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1994 estimates for Porgera are probable and proven reserves of 58 200 000 t of ore grading 5 g/t Au. Gold mineralisation is related to an intrusive complex emplaced at shallow levels in poorly consolidated sedimentary rocks. The complex is located in a zone of fold-and-thrust deformation, whose formation may have been initiated shortly before emplacement and continues locally today. Abundant primary magnetite in the complex gives an intense, 5 km wide aeromagnetic anomaly. The deposit formed during two main stages of mineralisation, the first related to early magmatic-hydrothermal activity and the second representing later epithermal overprinting centred on the Roamane fault. Hydrothermal alteration followed closely on emplacement indicating a close genetic relationship between magmatism and mineralisation. Both stages of hydrothermal activity post-date and overprint early propylitic alteration. Several factors have acted in unison or sequentially to concentrate metals at the deposit, including an extensional or trans-tensional tectonic setting within an arc or collisional environment, the exsolution of a magmatic hydrothermal fluid prior to sulphur saturation in the melt, the development of the hydrothermal system into one favourable for transporting gold, the action of late-stage faulting in focusing epithermal fluid flow, and the role of dissolved gases in promoting fluid phase separation and high-grade ore deposition

Jun 19, 1905

By R. I. Jeffery, J. W. Summers

An account is given of the verification and calibration of a numerical modelling technique that has been developed for the prediction of subsurface strata deformation following the extraction of coal by longwall mining methods.

Jan 4, 1992

By J. Plant

Stream-sediment sampling undertaken to define the regional geochemistry of northern Scotland is described with particular reference to the errors involved. The region is underlain essentially by Moine schists, Caledonian granites and Old Red Sandstone sediments, which are generally characterized by low geochemical relief. Factors in the secondary environment obscure the relationship between trace-metal concentrations in stream sediments and bedrock geology. Investigation of sampling and sample preparation methods indicates that the -100-mesh material is the optimum size fraction for the regional survey of this area: it provides adequate geochemical contrast: it reduced the incidence of spurious high values in the samples investigated and it is available in amounts which are adequate for all the analyses required. Grinding samples improves precision and reduces the preferential volatilisation of metals coprecipitated with hydrous manganese and iron oxides for the optical emission spectroscopic method used initially. A study of the dispersion of metals in the drainage system of an area of Pb-Ba-Mo mineralisation and an area of U-Pb mineralisation, respectively, indicates that a sampling interval of 1 per 2 km2 based on second- or third-order streams is adequate to define anomalous metal concentrations. Regional variation can also be represented on the same interval. Modifications to the sampling procedure to reduce the effects of the secondary environment are complicated by the primary association of Mn and Fe with mineralisation in the area. The ratio of analytical and sampling error to regional variance shows that procedural precision is adequate to prepare regional geochemical maps of northern Scotland, with the exception of Cr, Cu at low concentrations and Pb.

Dec 1, 1971

By T. T. Chen, J. E. Dutrizac, C. Canoo

The calcine consists principally of ZnO and ZnFe2O4, which occur as banded and porous grains, together with lesser amounts of Zn2SiO4, Zn-Fe-Pb silicate, sphalerite, quartz, PbSO4 and Fe2O3. Al is present in solid solution in most of the Fe-bearing phases and also as residual aluminosilicate minerals from the original concentrate. Si occurs mostly as Zn2SiO4, Zn-Fe-Pb silicate and as residual silicate minerals. As is commonly found in the ZnFe2O4, Fe2O3 and Zn-Fe-Pb silicate phases. The major As carrier may be calcium arsenate particles less than 1 micrometre in size which are dispersed throughout the calcine. The neutral leach residue consists mainly of ZnFe2O4 and precipitated masses of iron gel-silica gel. Lesser amounts of ZnO, Zn2SiO4, Zn-Fe-Pb silicate, PbSO4, sphalerite, Pb-K-jarosite and basic zinc sulphate are also present. Al occurs in minor concentrations in most of the Fe-bearing phases and in the Zn-Fe-Pb silicate. The residual aluminosilicates are also an important Al carrier. The major As carrier is the precipitated iron gel-silica gel phase, but some As is also present in the Zn-Fe-Pb silicate, ZnFe2O4 and Fe2O3 phases. Silicon is divided about equally between the iron gel-silica gel, Zn2SiO4, Zn-Fe-Pb silicate and residual silicate minerals. The weak acid leach residue is generally similar to the neutral leach residue except for its reduced content of ZnO and basic zinc sulphate.

