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The following procedure was used to determine cut-off grades: define the orebody profile; plan the stope layout and quantify the work involved; formulate equipment-performance norms; calculate unit costs; input process recoveries and metal prices; and calculate the cut-off grade. Use of the method is illustrated using data from a copper mining complex in India. Results from the study led to the following conclusions for underground mines in general. Cut-off dependent costs vary significantly with the stoping method employed, orebody thickness, the degree of mechanisation and the working efficiencies of the workforce and equipment. This applies even within the same deposit. Sub-level stoping and its variants can be operated at a lower cut-off grade than cut-and-fill and its variants. Thinner orebodies affect cut-off grades adversely, but with thinner orebodies very little further reduction in cut-off grade can be achieved once a certain minimum width has been exceeded. For the same stoping method and in the same mine the cut-off grade varies with the degree of mechanisation. Labour-intensive methods require higher cut-off grades. An allowance for working efficiency should be made when calculating cut-off grades. Higher process recoveries allow a significant lowering of cut-off grades

Jul 1, 1996

By P Shead, M A. Tuck

Both climate and methane control have been a prime concern in the development of the workings within the Deep Soft seam at Harworth Colliery. This paper describes the numerous methods employed over the past 15 years to effect control over these two major environmental pollutants at Harworth and describes a future method of working which will enable the output levels required to be achieved, whilst effecting the required level of both climatic and methane control. Firstly, the paper gives a broad historical overview of the steps taken since 1981, when production started in the Deep Soft seam at Harworth Colliery, to effect control over the main environmental pollutants in the seam. Secondly, the paper details the results of planning exercises undertaken to assess the various options with respect to panel layout, to achieve environmental control in future production districts. Finally, the recommended method of panel design to achieve the levels of production required is detailed.

Jan 7, 1997

Discussions of the papers with a written contribution on Paper No. 11 and authors' written replies. Also brief obituary of Dr. T. David Jones on p146.

Jan 1, 1947

By J. E. Rouse, D. L. Buchanan

"During the emplacement of the Bushveld Complex in the Potgietersrus area magma reacted with the original floor rocks— Archaean granite or Malmani dolomite and overlying Penge handed ironstone or sedimentary rocks of the Pretoria Series. The complex sequence of sulphide-rich mafic rocks that formed along the contact is known as the Platreef. Associated with the sul­ phide mineralization are important concentrations of platinum-group metals, copper and nickel. Xenoliths of Malmani dolo­ mite have been incorporated into the Platreef and previous work has suggested that anhydrite is likely to have been present in the dolomite. The sedimentarv-derived sulphur thus introduced into the magma exercised an important control on the forma­ tion of the sulphides.Petrographic studies on the Platreef rocks from the Tweefontein area indicate that the original magma reacted with the banded ironstone to form iron-rich pyroxenites. In the Turfspruit area, to the south, the footwall rocks consist of sediments of the Timeball Hill Series. Original argillaceous rocks have been metamorphosed to cordierite-, corundum- and spinel-bearing hornfelses. Graphite was present in the contact zone in both the Tweefontein and Turfspruit areas. Anhydrite-bearing hornfels rocks are also present on Turfspruit.The Platreef rocks that overlie the corundum- and spinel-bearing hornfelses on Turfspruit are peridotitie, and pyroxenites are present in areas underlain by cordierite-bearing hornfels. The absence of orthopyroxene in the peridotite is probably indicative of low silica activity in the original magma. The pyroxenites have, however, undergone silica contamination from the underlying more siliceous cordierite hornfels.Carbon isotope studies indicate that the graphite in the Tweefontein and Turfspruit samples represents organic material orig­ inally associated with the footwall sediments. Sulphur isotope determinations on the anhydrite-bearing floor rocks indicate that this phase is clearly of sedimentary origin and was probably derived from an evaporitic unit within the carbonate sequence. This provides firm support for a model of ore genesis that involved the introduction of additional sulphur into the Bushveld magma. Isotope studies on sulphides associated with the banded ironstone and graphite indicate that these units were not the source of additional sulphur. Experimental studies predict, however, that a magma contaminated with iron- and carbon-rich material would have a high sulphur-carrying capacity. Where additional sulphur is available the magma would achieve saturation early in its crystallization history and precipitate an immiscible sulphide phase. Experimental work has also shown that sulphide precipi­ tation can be triggered by the introduction of salic material into a magma close to sulphur saturation. This mechanism probably played a role in the control of the sulphide mineralization in the Turfspruit area."

