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By K. Vanstaen, K. M. Cooper, S. Ware, S. L. Boyd

Remediation and restoration of offshore marine habitats is a relatively new concept with attempts in European regions largely being instigated by requirements of various strategic directives including Article 2 of the Habitats Directive (1992), the EC Water Framework Directive (2000, Article 2 of the OSPAR Convention (1992) and the developing European Marine Strategy Directive. A field experiment to establish the practicality of various options for rehabilitating the seabed on the cessation of dredging has been successfully set-up. The purpose of this experiment is to investigate the practicality and effectiveness of gravel seeding as a potential restorative method which could be applied at marine aggregate extraction sites following cessation of dredging. Zone 2, within Area 408 (offshore Humber) was chosen as the experimental site as there is some evidence for persistence of sand which may have resulted from screening operations at this site.

Aug 24, 2006

By C. A. Heiland

MEASUREMENTS of gravity with gravimeters have come into increased use in this country and abroad in the past five years. Probably 100 to 125 gravimeter parties are working in the United States alone. In oil exploration, gravimeter methods have relegated the gravity pendulum definitely to second place, if not third, and now closely rival and possibly surpass the torsion balance in many applications. Gravimeters have lately been applied in mining, although it is doubtful whether they will ever replace electrical or magnetic methods in this work. Notwithstanding the widespread application of gravimeters, there has been no article covering the entire field in the domestic or foreign literature. The purpose of this paper is to meet the demand for com-prehensive engineering information on the subject. The working principles of a number of gravimeters will be, illustrated and treated in relation to the action of corresponding seismometers and astatization methods. The mathematical discussion of theory has been confined to the most necessary fundamentals and been given in as ele-mentary form as possible. A description of calibration methods con-stitutes the last part of the paper. The symbols shown at the top of page 2 will be used in equations throughout the paper.

Jan 1, 1939

"The gravimetric dust sampler is one of the tools now available to the industrial hygienists for determining the worker 's exposure to the numerous types of particulate matter that may be present in the workplace. The paper ' reviews the different sampling trains that can be used for the two major criteria for respirable dust and some of the sources of error in this dust assessment technique.IntroductionIt may be stated simply that the measurement of airborne dust in the working environment is done for one or two reasons: namely, for engineering control purposes and! or to evaluate the potential for toxicological insult arising from the inhalation of dust particles.This paper reviews the progress made in the development of dust-assessing instruments, particularly the gravimetric types designed to meet British and U.S. dust criteria , and discusses the limitations in their use for this purpose."

Jan 1, 1981

By A. H. Miller

THIS survey is one of the more recent tests of geophysical methods of prospecting by the Dominion Observatory and the Geological Survey of Canada, of which the purpose is to find out what application such methods may have to geological problems in Canada. The Malagash salt deposit lies on the north shore of Nova Scotia about 40 miles east of the New Brunswick boundary, and forms a part of faulted and folded Carboniferous strata. The salt beds are exposed only in the mine workings, which are about 1000 ft. deep and at one place extend for 1000 ft. along the strike. Lack of rock exposures, complicated folds, and faults make it impossible to predict the location of salt away from the mine. A survey of an area in the vicinity of the mine was therefore undertaken to find out whether the salt could be located by the torsion balance and whether its extension from the mine workings could be traced. As the gravitational effects at Malagash may be fairly typical of those at other concealed salt deposits in the Carboniferous rocks of the Maritime Provinces of. Canada, the survey has a direct bearing on prospecting for other deposits. The survey was made in 1934 by A. H. Miller in collaboration with Dr. W. A. Bell, of the Geological Survey of Canada.. Observations began on June 15 and were completed four months later, on Oct. 15. Definite gravitational effects including a lowering of gravity were observed over the deposit. The survey also disclosed one other area of low gravity east of the mine but whether this area is underlain by a large body of salt is not yet established.

Jan 1, 1936

By A. H. Miller

THIS survey is one of the more recent tests of geophysical methods of prospecting by the Dominion Observatory and the Geological Survey of Canada, of which the purpose is to find out what application such methods may have to geological problems in Canada. The Malagash salt deposit lies on the north shore of Nova Scotia about 40 miles east of the New Brunswick boundary, and forms a part of faulted and folded Carboniferous strata. The salt beds are exposed only in the mine workings, which are about 1000 ft. deep and at one place extend for 1000 ft. along the strike. Lack of rock exposures, complicated folds, and faults make it impossible to predict the location of salt away from the mine. A survey of an area in the vicinity of the mine was therefore undertaken to find out whether the salt could be located by the torsion balance and whether its extension from the mine workings could be traced. As the gravitational effects at Malagash may be fairly typical of those at other concealed salt deposits in the Carboniferous rocks of the Maritime Provinces of Canada, the survey has a direct bearing on prospecting for other deposits. The survey was made in 1934 by A. H. Miller in collaboration with Dr. W. A. Bell, of the Geological Survey of Canada. Observations began on June 15 and were completed four months later, on Oct. 15. Definite gravitational effects including a lowering of gravity were observed over the deposit. The survey also disclosed one other area of low gravity east of the mine but whether this area is underlain by a large body of salt is not yet established.

