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By J. P. Dreyer

Note: The development of AGIT AIR flotation machines by J. P. DREYER HISTORY The first AGITAIR flotation machine was developed and patented in 1932. It has a capacity of 5 ft3t and was named the No. 20. Next in line was the No. 24. Built in 1933, it had twice the capacity of the No. 20 unit. Then, in 1934 and 1939 came the No. 36 (22,5 ft3) and No. 48 (40 ft3) respectively.

Jan 6, 1976

By P. R. Jamisch

The limitations of gold-mine evaluation by P. R. JANISCH, B.Sc. (Sur.) (Natal) (Visitor) Inherent uncertainty in the choice of parameter values places theoretical and practical limitations on the interpretation of a gold-mine valuation that are not necessarily removed by comparison of two valuations on the same assumptions. These limitations arise mainly in the estimates made of cost inflation and gold-price escalation, and lead to inconsistencies in the 'league table' method of investment analysis. The choice of discount rate is also critical in many cases. An approach to the overall problem that takes these limitations into account is suggested.

Jan 6, 1976

By O. Korhonen, T. Leskinen

The use of large OK-16 flotation machines at the concentrators of Outokumpu Oy by o. KORHONEN and T. LESKINEN(Visitors) The development ofthe OK-16 flotation machine is described briefly, and an account is given of its use at various concentration plants in Finland. The benefits arising from the use of larger flotation machines are listed, and the technical specification of the OK-16 machine is detailed in an appendix.

Jan 6, 1976

Colloquium and General Meeting A General Meeting and Colloquium was held on 'New Advances in Non-ferrous Pyrometallurgy' in Kelvin House, Johannesburg, on Wednesday, 17th March, 1976. The President, Dr R E. Robinson, opened the proceedings at 1OhOO,by welcoming the authors and delegates, who numbered approximately one hundred and twenty. Tinplate Conference The Tin Research Institute is organizing the 1st International Tinplate Conference, which is to be held in London from 5th to 8th October, 1976.

Jan 6, 1976

By P. Kohler, T. D. Sampson, T. H. Tunley

The Metsep Process for the separation and recovery of zinc, iron, and hydrochloric acid from spent pickle liquors by T. H. TUNLEY, B.Sc. (Ch em. Eng.) (Visitor), P. KOHLER (Visitor), and T. D. SAMPSON, Pr. Eng., B.Sc. (Chem. Eng.), B.Econ. (Visitor) A spray roaster has been installed in the Johannesburg area for the treatment of spent liquors from a variety of small pickling operations. A new process was developed for the processing of the liquor that is contaminated with zinc chloride, and a commercial plant was built incorporating this process. An ionexchange plant separates the zinc from the iron chloride, and a liquid-liquid-extraction plant converts the zinc chloride to zinc sulphate and recovers the hydrochloric acid.

Jan 5, 1976

By M. T. Scholtz, I. J. Corrans

Akinetic study of the leaching of pentlandite in acidic ferric sulphate solutions by I. J. CORRANS, (Pr. Eng.). B.Sc. (Chem. Eng.) (Wits.). M.Se. (N.S.W.). Ph.D. (Natal) (Member) and M. T. Scholtz. B.Sc. (Chem. Eng.) (C. T.). Ph.D. (Toronto) (Visitor) A study was made of the kinetics in the leaching of nickel from pentlandite in dilute-acidic ferric sulphate solutions as a basis for subsequent studies on bacterial leaching. The chemical leaching rate was found to be highly dependent on the temperature and the concentration of ferric ions. The proposed mechanism for the leaching process is one involving rate control by chemical processes and mass transport. Good agreement was found between the experimental data and the proposed mechanism.

Jan 5, 1976

By G. R. W. Walker

A unique means of obtaining sea-water by G. R. W. WALKER, Pr. Eng., B.Sc. (Hons.) (Min. Eng.) (Member) Although the mining and treatment operations at The Consolidated Diamond Mines of South West Africa, Limited, are located within an average distance of I km from the Atlantic Ocean, the supply of clear sea-water in large and continuous quantities for use in treatment plants is made difficult by siltation of water-holes and the amount of sand in suspension in the sea itself. The need for sixty million litres of sea-water per day at the new No. 2 treatment plant necessitated the construction of a system that would ensure a continuous and reliable supply. Several sea-water intake schemes were proposed. This paper outlines the need for an improved means of obtaining water and describes the construction of the scheme eventually chosen - a tunnel driven through bedrock for over 400 m beneath the Atlantic Ocean. At the end of the tunnel, two large chambers were excavated from which vertical holes were drilled to intersect the sea-bed.

