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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 P. K. Kaiser, R. K. Brummer

Paper presented at the conference Risk assessment in the extractive industries, held in Exeter, 23-24 March 1994. A risk-based decision-making procedure has been developed for selecting rockburst-resistant tunnel support in burst-prone mines. The method is based on a risk-cost-benefit analysis and uses support cost data, costs associated with the risk of support failure or excavation loss, costs associated with accidents, injuries and deaths, and the benefits achieved by installing rockburst-resistant support. It takes into account the risk of damage to the support systems due to rockbursts, potential loss of production and the need to rehabilitate in the event of a damaging rockburst. A practical example is provided to illustrate the principles involved in the decision process

Jun 17, 1905

By A. L. W. Lips, T. J. R. Barclay, E. Rothery, S. H. White

Paper presented at the conference Economic geology in Europe and beyond II, models for mineral deposits in sedimentary basins, held in Keyworth, UK, 13-14 April 1994 (originally entitled: The Broken Hill base metal deposit - a tectonically transported and modified basinal deposit within the Proterozoic Willyama fold and thrust belt). A regional structural study was undertaken which incorporated the role of shears. Their positions were identified from earlier mapping, from regional aeromagnetic data and by additional field work. Kinematic studies determined movement histories and petrological studies of the fault rocks formed within the shears identified the relationship between the movements and regional metamorphism. It was found that the shears formed a part of an earlier, major thrust event with transport from NW to SE and a later, minor one in the reverse direction. Neither had any significant effect on the mineralisation apart from local displacement, but the shuffling of the basin stratigraphy adds to the difficulty of recognising the original volcanic and sedimentary protoliths of the metamorphosed sequence. The mineralisation at Broken Hill mine is confined to a single recognisable thrust slice within a shear corridor. It is stratabound with locally transgressive remobilisation due to the high-temperature thrusting and some metasomatic alteration as a result of the retrograde shearing. This variation accounts for the different genetic models applied to the deposits in the past

Jun 17, 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 D. J. Spottiswood, R. K. Tuteja

Axial grade profiles were analysed for a pilot column operating in reverse flotation mode to float talc from a gold-bearing sulphide ore. It was found that concentration gradients in the pulp are very low. Most of the cleaning action, both upgrading of valuable minerals and rejection of gangue, occurs in the froth zone

Jun 17, 1905

By R. T. Grant, C. Bazin, D. Hodouin

It is shown that most of the variation in the results of semi-batch flotation tests is related to the unavoidably stochastic nature of the flotation process. The preparation and analysis of flotation samples and, to some extent, operator error in performing the flotation test procedure are responsible for a small proportion of the observed variability of the calculated flotation performance indices

Jun 17, 1905

By D. H. Watkinson

Paper presented at the IAGOD international symposium on mineralisation related to mafic and ultramafic rocks held in Orleans, France, 1-3 September 1993. Part of the contact of the 4b orebody with the enclosing Murray granite is characterised by the presence of recrystallised and biotitic Sudbury Breccia; in places the contact is faulted and sheared. In other areas of the contact partly silicified granite contains disseminated chalcopyrite and quartz-chalcopyrite veins with other minor minerals. Both ore and veins contain platinum group minerals (PGM); predominant PGM are michenerite, kotulskite, merenskyite and sperrylite with Au, galena and Bi-tellurides. At some silicified-granite contacts Mn-rich garnets, some containing inclusions of PGM and quartz, are associated with biotite + epidote + stilpnomelane + quartz. PGM and Au also occur within Cl-rich biotite and ferropyrosmalite in massive sulphide and in siliceous ore. Quartz, chalcopyrite and feldspar in the contact rocks and in veins contain abundant, highly saline fluid inclusions. Studies showed that the fluids were trapped at intermediate temperatures. The 4b orebody is surrounded by a sheath of brecciated granite but is close to the Contact Sublayer. During and after emplacement of sulphide magma, saline formational fluid that was resident in the breccia interacted with hot massive sulphides in and near the Sublayer and remobilised Cu, Au and PGE. This fluid reacted with cooler rocks and ore in footwall fractures, enriching the 4b protore and producing the adjacent Cu- and PGE-enriched quartz veins. Exploration for Cu and PGE enrichment in footwall rocks of the Sudbury South Range is warranted not only in zones of magmatic ore in the Contact Sublayer but also in fractures and permeable units within Sudbury Breccia

Jun 16, 1905

By V. Distler, E. F. Stumpfl

Paper presented at the IAGOD international symposium on mineralisation related to mafic and ultramafic rocks held in Orleans, France, 1-3 September 1993. The massif contains large chromite bodies of "Alpine-type", ophiolitic affinity. Orebodies reach thicknesses of 150 m and sizes of more than 150 000 000 t chromite ore with average grades of 55-60 wt% Cr2O3. Chromites in the Main ore field are low-Al, high-Cr spinels which exhibit some variation in their Mg-Fe distribution. This differs markedly from high-Al spinels in peridotite host rocks and in narrow chromite pods which occur in the western and northern parts of the massif. Chromites carry silicate inclusions, often hydrous silicates such as amphibole. Chromites in massive chromitites contain micron size inclusions of platinum group minerals (PGM). Composite grains containing two PGM and, occasionally, a hydrous silicate are common. Os-Ir alloys rimmed by PGM sulpharsenides occur in narrow serpentine veinlets that cut chromite and are evidence for the reconcentration of PGE concomitant with introduction of As, probably during serpentinisation. Whole-rock PGE contents are highest in massive chromitites of Diamond Pearl mine (totals of 500 ppb). Chondrite-normalised PGE patterns of chromitites show negative slopes which are typical for ophiolitic, podiform chromitites in mantle sequences. The PGE patterns of host rocks are flat and rather depleted compared with those of chondrites and chromitites. Petrological data from unaltered host peridotites suggest a high temperature overprint leading to sub-solidus re-equilibration of olivine and spinel and to the growth of pargasitic and edenitic amphiboles

