degrees of freedom whose topology and parameters are determined by structure- and parameter identification methods are used in the sense that the functions derived from measurements are reproduced as well as possible. This paper provides an evaluation of this methodology and defines its range of application as well as its limits.

Jan 6, 2006

There has been a substantial increase in the use of rubber-tired front-end loaders in the mining industry in recent years. Concurrent with this increased usage, in the period of 1966 to 1970, there were at least 74 mining industry fatalities involving front-end loaders, or (on the average) in excess of one fatality per month. When the usage of front-end loaders by the construction industry and other industries, organizations, and agencies, such as the Government (i.e., Department of Defense), along with the uncounted numbers of serious, but non-fatal accidents, are included in the picture, the safety record for front-end loaders, of necessity, becomes a serious subject for study. There is an urgent need for attempts to be made to eliminate or reduce the number of safety hazards; to decrease the confusing diversity of controls designs found on present front-end loaders; to improve the maintenance and operating procedures; to formulate better personnel policies; to increase management and official awareness of the extent of the problem, in both industry and the Government; etc.; in order to decrease the number of accidents. Part of the problem may be traced to the fact that the operator of a front-end loader is frequently designated a "heavy equipment operator." This implies that he is automatically qualified to operate any model, of any manufacturer&apos;s, wheeled or tracked, front-end loader as well as many other types and classes of heavy equipment. Contrary to automotive practice, the complement of primary operating and emergency controls varies widely from model to model, as well as from manufacturer to manufacturer. Not only are certain controls present on one front-end loader model and absent on others, but there are significant differences in the modes of control operation, in the functions performed by superficially similar controls, in the location of the various controls, etc.

Jan 1, 1973

By William P. Blake

We are so familiar with water in its liquid and its solid form, that we seldom think of it as a mineral, and still less as a mineral product of any considerable industrial importance, though in the form of ice it is mined and stored up in enormous quantities yearly. The industry is peculiarly American, and in no other country has the business of cutting and storing ice been so well systematized and perfected. The interest has grown steadily from year to year, until it has attained large proportions, the annual production being counted in millions of tons, requiring, in the aggregate, a large investment of capital in all the Northern States. It gives employment, also, to thousands of men and horses, in the depth of winter, when farming work cannot be carried on. Ice is not only a luxury, but a necessity, in our climate, and is indispensable in many manufacturing operations: and finds constantly increasing applications and uses. As the industry has grown, so the necessity for suitable implements and tools has grown with it, and it has become necessary to systematize and cheapen the methods of handling such a large amount of material with rapidity and economy. As the industry is properly a branch of mining, and as our mining literature does not, to my knowledge, contain any description of the methods and appliances used in it, it seems desirable to place a brief description on record in our Transactions, and I therefore offer to the Institute the following outline description, based partly upon observations for several years past of the methods and processes employed, and partly upon the information obtained from prominent ice-miners and from the manufacturers of ice-tools. My acknowledgments are particularly due to the firm of W. T. Wood & Co., of Arlington, Massachusetts, for much information in detail, and also to the Knickerbocker Ice Company, of Philadelphia. The wood-cut blocks used in the illustration of this paper, have been kindly lent by both of these firms. The sequence of operations in getting ice is as follows : 1. Wetting down a light snow. 2. Scraping off an excess of snow, if present. 3. Marking out the field. 4. Ploughing and cross-ploughing. 5. Cutting the channel and detaching large floes.

Jan 1, 1883

Residual aeolian placers (RAPs) are formed by the wind, by preferential entrainment and removal of small and low-density detritusfrom a pre-existing, typically sedimentary sequence containing heavy minerals. Heavy minerals that are resistant to chemical alteration and either soft and malleable (gold), or extremely hard (diamond, sapphire, ruby, etc), are concentrated as a residual on the wind deflation surface, typically in the interstices between larger resistant clasts. RAPs form preferentially in arid or semi arid areas, where the vegetation is sparse or absent, and where topography and surface gradients are low, but may also form on beaches and in periglacial environments. RAPs consist of a continuous or discontinuous, planar or gently undulating horizon of heavy minerals in a single-clast-thick pavement of resistant pebbles, cobbles, or boulders, which mantles the present topography or palaeo-topography. Extreme wind erosion and surface deflation may condense the full pre-existing sequence into a layer of heavy minerals only. The grade of RAPs is substantially higher than in the precursor deposit, and commonly much higher than those typically found in most other placer types. Aside from their general occurrence as a thin pavement of resistant clasts, the best indicators of residual aeolian gold placers are the presence of wind-eroded stones (ventifacts) on the pavement, and the distinctive and unique shapes of aeolian gold grains themselves. The shape of the gold grains is progressively transformed by sand blasting during placer development, from grains with thickened rims, to toroidal grains on which the rims are æsplitÆ and peened inward toward the grain centre on one or both of the grain sides, to hemispherical or sub-spherical grains that are fully encapsulated by the in-turned rims. Gold that has undergone aeolian shape transformation is difficult to entrain and transport away from the site of aeolian concentration by anything other than mass movement or glacial processes. It is also easily retained by commercial recovery plants of any configuration.

Jan 1, 2004