Jan 5, 1976

By D. G. Krige

Some basic considerations in the application of geostatistics to the valuation of ore in South African gold mines by D. G. KRIGE, Pr. Eng., D.Se. (Eng.) Rand (Fellow) There is much room for improvement in the statistical procedures that have been used by gold mines over the past decade in the valuation of their ore reserves. Improvement depends on the establishment of the extent to which the patterns of frequency distributions and the directional variograms for the gold values vary from area to area within each section of a mine. The application of the lognormal distribution and of the De Wijsian variogram model for routine ore-reserve valuations requires detailed study before some of the reservations still held by mathematical statisticians can be met. This paper provides some preliminary evidence of the extent to which these models can be used with confidence, as well as suggesting how they can be applied to their full potential.

Jan 4, 1976

By H. M. Wells

The investment decision under uncertainty by H. M. WELLS, Pr. Eng., M.Se. (Fellow) The future outcome of a proposed investment is uncertain at the time the decision must be made to accept it or reject it. This uncertainty can be expressed in the form of a probability distribution. An attempt is made to rationalize the investment decision under these circumstances, especially when the range of possible outcomes extends into both the acceptable and unacceptable domains. A rigorous definition of risk is proposed, and a criterion of risk aversion is developed that forms the boundary between acceptable risk and unacceptable risk (called the loss limitation line). It is shown that this decision criterion can also serve as a quantitative yardstick in the evaluation of various possibilities for 'tailoring' the proposal to mlke it more compatible with the particular financial circumstances of the company concerned.

Jan 4, 1976

The optimization of sample spacing In South African gold mines by J. M. RENDU*, Eng. Se.D., M.S. (Min.) U.S.A. (Graduate Member) A first attempt is made at optimization of sample spacing in South African gold mines. The De Wijs model, which is shown to give a good representation of the geostatistical properties of gold values, is used to analyse the influence of the distance between samples along a stope face on the error of estimation of the stope value. The influence of other factors such as the face advance before resampling, the sample density, and the stope size, is also considered. Practical conclusions are drawn concerning the optimum sampling policy to be followed in various situations, and it is shown that sampling on a regular grid does not necessarily give the best results.

Jan 4, 1976

By G. S. Hansford, J. W. de Kock, C. D. Levy

Rheological measurements on pulps from South African gold mines by G. s. HANSFORD, Ph.D. (Pennsylvania), M.Sc. (Cape Town), C. D. LEVY, B.Sc. (Eng.), and J. W. DE KOCK, Ph.D. (Cantab.), B.Sc. (A.I.C.) (Visitors) A method is described for the determination of the rheological parameters of a fast-settling slurry with conventional viscometric measuring equipment. The effect of concentration, temperature, and pH on these parameters is investigated. The results agree with those obtained by previous workers using different viscometers, but this method allows a more detailed characterization of all the properties. From a literature survey, two semi-empirical equations were found that allow the effect of concentration, temperature, or pH on the rheological parameters to be correlated.

Jan 3, 1976

By P. Kind

Design criteria and recent developments in large-capacity Wemco flotation cells by P. KIND, Ph.D. (Clausthal), B.Sc. (Visitor) The scaling-up of the large flotation cells that have been developed during the past few years has been based on hydrodynamic considerations and has resulted in a 500 ft3 cell unit. Plant results on a porphyry copper ore show that the 500 ft3 unit is equivalent to the previously used 300 ft3 model.. . Plant tests on the use of 300 ft3 flotation cells for the recovery of phosphate, particularly from the coarse size fractions, are also described.

