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By H. Forster, F. H. Koenemann, U. Knittel

The greenstone belt developed along the Sandawana line, an anastomosing, transcrustal shear zone. The lode gold is concentrated in veins and along brittle-ductile shear zones and other faults. Gold contents of 200 rock samples were found to be well below economically significant levels, excluding purely syngenetic deposit formation. Average gold content of unmineralised banded iron formation decreases from 7.3 ppb in the east (Manica) to 1.6 ppb in the west (Odzi), where depletion reflects hydrothermal leaching. The mineralising fluids may have been generated during deep crustal deformation, metamorphism and magmatism. Gold was hydrothermally deposited during carbonatisation and sericitisation of ultramafic and mafic rocks and during hydrothermal overprinting of banded iron formation and felsic rocks. It is present in native form and as microscopic to submicroscopic inclusions in pyrite, arsenopyrite and pyrrhotite. Argentiferous galena and other sulphides are commonly observed. Rezende, which produced over 38 t Au, is hosted by a granodiorite stock. By-product gold was produced from Cu-Ni sulphides at Mundonguara. The deposits are related to the older, but not the younger, of the granitoids intruding the belt's supracrustal sequences; the estimated age of mineralisation is 2700-2600 Ma. Odzi district, with 61 mines, has produced only 3.5 t Au as its higher-level host rocks have apparently been eroded. Mutare (formerly Umtali) district, with 133 mines and 9 placers, has produced 68 t Au (65 t from Rezende and adjacent deposits), and Manica district, with 23 mines and 8 placers, 12 t Au. Estimated reserves for the Rezende area are 20 t Au and for Manica district 4 t lode Au and 19 t placer Au

Apr 1, 1996

By R. A. Halatchev

A risk model for assessment of the uncertainty in the forecasts of the planned profit is developed. It is based on the selling price of the metal recovered from the ore and the production per shift of the excavators. These two critical variables characterise the economic and technical aspects of the mining venture. Time-series methodology is used to describe the behaviour of the economic variable, which improves the adequacy of the modelling. A hypothetical open-pit gold mine is used to illustrate the application of the model. Results obtained show that the model is a good alternative to sensitivity analysis in taking account of the stochastic character of the price of the metal recovered from the excavated ore and the production per shift of the excavators used. The model can be extended by the inclusion of new variables that have a probabilistic nature

Dec 1, 1996

By F. M. Vokes, P. M. Ihlen

Paper presented at Mineralisation in the Caledonides, the Mike Gallagher memorial meeting held in Edinburgh, 27-28 June 1996. Ore deposition was related to three major stages: continental rifting and separation (Vendian-Late Cambrian), convergence (Late Cambrian-Early Silurian) and collision (Early Silurian-Devonian). The first stage included deposition of volcanogenic massive sulphide Zn-Cu and stratabound or stratiform Fe and Zn-Pb(-Cu) on continental margins, as well as less economic Nb and Fe in carbonatites, U, Mo, Ni and V in Alum Shales and orthomagmatic Cr, Fe-Ti and Ni(-Cu). The numerous volcanogenic massive sulphides formed during convergence included Early Ordovician Cu-Zn, mature-arc Cu, Zn, Pb and Fe-oxide deposits, Besshi-type deposits dominated by Cu or Zn in gabbro-intruded sediments and minor Cu-Ni(-PGE), Cu-Mo and skarn deposits. The collisional stage is represented by epigenetic deposits including sandstone Pb deposits (Pb, Zn, Ba, F and Cu) and minor vein deposits with variable Au, Ag, Pb, Cu, Zn, Fe, As, Sb, W and Mo

Jun 19, 1905

By A. K. Tripathy, P. K. Pattnayak, H. S. Ray

The effects of water addition on the solid-state reaction between Cr2O3 and Na2CO3 at low temperatures (up to 873 K) were investigated to determine its possible influence on the reaction rate and the degree of conversion to soluble chromate. Experiments at high temperatures were conducted for comparison. It was found that adding water to the mixture before roasting enhanced both reaction rate and yield significantly. The reactions followed the Lesokhin-Tempelman equation at low temperature and the Ginstling-Brounshtein equation at above 973 K; the respective activation energies were 95 and 22 kJ/mol

