A review of sediment-hosted gold deposits of the world with special emphasis on recent discoveries outside the U.S.A
- Authors: Daglioglu, Yasar Mehmet
- Date: 1996
- Subjects: Gold ores , Sedimentation and deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4997 , http://hdl.handle.net/10962/d1005609 , Gold ores , Sedimentation and deposition
- Description: Most of the Great Basin sediment-hosted gold deposits are located along well defined, northwest-striking trends. Trends coincide with faults, intrusive rocks and magnetic anomalies. Sedimentary host rocks are siltstone, sandstone, conglomerate, argillic, interbedded chert and shales. Silty bedded silty dolomites, limestone and carbonaceous shales are the most favourable hosts. High, and locally, low-angle faults are very important structural features related to the formation of the ore bodies. High-angle faults are conduits of hydrothermal fluids which react, shatter and prepare the favourable host rock. Decalcification, silicification, and argillization are the most common hydrothermal alteration types. Jasperoid (intense silica replacement) is a significant characteristic; not all of these deposits are gold-bearing. Most deposits contain both oxidized and unoxidized ore. Fine grained disseminated pyrite, arsenian pyrite, and carbonaceous material are the most common hosts for gold in many deposits. These deposits are also characterized by high Au/Ag ratios, notable absence of base metal and geochemical associations of Au, As, Sb, Hg, Ba and TI. Recently numerous sediment-hosted gold deposits have been recognized in different regions of the world. They vary in their size, grades, textwe, host rock lithology, degrees of structural control and chemical characteristics. However, they have many common features which are very similar to the general characteristics of sediment-hosted gold deposits in the Great Basin, U.S.A. Besides these similarities, several unusual features are recorded in some newly discovered deposits elsewhere, such as predominant fault controlled paleokarst related mineralization and the lack of two very common trace elements (Hg, TI) in Lobongan/Alason, Indonesia; and Early Proterozoic age metamorphosed host rocks and lack of Sb in Maoling, China. The discovery of the deep ores in the Post-Betze and Rabbit Canyon, Nevada, proposed sediment-hosted Au emplacement at deeper level (4 ± 2 km; Kuehn & Rose, 1995) combined with a lack of field evidence for paleowater table and paleosurface features has ruled out a shallow epithermal origin. Recent discoveries in other parts of the world throw important new light on the ongoing genetic problems. Intrusive rocks are present in nearly all sediment-hosted gold deposits. Numerous intrusion-centred districts worldwide are characterized by tWo or more different mineralization types and consequently by metal zoning. Sediment-hosted gold deposits are proposed as a distal part of intrusion-centred magmatic hydrothermal systems (Sillitoe &Bonham, 1990).
- Full Text:
- Date Issued: 1996
- Authors: Daglioglu, Yasar Mehmet
- Date: 1996
- Subjects: Gold ores , Sedimentation and deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4997 , http://hdl.handle.net/10962/d1005609 , Gold ores , Sedimentation and deposition
- Description: Most of the Great Basin sediment-hosted gold deposits are located along well defined, northwest-striking trends. Trends coincide with faults, intrusive rocks and magnetic anomalies. Sedimentary host rocks are siltstone, sandstone, conglomerate, argillic, interbedded chert and shales. Silty bedded silty dolomites, limestone and carbonaceous shales are the most favourable hosts. High, and locally, low-angle faults are very important structural features related to the formation of the ore bodies. High-angle faults are conduits of hydrothermal fluids which react, shatter and prepare the favourable host rock. Decalcification, silicification, and argillization are the most common hydrothermal alteration types. Jasperoid (intense silica replacement) is a significant characteristic; not all of these deposits are gold-bearing. Most deposits contain both oxidized and unoxidized ore. Fine grained disseminated pyrite, arsenian pyrite, and carbonaceous material are the most common hosts for gold in many deposits. These deposits are also characterized by high Au/Ag ratios, notable absence of base metal and geochemical associations of Au, As, Sb, Hg, Ba and TI. Recently numerous sediment-hosted gold deposits have been recognized in different regions of the world. They vary in their size, grades, textwe, host rock lithology, degrees of structural control and chemical characteristics. However, they have many common features which are very similar to the general characteristics of sediment-hosted gold deposits in the Great Basin, U.S.A. Besides these similarities, several unusual features are recorded in some newly discovered deposits elsewhere, such as predominant fault controlled paleokarst related mineralization and the lack of two very common trace elements (Hg, TI) in Lobongan/Alason, Indonesia; and Early Proterozoic age metamorphosed host rocks and lack of Sb in Maoling, China. The discovery of the deep ores in the Post-Betze and Rabbit Canyon, Nevada, proposed sediment-hosted Au emplacement at deeper level (4 ± 2 km; Kuehn & Rose, 1995) combined with a lack of field evidence for paleowater table and paleosurface features has ruled out a shallow epithermal origin. Recent discoveries in other parts of the world throw important new light on the ongoing genetic problems. Intrusive rocks are present in nearly all sediment-hosted gold deposits. Numerous intrusion-centred districts worldwide are characterized by tWo or more different mineralization types and consequently by metal zoning. Sediment-hosted gold deposits are proposed as a distal part of intrusion-centred magmatic hydrothermal systems (Sillitoe &Bonham, 1990).
