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By G. S. Camm

Gwynfynydd is a small, high-grade black shale-hosted vein-gold deposit. The Chidlaw Link Zone is the only area being mined and contains 24 000 t ore grading 15.2 g/t gold. Within the Link Zone a complex vein structure occurs consisting of a mother vein up to 5 m thick and narrow (less than 0.5 m) leader veins. The former shows minor variations in dip, strike and thickness, whereas the latter show marked changes in all three. The leader veins are hosted within the footwall zone of the mother vein and both are composed of quartz with galena, sphalerite, chalcopyrite, pyrite and minor arsenopyrite. The vein system is transected by a series of cross-vein and intra-vein dip-slip faults. Pockets of gold occur at vein intersections or branches and within the complex footwall zone and are often related to variations in vein attitude and/or geometry. The Chidlaw Link Zone displays a complex, erratic distribution of gold mineralisation and a multi-stage history of structural activity, fluid flow and mineral deposition

Jun 18, 1905

By B. M. England, L. C. Mackey

Magnesia minerals are included in most iron ore sinter mixes to provide the MgO requirements of blast furnace slag. The properties of these minerals have an influence on the eventual sintering properties of the mixes. A detailed study was undertaken of serpentine and dolomite and the use of limestone, olivine and magnesite was also investigated. A consideration of particle properties indicated that as these materials calcine a reduction in size can occur together with cracking and changes in surface properties. These changes could affect the permeability of the sintering bed and sintering performance. Studies of sintering reactions showed that magnesium and calcium, formed from the calcination of dolomite, are extremely mobile before the formation of melt. Evidence suggests that the movement of these oxides into surrounding areas is via a solid-state diffusion process. The diffusion of Ca into the surrounding hematite particles is faster than that of Mg, resulting in the formation of dicalcium ferrite and magnetite or magnesioferrite, the last two subsequently being converted to dicalcium ferrite in the presence of Ca with removal of Mg from the structure as ferroan periclase. Studies of pilot-plant sinters indicated that reaction mechanisms formulated from the bench-scale studies were occurring in actual sintering processes. The differences in sintering reactions between dolomite and serpentine were considered to be the major cause of differences in the availability of lime for bonding phase formation. Pilot-scale studies indicated that the sintering properties of a mix containing dolomite could be improved by increasing the basicity of the sinter mix while keeping the MgO level constant

Jun 18, 1905

By S. Kelebek

DETA exhibits a highly selective depressant action on pyrrhotite without adversely affecting the collectorless flotability of pentlandite and chalcopyrite in nickel-copper ores of the Sudbury region. A simplified Eh-pH diagram has been constructed to illustrate the extended stability of elemental sulphur and to explain the collectorless flotation of pentlandite and chalcopyrite. Cu and Ni ions, which are known to exist on the surface of pyrrhotite, promote the flotation of this mineral whether a collector is present or not. Thermodynamic calculations indicate that the action of DETA involves the sequestration of Cu and Ni ions from surfaces under a wide range of redox conditions; analysis of flotation test filtrate indicates as much as a 20-fold increase in the concentration of Ni and Cu ions. It appears that DETA may enhance the self-hydrophobicity of chalcopyrite and pentlandite by exposing more of the sulphur-rich surface sites for bubble contact in flotation. There are various possible explanations for its depression of pyrrhotite

Jun 18, 1905

By G. B. Harris, A. R. Laplante

Fine tungsten was used to mimic gold and fine and coarse silica and magnetite to mimic gangue. The optimum flow rate of fluidisation water varied from 1.7 l/min for fine silica to 5.6 l/min for coarse magnetite. Overloading at optimum flow rate was then investigated. With fine silica gangue no overload occurred under any of the conditions studied, and there was very little overload with fine magnetite. Coarse silica caused appreciable overload, but only after a significant bed of tungsten had been formed; with fine magnetite gangue the onset of overloading occurred earlier. Finally, with coarse magnetite severe overloading occurred almost immediately. Overloading was modelled using a first-order kinetic rate constant for erosion of the concentrate bed and a critical mass of constant above which it takes place. The results clearly demonstrate the importance of removing oversize to maximise recovery, particularly with a high-density gangue