Jan 3, 1976

By C. H. Johannes, N. B. Strydom, C. H. Van Graan, J. G. A. Van Heerden

Note: The practical application of microclimate cooling in an underground stope in a gold mine by C. H. JOHANNES, C. H. VAN GRAAN, N. B. STRYDOM and J. G. A. VAN HEERDEN INTRODUCTION Although much information was available on the use of pre-frozen jackets as micro climate coolers in underground situations!, 2, no information was available on their performance under practical conditions in stopes. The objectives of this study were. O.F .S. Branch Minutes of the General Meeting held in the upstairs lounge at the Harmony Country Club, Harmony G.M. Co. limited, on Wednesday 12th November, 1975 at 4.00 p.m. NIM reports Report no. 343 A mineralogical investigation of gold-bearing sulphidic ore from the Florence-Devonian Mine, Barberton.(20th May, 1968; re-issued Dec. 1975). Report no. 1384 . Flotation tests on samples of Canadian copper-zinc ores. (12th Nov., 1971; re-issued Nov. 1975). The results are given of laboratory Report no. 1488 Extraction of rutile from Highveld smelter slags. (28th Sep., 1972; re. issued Nov., 1975). Report no. 1499 The production of medium -carbon ferrochromi'um. (4th Dec., 1972; reissued Nov. 1975). Report no. 1521 The dissipation of electrical power in the burden of a submerged-arc furnace. (15th Feb., 1973; re-issued Nov. 1975). Report no. 1527 The physicochemical properties of slags associated with the smelting of nickel sulphide concentrates. (21st Feb., 1973; re-issued Nov. 1975). Report no. 1544 The recovery of salable ferrochromium from material discarded by Ferrometals Limited. (11th Jun., 1973; re-issued Nov. 1975). Report no. 1547 Physicochemical and thermodynamic properties of slags in the system MgO-AlOl.5SiO2. (23rd Aug., 1973; re-issued Nov. 1975). Report no. 1548 Physicochemical properties of slags in the system MgO-Al2O3-SiO2 and their application to the technology of ferro-alloy smelting. (13th Jul., 1973; re-issued Nov. 1975). Report no. 1553 Characterization of the flotation properties of fluorspar from smallscale batch and pilotplant tests. (27th Sep., 1973; re-issued Nov. 1975). Report no. 1555 The analysis, by atomic-absorption spectrophotometry, of matte-leach residues. (2nd Oct., 1973; re-issued Nov. 1975). Report no. 1590 The separation of osmium from ruthenium in hydrochloric acid solutions. (18th Jan., 1974; re-issued Oct. 1975.) Report no. 1606 The electrical-resistance characteristics of the charge in the electric reduction furnace. (1st Feb., 1974; re-issued Oct. 1975). Report no. 1622 The electrical conductivity of the charge in a ferrosilicon furnace. (2nd Apr., 1974; reissued Oct. 1975).

Jan 3, 1976

By M. J. H. Tonkins, C. C. Crosson, G. Paterson

The development of drilling and blasting practice at Palabora Mining Company Limited by c. C. CROSSON, Pr. Eng., A.C.S.M. (Hons), BASe. (Min. Eng.) Toronto, M.!.M.M. (Member), M. J. H. TONKING, Pr. Eng., A.C.S.M., BASe. (Min. Eng.) Toronto, M.I.M.M. (Member), and G. PATERSON, B.Se. (Min. Eng.) Glasgow, M.!.M.M. (Visitor) Open-pit drilling and blasting practice at the Palabora Mining Company Limited is described, with particular reference to the development of aluminized slurry explosives. Rotary drilling of primary drill holes, drilling patterns, and blasting techniques for use with slurry explosives are described.

Jan 2, 1976

By N. C. Joughin, A. C. Buckmaster

The use of face conveyors in gold mines by N. C. JOUGHIN. B.Sc. (Eng.). Ph.D. (Wits) (Member) and A. C. BUCKMASTER; M.A. (Cantab.) A mechanized stope-cleaning system has been developed around an armoured face conveyor, which was tested on the surface and in two underground trials. In the second underground trial, an average face advance of 8,5 m per month was obtained with a labour productivity of 27 ca/worker/month on a two-shift blast cycle. Two new face cleaning systems have been built, each incorporating an armoured face conveyor, a loading plough, a collapsible self-advancing barricade, and an integral roof-support system. These are about to be tested. A new type of reciprocating flight conveyor is being developed for stope use. This is cheaper, lighter, and more compact, and exhibits better wear characteristics, than an armoured face conveyor. In the early stages of the trials, this conveyor frequently achieved a singleshift blast cycle. It should be possible to achieve face advances of up to 40 ca/worker/month with a consistent one-shift blast cycle. The use of drill rigs and a self-advancing roof-support system would improve the productivity to over 50 ca/worker/month.