- Full Text:
- Date Issued: 1996
An investigation into some critical computer networking parameters : Internet addressing and routing
- Authors: Isted, Edwin David
- Date: 1996
- Subjects: Computer networks , Internet , Electronic mail systems
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4608 , http://hdl.handle.net/10962/d1004874 , Computer networks , Internet , Electronic mail systems
- Description: This thesis describes the evaluation of several proposals suggested as replacements for the currenT Internet's TCPJIP protocol suite. The emphasis of this thesis is on how the proposals solve the current routing and addressing problems associated with the Internet. The addressing problem is found to be related to address space depletion, and the routing problem related to excessive routing costs. The evaluation is performed based on criteria selected for their applicability as future Internet design criteria. AIl the protocols are evaluated using the above-mentioned criteria. It is concluded that the most suitable addressing mechanism is an expandable multi-level format, with a logical separation of location and host identification information. Similarly, the most suitable network representation technique is found to be an unrestricted hierarchical structure which uses a suitable abstraction mechanism. It is further found that these two solutions could adequately solve the existing addressing and routing problems and allow substantial growth of the Internet.
- Full Text:
- Date Issued: 1996
An investigation into some critical computer networking parameters : Internet addressing and routing
- Authors: Isted, Edwin David
- Date: 1996
- Subjects: Computer networks , Internet , Electronic mail systems
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4608 , http://hdl.handle.net/10962/d1004874 , Computer networks , Internet , Electronic mail systems
- Description: This thesis describes the evaluation of several proposals suggested as replacements for the currenT Internet's TCPJIP protocol suite. The emphasis of this thesis is on how the proposals solve the current routing and addressing problems associated with the Internet. The addressing problem is found to be related to address space depletion, and the routing problem related to excessive routing costs. The evaluation is performed based on criteria selected for their applicability as future Internet design criteria. AIl the protocols are evaluated using the above-mentioned criteria. It is concluded that the most suitable addressing mechanism is an expandable multi-level format, with a logical separation of location and host identification information. Similarly, the most suitable network representation technique is found to be an unrestricted hierarchical structure which uses a suitable abstraction mechanism. It is further found that these two solutions could adequately solve the existing addressing and routing problems and allow substantial growth of the Internet.
- Full Text:
- Date Issued: 1996
Anaesthesia in abalone, Haliotis midae
- Authors: White, Hermien Ilse
- Date: 1996
- Subjects: Abalones , Animal anesthesia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5216 , http://hdl.handle.net/10962/d1005059 , Abalones , Animal anesthesia
- Description: The principle aim of this study was to isolate a chemical for the "safe anaesthesia" of abalone under commercial farming conditions. "Safe anaesthesia" implied that the anaesthetic had no immediate detrimental or long term sublethal effect on the abalone, that it was safe for the farmer, the consumer and the environment. Four chemicals, magnesium sulphate (MgS0₄), ethylenediamine tetra-acetic acid (EDTA), 2-phenoxyethanol and procaine hydrochloride were shown to effectively inhibit the in vitro contraction of isolated tarsal muscle of Haliotis midae. This identified them as potential anaesthetics for abalone. Since abalone, like any other aquaculture species, would be subject to frequent size-sorting during the grow-out period, size related dosage tables were developed for the four chemicals at a temperature of 18⁰C. Dosage tables were also developed for benzocaine and carbon dioxide (C0₂), Three size classes (5-15, 20-50 and 60-90 mm shell length (SL)) of abalone were considered. Only three of the six chemicals, viz. MgS0₄, 2-phenoxyethanol and CO₂, met the criteria of an effective abalone anaesthetic in that they effected rapid and mortality-free anaesthesia. The other three chemicals caused mortalities and were considered to be unsuitable for commercial scale anaesthesia. Temperature related dosage tables were then developed for MgS0₄ and CO₂, MgS0₄ concentrations and CO₂ flow rates for effective anaesthesia in abalone were found to be inversely related to temperature. The three size classes of H. midae were intermittently exposed to MgS0₄ and 2-phenoxyethanol anaesthesia for an eight month period to determine the effect of the anaesthetics on growth rate. Because of an increased resistance to the efficacy of 2-phenoxyethanol and high monthly mortalities it was concluded that this chemical was unsafe and unsuitable for commercial use. MgS0₄, on the other hand, had no effect on growth of abalone and no significant effect on the rate of mortality. MgS0₄ also had no measurable effect on H. midae muscle ultrastructure and, by implication had no effect on flesh texture. The use of MgS0₄ as an anaesthetic would, therefore, not affect marketability. Moreover, no magnesium residues were found in H. midae muscle tissue after short term or intermittent long term exposure to MgS0₄ anaesthesia. It was found that the three size classes of H. midae used in this study could be safely exposed to the recommended MgS0₄ concentrations for up to 40 minutes without any mortalities. This is more than adequate for routine farming procedures. Medium size abalone (20-50 mm SL) were also safely exposed to 14 g.100 ml⁻¹ MgS0₄ for up to 6 hours without any mortalities. The results have shown that MgS0₄ was undoubtedly the best chemical that was evaluated for anaesthesia of H. midae in this study. It fulfils the requirements set forth by the U.S.A. Food and Drug Administration (FDA) in that it is safe for the abalone, the farmer, the consumer and the environment.
