M.Com. (Economics) / The objective of the thesis was to examine the relationship between the grade of ore, physical electricity consumption and working cost in the South African gold mining industry for the period 1965 - 1982. The South African economy is heavily dependent on the gold mining industry, which is a major earner of foreign exchange and a large consumer of labour and agricultural and industrial output. The industry is also important as a source of finance for both the private sector and the Treasury. Curtailment of activity within the industry by closing down the more marginal mines or by shortening the life of the industry' as a whole because of rising costs and/or a hesitant gold price, will harm the South African economy in a number of ways. The industry has no option but to regard the gold price as given. The remaining ore reserves tend to be of a lower grade and/or to be found at greater depth. Controlling the working costs would seem to be almost the only option open to the industry.

M.Sc. (Geology) / Within the Black Reef Formation, which forms the basal unit of the Transvaal Supergroup, an auriferous and uraniferous reef occurs. This is known as the Buckshot Pyrite Leader reef. This reef is a conglomerate-hosted gold and uranium deposit, which is similar to the Witwatersrand reefs as they both contain significant amounts of pyrite and have similar depositional environments. This study seeks to identify the geometallurgical characteristics of the gold uranium and thorium that are hosted in the Black Reef at the Modder East operation in Springs. In terms of methodology, a detailed petrographic study was completed on the samples taken from underground and the surface run of mine samples. Mineralogy was conducted on these samples using SEM-based automated technology, namely the FEI Mineral liberation analyser (MLA). Using this, I could further characterise the gold and uranium bearing phases found across the Black Reef. Additionally, mill testing, grading analysis, major and trace element chemistry, density separation, gold and uranium dissolution as well as flotation testing was conducted on the ore in order to determine its geometallurgical characteristics. Through the combination of these methods, this study aims to evaluate the Au, U and Th within the Black Reef with regards to: the metallurgy; the extraction process in relation to the mineralogy of the samples; and the possible implications that these factors could have on the overall recovery of the economic minerals.

Although bacterial leaching of sulphidic minerals is a well-known phenomenon, it is only in the last ten years that full-scale bacterial leaching plants have been commissioned for gold processing. In order for bacterial leaching to compete successfully with other pretreatment processes for refractory ores, particularly with established technologies such as roasting and pressure leaching, it needs to be efficient. This requires the optimization of the parameters affecting the leaching reaction and the growth of bacteria. The entire biotreatment process is agitation leaching, carried out in stirred reactors or Pachuca type reactors. The bacterial oxidation is a complex reaction involving gaseous, liquid and solid phases. The interactions are highly complex, and analysis is complicated by the presence of solids in the leaching medium. Inspite of the amount of research that has been performed, kinetic and process models are underdeveloped. Since kinetic data varies widely with the type and source of concentrate, experimental data should be generated before doing the full-scale reactor design. In sizing reactors for a commercial scale process, it would be useful to have a mathematical model that one could use to predict the amount and rate of release of metal, as a function of the various operating parameters of the system. G.R.Halli arsenical gold sulphide concentrate obtained from Hutti Gold Mines Ltd., Karnataka, was chosen for our study, because of its high refractoriness. An indegenous strain of Thiobacillus ferrooxidans was used for biooxidation. The experiments were conducted in a well-agitated stirred tank reactor under controlled conditions. Sparged air was supplemented with carbon-dioxide for optimized growth. In this work, more than 90% gold and 95% silver could be recovered from the sulphidic gold concentrate when bioleaching was used ahead of cyanidation, compared to 40% and 50% by direct cyanidation. A generalized model, which accounts for both direct bacterial attack and indirect chemical leaching, has been proposed for the biooxidation of refractory gold concentrates. The bacterial balance, therefore, accounts for its growth both on solid substrate and in solution, and for the attachment to and detachment from the surface. The overall process is considered to consist of several sub-processes, each of which can be described in terms of a mechanism and related rate expressions. These sub-processes were studied seperately under kinetically controlled conditions. The key parameters appearing in the rate equations were evaluated using the experimental data. Since the refractory concentrate contains pyrite and arsenopyrite as the major leachable entities, leaching studies have been done on pure pyrite and arsenopyrite as test minerals and the key parameters in the rate equations are evaluated using this data. The model so developed is tested with the leaching kinetics of the concentrate. The growth of bacteria is dependent on the availability of the substrate, ferrous iron, and the dependence is modelled by the widely accepted Monod equation. The effect of carbon dioxide supplementation on the bacterial activity was studied and the optimal concentration for growth was found to be l%(v/v). Studies on indirect chemical leaching showed that the rate is sensitive to surface area of concentrate. Indirect rate constant of arsenopyrite was found to be greater than that of pyrite, since pyrite is more nobler than arsenopyrite. Conditions of direct leaching alone was obtained at high pulp density and using substrate adapted bacteria. The rate constant of arsenopyrite was found to be greater than that of pyrite. The parameters obtained were tested with the overall batch leaching data of the concentrate and favourable comparision was obtained. Thus, it has been possible to isolate the various simultaneous sub-processes occurring during the leaching and propose useful models to describe these processes in some detail. The model has been extended successfully to predict the continuous leaching behaviour using the parameters obtained from the batch data. Studies on the effect of residence time and pulp density on steady state behaviour showed that there is a critical residence time and pulp density below which washout conditions occur. The critical residence time at 10% pulp density was found to be 11 hrs. Operation at pulp densities lower than 5% and residence times lower than 72 hrs is not favourable for efficient leaching. Studies on the effect of initial ferric iron concentration showed that there exists an optimum concentration of ferric iron at which the time required to reach steady state is minimum.