Jun 18, 1905

By Seong-Taek Yun, Chil-Sup So, Seung-Jun Youm

The greisen-bordered quartz veins are spatially, temporally and genetically associated with a late Cretaceous granite intruding an early Palaeozoic, limestone-rich formation. Paragenetic data indicate three stages of hydrothermal mineralisation, the first typically in or within 500 m of the granite stock and showing vertical zoning between deeper Mo and higher W, the other two more abundant in the upper and outer parts of the mineralised area. Fluid inclusion and stable isotope data indicate that hydrothermal veins formed over a temperature range of 120-395 degrees C from low-salinity fluids. Early wolframite and molybdenite deposition in stage I occurred at temperatures of 300-395 degrees C from magma-derived, low-salinity, CO2-rich fluid, mainly as a result of fluid boiling and associated CO2 effervescence. Progressively larger volumes of local meteoric water entering the system led to the successive deposition of scheelite in stage I vugs, stage II base-metal sulphides and stage III fluorite-carbonates. Remobilisation of W and its later deposition of scheelite in the outer and shallower portions of the system occurred at 215-275 degrees C and stage II and III mineralisation from lower-temperature fluids that became progressively lighter in stable isotopes. It is concluded that the influx of meteoric water increased with distance from the cooling pluton

Jun 18, 1905

By L. E. Mordberg, E. N. Nesterova

Geochemical studies of the bauxite deposits show that the primary composition is gibbsitic. Some trace elements were relatively mobile during bauxite formation with the content of Th, U and Zr increasing and that of Rb, Ni and Co decreasing. Y and Pb were relatively immobile during lateritisation; their contents and ratios were inherited from different types of underlying rocks. The supply of Ni and Co took place at the diagenetic or epigenetic stages; their ultimate source was the crystalline basement in the region. The studies support the view that the bauxite was likely to have originated as a result of in-situ lateritisation and not through sedimentary transport and redeposition

Jun 18, 1905

By Bakker J. de, P. A. Leest, W. L. Dalmijn, H. J. Glass

The test facility at the Delft University of Technology, in the Netherlands, was characterised. Advantages include the possibility of separating particles with high but different densities up to 9 g/cm3, the ease of adjustment to any required separation density and the absence of moving parts. Simultaneous separation of more than two types of particles is possible and the magnetic fluid is safe and convenient to use compared with other heavy liquids. Disadvantages include loss of magnetic fluid with outgoing particles (cost approx US $10/l) and degeneration of fluid due to bacterial activity, reaction with particles and with surroundings. Only non-magnetic materials can be separated, there is limited potential for scaling up and high investment is required on account of the cost of magnets. Future improvements in the design of the apparatus and the properties of the magnetic fluids can only enhance its attractiveness for commercial applications

Jun 18, 1905

By L. J. Barnes

The process for bio-remediation of sulphidic slag (BROSS) operates at 45 degrees C in a neutral (pH 7), aerobic aqueous environment in which sulphide in the slag is converted to sulphate. A two-stage version has been developed that involves quantitative chemical pre-oxidation of total sulphide to thiosulphate, followed by complete biooxidation of thiosulphate to sulphate. Ferric hydroxide, also produced, acts as a flocculant in the bioreactor effluent, concentrating heavy metal precipitates in the thickener as a sludge which can be returned to the smelter. The process has a high sulphate production rate and low acid and nutrient consumptions. Microorganism growth is the rate-limiting stage, requiring a minimum liquid residence time in the bioreactor of about 7 h. Although large quantities of oxygen are needed, sufficient gas mass transfer can be attained in an air-lift reactor. Products are an aqueous stream containing sodium sulphate with only trace levels of toxic heavy metals and a benign, toxic metal-containing sludge

