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By S. J. Parry, D. M. Evans, D. L. Buchanan

The reef is a PGE-enriched sulphidic zone, stratigraphically associated with and overlapping the C1d chromitite layer, that was formed by magmatic processes at the 1e-1d subunit boundary. Two distinct patterns of PGE enrichment are related to the presence or absence of Cr2O3 oversaturation during sulphide liquation that occurred during a complex sequence of changes at this boundary

Apr 1, 1996

By M. K. Abd El-Rahman

A complete chemical analysis of the waste showed that it contains 15.64% P2O5; X-ray diffraction analysis revealed that it is composed mainly of francolite, calcite, pyrite, quartz and dolomite. The phosphate values were recovered and the settling rate of the wastes enhanced by the use of hydrocyclone and flocculation techniques. The hydrocyclone produced an underflow enriched in phosphate and an overflow enriched in clays. The former represented 39.8% by weight of the phosphatic clay waste and assayed 26% P2O5 at a recovery of 66.36%. The results of flocculation of the phosphatic clay waste showed that both the degree and rate of settling were increased and that the process water could be recycled. The settling rate was 37 times greater when anionic polyacrylamide A130 was used

Jun 21, 1905

By A. H. G. Mitchell

Most, if not all, of the six recognised post-Cretaceous, predominantly andesitic mineralised belts in the region are now thought to be subduction-related magmatic arcs. The Inner Carpathian arc and the Eastern Bosnia or Drina-Rhodope arc host numerous vein and replacement deposits with epithermal features and Zn-Pb+/-Ag as the predominant economic minerals. In contrast, the south Apuseni Mountains have produced over 1 600 t Au from epithermal veins but very little Zn-Pb. Recent age determinations and geophysical data from the Baia Mare district of the Inner Carpathians suggest that mineralisation succeeded volcanism by 1-2 m.y. and accompanied crustal extension and the cooling of a large, mushroom-shaped pluton whose boundaries define the mineral district. In the south Apuseni district, mineralisation can be explained by mixing of meteoric with low-salinity metamorphic water expelled during intrusion of mafic rocks into the middle or lower crust. The more continental or cratonic crust in the Drina-Rhodope and Inner Carpathian arcs precluded the input of low-salinity, Au-bearing metamorphic water; the Zn-Pb deposits formed where convecting meteoric water mixed with saline water, possibly introduced through carbonate rocks in the basement

Aug 1, 1996

By A. G. Pasamehmetoglu, N. Bolukbasi, O. Koncagul

A study has been undertaken to establish the relationships between the O&K wedge test cutting resistances and the geotechnical parameters of rock materials in the context of bucket-wheel excavator operation. Prediction equations were formed to estimate the cutting resistance from the geotechnical parameters by multiple regression analysis. The cone indentor index, uniaxial compressive strength and Shore hardness parameters have been found to be the most significant predictors

Sep 1, 1991

By R. A. Lord, H. M. Prichard

efficiency is discussed from both experimental and

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 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 P. H. Carr, G. G. Marino, K. A. Patel

Extensions to a correctional institution at Wabash Valley, Indiana, required development over abandoned coal-mine workings, at 90 m depth, where subsidence was possible at surface. Backfilling of the flooded mine in critical areas was determined to be the most cost-effective method of limiting the risk of damage to the buildings. Containment grout was first placed in selected entries and cross-cuts of each mine area; the remaining volume was then filled with a readily flowing infill grout. Where a high proportion of an area was taken up by rubble, calcium lignosulphonate was used as a retarder and plasticiser to increase penetration. Grout movement was monitored from adjacent boreholes with an electrical resistivity probe during grouting, while after the work was finished core samples were obtained from verification holes drilled in the backfilled areas

Jun 19, 1905

By P Stone, J. M. Cook, P. R. Simpson, C Mcdermott

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. The SW part of the Southern Uplands is a back-arc section of an accretionary thrust system, divided into structural blocks by major NE-SW shear zones and NW-SE faults forming the margins of Permian half-grabens. The highest arsenic levels in stream sediments (over 65 ppm) are associated with those blocks carrying brittle-ductile transition fabrics. Three factors combine to recomend the area as having potential for gold mineralisation: As-rich greywackes as country rock, felsic intrusions and a major shear zone. Selected stream sediments were analysed for gold using lead fire assay with ultra-pure flux and ICP-MS finish. Several localities showed over 15 ppb Au, the three most significant being within the hanging wall of the Orlock Bridge Fault and each having distinct characteristics

Aug 1, 1995

By R. Patel, D. R. Taylor, P. M. Varley

In-situ measurements of ground stress were made from surface boreholes, using overcoring and hydrofracturing techniques, to obtain data for the detailed design of the underground works at Pergau. Unexpectedly low stresses were measured and appeared to correlate with apparent hydrofracturing observed during permeability testing. The low values of the minor principal stress had a major impact on design, particularly of the lining for the pressure tunnel and shaft. Additional hydrofracture tests were made underground during construction of the low- and high-pressure headrace tunnels and the pressure shaft, to define the vertical reduction in the minor principal stress with overburden. These data were then used to locate and design the steel and reinforced concrete linings