Jan 4, 1993

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

Discussion by B.P.J. Stevens of the paper, published in Trans. IMMA, vol.104, 1995, p.B1-B17, is presented together with the authors' response. Stevens questions the authors' radically different interpretation of the structural geology of the Broken Hill Block, considering that the descriptive part of the paper is a useful addition but that the conclusions are unwarranted on the basis of the data presented. A number of major points of disagreement are outlined and half a dozen additional minor points listed. In response, the authors admire Stevens's contribution to unravelling the geology of the area but defend their attempts to take the regional studies a step further, pointing out that he has misquoted what they wrote and arguing that because of the assumptions underpinning the derivation of the present stratigraphy it cannot be used to constrain structural models. With regard to shear zones, they cite the extensive earlier literature and refer to horizontal displacements shown on maps produced by Stevens et al. Detailed discussion follows of the stratigraphy and of the stratigraphic correlation problems resulting from failure to recognise the presence and significance of shears, particularly those parallel to stratigraphy. The remobilised position of the Pb mineralisation in the North Mine open cut is reiterated. It is concluded that there is an urgent need for systematic isotopic dating in the area to constrain the stratigraphy

Apr 1, 1996

Paper presented at the Mining Institute of Scotland's annual general meeting held in Glasgow, 8th April 1916. Although there is nothing novel or difficult about the sinking described, circular shafts are not numerous in Scotland so the details connected with such a sinking may be of interest. The shaft was sunk at Dykehead Colliery, Larkhall, which has been worked for over 50 years from the upper seams. It became necessary to sink another shaft to serve as a replacement downcast, by which the output might be maintained and some of the lower seams won. As the sandy clays regularly caused bulging into the rectangular shaft and sinking of the surrounding ground it was decided to make the new shaft circular and to enclose its mouth in a foundation-block of concrete resting on the solid clay. Details are given of the sinking, brick seating and lining, kettle strike, water-rings and doorhead lintels as well as the permanent fittings, winding gear and the cages themselves

Dec 1, 1916

By S K. Das

An intensive investigation into modern roof support technology, including hy draulic and control systems, has been carried out against the perspective of global development and support behaviour on longwall faces across the Indian sub-continent. The wide ranging study examined various types and designs of modern supports used in seams of varying thickness and inclination where caving and stowing were practised. Consideration has been given to structural analysis, support resistance, the various forces acting over and on the powered supports and to support compatibility. The examination of the phy sical parameters has been allied to field experience and, together, have led to the formulation of standard designs for both the powered support structure and structural systems. A realistic mathematical model has been formulated for calculating the capacity of roof support requirements resulting from the actual behaviour of the immediate roof stratum. As a result of the work, it should be possible to readily select the most appropriate type of support sy stem for the conditions and longwall mining method that is to be employed.

Jan 4, 1997

By D. C. Yates, G. V. Jolliffe

In the five coalfields of Staffordshire, there have been some 43 incidents of spontaneous fires and heatings which have required special attention in the past ten years. This total excludes incidents in the Thick Coal Seam of South Staffordshire, which was worked until 1967, and which was subject to an almost continuous series of heatings. The incidents have been classified to show the sites of occurrence, the contributory factors which may have caused them and the treatments applied to them. The remedial techniques, as practised in Staffordshire, are dealt with in detail, with particular reference to standard methods of stopping-off. Precautionary measures taken are described, including a "liability to spontaneous combustion" classification of all seams, and the setting up of an emergency organization with emergency stocks of materials and equipment. The paper is concluded by a few words on the organization and control at the time of an incident.

May 23, 1905

By R. W. Ruddle

The present state of knowledge on this subject may briefly be summarized as follows: (1) The copper content of the slag increases with the grade of the matte in contact with it; on the other hand, the proportion of copper lost decreases as the matte grade increases, because as a general rule a smaller volume of slag is produced when a high-grade matte is made. (2) The presence of CaO and MgO in the slag decreases the copper content of the slag, and the presence of ZnO increases it; the presence of A1203 seems to have little effect. The influence of the silicate degree is not yet clarified, but on theoretical grounds it seems likely that the copper content increases with the silicate degree of the slag. (3) High slag viscosity, high magnetite contents and low density difference between matte and slag all tend to increase the copper loss. The volume of slag is also an important factor. (4) The effect of bath temperature on the copper loss is not clear and further investigation of this point is needed. (5) It appears possible to recover a large part of the copper in the slag by adding FeS, CaS and other sulphides

Jan 1, 1953

The first part describes a model (the C model) based on the motion of the grinding charge. The charge is treated as a continuum, which allows analytical solutions to the equations that are developed. The C model is equally applicable to ball-, semi-autogenous and autogenous mills and contains a description of the power draw of both the cylindrical section and the cone-ends. Differences between the power draw of grate- and overflow-discharge mills are described from consideration of the different shapes and compositions of their charges. A large database of industrial mill data is used to demonstrate the accuracy of the model. Part 2 describes a simpler, empirical model (the E model) whose performance is based on that of the C model. The same database was used to assess the predictive capabilities of the E model. The model was shown to be only slightly less accurate than the C model despite its much simpler structure