No description available.

Thèse (D.R.Min.) -- Université du Québec à Chicoutimi, 1992. / These présentée en collaboration de l'Université du Québec à Chicoutimi et Institute of geochemistry, Academia Sinica. CaQCU Document électronique également accessible en format PDF. CaQCU

The Beaverdell silver, gold, lead, zinc, vein camp is located approximately 88 km south of Kelowna, in south-central British Columbia at 49.43° north latitude and 119.06° west longtitude. The camp has been a silver producer since the turn of the century and some gold was produced in the early part of the century. This thesis examines the deposits in the regional area and examines, in detail, zoning in the Lass vein system on Wallace Mountain, and represents the first comprehensive study of zoning and genesis of the veins. Galena-lead isotopes are examined within the regional setting of the deposits. Fluid inclusion, sulphur isotope, mineralographic and major and minor element zonation studies yield definitive information about the genesis of the deposits. Granodiorite of the Westkettle batholith, probably Jurassic, underlies much of the area and has been Intruded by stocks of Tertiary quartz monzonite, such as the Beaverdell stock. Remnants of pendants and/or screens of Wallace Formation metamorphosed volcanic and sedimentary rocks, believed to be Permian, are contained in the granodiorite. Silver mineralization occurs in the Beaverdell mines on Wallace Mountain mainly within the West-kettle batholith. Numerous showing and old workings of silver and/or gold mineralization are found throughout the surrounding region. The gold-bearing veins at Carmi contain a different mineral assemblage than the silver-bearing veins on Wallace Mountain. Galena-lead analyses of samples collected throughout the region fall into two distinct clusters on the ²º⁶Pb/ ²º⁴Pb versus ²⁰⁷Pb/ ²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb versus ²⁰⁸Pb/²⁰⁴Pb diagrams. The first group is represented by the Carmi gold veins and the second by the Beaverdell silver veins. Models for the generation of lead in these deposits used Permian (0.27 Ga), Jurassic (0.15 Ga) or Tertiary (0.05 Ga) ages of mineralization on the basis of geological and K-Ar data. The model that is believed to be the best approximation of the system that formed these deposits assumes that the two groups of deposits formed at different times, under markedly different geological conditions. The parameters of this model indicate that: 1. the Carmi-type, gold-bearing vein mineralization is probably Jurassic and formed as a result of the intrusion of the Westkettle batholith, with the metamorphosed Wallace Formation as the probable lead source; 2. the Beaverdell-type, Silver-bearing vein mineralization is probably Tertiary and can be linked genetically to intrusions of that age, such as the Beaverdell stock; 3. ore fluid flow direction for the solutions that formed the Beaverdell-type mineralization was outward through the Westkettle batholith, away from the Beaverdell stock. Within the Lass vein system on Wallace Mountain, a distinctive, depth related, east-west zonation pattern in Au, Ag, Pb and Zn can be defined. Many of the other 11 elements analysed (Cu, Fe, Mn, Cd, Ca, Mg, Co, Ni, Hg, As, Sb) also show this pattern. Two zones are defined. The deeper portions of the orebody (at the east end of the vein system) contain high gold values, low silver values, and moderate to high zinc and lead values. High silver values, accompanied by moderate lead and zinc values, are found at a higher elevation in the system, in the western part of the vein system. Veins in the lower section have a greater average thickness than those in the western, upper section, and generally contain less gangue material. Fluid inclusions in sphalerite and quartz samples from the Lass vein system can be divided into three groups based on their homogenization temperatures. These are: Group 1: primary inclusion (with and without CO²), formed between 260°C and 310°C, from solutions with an average of 13 equivalent weight percent NaCl; Group 2: pseudosecondary inclusions formed between 230°C and 260°C, with salinities from 0.6 to 