Jun 16, 1905

Paper presented at the conference Risk assessment in the extractive industries, held in Exeter, 23-24 March 1994. Sensitivity analyses based on financial variables are now routinely applied to the forecast financial results of mining projects especially during the feasibility stage. Risk analysis is gaining acceptance but is still almost universally confined to the effects of variations in financial variables. The single most sensitive factor in almost all mining projects is the ore reserve, but it is either ignored or improperly used in sensitivity and risk analyses. Unlike financial variables, the components of the ore reserve (grades and tonnages of mining blocks) are a function of location within the orebody. Physical (mining) access to these components is therefore a function of time which has a crucial effect on forecast cash flows. It is critical that these fundamental concepts are included in risk analyses of mining projects. The effects are considered of the uncertainty of the ore reserve on feasibility studies and open-pit mine design for a small gold mining venture. Geostatistical simulation is used as a method of quantifying the risk in using grades and tonnages estimated from sparse data

Jun 16, 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 J. J. Mackay

The Parliamentary Under-Secretary of State at the UK's Department of Transport introduced the symposium, approved its emphasis on environmental planning and the mitigation of environmental impact, discussed the publicity resulting from the recent opening of the Channel Tunnel as well as the role of private financing, and pointed out the leading role played by the Department of Transport in the introduction of the New Austrian Tunnelling Method to projects such as the Jubilee Line extension and the Heathrow Express (an editor's footnote, however, mentions with regret the Heathrow subsidence that occurred just before the journal went to print)

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

By A. C. Dunham, Y. D. Drakapoulos, P. W. Scott

The Pt and Pd occur alloyed with copper in small, irregularly-shaped grains, 0.25-5.0 micrometers in maximum dimensions. Grains of unalloyed native copper are also present. The grains are completely surrounded by or marginal to magnetite with inclusions of Ni-Fe-Co sulphides and native Ni-Fe, which is apparently a product of the serpentinisation process. Crystallisation of the Pt-Pd-enriched copper probably occurred at the same time, at low temperature, but the previous form of the Pt and Pd is unknown as no earlier PGE phases have been found. While Pt and Pd minerals are usually important in early-magmatic base-metal sulphides, Pt alloyed with Cu is extremely rare and apparently occurs only very late in the paragenetic sequence. A Cu alloy with Pd dominant over Pt and only minor amounts of other elements appears not to have been reported

Jun 14, 1905

A study of the thermodynamic properties of magnesium chloride ammines was carried out with the ultimate objective that the thermal decomposition of the hexammine MgCl2.6NH3 may prove successful on a commercial scale for the manufacture of anhydrous magnesium chloride, which is required for the efficient electrolytic production of magnesium. The experimental data are presented in the form of an equilibrium diagram that aids the understanding of the conditions associated with the thermal decomposition of ammines

Jun 13, 1905

By T. Guyaguler

An analytical technique using computer-based multiple-regression methods was employed to determine the relation between the dust-producing index and inherent rock properties of typical samples from a coal-producing area, one of the aims being to provide a preliminary predictive tool for practical use. The investigation demonstrated that factors varied in their influence under different conditions, the brittleness:toughness ratio and the hardness being the most significant inherent properties with hardness showing the highest positive correlation coefficient

Jun 13, 1905

By C. A. Pickles, S. J. Splinter, J. Cameron

The addition of copper oxide to a borosilicate slag resulted in the breakdown of the silicate network and a dramatic decrease in viscosity. With increasing borax to silica ratio the viscosity was reduced by two mechanisms. First, rising sodium oxide content promoted cleavage of the Si-O bonds. Second, increasing boric oxide (B2O3) content increased the number of trigonal borate units that were converted to tetrahedral borate units by sodium oxide and copper oxide. The BO4(4-) tetrahedra decreased the local silicate symmetry, thus disrupting the silicate network and lowering the viscosity. The activation energy decreased with increasing temperature and increasing copper oxide content

Jun 13, 1905

By E. A. Brocchi, D. H. Gameiro, P. K. Jena

Carbon tetrachloride was found to be a very efficient chlorinating agent for anatase concentrate, even at the low temperatures that were investigated (250-400 degrees C). For example, at 400 degrees C about 90% of the anatase concentrate was found to have been chlorinated within 60 minutes

Jun 13, 1905

By O. E. Polter, W. J. N. Fernando

Smelter-grade alumina is usually produced by the calcination of gibbsite. The ideal energy requirements for the calcination of gibbsite have been analysed and compared with the actual energy consumption of some industrial calcination processes. The consumption of most of these is considerably in excess of the ideal. Methods suggested for calcining dry gibbsite feeds which claim energy savings of 10-14% consume 26-34% more than the ideal energy requirement for dry feeds. This study indicates that it should be possible to recover appreciably more energy, giving further improvements in fuel efficiency, both in existing gibbsite calcination processes and in methods that have been proposed for the stagewise calcination of dry gibbsite

Jun 13, 1905