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By R. A. Ixer, R. A. Lord, H. M. Prichard, A. J. Boyce, P. McConville, C. T. Pillinger, I. P. Wright, J. Maynard

Analysis of 62 samples show that the sulphides throughout the igneous stratigraphy have a magmatic signature, with the exception of the uppermost gabbros and the lowermost basal thrust talc-carbonate lithologies. Mean delta-34S values for whole-rock samples from harzburgites, dunite pods in harzburgite, crustal dunites and wehrlites, the main and high-level pyroxenites and gabbros suggest that the primary sulphides derived their sulphur from a magmatic source enriched in 34S. This finding is compatible with the proposed origin of the ophiolite above a subduction zone. Values for pyrite mineralisation in the uppermost part of the gabbros are thought to result from precipitation from a seawater-derived fluid, while isotopically light sulphur in the basal thrust could have been introduced from underlying metasediments. The replacement of pentlandite by heazlewoodite has not led to sulphur fractionation

Jun 19, 1905

By T. Yalcin

In the Box-Wilson method, the correlation between dependent and independent variables is represented by a polynomial response function, whose constant and coefficients are determined by applying regression analysis to the experimental data collected. The five levels used for each variable consist of a minimum, a maximum and three intermediate values. A study was carried out using Ni-Cu ore from Sudbury, Ontario, in which 15 experiments designed according to the Box-Wilson method were carried out in random order and in duplicate. The two sets of replicate data showed close similarity, with an overall variance of 0.311 for the five parameters studied. The response functions were used to optimise frother dosage, collector concentration and air flow rate and an experiment was then carried out under the optimised conditions; the results agreed closely with those predicted by the response functions

Jun 21, 1905

By A. M. Tunstall, N. Djordjevic, H. A. Villalobos

The damage zone behind a typical smooth-wall blast in the open pit was assessed by visually examining diamond drill core to identify blast-induced cracking, mapping core rock quality designations to identify changes in fracture frequency and conducting uphole seismic testing to determine changes in rock mass characteristics. The results from the three techniques show reasonable correlation. They suggest that major damage, in the form of fracturing of intact rock, occurs at least 7 m behind the smooth-wall blast and significant damage, in the form of opening and extension of calcite-filled fractures, at least 12 m from the blast. At greater distances the dominant damage mechanism is the loosening of existent joints within the rock mass. In the trachytes at El Soldado these damage mechanisms correspond to peak particle velocities of 2 000, 900 and 500 mm/s respectively

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 S. Kelebek, J. A. Finch, Zhenghe Xu, S. R. (Ram) Rao

To improve SO2 emission compliance, pyrrhotite from Sudbury copper-nickel ores is being depressed with DETA. To understand the mechanism of depression, the role of complexing in controlling metal-ion activation of pyrrhotite was investigated. DETA was found to remove Cu and Ni ions but leave hydrophilic ferric species on the pyrrhotite surface. The metal:DETA ratio appeared to be 1:2. Cu was more readily removed than Ni, but the combination of DETA with sulphur dioxide was equally effective for both metal ions. Certain combinations of DETA, Ni ions, xanthate and dithionite (S2O4) or dithionate (S2O6), as representative derivatives of SO2 in water, produced hydrophilic precipitates. These may enhance pyrrhotite depression

Jun 19, 1905

By J. Hurdley, J. A. Plant, H. Robotham, P. R. Simpson, G. C. Lalor

Paper presented at the 28th International Geological Congress held in Washington DC, July 1989 (International geochemical mapping sessions). The results of orientation studies for a regional geochemical survey of Jamaica and the CARICOM countries of the Caribbean region are described. The survey is designed to provide systematic geochemical information for a wide variety of applications and, especially, to form a basis for agricultural development in the region

Jul 1, 1991

By J. A. Finch, Zhenghe Xu

The competitive adsorption of xanthates on sulphide minerals in a binary mineral system (pentlandite and pyrrhotite) was studied using the pseudo-in-situ technique of attenuated total-reflectance FTIR spectroscopy. The minerals were placed in the same collector solutions, either separated by a glass wall or in direct contact with each other before magnetic separation and separate analysis. The effect of mineral interaction on xanthate adsorption was clearly demonstrated spectroscopically for the first time. At low concentrations of xanthate, its adsorption on pentlandite was activated by physical contact with pyrrhotite; the effect may be attributed to the enhancement of electron transfer through electrical contact between the two minerals. The results emphasise the need for caution in extrapolating results obtained from single-mineral studies to flotation practice

Jun 18, 1905

By A. J. Davidson

A Cu-conducting solid electrolyte was used to develop the sensor. Instead of measuring the potential across the electrolyte from the reference material to the Cu-containing phase, a potential was applied and the stable current measured. This gave reasonable readings for copper-tin alloys, which agreed with the theoretical calculations, but was less satisfactory in the case of mattes because the surface area of electrolyte presented to the matte phase varied from sensor to sensor. To overcome this problem the potential was applied, the current was measured and then reversed and remeasured and the ratio of the currents was calculated. The current ratio is shown to be independent of the resistance of the electrolyte and the surface area of the electrolyte offered to the melt, but strongly dependent on the activity of the copper