Jan 2, 1976

Book review Pearson, J. S. Ocean floor mining. Park Ridge (New Jersey), Noyes Data Corporation, 1975. 201 pp. NIM reports Report no. 308 A mineralogical study of gold particles in pulp residues from the Bracken Gold Mine. (7th Mar.,1968. Re-issued Oct. 1975.) Report no. 377 Examination of pulp samples, treated with cyanide, for coated gold.(7th Aug., 1968. Reissued Oct.1975.) Report no. 385 The determination of the nature of coatings on gold particles. (2nd Aug., 1968. Reissued Oct. 1975.) Report no. 452 The Purlex Process - a description of the pilot plant leading to the use of the process in South Africa. (13th Jan., 1969. Re-issued Oct. 1975.) Report no. 482 Review of work on the treatment of pegmatites. (9th Apr., 1969. Reissued Sep. 1975.) Report no. 1443 Gravity concentration tests on four samples from Tantalite Valley,S. W.A. (5th Jul., 1972. Re-issued Sep. 1975.) Report no. 1489 The breakage of S oderberg electrodes. (10th Nov., 1972. Re-issued Nov. 1975.) Report no. 1545 A mineralogical investigation of leach residues from the Blyvooruitzicht Gold Mine. (22nd May, 1973. Re-issued Nov. 1975.) Report no. 1583 Preliminary tests on winnowing for the recovery of mica. (12th Nov., 1973. Re-issued Sep. 1975.) Report no. 1652 The identification of diamonds from Premier, Finsch, and Jagersfontein Mines by statistical analysis of data obtained from instrumental neutron-activation analysis. Report no. 1723 The determination of zirconium and aluminium in zirconiumaluminium alloys. Report no. 1739 The determination of trace amounts of noble metals in sulphate media. Report no. 1771 The determination of silver, selenium, tellurium, antimony, tin, lead, and arsenic in anode sludges. Report no. 1772 A study of copper recovery by lime roasting and leaching. Corrigendum The Special Issue of Volume 76 of the Journal ('Recent Advances in Mineral Dressing, October 1975) should be corrected as follows. The South African Institute Of Mining And Metallurgy - Information On Membershlp The Institute was founded in 1894 as the Chemical and Metallurgical Society of South Africa. In 1904 it was reconstituted as the Chemical, Metallurgical and Mining Society of South Africa and in 1956 it became the South African Institute of Mining and Metallurgy. Die Suid-Afrikaanse Instituut vir Mynbou en Metallurgie - Inligting Oor Lidmaatskap Die Instituut is in 1894 gestig as die Chemiese en MIetallurgiese Vereniging van ::!nid-Afrika. In 190-1is dit omvorm tot die Chemiese Metallurgiese en Mynbouvereniging van Sllid-Afrika en in 1956 het dit die Suid-Afrikaanse Instituut vir Mynbou en l\Ietallurgie geword.

Jan 2, 1976

By N. C. Joughin

Potential for the mechanization of stoping in gold mines by N. C. JOUGHIN B.Sc. Eng., Ph.D. (Rand) (Member) The basic requirements for stoping machines are identified first by examination of the mining rates and productivities attained in conventional stoping, and then by examination of a series of problem areas associated with the shape of the reefs, rockbreaking, rockhandling, and the support and design of the machines. Some of the more important machines being developed are described briefly, and their principal features are compared with the basic requirements identified in the first part of the paper. An estimate of the potential demand for the different types of machines is given.

Jan 1, 1976

By P. C. Seligmann

Primary fracture from an array of shotholes by c. M. LOWNDS. B.Sc. Hons. (Rhodes). Ph.D. (Cape) (Visitor) and P. C. SELIGMANN. B.Sc. (Witwatersrand) (Visitor) The effects of stress on the directions of cracks that are propagating in a brittle medium are described. It is shown that the superimposition of stress fields from the holes of an array always adversely affects fragmentation. Consequently, the best fragmentation will result when holes are fired far enough apart in space or time for each to develop its whole crack pattern without disturbance from the others. This concept leads to a philosophy for the design of more effective blasting patterns, which has been verified on model scale and which explains many published, empirical results.

Jan 1, 1976

By B. P. Christos

The improved rate of stope-face advance at Buffelsfontein Gold Mining Company Limited by B. P. CHRISTOS (Associate) To achieve a higher rate of stope-face advance. it was necessary to examine al.1aspects of the stoping operation, to identify bottlenecks, and to eliminate them or reduce their effect. The cleaning cycle was fund to be the most significant bottleneck. and this problem was aggravated by long panel lengths. under-capacity winches In strike gullies. and excessively long strike scraping distances.

Jan 12, 1975

By M. T. G. Davis, J. V. Cleasby, H. J. Wright

Mining practice in the Kimberley Division of De Beers Consolidated Mines Limited by J. V. CLEASBY. B.Sc.. A.R.S.M. (Fellow). H. J. WRIGHT. B.Se.. M.Sc.. (Fellow). And M. T. G. DAVIES. B.Sc. (Visitor) T his paper highlights the changes that are taking place at De Beers Consolidated Mines Limited in mining methods, mechanization, and employment practices. De Beers has four underground mines in Kimberley itself (Dutoitspan, Bultfontein, De Beers, and Wesselton), and two open-cast mines outside Kimberley (Finsch and Koffiefontein). Emphasis is placed on the new method envisaged for Koffiefontein when it becomes an underground mine. The paper also includes notes on chemical drilling and on winding practices.

Jan 12, 1975