- Full Text:
- Date Issued: 1996
- Authors: White, Hermien Ilse
- Date: 1996
- Subjects: Abalones , Animal anesthesia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5216 , http://hdl.handle.net/10962/d1005059 , Abalones , Animal anesthesia
- Description: The principle aim of this study was to isolate a chemical for the "safe anaesthesia" of abalone under commercial farming conditions. "Safe anaesthesia" implied that the anaesthetic had no immediate detrimental or long term sublethal effect on the abalone, that it was safe for the farmer, the consumer and the environment. Four chemicals, magnesium sulphate (MgS0₄), ethylenediamine tetra-acetic acid (EDTA), 2-phenoxyethanol and procaine hydrochloride were shown to effectively inhibit the in vitro contraction of isolated tarsal muscle of Haliotis midae. This identified them as potential anaesthetics for abalone. Since abalone, like any other aquaculture species, would be subject to frequent size-sorting during the grow-out period, size related dosage tables were developed for the four chemicals at a temperature of 18⁰C. Dosage tables were also developed for benzocaine and carbon dioxide (C0₂), Three size classes (5-15, 20-50 and 60-90 mm shell length (SL)) of abalone were considered. Only three of the six chemicals, viz. MgS0₄, 2-phenoxyethanol and CO₂, met the criteria of an effective abalone anaesthetic in that they effected rapid and mortality-free anaesthesia. The other three chemicals caused mortalities and were considered to be unsuitable for commercial scale anaesthesia. Temperature related dosage tables were then developed for MgS0₄ and CO₂, MgS0₄ concentrations and CO₂ flow rates for effective anaesthesia in abalone were found to be inversely related to temperature. The three size classes of H. midae were intermittently exposed to MgS0₄ and 2-phenoxyethanol anaesthesia for an eight month period to determine the effect of the anaesthetics on growth rate. Because of an increased resistance to the efficacy of 2-phenoxyethanol and high monthly mortalities it was concluded that this chemical was unsafe and unsuitable for commercial use. MgS0₄, on the other hand, had no effect on growth of abalone and no significant effect on the rate of mortality. MgS0₄ also had no measurable effect on H. midae muscle ultrastructure and, by implication had no effect on flesh texture. The use of MgS0₄ as an anaesthetic would, therefore, not affect marketability. Moreover, no magnesium residues were found in H. midae muscle tissue after short term or intermittent long term exposure to MgS0₄ anaesthesia. It was found that the three size classes of H. midae used in this study could be safely exposed to the recommended MgS0₄ concentrations for up to 40 minutes without any mortalities. This is more than adequate for routine farming procedures. Medium size abalone (20-50 mm SL) were also safely exposed to 14 g.100 ml⁻¹ MgS0₄ for up to 6 hours without any mortalities. The results have shown that MgS0₄ was undoubtedly the best chemical that was evaluated for anaesthesia of H. midae in this study. It fulfils the requirements set forth by the U.S.A. Food and Drug Administration (FDA) in that it is safe for the abalone, the farmer, the consumer and the environment.