Jun 18, 1905

By D. C. Kaliampakos, A. K. Moutsatsou, J. K. Skotaras

The wastes from marble extraction in the Thasos- Kavalla-Drama region of northeastern Greece could be utilised as a new source of high-quality white carbonate fillers for the European market. Large deposits, satisfactory properties, acceptable processing costs and environmental benefits are among the factors that would have a positive bearing on a proposal for their use in this way. DTH, the waste arising from dolomitic marble quarrying operations on the island of Thasos, appears to be the more suitable material than DA waste from Nikissiani on the mainland because of the lower cost of primary grinding and the higher production rate of ultrafines with a mean particle size of 5 micrometres (the optimum size for filler properties in the case of both DTH and DA), its superior whiteness, the benefits that such use would bring to a very severe and complex environmental problem and the lower transport cost

Jun 18, 1905

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 D. Witchard, G. C. Penny

An important conclusion of the study is that altering the properties of the granulation water is a practical way of improving the sintering performance of blends that contain porous ores, and more work is under way to investigate other additives. Previous studies of iron ore blends containing pisolite ore showed that losses in sintering productivity were a result of deteriorating green-bed permeability. Pisolite ores are extremely porous and absorb a proportion of the water added during granulation. Although increased water addition could be used to counteract losses in productivity, the current study examined methods of inhibiting water absorption by pisolite ore as a means of improving productivity. Additives were used to alter the properties of the granulating water. With no increase in mix moisture contents pilot-scale sintering studies showed that sugar-based additives gave productivities that are higher than those obtained for a comparable ore blend containing haematite rather than the pisolitic ore. Several techniques of adding the sugar to the sinter mix were examined and found to increase productivity to varying degrees. Theoretical considerations, in some cases supported by experimental results, indicate that sugar-based additives not only inhibited water absorption by porous ore particles but also improved the permeability of the sintering bed. The study also suggested that, contrary to some commonly held views, the highly reactive nature of Yandi ore from Western Australia is beneficial for sintering. Porous ores enabled the formation of a strong sinter at fast flame-front speeds-both good strength and a short sintering time are requirements for high-productivity operation

Jun 18, 1905

By M. A. Leosson, S. H. Bottrell, R. J. Newton

Sylvite at Boulby is mined 1 140 m beneath the sea and the mine suffers from the influx of water. This is of two kinds: persistent flows originating in the Sherwood Sandstone aquifer and entering the evaporite sequence through fractures in the intervening mudstone, and impersistent flows which are transient in nature and of uncertain origin. Water from the overlying sandstone has become enriched with NaCl and large amounts of KCl and some Mg and Br have been added by interaction with the evaporites. Waters from the transient flows are isotopically distinct from those in the Sherwood Sandstone, being enriched in H and O. They are also saturated with respect to halite and sylvite, but have higher K/Na than the persistent flows and are much more enriched in Mg and Br

Jun 18, 1905

By P. J. O'Connor, V. Gallagher

The addendum, to the paper published in Trans. IMM B, vol.103, 1994, p.B175-B187, acknowledges data from Celtic Gold plc at Navan and apologises for the omission

Jun 18, 1905

By D. K. Bose, R. H. Rakhasia, V. D. Shah, J. C. Sehra

A series of experiments was conducted to determine the effects of roasting temperature, soaking period and quantity of soda ash added. At a laboratory scale, under optimum conditions of roasting at 873 K for 2 700 s with soda ash 10 wt% in excess of stoichiometric, molybdenum recovery was 99%. The investigations indicate the technical feasibility of producing high-purity MoO3 by combining the roasting process with carbon adsorption/desorption. The process uses low-cost chemicals, can be scaled up readily and is free of the SO2 pollution generated by conventional roasting, as the sulphur content of the concentrate is converted to sodium sulphate

Jun 18, 1905

By P. J. Baguley

The model has been developed on the basis of the observation that the partitioning behaviour of a particle is related to its calculated terminal velocity. It utilises a theoretical calculation of the terminal velocity of each particle class. This is then correlated with the observed partition data for a plant separator using empirically-derived functions of operating conditions which take into account effects such as bath turbulence, holes in drum lifters and feed arrangements. The model successfully decouples the effects of medium density and viscosity and is appropriate for any bath-type separator. The correlation between calculated terminal velocity and actual partitioning behaviour was established and modelled using data obtained from two Wemco drums treating Fe and Mn ores. The model can be used to predict the prevailing size-by-size partition curves and the separation (product grades/recoveries) given the washability of the feed and operating conditions. Simulations are used to show that, for the treatment of Fe ore, there is a maximum medium density beyond which product grades fall and that this maximum decreases as the proportion of magnetite in the medium increases. This is attributed to the dominant effect of viscosity at higher medium solids concentrations