Jun 18, 1905

By M. Gallego, R. Oyarzun, L. Ortega

Evidence of metallogenic activity in an area dominated by Upper Precambrian and Palaeozoic metasediments was partially explained in the 1980s when drilling and a geophysical survey detected hidden intrusions, but questions remained to be answered about the nature of the fluids. Sb mineralisation at El Juncalon vein-type deposit was selected for geological, geochemical and fluid inclusion studies as a model with a relatively simple quartz-stibnite-pyrite paragenesis. Many of the characteristics were those of Chinese-type vein Sb deposits, which can be regarded as atypical of the epithermal type as they are hosted by clastic rocks

Aug 1, 1995

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

By H. Y. Sohn, Hang Goo Kim

Computer simulations were carried out using calcium ferrite slags containing 25 wt% CaO, and the results compared with those obtained using fayalite slags. There was little difference in overall elimination of Pb and Bi, but elimination of Sb and As was much lower with calcium ferrite slag. When calcium ferrite slag is used only in the converting stage and fayalite slag in the smelting stage, as in the Mitsubishi process, the contents of Sb and As in the blister copper can be kept to reasonable levels. This allows advantage to be taken of the considerably higher iron oxide-holding capacity of calcium ferrite slag than of fayalite slag at the high oxygen potential under converting conditions, thus preventing precipitation of magnetite. Satisfactory agreement was obtained between predicted values and observed data from a Mitsubishi converter

Jun 18, 1905

By D. J. Burdon, Anthony Caplan

"(1) The radiological appearances of pneumokoniosis on the Kolar Gold Field is described in detail. The characteristic abnormality is the. presence of a diffuse, fine annular and punctate mottling. (2) The frequency of symptoms could not be determined with any degree of accuracy, but it is believed that symptoms are absent and there is no incapacity until profuse radiological mottling is present, i.e., after long exposure to dust. (3) There is an increased predisposition to tuberculosis, which, if it occurs, affects the prognosismost unfavourably.(4) Pathological examination shows that the radiological mottling is due to the presence inthe lung of numerous small dust-cdll aggregates (up to T5 mm. in dia.) deposited around the smaller bronchioles and blood-vessels.(5) The dust-cell aggregates are relatively acellular but when tuberculosis is superadded thereis an excessive cellular and fibrotic reaction.(6) The difficulties of defining the radiological and pathological appearances of early pneumokoniosisare discussed.(7) The incidence of pneumokoniosis in 7,653 workmen with 5 or more years’ undergroundservice was 43-75%, but it is suggested that in future the incidence will be appreciably lower.(8) The methods of- dust production and the chemistry of mine dust are described. It isshown that the free silica-content of air-borne mine -dust is relatively low.(9) The aetiology'of the pneumokoniotic lesion is discussed."

Jan 1, 1947

By V. A. Melezhik, P. K. Skufin, L. P. Nilsson

these factors into account. Theoretical and

Aug 1, 1994

By T. B. Colman

Paper presented at the MEP '89 conference held in Madrid, 13-15 November 1989. Britain has sustained an important metalliferous mining industry over many centuries. Recently, new geological concepts and exploration techniques have indicated that there is considerable potential for the discovery of a variety of deposit styles, often in previously neglected areas. The recent discoveries at Aberfeldy (Ba-Zn-Pb), Gairloch (Cu-Zn) and Cononish (Au-Ag)in Scotland and Curraghinalt (Au-Ag) and Lack (Au-Ag-Pb) in Northern Ireland are illustrations of this potential. Some of the prospective areas for future exploration are described and an indication is given of the legislative framework within which mineral exploration and development are carried out

Jan 1, 1991

By P. E. J. Pitfield, S. D. G. Campbell

The regional structure of shear and deformation zones in the belt, which is recognisable in plan view on Landsat TM images, is interpreted in terms of a conjugate-shear model. Gold mineralisation is related to this framework at a variety of scales. The principal recurrent structural geometries hosting deposits at mines such as Motapa, Durban, Charliesona, Cecil, Sunace, Turk group, Queens district, How, Peter Pat, Matabele Sheba, Goodenough, Old Nic and Bushtick are associated with shear zones and folds and include conjugate systems (shears, shear intersections, kink sets), side-step systems (en echelon segmentation, duplexes, monoclinal inflections, antiform-synform couplets) and interactions of the two. Linear sections of shear zones are generally poorly mineralised. The same geometries are identifiable on all scales from local to regional, so sections of regional structural lineaments or areas within mines should be prioritised for further investigation or development on the basis of the gold-bearing geometries observed to be dominant locally

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 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 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