- Full Text:
- Date Issued: 1996
Aspects of nutrition of the swordtail fish, Xiphophorus Helleri, (Family : Poeciliidae) under intensive culture conditions
- Authors: Kruger, David Philip
- Date: 1996
- Subjects: Xiphophorus helleri -- Nutrition , Fish culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5219 , http://hdl.handle.net/10962/d1005062 , Xiphophorus helleri -- Nutrition , Fish culture
- Description: The aim of this work was to investigate the nutrition of a popular ornamental fish, the swordtail (Xiphophorus helleri), under intensive aquaculture conditions. The study focused on the formulation and manufacture of artificial dry diets, as well as the influence of livefeed supplementation on growth and nutritional indices of both juvenile and broodstock fish. A combination of 65% fishmeal and 35% soya oil cake meal was found to closely approximate the essential amino acid profile of X helleri (r² = 94,3%) and lysine was identified as the first limiting amino acid. The influence of dietary protein and energy on the growth of X helleri was investigated by means of a growth trial comparing a range of nine test diets combining 3 crude protein (45,38 and 30%) and 3 digestible energy (16,5, 14,5 and 12,5 kJ/gram) levels. A high crude protein content (45% dry matter) and a protein to energy ratio of ≥ 27 mg protein per kJ digestible energy was shown to promote optimal growth rate and feed conversion ratio in juvenile X helleri. The final body protein and lipid content of the fish were significantly correlated with the dietary protein to energy ratio. The nutritional value of identical dietary formulations prepared by drum-drying or cold extrusion techniques and presented either as flake or crumble particles was evaluated in a growth trial and through analysis of vitamin C levels in the diets. Up to 27% of vitamin C activity was destroyed during the drum-drying of flake diets, while 80% of the remaining vitamin C was lost through leaching within 10 minutes of immersion in water. A crumble-type diet was shown to be acceptable to X helleri, and yielded significantly better growth rate and feed conversion than the equivalent flake feed. Almost 19% of fish fed the flake diets developed vitamin C deficiency symptoms including scoliosis and lordosis, while this was completely prevented by feeding crumbles, indicating a significant restriction of leaching losses from this type of particle. The use of livefeed (Daphnia spp.) as a daily supplement to dry feeds was shown to result in a significant improvement in growth rate and survival of juvenile swordtail fish. Furthermore, the synergistic action of nutrients contained in the livefeed resulted in an improvement in the feed conversion efficiency of the artificial formulation. While mortalities of 13,4% and 15% were recorded in fish fed exclusively on flake feed or Daphnia, no mortality occurred in the group fed the supplemented diet. Furthermore, the incidence of vitamin C deficiency symptoms was prevented by daily supplementation with Daphnia. Fish fed exclusively on Daphnia exhibited significantly more intense pigmentation due to carotenoids contained in the livefeed. In broodstock fish maintained primarily on flake diets, growth rate, feed conversion ratio as well as reproductive performance, as measured by fecundity, were significantly improved by daily livefeed supplementation. Weekly supplementation showed no measurable advantage over flake feed only. A direct correlation was demonstrated between fecundity and size of female fish with a mean fecundity of 190 embryos per female in those fed a daily Daphnia supplement. This was significantly higher than the yield from the non-supplemented or weekly supplemented treatments (133 and 140 embryos per female respectively). Despite these differences, the number of young harvested during the experiment did not differ between treatments and this discrepancy was ascribed to parental cannibalism of newborn juveniles. This phenomenon constitutes a major potential bottleneck in production with estimates of up to seventy percent of young lost in some exp experimental tanks. In conclusion, the present study demonstrated that established aquaculture nutrition principles and techniques are applicable to the tropical ornamental fish species, X helleri. It was demonstrated that by using balanced crumble feed formulations, and regular livefeed supplementation, production yields under intensive conditions may be significantly improved. Suggestions for future work on poeciliid production in South Africa include investigation of the economic implications of the recommendations stemming from this project, and further research into effective restriction of parental cannibalism of newborn fish.