Jun 19, 1905

By F. Tailoka, G. Zhao

Pb is an unwanted impurity in Al for which there is no established method of removal. As it interacts strongly with alkali metals, separation was achieved by adding Na or K to molten Al at 953-1 003 K. Direct Na addition led to considerable evaporative loss but in-situ addition by electrochemical titration from a eutectic NaCl-KCl or KCl-BaCl2 mixture was found far more effective, in some cases reducing Pb content below detection levels within 2 h of titration. K appeared more effective than Na at low Pb concentrations but the use of Na was preferred as it is less toxic and explosive. Na removal from Al-Na and Na-Pb alloys was also carried out electrochemically, the use of these two alloys rather than the eutectic salt as a source of Na avoiding liberation of Cl2 at the anode

Apr 1, 1995

By R. Ciccu, P. P. Manca, A. Bortolussi, G. Massacci

Tool performance and the unit cost of cutting depend on a number of operational variables (peripheral velocity, pull-back force, water injection rate, angles of the sections of wire outside the rock) as well as on the geometric features of the cut itself (area and shape). Cutting rate and wire productivity are also influenced by the type and number of diamond beads per unit length of wire and by the characteristics of the rock (granite or marble). A computer program aimed at handling a problem of this complexity has been developed and tested with the use of available field and laboratory data and has been found acceptably reliable. Discrepancies between current industrial data and some of the results suggest future lines of research, while the simulation should also be extended to include different types of rock and tool and a variety of bench face geometries

Aug 1, 1994

By A. S. W. Kurny, M. Z. Huq

Bangladesh ilmenite is partially altered, containing pseudorutile, rutile and haematite as well as the predominant ilmenite phase. A typical analysis is 39.45% TiO2, 24.19% FeO and 33.0% Fe2O3. Reduction of the ilmenite by charcoal was found to involve two major reactions: conversion of pseudorutile into ilmenite and rutile, and change of ilmenite into metallic iron and rutile. The first, which was much the faster reaction, was responsible for an initial increase in ilmenite content with reduction time at lower temperatures. Apart from these two major reactions, rutile was reduced to lower oxides at 1 100 degrees C with a consequent decrease in its XRD peak height

Jun 19, 1905

By A. D. Mukherjee, H. N. Bhattacharya

Middle Proterozoic sulphide ore mineralisation occurs in isolated blocks of the NE-SW trending Delhi fold belt composed of Delhi Supergroup rocks. The Ajari-Basantgarh-Pipela belt forms part of the longest, widest and westernmost tectonic unit of the Delhi fold belt and consists of amphibolites, metapelites, quartzites and carbonates. The metapelite lenses and associated amphibolites host pyritic copper mineralisation. Mineralisation takes the form of sheet-like bodies consisting of ore lenses of various sizes interlayered with host or associated rocks. Massive, banded and disseminated varieties of ore are found. Pyrite is dominant with subordinate chalcopyrite and sphalerite. Pyrrhotite, galena, cubanite, mackinawite, marcasite and freibergite constitute the minor minerals. The characteristic features of the ores suggest a possible correlation with Besshi-type deposits, and the closely associated amphibolites are interpreted as low-K tholeiites of a fore-arc setting

Jun 19, 1905

By A. P. Gize, J. F. W. Bowles, D. J. Vaughan, S. J. Norris

Paper presented at the IAGOD international symposium on mineralization related to mafic and ultramafic rocks held in Orleans, France, 1-3 September 1993. Geological evidence from tropical laterites indicates clearly that platinum group metals are taken into solution and precipitated to form grains larger than those in the source rocks. Platinum and palladium move differentially in the surface environment, with Pt partitioning into soils and eluvial or alluvial deposits while Pd remains more mobile in natural waters. Natural organic acids, particularly humic acid, can interact with platinum-group elements and concentrate them even in areas where their content in rocks is very low. Experimental work has confirmed that Pt and Pd can be taken into solution by humic acid at room temperature and in geologically short time-spans. Solubility and deposition may be controlled by physicochemical conditions, reaction kinetics or an adsorption effect, or there may be two competing reactions, solubilisation assisted by organic matter and a kinetically slower metal precipitation