Jan 1, 1936

By J. Leon-Torres, D. M. Stefanescu, P. A. Curreri, S. Sen

"Experiments were performed under terrestrial gravity (lg) and during parabolic flights (10·2 g) to study the solidification and macrosegregation patterns of Al-Cu alloys. Alloys having 2% and 5% Cu were solidified against a chill at two different cooling rates. Microscopic and Electron Microprobe characterization was used to produce rnicrostructural and macrosegregation maps.In all cases positive segregation occurred next to the chill because of the shrinkage flow, as expected. This positive segregation was higher in the low-g samples, apparently because of the higher heat transfer coefficient.A 2-D computational model was used to explain the experimental results. The continuum formulation was employed to describe the macroscopic transports of mass, energy, and momentum, associated with the solidification phenomena, for a two-phase system. The model considers that liquid flow is driven by thermal and solutal buoyancy, and by solidification shrinkage. The solidification event was divided into two stages. In the first one, the liquid containing freely moving equiaxed grains was described through the relative viscosity concept. In the second stage, when a fixed dendritic network was formed after dendritic coherency, the mushy zone was treated as a porous medium.The macrosegregation maps and the cooling curves obtained during experiments were used for validation of the solidification and segregation model. The model can explain the solidification and macrosegregation patterns and the differences between low- and high-gravity results."

Jan 1, 1999

By W. Blaschke, E. Malysa

INTRODUCTION In recent years in Poland, a problem connected with the occurrence of a considerable amount of liberated galena grains in size fractions under 1mm has arisen in the zinc-lead processing area. Operating practices have included crushing of ore particles under 0.2 mm followed by flotation. Jigs were applied to separate the concentrates from size fractions under 10 mm and to prevent the galena overgrinding. However, the fractions being too wide, the jigs have not worked effectively, in spite of the great differences in specific gravities of galena, blende and gangue minerals. Fine galena grains move into light fractions in considerable amounts and hence are overground. Therefore, the flotation becomes difficult and galena is lost in its tailings. These losses could be avoided by introducing separation in the grinding and classification circuits. The amount of 0-1 mm fraction is great; therefore, the application of concentrating tables or other kinds of jigs is impossible from an economic point of view. Taking these factors into account, the possibility of application of pinched-sluices was investigated. These are simple devices without moving parts, they have a high output for the unit areas, and their water and energy consumptions are low. In this paper, the results of zinc-lead ores beneficiation in pinched-sluices are presented.

Jan 1, 1980

By B. H. Sage

VARIATIONS in the composition of the liquid phase of natural reservoirs which are continuous through significant ranges in elevation have been noted by petroleum technologists. In general, there is a greater gas-oil ratio and the gravity of the oil is higher in production from the upper parts of the formation. In the present paper the possible changes in composition with elevation which would result from the attainment of thermodynamic equilibrium in a uniform gravitational field have been evaluated for a naturally occurring hydrocarbon liquid, a binary hydro-carbon liquid phase and a binary hydrocarbon gas. The results indicate a progressive decrease in the mole fraction of the components from methane through the butanes with increasing depth, accompanied by a corresponding increase in the amount of the heavier components making up the system. The magnitude of these variations is perhaps insufficient to explain completely the variations in the properties of the liquid phase that are encountered at various elevations within a particular producing horizon. However, the changes are significant and the treatment presents an example of the application of thermodynamic data to the evaluation of the properties of hydrocarbon fluids under the conditions approaching those encountered in natural reservoirs.

Jan 1, 1938

Measurement of densities, susceptibilities, permanent magnetization, and calculation of demagnetization factors has allowed computer modelling of gravity and magnetic data over the Middleback Range iron formations of South Australia. As well as providing structural information, the study emphasizes the effects of weathering on the interpretation of magnetic data.