Jan 1, 1984

By A. D. Read

Selective flocculation was investigated as a possible method of recovering values from mineral slimes which are too finely divided to be treated by conventional mineral processing methods. It has proved possible to flocculate selectively either haematite or a silicate from a stably dispersed mixture by varying the anionic character of the high-molecular-weight, partially hydrolysed polyacrylamide employed. Different separation methods have been developed for hard and soft water media. Electrokinetic and infrared techniques have been employed to elucidate the mechanism whereby selectivity has been attained in the different cases. The following influences on the various selective flocculation parameters have been investigated: (a) the level of the different reagent additions and (b) the shear conditions during and after flocculant addition. A feature of the particular system studied was the high solids content at which it was possible to achieve good selectivity. Probable reasons for this are advanced, and the possibilities and potentialities of the process are discussed.

Dec 1, 1971

By J. H. Chesters

The main, though rarely mentioned advantage, is likely to be the standardisation of best practice and product. In a batch process conditions vary cyclically, but with a continuous process they would, at least ideally, remain the same for long periods of time. The other main advantages of continuous over batch processes are likely to be reduced operating and capital costs, the improved possibilities for automatic control, and more consistent product quality. Recent developments are surveyed for ironmaking and steelmaking with reference to blast furnaces; solid-product and molten-product direct reduction; the trough-type processes of Thring, Worner, the Japanese National Research Institute for Metals and Glinkov; basic-oxygen furnace (LD) variants; spray steelmaking; continuous casting and vacuum degassing; rolling; and coating. Encouragement in the devleopment of continuous processes may be drawn from the way unexpected difficulties, such as trouble with sulphur and refractories, were tackled and overcome to achieve the float glass process

Dec 1, 1971

Summary of the morning's events with a Written Contribution to Paper No. 4 and author responses

Jan 1, 1947

By J. H. E. Jeffes, K. T. Jacob

The activity coefficients of oxygen in liquid Pb-Sn alloys have been measured between 550 and 1100°C by use of solid oxide galvanic cells: Pt, Ni-NiO | Zr02 Solid electrolyte | O (Pb + Sn), Cermet, Pt; and Pt, Fe-FeO | Zr02 Solid electrolyte | 0(Pb + Sn), Cermet, Pt. Alcock and Richardson's quasi-chemical equation, with the coordination number of atoms set to 2, is found to predict successfully the activity coefficients of oxygen in these alloys. The relative partial molar enthalpy and entropy of oxygen at 1 atom per cent in the alloys have been calculated from the variation of the activity coefficient with temperature. The addition of Sn to an unsaturated solution of O in Pb is shown to decrease significantly both the partial molar enthalpy and entropy of O. As the measurements were restricted to a narrow range between 750 and 1100°C in Pb-rich alloys, however, the pronounced variation of the partial molar enthalpy of O with temperature at constant alloy composition predicted by the quasi-chemical model could not be verified.

Dec 1, 1971

By R. I. Jeffery, J. W. Summers

An account is given of the verification and calibration of a numerical modelling technique that has been developed for the prediction of subsurface strata deformation following the extraction of coal by longwall mining methods.

Jan 4, 1992

By M. J. Russell, W. E. Stephens, D. B. Mohamad, A. B. MacKenzie

Redox front processes in rocks are important in the context of both radioactive waste disposal and the development of orebodies. Results are presented from a study of the distribution of uranium and thorium and the natural decay series equilibrium about redox fronts in a granite at the Criffel pluton and Craignair quarry, Dalbeattie in southwest Scotland. The results are considered in the context of large scale uranium aqueous transport in the region and compared with those from a previous study of highly developed redox fronts at Pocos de Caldas, Brazil. Results show that the Criffel pluton has experienced a recent and rapid removal of uranium from the uppermost section of the granite whereas thorium has remained relatively immobile. The radium and uranium distributions indicate that diffusion processes probably control the distribution of radionuclides about the front. These processes are similar to those observed at Pocos de Caldas. The trends of concentration and activity ratio about the Dalbeattie redox front are less pronounced than those at Pocos de Caldas owing to the shorter time available for the process and the lower intensity of weathering at Dalbeattie.