Apr 1, 1994

By M. V. Swain, N. Bristow, R. D. Dukino

During mining, crushing and handling the size of iron ore lumps decreases. Key factors in determining the amount and size of fines that are produced are the mechanical properties of the ore. In a continuation of earlier work on the same ores the mechanical properties of three Australian iron ores from Yandi, Koolan and Mt. Whaleback were determined. In particular, fracture toughness was investigated in greater detail by examining its relationship to crack length using the compact tension test. The elastic modulus and strength of the ores were also determined in flexure and compression. The results were interpreted using Weibull statistics, enabling the ores to be ranked according to strength and elastic modulus. These results, together with data on the mechanical response of the ores to stress and observations concerning the effect of mineralogy on cracking, provide a coherent understanding of the mechanisms involved when the ores fracture

Jun 18, 1905

By L. J. Cabri

Although no complete mineralogical balances have been published, the background knowledge and proven, highly sensitive analytical techniques to produce them already exist. For PGE-Cu-Ni sulphide ores a combination of ore microscopy, image analysis and electron microprobe analysis with proton microprobe analysis of sulphides for Pd, Rh and Ru and ion microprobe analysis for Pt, Ir and Rh (in some minerals) should provide the necessary data when combined with reliable assays. Other sulphide ores, such as the Cu-Ni-(PGE) ores of Sudbury, Ontario, require a similar approach except that the ion microprobe would be more suitable for the analysis of Pd, Pt and Rh because of its greater sensitivity. Oxide-silicate ores may be harder to deal with quantitatively, although the potential to confirm the presence of trace PGE within silicates and oxides may be greater than in PGE sulphide and Cu-Ni-(PGE) sulphide ores. However, solid solution of PGE in oxides and silicates still requires thorough documentation and evaluation in terms of their significance for the overall metallurgical balance

Apr 1, 1994

By G. Richards

Research shows that having more women in the top mining jobs can bring bottom-line benefits. Mining companies are starting to embrace the need for greater gender diversity at board and senior management levels, figures and examples are given.

Jul 1, 2015

By P. P. Jenkins, T. G. Ball

Paper presented at the Drillex '90 conference held in London, 5 April 1990. Two drilling techniques are employed - guided longhole drilling and reverse circulation coring - for underground longhole exploration of the coal reserves and the fault structures that affect them. These are complementary to, or replacements for, surface boreholes, underground development drivages and seismic techniques. The developments of the drilling techniques and some case histories are presented in detail.

Jan 1, 1991

Errors in ore reserve estimation can occur during drilling and sampling, sample preparation and analysis, geological logging and modelling, database construction, statistical or geostatistical evaluation, selection of economic parameters, selection of ore reserve method and assessment of mining constraints. Core sample recovery can be a major source of error, and it is proposed that the modelling of grade, metal accumulation and thickness should be accompanied by the modelling of core recovery (or core loss) so that for each ore block a weighted block recovery factor is obtained. This gives a good indicator of the reliability of a reserve estimate. It is suggested that a resource reliability rating (RRR) system be established to quantify what is meant by geological assurance and to combine this with an estimate of the precision of estimation as gained by geostatistical analysis. Proven and probable minable reserves would be those with an RRR better than 50% and a precision of estimation better than 20%

Dec 1, 1996

By D. Bitzios, A. Gracia, V. Meggiolaro, J. D. Baker

Synthesis report on a project carried out under the EC-funded BRITE-EURAM programme. A large deposit in Spain and several smaller ones in Greece and Sweden were investigated. Beneficiation testwork, including the development of an innovative wet circuit, was undertaken in Italy. The Spanish Ilustracion deposit lies occurs in thin, white layers throughout a zone 35-40 m thick and 1.5 km long, in laminated calcsilicates. Total resources of more than 100 000 000 t include proven open-pittable reserves of 4 500 000 t averaging 35% wollastonite. The beneficiated product is suitable for various applications, including ceramics. The Swedish and Greek marble-hosted skarn deposits include Albatross, with 2 500 000 t of reserves at 30% wollastonite, and Panorama, with reserves estimated at more than 700 000 t