Jan 1, 1975

By Case JE

Complete Bouguer and isostatic anomaly maps compiled for Costa Rica provide new insights into the crustal structure and mineralization. Terrain corrections were approximated from the station to a radial distance of 167 km by computer using a 3- minute digital elevation model of Costa Rica and surrounding areas. Isostatic corrections, based on Airy-Heiskanen compensation, were also calculated from 0 to 167 km using the 3- minute elevation model and from 167 km to 180 degrees using combined topographic and isostatic reduction maps. Costa Rica can be divided into four main terranes based on gravity data: a Pacific coastal region, a Pacific inland area, a central region, and a Caribbean coastal region. Negative gravity anomalies along the Pacific coastal margin correlate with an offshore sedimentary basin, and large positive anomalies correlate with mafic and ultramafic igneous rocks on the Santa Elena, Nicoya, and Osa Peninsulas, and at Puerto Quepos. Pacific inland anomalies are separated from the Pacific coastal region by a steep gravity gradient, and over the Coast Ranges a major gravity low overlies a thick section of low- density sedimentary rocks. In the central region, a major gravity low occurs over a thick low-density Quaternary volcanic complex in the Cordillera Central, north of San Jose. A prominent feature of the Caribbean coastal region is an interrupted gravity low over the Limon Basin that reflects a thickening of low-density sedimentary rocks. A conspicuous gravity lineament, trending northeast separates northern and southern Costa Rica. The lineament is defined by the termination of several major gravity anomalies including those over the Coast Ranges, Cordillera Central, Puerto Quepos, and Limon Basin. In addition, the lineament correlates with other geological and geophysical data including: northeast-trending faults, the southern limit of large Quaternary volcanoes, the segmentation of the middle America volcanic belt, and a seismicity gap. This lineament may be the expression of a previously unrecognized major northeast- trending fracture zone in central Costa Rica. An important economic implication of the gravity lineament is a correlation with the termination of gold and porphyry copper deposits in Costa Rica.

Jan 1, 1987

By Albert Hoskinson

PROGRESS on the earth depends to a large extent upon the rapid inter-change of ideas and commodities between the various nations of the world. The smooth flow of commerce, by which these ideas and com-modities move, is accelerated by accurate and complete maps of the various land and water areas of the earth, The production of accurate maps depends upon a complete knowledge of the figure and dimensions of the object to be charted, therefore a knowledge of the shape of the earth is a prime necessity for accurate charting purposes. Gravity observa-tions were first undertaken to aid in determining the shape of the earth so that the geodetic surveys of its land and water areas might be more accurately connected to form an undistorted map. A large part of the earth's surface is water and it is therefore necessary to get gravity values at sea as well as on land before a complete and accurate figure of the earth can be determined. Dr. F. A. Vening Meinesz, of Holland, was the first scientist to perfect a pendulum instrument that would accurately measure gravity at sea. He had previously developed a multiple pendulum apparatus for measur-ing gravity upon swampy and unstable land areas in Holland and it was therefore quite natural that he should adapt the instrument to give accurate results upon a still more unstable support, the surface of the sea. His instrument as perfected gives satisfactory results when mounted in gimbals on any vessel where the roll and pitch are not more than about 5° and where the vibrations from rotating machinery and wave action are not large enough to cause the pendulums to shift on the knife-edges. This degree of stability can be obtained on surface craft only in protected waters or on very calm days. Therefore, Dr. Meinesz mounted his instrument in a. submarine so that he could submerge below the disturbed surface waters and get the desired stability in nearly any kind of weather by simply diving to greater depths. Most of the gravity-at-sea work has been done with a Meinesz instrument and a very large number of the observations have been made by Dr. Meinesz himself. He has occupied nearly 1000 sea stations and probably has traveled as many miles by