Jan 12, 1992

By D. G. Skinner, J. H. Griffiths, F. T. Williams, A. G. Withers

"The absence of homogeneity, in dust-clouds underground indicates the use of a method in which the volume of air sampled is an appreciable proportion of the total volume under consideration. Of the available methods, only the impinger and gravimetric techniques seem to comply with this requirement. In practice, greater efficiency of collection of the smaller particles is possible by the use of a gravimetric filter than with the impinger. For this reason if, as seems desirable, a standard method of sampling be sought, the adoption of a gravimetric technique is to be recommended.Provided that the amount of dust collected is reasonably large, the paper filter would seem to be preferable to the solid crystal type of filter on account of its greater convenience in use.Alternative methods of sampling are desirable to cover the wide range of practical conditions."

Jan 1, 1947

By R. W. Ruddle

The advent of new methods of roasting, “flash roasting and fluidisation”, which are now under development, combined with the use of oxygen-enriched air, may markedly increase the SO2 content of roaster smokes. Skogmo suggests that the production of smokes containing as much as 50 per cent SO2 should be feasible. The use of flash smelting processes may well enable a similar increase in the SO2 content of smelter smokes to be made. In this event the recovery of sulphur would be greatly cheapened and the process might well be much more economic, even if allowance is made for the cost of generating the oxygen

Jan 1, 1953

By T. Piirainen, T. Alapieti

"The Koillismaa layered igneous complex is the result of igneous activity that occurred 2436±5 m.y. ago. Its crystallization took place in three separate but connected magma chambers, the total volume of which is estimated at more than 2000 km'. These chambers were located partly in a feeder system within Archaean granitoids and partly in an unconformity between these grani­ toids and Early Proterozoic supracrustal rocks. The composition of the parental magma that initially filled the chambers is thought to have been that of a relatively MgO-rich tholeiite. Sulphides and platinum-group minerals are mainly concentrated in the marginal series of the western part, where they are encountered over a distance of 25 km. This marginal series is an originally nearly horizontal series of rock types that displays a reversed differentiation trend, grading inwards from gabbroic to ultramafic rocks, followed bv rocks of the layered series. The chilled margin is not encountered anywhere in its original position at the contact, probably as a consequence of magmatic erosion, but remnants are to be found in the form of elongated xenoliths. Partly melted siliceous fragments from gneissic country rock typical of the lower part of the marginal series indicate pronounced contamination.Chalcopyrite, pentlandite and pyrrhotite±pyrite are the predominant sulphides. The accessory sulphide minerals include covellite, violarite, marcasite, mackinawite, sphalerite and argentian pentlandite. Platinum-group minerals are represented by froodite, michenerite, merenskyite and sperrylite. Other accessories that have been identified are electrum and native copper and gold. The mean of the Cu/(Cu+Ni) ratio in the mineralizations is 0.67 and Pt/(Pt+Pd) 0.31.It is suggested that the sulphide phase was formed in the marginal series as the solubility of sulphur in the basic magma was lowered by contamination, possibly assisted by some other factors. The sulphur isotope data support the juvenile origin of the sulphur."

Jan 1, 1984

Discussion at the North of England Institute of Mining and Mechanical Engineers' general meeting held in Newcastle-upon-Tyne, 8th April 1916, on the paper published in Trans. I.Min.E., vol.LI, 1916, p.72-90, included written contributions on size and gauge standardisation by Lupton A., Peck W.R., Dean S., Mayer R.W. and Ashworth J., with the author's written response, and by Bulman H.F. and Brown M.

Dec 1, 1916

By NA NA

A round up of recent industry matters. Davis Derby acquisition of Safecom UEP Ltd. Record Output by Longannet Mine.

Jan 7, 1997

By Groom P.

Discussion of the paper presented at the Midland Institute of Mining, Civil, and Mechanical Engineers' general meeting held in Leeds, March 21st, 1916, with T. Beach, vice-president, in the chair included contributions by Beach T., Fearnsides W.G., Lloyd W.D., Gill J. and Nadin R.