Jun 18, 1905

By R. Scheepers, J. E. Misiewicz, A. C. Fitzgerald

Discussion by A.C. Fitzgerald of the paper, published in Trans. IMM A, vol.104, 1995, p.B121-B135, is presented together with the authors' response. Fitzgerald points out a number of problems with the idea of mineralising fluids leaving no trace in the large volumes of rock traversed before depositing all minerals of value in a particular horizon or rock type with which the required isobaric or isothermic surface also coincides. He suggested that in the case of the Rooiberg tin deposits, the Lebowa Granites may be batholiths that reached the surface and were capped by sheets of their own volcanics. The authors agree that they had considered a possible syngenetic origin for the stratabound deposits, explain that no conclusive evidence for this could be found, discuss the relative ages of the sediments and volcanics of the Rooiberg Fragment and explain the role of its low-intensity deformation and flat dip in the coincidence of an isobaric-isothermic surface with the lithological stratification

Jun 18, 1905

By T. From

The organisation's mission is to promote research and technological development in processes relevant to the minerals industry by providing expertise, developing and managing jointly funded projects, undertaking commissions and education and establishing and maintaining research and development networks. It was responsible for the administration of the Mining Technology 2000 national programme to reduce production costs per metallic unit by 50% over 5-8 years, which involved 120 projects in all. Technical areas included ore characterisation/delineation and mine planning, rock fragmentation, rock mechanics, maintenance, energy and ventilation, automation and information systems, cut and fill, bulk mining methods, drifting and production-face development. Other projects have been the Ore Geology Related to Prospecting (PIM) programme to raise the standard of ore geology research in Sweden and promote exploration for volcanogenic massive sulphides in three key regions, and a joint research project on ventilation control according to requirement, including development of fan and gas monitoring systems and an improved, adjustable and intelligent fan

Jun 17, 1905

By A. M. R. Neiva

The WNW-ESE-trending hydrothermal veins cut alternating mica schists and quartzites of mainly Ordovician age and, to the west, a Hercynian muscovite-biotite granite. They have been prospected and developed to a depth of 300 m and reserves of 20 t Au estimated. The paragenetic sequence and chemical compositions of the ore minerals are generally similar to those at Jales to the south. Gold, electrum and aurian silver form inclusions in arsenopyrite, pyrite, galena, sphalerite, pyrrhotite and quartz and also occur in veinlets that cut these minerals. Silver has been found in gold, electrum, aurian silver, tetrahedrite, freibergite and the Ag-Pb-Sb sulphide owyheeite. Early arsenopyrite crystallised at an estimated 480 degrees C and the more common, later arsenopyrite in which Au and Ag are generally included at 430-300 degrees C. Sphalerite crystallised at 307-100 degrees C. Monoclinic pyrrhotite may have been formed by the inversion of hexagonal pyrrhotite at 248 degrees C

Jun 16, 1905

By J. Temporal

An introduction to the conference material in this issue is given together with the issue contents list, closing remarks by its chairman Dr. J. Temporal, the list of contributors and their companies, and the information that the 26th Sir Julius Wernher memorial lecture had had to be presented by the lecturer's wife, M. Biggart, in his absence due to site problems on the Storebaelt project

Jun 16, 1905

By M. P. O'Reilly

A personal overview and assessment is given of the 42 papers delivered over the three days of the symposium. As well as 18 from the UK there were presentations from 16 other countries; 20 were on rock tunnels, 13 on soft ground and 3 on both; there were 17 case histories and 16 discussions of tunnelling machines but, for the first time in the conference series, almost no papers on tunnelling for mining purposes. Some projects, such as the Lesotho Highlands Water Project and the London Ring Main, attracted a number of papers addressing their different aspects

Jun 16, 1905