- Full Text:
- Date Issued: 1996
- Authors: Kruger, David Philip
- Date: 1996
- Subjects: Xiphophorus helleri -- Nutrition , Fish culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5219 , http://hdl.handle.net/10962/d1005062 , Xiphophorus helleri -- Nutrition , Fish culture
- Description: The aim of this work was to investigate the nutrition of a popular ornamental fish, the swordtail (Xiphophorus helleri), under intensive aquaculture conditions. The study focused on the formulation and manufacture of artificial dry diets, as well as the influence of livefeed supplementation on growth and nutritional indices of both juvenile and broodstock fish. A combination of 65% fishmeal and 35% soya oil cake meal was found to closely approximate the essential amino acid profile of X helleri (r² = 94,3%) and lysine was identified as the first limiting amino acid. The influence of dietary protein and energy on the growth of X helleri was investigated by means of a growth trial comparing a range of nine test diets combining 3 crude protein (45,38 and 30%) and 3 digestible energy (16,5, 14,5 and 12,5 kJ/gram) levels. A high crude protein content (45% dry matter) and a protein to energy ratio of ≥ 27 mg protein per kJ digestible energy was shown to promote optimal growth rate and feed conversion ratio in juvenile X helleri. The final body protein and lipid content of the fish were significantly correlated with the dietary protein to energy ratio. The nutritional value of identical dietary formulations prepared by drum-drying or cold extrusion techniques and presented either as flake or crumble particles was evaluated in a growth trial and through analysis of vitamin C levels in the diets. Up to 27% of vitamin C activity was destroyed during the drum-drying of flake diets, while 80% of the remaining vitamin C was lost through leaching within 10 minutes of immersion in water. A crumble-type diet was shown to be acceptable to X helleri, and yielded significantly better growth rate and feed conversion than the equivalent flake feed. Almost 19% of fish fed the flake diets developed vitamin C deficiency symptoms including scoliosis and lordosis, while this was completely prevented by feeding crumbles, indicating a significant restriction of leaching losses from this type of particle. The use of livefeed (Daphnia spp.) as a daily supplement to dry feeds was shown to result in a significant improvement in growth rate and survival of juvenile swordtail fish. Furthermore, the synergistic action of nutrients contained in the livefeed resulted in an improvement in the feed conversion efficiency of the artificial formulation. While mortalities of 13,4% and 15% were recorded in fish fed exclusively on flake feed or Daphnia, no mortality occurred in the group fed the supplemented diet. Furthermore, the incidence of vitamin C deficiency symptoms was prevented by daily supplementation with Daphnia. Fish fed exclusively on Daphnia exhibited significantly more intense pigmentation due to carotenoids contained in the livefeed. In broodstock fish maintained primarily on flake diets, growth rate, feed conversion ratio as well as reproductive performance, as measured by fecundity, were significantly improved by daily livefeed supplementation. Weekly supplementation showed no measurable advantage over flake feed only. A direct correlation was demonstrated between fecundity and size of female fish with a mean fecundity of 190 embryos per female in those fed a daily Daphnia supplement. This was significantly higher than the yield from the non-supplemented or weekly supplemented treatments (133 and 140 embryos per female respectively). Despite these differences, the number of young harvested during the experiment did not differ between treatments and this discrepancy was ascribed to parental cannibalism of newborn juveniles. This phenomenon constitutes a major potential bottleneck in production with estimates of up to seventy percent of young lost in some exp experimental tanks. In conclusion, the present study demonstrated that established aquaculture nutrition principles and techniques are applicable to the tropical ornamental fish species, X helleri. It was demonstrated that by using balanced crumble feed formulations, and regular livefeed supplementation, production yields under intensive conditions may be significantly improved. Suggestions for future work on poeciliid production in South Africa include investigation of the economic implications of the recommendations stemming from this project, and further research into effective restriction of parental cannibalism of newborn fish.
- Full Text:
- Date Issued: 1996
Aspects of the physiology of the South African abalone, Haliotis Midae L., and implications for intensive abalone culture
- Authors: Lyon, Robert Gary
- Date: 1996
- Subjects: Abalones -- Physiology , Abalone culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5226 , http://hdl.handle.net/10962/d1005069 , Abalones -- Physiology , Abalone culture
- Description: A physiological study was carried out to determine the effects of temperature, quantity of food fed, feeding activity and size class on the oxygen consumption and ammonia production of the South African abalone Haliotis midae L.. A set of intermittent flow respirometer chambers were used in a recirculating system to measure the oxygen consumption rates of fed (postprandial) and unfed (postabsorptive) abalone for three different size classes (15, 30, and 50mm) at three different temperatures (16°, 20° and 23°C) over a 24 hour period. Ammonia production rates and food consumption rates were simultaneously determined. Oxygen consumption and Ammonia production rates per gram abalone were linear functions of abalone size, temperature, and mass of food consumed. Oxygen consumption and ammonia production rates were found to increase proportionally to temperature and in inverse proportion to abalone size. These rates were significantly higher for fed as opposed to unfed abalone. Equations were derived to predict oxygen consumption and ammonia production for fed and unfed animals for a range of temperatures and size classes of abalone. A 96h LC50 lethal toxicity test for exposure to ammonia established 1.08mg.1⁻¹ of unionised ammonia as the lethal limit. A test on the long term effects on growth of acute exposure (12h) to various sublethal concentrations of ammonia showed no significant effects on growth for concentrations below 0.88 mg.1⁻¹. A safe chronic exposure level of 0.02 mg.1¹ NH₃-N was used to predict optimal flow rates required per kilogram of abalone in a rearing tank over a range of size classes and temperatures. The physiological and biological requirements of H. midae and the implications of this knowledge for rearing tank management and optimal design are discussed.