Jan 1, 1938

By Michael A. Zappia

INTRODUCTION The San Manuel mine of Magmacopper Company is located approximately 72 km northeast of Tucson, Arizona. The mine, concentrator, smelter, electrolytic refinery and continuous rod casting are located on the west side of the San Pedro River valley. Ore Production: 58 1W mtpd Production To Date: Over 340 000 000 mt since 1956. Ore Grade: 0.70% net sulfide cu. As conceived at the present time, the San Manuel ore body is the lower half of what was originally an elliptical (In cross sect ion) cylinder same 2400 m long with major and minor cross sectional axes of 1500 m and 760 m. After emplacement, the cylinder was diagonally sliced along its long dimension by the San Manuel fault, which separated it into halves, moving the upper half same 2500 m down dip and bringing a wedge-shaped blanket of tertiary conglomerate into position over the lower segment of the cylinder. The lower segment is the San Manuel ore body. The upper part, moved down dip, is the Kalamazoo ore body. Originally, these were one ore body. The San Manuel ore body is a structurally weak and highly fractured quartz monzonite, the principal ore minerals being chalcopyrite, with small amounts of molybdenite. The present mining method is full gravity diagonal retreat panel caving by block. This is shown on Figure 2 , (Block Sequence 56, 57, 58, 59 --on the following page.) The ore mined is hoisted to the surface for transportation to the concentrator. BLOCK CAVING MINING SEQUENCE HISTORY The San Manuel mine was planned and developed as a full gravity block caving mine. It continues as a full gravity block caving mine. Since its initial start, the major changes in mining have been in the areas of ground support, rate of draw and undercut sequence. Ground weight resulting from block caving plays a dual role. It can cause extensive damage to ex- traction openings, yet it is necessary to break the ore into easily handled size. The ground- weight problem resolves itself into finding ways to make it manageable. The initial early ground support in the production areas consisted of timber sets and various combinations of steel and timber sets. This sup- port system proved unsatisfactory and a new support system utilizing concrete was developed. Concrete support, 30 cm to 45 cm thick, proved satisfactory. Rates of draw were experimented with. A draw rate of 45 cm to 61 cm (32 to 45 mt) per draw point per day was determined as optimum in con- trolling ground weight. Undercut sequence or mining sequence was recognized as a major contributing factor to ground weight. This is the most difficult factor to change. The lead time from primary development to undercut can be as much as two years. Initial Checkerboard Pattern The initial undercut sequence was in a checker- board pattern (Figure 2). Blocks Sequence 1, 2, 3, 4, 5, 6--next page.

Jan 1, 1981

By Byron T. Darnton

Gravity concentration at the Pegasus Gold/Montana Tunnels Mine, near Helena, MT, began in June 1991 when a coarse-gold-scalping circuit was commissioned. It processes a small portion of the ball-mill circulating load to reduce the risk of gold particles that are too coarse to float from advancing to flotation. The circuit also cost-effectively enhances overall gold recovery and payable gold ounces. This gravity circuit has been a major success. Since the circuit was commissioned, throughput has increased 30%. Several modifications and improvements were made during the last three years that allowed the gravity circuit to keep pace with the higher tonnage. The overall approach to gravity concentration at Montana Tunnels has always been to optimize production rather than maximize the gold ounces produced. This philosophy has now yielded a circuit expansion and relocation project. It will allow for an estimated 50% increase in gravity gold production, while significantly reducing the unit costs of production.

Jan 1, 1995

By B. T. Darnton

Gravity concentration at the Pegasus Gold Montana Tunnels Mine was initiated in late June, 1991 with the commissioning of a coarse gold scalping circuit that processes a small portion of the ball mill circulating load. The primary objective for the circuit was to reduce the risk of gold particles advancing to flotation that are too coarse to float. The secondary objective was to enhance overall gold recovery and payable gold ounces in a cost effective manner. The gravity circuit has proven itself to be a major success. The above mentioned goals have been achieved, and they have been maintained at record throughput rates that are 30% higher than when the circuit was commissioned. A number of modifications and improvements were made over the last three years which allowed the gravity circuit to keep pace with the higher tonnage, these are discussed in detail in the body of this paper. The overall approach to gravity concentration at Montana Tunnels has always been to optimize production rather than maximize the gold ounces produced. This philosophy has now yielded a circuit expansion and relocation project which will allow for an estimated 50% increase in gravity gold production, while reducing the overall unit costs of production significantly. This paper will review historical gravity circuit performance, improvements, and the current relocation and expansion project.

Jan 1, 1995

By Ishwinder Grewal, Michael Fullam

Many factors affect the overall performance of a gravity circuit beyond that of the primary gravity recovery device. It is critical to examine the gravity circuit in its entirety in order to determine the dominant operating variables that affect overall performance. Knelson has developed a mathematical model which has been used to assist in the design of gravity circuits, and in particular, in making accurate predictions of plant scale gravity recovery. More recently, inclusion of recovery by particle size class and additional data from various mine sites and research studies has made the model more robust. The model is now able to predict GRG (gravity-recoverable-gold) recoveries using various devices such as centrifugal concentrators, shaking tables, jigs and flash-flotation within the grinding circuit. The benefits derived by these recent advancements in modeling capability are two-fold; the first is as a tool to assist in circuit design and correct equipment selection and the second is as an analytical tool to help to evaluate and enhance the performance of existing gravity circuits.