Dec 1, 1916

By D. Mireku-Gyimah, R. S. Suglo

Ghana contains auriferous belts which cover 51 800 km2 of its small area of 239 400 km2. From 1493 to 1600 35.5% of the world gold production was from the Gold Coast (renamed Ghana in 1957). This dropped to 8.9% from 1701-1800. For the past fifteen years annual production has averaged less than 2% of the world total. By 1985 only four gold mines were operating, compared with 45 in 1934 and 11 in 1945. Since 1987 Ghana has experienced a boom in gold mining activities. By 1991, 83 new companies had acquired prospecting licences. At least five new companies have started large-scale production. About 650 licensed small-scale mining groups are in operation. The economic and technological factors that have contributed to the decline of gold production in Ghana are discussed. A summary is given of the methods used to mine and recover gold. These cover small-scale workings, dredging, open cast operations and underground mining. The advantages and disadvantages of these technologies and the future of gold mining in Ghana are considered.

Jan 4, 1993

By K. C. Misra, W. Wrightson Jr.

The Lick Fork prospect shows appreciable nickel sulphide mineralization in a narrow, steeply dipping, layered sequence of metamorphosed hornblende peridotite, gahhro and hornblende gahhro, intrusive into the Pedlar Formation (charnockitic pyroxene granulite) of the Virginia Blue Ridge Complex (Precambrian). Rocks of the intrusion have equilibrated to granulite- facies metamorphism, as indicated by pervasive polygonal texture of silicate aggregates, development of biotite- and hornblende-preferred orientation, compositional equilibration of the silicate minerals, the Mg-Fe2+ (orthopyroxene-dino- pvroxene) distribution coefficients (average 0.57), (MgO + FeO + Fe20 3)/Al20 3ratios in orthopyroxenes, and Ti contents and AI(i\)/A I(\i) ratios of hornblendes. The sulphides, consisting of pyrrhotite-pentlandite (with up to 4 wt% Co)-chalcopyrite-pyrite-marcasite-violarite- bornite—mackinawite, are virtually restricted to the ultramafic unit of the intrusion and constitute 20-30% of the samples of hornblende peridotite studied. Although the basal accumulation of the sulphides may suggest magmatic segregation, sulphide- silicate textures typical of sulphide liquid immiscibilitv are not present, even in the sparsely mineralized gahbro units. On the other hand, the transgressive and relict textures are strongly suggestive of replacement of the silicate minerals by sulphides. These include chaleopyrite ± pyrrhotite ± pentlandite (violarite) ± pyrite ±magnetite veins crosscutting silicates, sulphide penetration into silicates at silicate-sulphide contact zones, rounding of silicate grains against sulphide matrix, and islands of silicate minerals (olivine, hornblende, pyroxene, biotite) in sulphide masses. Metamorphic mobilization of pre-existing sul­ phides is a possibility, but involvement of post-metamorphic, hydrothermal fluids is suggested by the following features: paucity of annealing and deformation textures in the sulphides, replacement of metamorphic and deformed silicates, lack of differential sulphide mobilization and the common occurrence of sulphides along grain boundaries and triple junctions of poly gonal silicate aggregates. The consistent association between sulphides and hydrothermal alteration products of silicates suggests that they are cogenetic. The hydrothermal fluids may have merely mobilized and concentrated the pre-existing, disseminated, magmatic sulphides, or there may have been significant addition of sulphides during this process. This question cannot be resolved unequivocally with the existing data.

Jan 1, 1984

By R. R. Hart, R. A. Evans

This paper outlines the the methods currently being used in the West Wales Area for preventing the occurrence of any outbreak of spontaneous combustion. Stress is placed on the importance of correlating the position of a Rider Seam which is prone to spontaneous combustion. The recent introduction of the UNOR Recorder has contributed to the ability to monitor the CO content of the general body of the air during any incident. The use of modern sealants and improved methods of applying them have enabled the few instances of spontaneous combustion in South Wales to be treated promptly and efficiently. The authors describe the current spontaneous combustion problems at two collieries.

May 23, 1905

By G. H. Blackwell

Sequences in open pit mining must be planned and regularly revised to incorporate changes in the variables which affect profitability. Interactive computer planning with colour graphic facilities is an effective tool for this purpose in the short and medium term. An interactive computer planning system for medium-size, low grade porphyry copper-molybdenum open pits is described. The planning system proved especially valuable during the critical stages of pushback mining when deep, inner pit ore was nearly depleted and the erratic grades of the next pushback provided ore and marginal material at a time of depressed metal prices.

Jan 8, 1993