Jun 21, 1905

By J. S. Coats, G. E. Patts, N. Hughes

Conventional sampling methods are known to suffer from the variable loss of fine gold by elutriation. Freeze sampling yields representative and quantitative data that, when combined with information on the sedimentology of gravel-bed rivers, may facilitate the development of improved dispersion models for source detection. It is suggested that freeze sampling may have particular application to the orientation stage of a large gold exploration survey

Jan 1, 1991

By W. D. Maier, H. V. Eales

Paper presented at the IAGOD international symposium on mineralization related to mafic and ultramafic rocks held in Orleans, France, 1-3 September 1993. A lithological and geochemical study revealed significant lateral variation of the interval over 170 km of strike, from about 30 m at the Union Section to 220 m near Brits. The cumulates also become more evolved and leucocratic with distance from the Union Section both towards the NE (Amandelbult) and SE (Impala, Rustenburg and Brits). It is inferred that the persistent heat flux from a putative major feeder zone near the Union Section impaired deposition of felsic cumulates in the vicinity, delaying crystallisation of successive phases in parts of the chamber near the feeder. New influxes were therefore deposited on a footwall of varying thickness and lithology in response to different degrees of crystallisation and accumulation along strike. The development of cyclic units of chromitite, harzburgite, pyroxenite, norite and anorthosite was interrupted at different stages in different parts of the chamber

Apr 1, 1994

By K. Nielsen, J. Kristiansen

A series of laboratory blasting and grinding tests on three types of hard and competent rock (coarse-grained monzonite, fine-grained granite and very fine-grained gabbro) showed that a higher level of applied explosive energy enhanced grindability and produced a larger amount of fine (-0.106 mm) material. This confirmed reported industrial experience and the results of previous investigations. However, the results did not provide any information on the quantitative relationship between the energy applied in primary blasting and that required in subsequent comminution. Only about 1% of energy consumed in conventional grinding is used to create new surfaces, while power efficencies in cone crushers have been estimated at 70-80%. In blasting, up to 20% of explosive energy may be transmitted to the surrounding rock as elastic strain energy, leading to both primary rock breakage and the generation of microcracks

Dec 1, 1995

By J Kokado, N Hatta, S Yabushita

A theoretical model is described for prediction of the capacity of fines from porous ores, such as cokes and sintered ores, to be removed by a pneumatic, horizontal-type classifier prior to charging into a blast furnace. First, the influence of variation in the apparent density and drag coefficient of porous ores on removal efficiency is analysed from a stochastic standpoint. The effect on efficiency of collisions between particles in the classifying region is then examined analytically in relation to the ratio of the mass flow rates of particles and air (the loading ratio). Finally, a theoretical model is constructed that takes these factors into account. Theoretical and experimental results are compared and classifying efficiency is discussed from both experimental and theoretical viewpoints.

Dec 1, 1993

By M. Feely, W. G. O'Keefe, C. O'Reilly, M. P. Holdstock

A petrographic and microthermometric study of fluid inclusions in the Kentstown Granite, crosscutting quartz (VI) and calcite+quartz (V 2) veins in the granite and calcite+quartz (V 2) veins in the overlying sediments was performed on samples taken from the borehole. Comparisons of the type 1, type 2 and type 3 fluid inclusion populations recorded in the present study with those from other Irish Caledonian granites strongly suggest a similar fluid evolutionary history. Furthermore, the low-temperature CaC12-rich brines (type 5) of this study, which must be syn- to post-Lower Carboniferous in age, have correlatives both in Irish Caledonian granites and in the Lower Carboniferous base-metal deposits of the Irish midlands

Jun 19, 1905