- Full Text:
- Date Issued: 1996
- Authors: Lyon, Robert Gary
- Date: 1996
- Subjects: Abalones -- Physiology , Abalone culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5226 , http://hdl.handle.net/10962/d1005069 , Abalones -- Physiology , Abalone culture
- Description: A physiological study was carried out to determine the effects of temperature, quantity of food fed, feeding activity and size class on the oxygen consumption and ammonia production of the South African abalone Haliotis midae L.. A set of intermittent flow respirometer chambers were used in a recirculating system to measure the oxygen consumption rates of fed (postprandial) and unfed (postabsorptive) abalone for three different size classes (15, 30, and 50mm) at three different temperatures (16°, 20° and 23°C) over a 24 hour period. Ammonia production rates and food consumption rates were simultaneously determined. Oxygen consumption and Ammonia production rates per gram abalone were linear functions of abalone size, temperature, and mass of food consumed. Oxygen consumption and ammonia production rates were found to increase proportionally to temperature and in inverse proportion to abalone size. These rates were significantly higher for fed as opposed to unfed abalone. Equations were derived to predict oxygen consumption and ammonia production for fed and unfed animals for a range of temperatures and size classes of abalone. A 96h LC50 lethal toxicity test for exposure to ammonia established 1.08mg.1⁻¹ of unionised ammonia as the lethal limit. A test on the long term effects on growth of acute exposure (12h) to various sublethal concentrations of ammonia showed no significant effects on growth for concentrations below 0.88 mg.1⁻¹. A safe chronic exposure level of 0.02 mg.1¹ NH₃-N was used to predict optimal flow rates required per kilogram of abalone in a rearing tank over a range of size classes and temperatures. The physiological and biological requirements of H. midae and the implications of this knowledge for rearing tank management and optimal design are discussed.
- Full Text:
- Date Issued: 1996
Basin analysis and sequence stratigraphy a review, with a short account of its applicability and utility for the exploration of auriferous placers in the Witwatersrand Basin
- Authors: Van Eeden, Johan
- Date: 1996
- Subjects: Geology, Stratigraphic , Sedimentary basins -- South Africa , Placer deposits -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4934 , http://hdl.handle.net/10962/d1005546 , Geology, Stratigraphic , Sedimentary basins -- South Africa , Placer deposits -- South Africa
- Description: The Witwatersrand basin is unique in terms of its mineral wealth. The gold in the Witwatersrand basin is mainly concentrated in the placers and two types of unconformities are associated with the placer formation. This paper attempts to quantitatively describe the origin and depositional process of placers within the context of basin analysis, geohistory and sequences stratigraphic framework. Several tectonic models have been proposed for the evolution of the Witwater~rand basin and it seems as if a cratonic foreland basin accounts for many of the observed features observed the Central Rand Group basin. The tectonic subsidence curve generated for the Witwatersrand Basin clearly implies foreland basin response which was superimposed an older, deep seated extensional basin. These compressive tectonics can be superimposed on extensional basins, where the shift from extensional to compressional tectonics lead to inversion processes. The critical issues about the Witwatersrand basin which were addresed in this review, is the validity of basin wide correlation of placer unconformuties and whether sequence stratigraphy is applicable to fluvial systems of the Witwatersrand sequence. It is believed that the Central Rand Group was deposited as alluvial - fan deltas by fluvially dominated, braidplain systems with minor marine interaction which had a considerable impact on the preservation of economically viable placers. Most important to the exploration geologist is the recognition of stacking patterns of the fluvial strata to determine change in the rate at which accommodation was created. Identifying sequence boundaries and other relevant surfaces important for identifying these stacking patterns of the sequences, depends entirely on the recognition of a hierarchy of stratal units including beds, bedsets, parasequences, parasequence sets and the surfaces bounding sequences. Placers are closely associated with the development of disconformities and therefore become important to recognise in fluvial strata. If these placers are to become economic, the duration of subaerial exposure of the unconformities that allowed the placers to become reworked and concentrated must be determined. In order to preserve the placer, a sudden marine transgression is necessary to allow for minimal shoreline reworking and to cap the placer to prevent it from being dispersed. The placers in the Witwatersrand basin occur in four major gold-bearing placer zones in the Central Rand Group. Accordingly they can be assigned to four supercycles, which are cyclical and therefore predictive. It is the predictive nature of these rocks and the ability of sequence stratigraphy to enhance this aspect, which is a pre-requisite for an effective exploration tool in the search for new ore bodies or their extension in the Witwatersrand basin.