14 equivalent weight percent NaCl; Group 3: pseudosecondary and secondary inclusions formed between 180°C and 220°C, from solutions containing 0.4 to 14 equivalent weight percent NaCl. Arithmetic means of salinities for pseudosecondary, and secondary inclusions are, respectively, 8 and 6 equivalent weight percent NaCl. Sulphur isotope thermometers calculated for sphalerite-galena pairs (268°C to 320°C) are in close agreement with temperatures of homogenization of primary fluid inclusions. Seven stages of mineral paragensis can be recognized in the Lass vein system. Therfirst three stages (pyrite, arsenopyrite and dark sphalerite) are associated with the higher temperature, higher salinity, CO₂-bearing, primary inclusions. Pseudosecondary and secondary inclusions appear to be related to stages 4 to 6, which consist of galena, paler sphalerite, silver minerals and late quartz. Estimated depths of formation, based on a system under hydrostatic pressure, fall into two groupings. The minimum estimated depths of formation for primary, group 1 inclusions average 720 m, while depths calculated for groups 2 and 3 overlap in range, with-averages of 370 m and 175 m. The model-developed to explain the formation of this orebody accounts for the major and minor element zonation in the vein, the decreasing temperature, salinity and pressure (depth), and the loss of CO2 from the ore-forming fluid. The model explains two spatially distinct areas of mineralization represented by: 1. a zone of high temperature, high salinity, .arid" moderate pressure below a throttling point; and 2. a lower temperature, low salinity area caused by ground water mixing on the lower pressure side of the throttling point. CO₂ is present in the system below the throttling point, but is not found in any inclusions in Groups 2 and 3, on the lower temperature side of the throttling point. The association of CO₂ with gold deposition, suggests that gold would be expected in those areas where CO₂ is present in some of the inclusions. The definition of these two zones is critical for exploration. High silver values would not be expected to reappear further at depth to the east of the present workings, because this type of mineralization would only occur above the throttle point. Gold mineralization can be expected to continue for some time at depth if this model holds true. The abrupt change from the gold to the silver zone represents the throttle point in this model, and is highly visible in the major and minor element distribution patterns for the Lass vein system. Several different analytical procedures have been shown to differentiate between the two types of vein mineralization in the Beaverdell area. The use of these methods for exploration and development would allow the determination of key parameters concerning mineralization prior to extensive development of a showing or property. The level within the hydrothermal system, and therefore the type of ore expected can be determined by fluid inclusion studies for the younger, Tertiary veins. The age of vein mineralization, and therefore, the type of mineralization, also can be predicted by the use of galena-lead isotope ratios. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

M.S.

No description available.

M.Sc. (Geology) / The Witwatersrand Supergroup is host to a number of auriferous and uraniferous conglomeratic reefs, which have been extensively exploited along the Witwatersrand Basin margins. The current study investigates the Vaal Reef, in the Klerksdorp gold field with particular focus on conducting a geometallurgical characterization of the ore which may ultimately enhance the recovery of gold and uranium and our understanding of how the ore responds to processing. Six samples were collected from AngloGold Ashanti’s Moab Khotsong mine and prepared for a chemical and mineralogical deportment study. These samples were milled and crushed down to 80% passing -75μm and processed for head chemistry assays, grading analysis as well as heavy liquid separation analysis as part of the chemical deportment. The samples were also submitted for gold cyanide, acid uranium and diagnostic leach tests.....