Jan 1, 2006

Traditionally, the gravity cleaning of coal has been evaluated in pilot plant tests. Attention is now turning to the development of empirical models of gravity cleaning equipment that can be used for the design and evaluation of circuits. This paper presents some preliminary information for spirals and water-only cyclones treating fine coals. Also discussed is how such information gives a better understanding of the operating and performance characteristics of this equipment, how realistic comparisons can be made between different types of equipment, and how small mobile plants could be designed for treating the fine coals 'stockpiled' at many NZ mines.

Jan 1, 1985

By R. O. Burt

The paper examines the role of gravity concentration in both an historical contest and within the modern mineral processing industry. It discusses the principles of the process on both a theoretical and practical level. The importance of ore mineralogy and its effect on the choice of the wide range of equipment available is discussed. The paper concludes with a discussion on the relative merits of gravity concentration to other forms of processing and seeks to answer the classical question - "Quo Vadis?"

Jan 1, 1982

By Frank F. Aplan

Introduction Gravity concentration may be defined as that process where particles of mixed sizes, shapes, and specific gravities are separated from each other by the force of gravity or by centrifugal force. The nature of the process is such that size and shape classification are an inherent part of the process in addition to separation on the basis of specific gravity from whence the process got its name. Mother nature has long practiced this form of mineral concentration by concentrating such heavy and relatively indestructible minerals as gold, platinum, cassiterite, ilmenite, zircon, and diamonds in placer or beach sand deposits. Once freed of their host granitic or other rock through natural weathering processes, these minerals are then subjected to stream or wave action producing a natural classification and concentration of the heavy minerals. Gravity concentration dates back to antiquity and was certainly the first ore concentration process used when selective mining and hand sorting would no longer suffice to produce the quality of concentrate desired. Forerunners of the present day sluice box and panning techniques were undoubtedly used by the ancient Egyptians on the upper Nile to separate gold from stream gravel. By the second century BC the extraction of gold from veins in quartz was well detailed by Agatharchides, but there is evidence that gold was brought into Egypt from the south as early as the XI1 Dynasty (~1900 BC).1 Most assuredly gravity concentration devices were used during the later Bronze Age to separate the heavier tin and copper minerals from their lighter gangue minerals. The Athenians used an elementary form of Rowing film concentration at their lead-silver mines at Laurium,2 and elementary jigging using wicker baskets was also probably developed at this time. Agricola's famous treatise De Re Metallica3 demonstrates that by the 16th century gravity concentration technology was well advanced and a large number of devices had been developed. Chinese

Jan 1, 1985

By C. Mills, A. O. Burt

"The paper examines the role of gravity concentration in both an historical context and within the modern mineral processing industry. It discusses the principles of the process on both a theoretical and practical level. The importance of more mineralogy and its effect on the choice of the wide range of equipment available is discussed. The paper concludes with a discussion on the relative merits of gravity concentration with other forms of processing.IntroductionIt is an unfortunate, albeit popular, misconception among otherwise enlightened engineers in the mineral processing industry that gravity concentration was a process developed in the dark ages, perfected in the middle ages, and abandoned in the modern ages.Gravity concentration was developed in the dark ages - long indeed before that. Agricolau: cited examples of gravity concentration, crude examples admittedly, being practiced over 3000 years ago. However, gravity concentration is not dead. Far from it. As recently as 1978 it was reported that the total mineral tonnage treated by this process in the United States was greater than that processed by flotation. Coal represents the bulk of the or e treated by gravity separation in the U.S.A., with iron ore representing a major portion of the balance."

Jan 1, 1985

By Barry Cloutt

Western Mining Corporation Limited owns and operates the St Ives Gold Plant located near Kambalda, approximately 90 kilometres south of Kalgoorlie in Western Australia. Production commenced in March 1988 at a design capacity of approxi­mately two million tonnes per year. The plant was quickly expanded as a result of new ore discoveries in the district and has been processing ore since 1993 at the rate of three million tonnes per year. The plant has recovered over 50 tonnes of gold since the operation began, The plant was able to maintain acceptable recoveries throughout the plant expansion phases. Further gains in recovery were possible since there was still free gold in the tailings after approximately 24 hours of leaching. Testwork carried out on prospective orebodies showed that some contained considerable quantities of free visible gold, while others were seen to be semi­refractory using a conventional grind - leach circuit. Alternative treatment techniques were considered because a substantial amount of revenue was lost with the treatment of these ore bodies using conventional milling techniquies. The basis for all the investigations was to maximise the gold recovery from each orebody while minimising the effective cost per ounce of gold produced,

Jan 1, 1995