Jun 19, 1905

By A. D. Fowler, M. T. Anderson

A phenomenological model is presented that relates Pb-Zn mineralisation to proximal geopressure zones. Typically, geopressure zones (GPZ) consist of masses of undercompacted sediment encapsulated within impermeable shales and are characterised by high formation fluid pressures. Heat flow is perturbed in some GPZ on account of their insulating properties. Geothermal gradients as high as 150 degrees C/km have been observed over short distances in the sediments of the US coast of the Gulf of Mexico. Some modern geopressure zones are known to reach temperatures of 120-150 degrees C at depths of 2.5-3.5 km. It is demonstrated that the zones may act as proximal sources of hydrothermal fluids, thus explaining the high temperatures of mineralisation observed in the deposits, which are hosted in basins characterised by thick, rapidly deposited, shale-rich clastic sequences

Jan 1, 1991

By J Hadijigeorgiou, R. W. Lawrence, R Pouling

The layered co-mingling method involves the disposal of waste rock with the addition, at predefined construction stages, of layers of dewatered mine tailings. The resulting waste structure displays bulk properties that are more favourable to acid rock drainage (ARD) control than the constituent materials alone. A laboratory test programme was conducted to examine the potential of this method. Columns containing different configurations of waste rock and tailings were percolation leached for 40 weeks and the leachates examined for various parameters. In the short term the chemical reactions that result from the introduction of dewatered tailings into rock waste can significantly improve the quality of the drainage. Columns with co-mingled material produced leachate with pH levels of 8, whereas leachate from the control column containing waste rock alone had a pH of 4. Larger-scale field tests are planned to determine the effect of the disposal method over the longer term

Apr 1, 1996

By T. M. Williams, P. M. Green

Paper presented at Mineralisation in the Caledonides, the Mike Gallagher memorial meeting held in Edinburgh, 27-28 June 1996. The sediment geochemistry of streams draining Southern Uplands and Lake District turbidites was compared with lithogeochemical data for the source greywackes, using stratigraphically defined catchments. Several systematic trends in element abundance variation between source and stream sediment can probably be applied more widely to interpretation of drainage geochemistry. Pb and Zr increase markedly from source rock to sediment, by adsorption on clay and zircon grain concentration. Variation of feldspar-related elements Rb, Sr, K and Ba appears to be controlled by source grain size and compositional maturity. Ni shows surprisingly little change and Fe and Co are only slightly raised. Cr is particularly useful, with variations superimposed in anomalously high regional levels. Abrupt changes in Cr distribution in stream sediment coincide with stratigraphical boundaries, allowing drainage data to be used as a surrogate for whole-rock values

Jun 19, 1905

By R. K. Dunham, D. J. Reddish, X. L. Yao

Paper presented at the conference: Risk assessment in the extractive industries, held in Exeter, UK, 23-24 March 1994, and first published London: IMM, 1994, preprint volume, 10pp., 10 refs. The integrated approach combines a powerful ground movement prediction program with a knowledge-based expert system. ESDAS (Expert Structural Damage Assessment System) was developed to evaluate mining subsidence damage in the form of risk and in terms of the three vital contributing components (mining factors, site factors and structural factors). Using a certainty factor risk assessment technique, the system can be used to predict the likely damage to a particular structure subjected to mining subsidence. A previously developed powerful ground movement prediction program, SWIFT (Subsidence With Influence Function Techniques), has been combined with the expert system to allow the mining factor to be more accurately determined in a broader range of mining layout. Since SWIFT can be calibrated to any particular coal field using local subsidence data, it is believed that the integrated system could be used in any coal field worldwide for the assessment and control of mining subsidence damage risks

Dec 1, 1995

By G. S. Pauley

Paper presented at a meeting on: Artificial intelligence in the minerals sector, held in Nottingham, UK, 20 April 1993 (original title: Case-based reasoning can be a catalyst for improvement). A new computer software technology known as Case Based Reasoning (CBR) can be used to produce small decision support systems that are economically viable. This is because the knowledge that they contain can be owned and maintained by their users. A CBR tool has been used to perform a pilot study with Anglesey Aluminium Metal Ltd. The results are encouraging. They suggest that a combination of CBR and participative design and implementation techniques (such as Checkland's Soft System Methodology) can achieve sustainable improvement in mineral processing functions. An explanation is presented of why traditional, rule based systems are often an ineffective way to implement support systems. It is shown that CBR may provide an appropriate technology solution. Methods of achieving sustainable benefit are indicated. The pilot study with Anglesey Aluminium Metal is used as a practical illustration of the development of a CBR application. A review of potential application areas and some observations about the implementation are presented