Jun 21, 1905

By R. H. T. Garnett

N.B. This paper provoked much (positive!) discussion in later issues, with responses from the author (and thanks also for the many private contributions he had received) - see under Garnett R.H.T. Expanded version of a paper originally presented at the Alluvial mining conference, London, 11-13 November 1991 and published in Alluvial mining, Barking: Elsevier Applied Science for IMM, 1991, p.115-156. The usual measure of performance in gold and tin dredging is the R/E factor. It compares actual production or recovered grade for a given period with that estimated from the original sampling. The factor is a multiple of four component factors, each ideally approaching 1.00. The factors are concerned with estimation, selection, excavation and treatment. The estimation factor reflects the errors involved in determining the grade and depth of single drill-holes or pits. An optimum selection factor is achieved by a higher drilling density. The excavation factor is affected by failure of the dredge to excavate the total volume contained within its course. The required dredge throughput rate influences not only the success in digging recovery but also the treatment factor. No two alluvial deposits are the same, but, in general, the greatest divergence from 1.00 is invariably demonstrated by the estimation factor. A major divergence in one of the other factors may also be the cause of the R/E factor being significantly different from 1.00. The component factors are examined in detail and historical trends in R/E factors are discussed

Sep 1, 1991

By F. C. Gennari, D. M. Pasquevich

With the gradual exhaustion of natural rutile, there has been extensive research into its synthesising from lower-grade titanium minerals. The removal of Fe from pseudobrookite (Fe2TiO5) by chlorination was studied, using both isothermal and non-isothermal thermogravimetric measurements. Correlation of the results obtained from element distribution maps, scanning electron microscopy, energy-dispersive X-ray analysis and phases detected by X-ray diffraction in the chlorinated samples showed clearly two associated processes. First, the pseudobrookite particles reacted with chlorine and iron was removed selectively as FeCl3(g), leaving a solid residue rich in the TiO2 phases anatile and rutile, separated from an inner layer of unreacted pseudobrookite by a distinct interphase boundary. Second, chlorine allowed TiCl4(g) to form in the reaction bed, where it removed iron from the Fe2O3 crystals as FeCl3(g) and substituted Ti through a pseudomorphic reaction

Jun 21, 1905

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 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 G. M. Steed, A. O. Oyinloye

The deposit lies in amphibolite-facies biotite granite-gneisses of Proterozoic age, 4 km east of a major crustal break known as the Ifewara-Zungeru fault. Gold mineralisation is contained in a zone of quartz-carbonate (mainly calcite) veins and hydrothermally altered gneisses with associated small-scale intrusions along a steeply dipping second-order fault zone that roughly parallels the main fault. Gold is present mainly at grain boundaries between quartz and carbonate as discrete particles up to 100 micrometres in size, in general association with sparse, scattered pyrite, pyrrhotite and some base metal sulphides. Adjacent to the gold-bearing zone the granite-gneisses have been hydrothermally altered with minor volume increase, most notable enrichment being in K2O, S, Pb and Cu (and Au). High concentrations of Th, Y, Ce and Zr in the granite-gneisses imply derivation from S-type granites. It is likely that their high heat production capacity maintained the high temperatures needed to transport gold in the hydrothermal systems. It is most probable that the mineralisation dates from the Pan-African orogeny (650-450 Ma)

Apr 1, 1996

By J. K. Whyatt, W. P. Blake, T. J. Williams

A study at the Idaho mine revealed that, despite the apparent randomness of seismic events, common characteristics defined five recurring types. These characteristics included the geological structure that slipped, the first-motion pattern and the location and intensity of damage. Many large events caused little or no damage, and where it did occur it was concentrated at intersections between slipping structures and mine openings. Of 39 events between 1989 and 1994 with local magnitudes of 2.5 or more, 10 were caused by slip on bedding planes in the southern limb of the mine, 6 occurred near the vein along a set of near-vertical faults that form the central shear zone, 8 were strike-slip events on the Southern Control Fault, 4 were by slip on the vein itself and 10 involved strike-slip and/or dip-slip movement along the North Control Fault. Strategies for control of mining-induced seismicity need to consider all five types of event, lest a strategy to reduce one type increases others

Jun 19, 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 S. P. Ball, A. J. Monhemius

In a laboratory study under acidic oxidising conditions, the thiocyanate system gave results at least as good as cyanide and considerably better than thiourea, with modest consumption of SCN (less than 1 kg/t ore). For both cyanide and thiocyanate lixiviants a residence time of about 24 h was required for maximum gold extraction, which was generally in the range of 92-96%. The adsorption of gold from thiocyanate leach liquors was found to be rapid, but activated carbon catalyses the autoreduction of ferric iron to ferrous iron in thiocyanate solutions, suggesting that ion exchange may be a better recovery route

Dec 1, 1995

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 J. S. Duval

Paper presented at the 28th International Geological Congress held in Washington DC, July 1989 (International geochemical mapping sessions). The compilation of the National Uranium Resource Evaluation aerial gamma-ray data to produce maps of the apparent surface concentrations of potassium, uranium and thorium for the conterminous USA has resulted in a reasonably accurate representation of the distribution of these elements in the surface rocks and soils. This claim is supported by the general agreement between the mapped geology and the patterns seen in the data

Jul 1, 1991

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 R. Poulin, C. F. Gleeson

The Birimian rocks of the region are gold-bearing and show many similarities to those of Burkina Faso. All three greenstone belts (Goroual, Tera and Sirba) host gold-bearing quartz veins. It appears that, contrary to previous misconceptions, lateritic terrain is not an unfavourable environment for exploration geochemistry. This is demonstrated by the results for the Koma Bangou area, where soil and termite-mound geochemistry have been successfully used in the search for gold. Soil provides an effective sampling medium where it is shallower than about 2 m; there is evidence that some soil anomalies are enhanced by the presence of secondary (botryoidal) gold. In areas of thicker, allochthonous soil cover, termite-mound sampling is more effective. At Koma Bangou an identified resource of some 11 100 000 tonnes with an average gold grade of 2.44 g/t has been reported. The gold mineralisation occurs in quartz veins and stockworks aand in the wallrocks of shear and fault zones that trend N, NW and NE. The host rocks are a granodiorite-syenite porphyry and intermediate metavolcanic rocks and tuffs

Apr 1, 1996