- Full Text:
- Date Issued: 1996
- Authors: Van Eeden, Johan
- Date: 1996
- Subjects: Geology, Stratigraphic , Sedimentary basins -- South Africa , Placer deposits -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4934 , http://hdl.handle.net/10962/d1005546 , Geology, Stratigraphic , Sedimentary basins -- South Africa , Placer deposits -- South Africa
- Description: The Witwatersrand basin is unique in terms of its mineral wealth. The gold in the Witwatersrand basin is mainly concentrated in the placers and two types of unconformities are associated with the placer formation. This paper attempts to quantitatively describe the origin and depositional process of placers within the context of basin analysis, geohistory and sequences stratigraphic framework. Several tectonic models have been proposed for the evolution of the Witwater~rand basin and it seems as if a cratonic foreland basin accounts for many of the observed features observed the Central Rand Group basin. The tectonic subsidence curve generated for the Witwatersrand Basin clearly implies foreland basin response which was superimposed an older, deep seated extensional basin. These compressive tectonics can be superimposed on extensional basins, where the shift from extensional to compressional tectonics lead to inversion processes. The critical issues about the Witwatersrand basin which were addresed in this review, is the validity of basin wide correlation of placer unconformuties and whether sequence stratigraphy is applicable to fluvial systems of the Witwatersrand sequence. It is believed that the Central Rand Group was deposited as alluvial - fan deltas by fluvially dominated, braidplain systems with minor marine interaction which had a considerable impact on the preservation of economically viable placers. Most important to the exploration geologist is the recognition of stacking patterns of the fluvial strata to determine change in the rate at which accommodation was created. Identifying sequence boundaries and other relevant surfaces important for identifying these stacking patterns of the sequences, depends entirely on the recognition of a hierarchy of stratal units including beds, bedsets, parasequences, parasequence sets and the surfaces bounding sequences. Placers are closely associated with the development of disconformities and therefore become important to recognise in fluvial strata. If these placers are to become economic, the duration of subaerial exposure of the unconformities that allowed the placers to become reworked and concentrated must be determined. In order to preserve the placer, a sudden marine transgression is necessary to allow for minimal shoreline reworking and to cap the placer to prevent it from being dispersed. The placers in the Witwatersrand basin occur in four major gold-bearing placer zones in the Central Rand Group. Accordingly they can be assigned to four supercycles, which are cyclical and therefore predictive. It is the predictive nature of these rocks and the ability of sequence stratigraphy to enhance this aspect, which is a pre-requisite for an effective exploration tool in the search for new ore bodies or their extension in the Witwatersrand basin.
- Full Text:
- Date Issued: 1996
Computer modelling of the thermal decomposition of solids
- Authors: De la Croix, Annemarie
- Date: 1996
- Subjects: Solids -- Thermal properties -- Computer simulation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4302 , http://hdl.handle.net/10962/d1004960 , Solids -- Thermal properties -- Computer simulation
- Description: Decompositions of solids are typically of the form: A(s) ----> B(s) + gases. Symmetry-controlled routes (based on known and hypothetical crystal structures) for transforming the solid reactant into the solid product were devised as possible decomposition pathways. Lattice energies of the reactants, of the postulated transient intermediate structures and of the final solid products were then estimated by crystal modelling procedures. Profiles of lattice energy changes during the proposed decomposition routes were constructed and any energy barriers were compared with experimental activation energies reported for the thermal decompositions. The crystal modelling was performed with the computer program WMIN. Calculation of the lattice energies involved the development of a model potential for the perfect lattice and the evaluation of the interatomic parameters. The potential was based on the Born model of ionic solids using the Buckingham potential (Ø(r)= Ae⁻r/p - C/r⁶) to describe the short-range energy contribution. Empirical fitting was used to establish reliable interatomic energy parameters. The reliability of the interatomic potentials was assessed by calculating crystal structures and lattice energies (which were not included in the fitting). The particular reactions selected for modelling were the decompositions of the alkaline-earth metal (Ca, Sr, Ba) peroxides and carbonates: M0₂(s) ---> MO(s) + ¹/₂0₂(g) MC0₃(s) ---> MO(s) + CO₂(g)The lattice energies calculated for the known structures were in good agreement with reported values, (except for Ba0₂ and BaC0₃) which provided support for the adequacy of the potential model used. Activation energies calculated for the decomposition of the carbonates were in the correct order but hlgher than experimental values, i. e., 422, 422, 465 and 499 kJ mol̄̄⁻¹ compared to the experimental values of 205, 87(?), 222 and 283 kJ mol̄̄⁻¹ for CaC0₃ (calcite), CaC0₃(aragonite), SrC0₃ and BaC0₃. The values calculated for the peroxides (91 and 100 kJ mol⁻¹ compared to the experimental values of 119 and 185 kJ mol⁻¹ for Sr0₂ and Ba0₂ respectively) were less satisfactory but could be a reflection of the poor structural data used for the peroxides. The significance of this approach to the modelling of solid decompositions is discussed.