Apr 1, 1994

By Gruenewaldt von

Paper presented at the IAGOD international symposium on mineralization related to mafic and ultramafic rocks held in Orleans, France, 1-3 September 1993. The principles of shear-driven aggregation of particulate matter suspended in fluids, a common industrial method of concentration and separation, were applied to a convecting magma to estimate the time required to sparge or strip the PGE and Cr content and concentrate it into the boundary layers. It was calculated that an ore-grade (e.g. 6 ppm PGE) boundary layer about 1 m thick would require 100 000 years at most to form from a body of magma 500 m deep with a PGE content of 20 ppb. Since concentration would be most vigorous when the magma was warmest, at least half of this concentration would take place in the first 10 000 years. The effect of dispersive pressure in the boundary layer would generate a concentration high of refractories just below the top of each boundary layer and another just above the bottom. If the magma was a double-diffusive system, it might evolve by the downward cascade of enriched boundary-layer material into the hotter, lower magma layers, where depending on saturation levels chromites would equilibrate and sulphides undergo partial or total resorption, enriching PGE levels in any remaining sulphides. This cascade process would in time greatly enrich the lower regions in PGE-bearing sulphides and chromites

Apr 1, 1994

By V. A. Melezhik, A. H. Green, L. N. Grinenko

Finally, a theoretical model is constructed that takes

Aug 1, 1994

By N. B. J. Kieser

Paper presented at the IAGOD international symposium on mineralization related to mafic and ultramafic rocks, held in Orleans, France, 1-3 September 1993. Platinum-group minerals (PGM) in the enriched zone at Dust Mountain occur in two separate parageneses, the first representing primary magmatic PGM and the second primary magmatic PGM that have been reduced to alloys during serpentinisation. Minerals in the first group were unaffected by hydrothermal alteration on account of their textural setting or stable chemical composition. Despite substantial alteration of the serpentinised assemblage, most evidence points to the dominant role of primary magmatic processes in determining PGM occurrence. Several base metals have nevertheless been introduced hydrothermally. With respect to surficial dispersion the single most important paragenetic factor was the reduction of sulphides to alloys, rendering them more susceptible to mechanical erosion and less so to chemical leaching. The different textural setting of Pd-group and Ir-group phases results in different dispersion characteristics, with major implications for stream sediment sampling

Apr 1, 1994

By O. R. Eckstrand, M. Asif, P. L. Schwann, A. J. Naldrett, R. J. F. Scoates

Paper presented at the IAGOD international symposium on mineralisation related to mafic and ultramafic rocks, held in Orleans, France, 1-3 September 1993. PGE-bearing sulphide mineralisation is contained in the lower 600 m of the Upper Central Layered Zone of the intrusion. There are four regimes with distinctive crystallisation characteristics. PGE content is low, both in bulk rock and in terms of metal in 100% sulphides, in the sulphide-rich cumulates but increases sharply in the sulphide-poor cumulates at the base of regime 1. Increases in regime 2 have no such clear relationship with incoming cumulus sulphides. PGE contents are low throughout regime 3, but regime 4 has sulphides with high PGE content, decreasing rapidly upwards, at the base of many of its cyclic units. The observations are interpreted as indicating that sulphide saturation occurred in the middle of a cyclic unit in regime 1, after which fractional segregation of sulphide caused a systematic decrease in PGE content. The resulting contrast between 40 000 ppb PGE in sulphides below the mineralised zone and less than 1 000 ppb above is of practical importance in exploration for such zones. In regime 2 the magma chamber was open to fresh influxes and PGE content was not so sensitive to sulphide saturation. In many regime 4 units influxes of new magma caused immediate sulphide saturation and PGE depletion, so that PGE-rich cumulates do not underlie PGE-bearing sulphide zones. Theoretical analysis indicates that regime 1-type behaviour is likely to characterise intrusions below the level at which plagioclase has entered as a cumulus phase and regime 4-type behaviour above

Apr 1, 1994

By G. X. Wang, R. E. Siemens, M. C. Fuerstenau, D. Chandra

Soda roasting of concentrates from Mouat, Montana, was performed in a temperature range of 450 to 650 degrees C and chromium was solubilised by water leaching at room temperature. It was found that high extraction yields of chromium were primarily dependent on the conversion of Cr3+ to Cr6+ during the roasting step, and this was enhanced significantly by simple attrition of chromite particles during this step. Gangue impurities (mainly Si) were more detrimental to Cr extraction than lattice impurities such as Al or Mg. It appears that oxidation proceeds into grains along a preferred crystallographic plane in the cubic lattice of the chromite. The effects of roasting time, temperature, soda to chromite ratio and particle size on the extraction of chromium are presented

Jun 18, 1905