- Full Text:
- Date Issued: 1996
- Authors: De la Croix, Annemarie
- Date: 1996
- Subjects: Solids -- Thermal properties -- Computer simulation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4302 , http://hdl.handle.net/10962/d1004960 , Solids -- Thermal properties -- Computer simulation
- Description: Decompositions of solids are typically of the form: A(s) ----> B(s) + gases. Symmetry-controlled routes (based on known and hypothetical crystal structures) for transforming the solid reactant into the solid product were devised as possible decomposition pathways. Lattice energies of the reactants, of the postulated transient intermediate structures and of the final solid products were then estimated by crystal modelling procedures. Profiles of lattice energy changes during the proposed decomposition routes were constructed and any energy barriers were compared with experimental activation energies reported for the thermal decompositions. The crystal modelling was performed with the computer program WMIN. Calculation of the lattice energies involved the development of a model potential for the perfect lattice and the evaluation of the interatomic parameters. The potential was based on the Born model of ionic solids using the Buckingham potential (Ø(r)= Ae⁻r/p - C/r⁶) to describe the short-range energy contribution. Empirical fitting was used to establish reliable interatomic energy parameters. The reliability of the interatomic potentials was assessed by calculating crystal structures and lattice energies (which were not included in the fitting). The particular reactions selected for modelling were the decompositions of the alkaline-earth metal (Ca, Sr, Ba) peroxides and carbonates: M0₂(s) ---> MO(s) + ¹/₂0₂(g) MC0₃(s) ---> MO(s) + CO₂(g)The lattice energies calculated for the known structures were in good agreement with reported values, (except for Ba0₂ and BaC0₃) which provided support for the adequacy of the potential model used. Activation energies calculated for the decomposition of the carbonates were in the correct order but hlgher than experimental values, i. e., 422, 422, 465 and 499 kJ mol̄̄⁻¹ compared to the experimental values of 205, 87(?), 222 and 283 kJ mol̄̄⁻¹ for CaC0₃ (calcite), CaC0₃(aragonite), SrC0₃ and BaC0₃. The values calculated for the peroxides (91 and 100 kJ mol⁻¹ compared to the experimental values of 119 and 185 kJ mol⁻¹ for Sr0₂ and Ba0₂ respectively) were less satisfactory but could be a reflection of the poor structural data used for the peroxides. The significance of this approach to the modelling of solid decompositions is discussed.
- Full Text:
- Date Issued: 1996
Distribution patterns of fishes in the head region of a turbid Eastern Cape estuary
- Ter Morshuizen, Leslie David
- Authors: Ter Morshuizen, Leslie David
- Date: 1996
- Subjects: Fishes -- South Africa -- Eastern Cape -- great fish river -- Geographical distribution
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5261 , http://hdl.handle.net/10962/d1005105 , Fishes -- South Africa -- Eastern Cape -- great fish river -- Geographical distribution
- Description: Two and a half years of data were collected from the Great Fish River and estuary using seine nets and gill nets to determine the fish species composition within these regions. The head region of the Great Fish River estuary was found to have a rich fish fauna, with the euryhaline marine fish component totally dominating the catch in all three regions. Gilchristella aesiuaria was the single most common species and several euryhaline marine species were captured in freshwater for the first time. Physical parameters were also measured in an effort to ascertain the possible factors which may affect the distribution and length frequency of the most common species within this area. Salinity was found to be the single most important factor affecting the species composition, and the sampling area was consequently divided into three regions, viz. river (< I ‰), head (1-4 ‰) and estuary (> 4 ‰). In addition, it was determined that river flow rate during the month prior to sampling also had a profound effect on species composition in all three regions. Based on the available evidence it is suggested that for most species this is related to conductivity levels rather than flow per se.
- Full Text:
- Date Issued: 1996
- Authors: Ter Morshuizen, Leslie David
- Date: 1996
- Subjects: Fishes -- South Africa -- Eastern Cape -- great fish river -- Geographical distribution
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5261 , http://hdl.handle.net/10962/d1005105 , Fishes -- South Africa -- Eastern Cape -- great fish river -- Geographical distribution
- Description: Two and a half years of data were collected from the Great Fish River and estuary using seine nets and gill nets to determine the fish species composition within these regions. The head region of the Great Fish River estuary was found to have a rich fish fauna, with the euryhaline marine fish component totally dominating the catch in all three regions. Gilchristella aesiuaria was the single most common species and several euryhaline marine species were captured in freshwater for the first time. Physical parameters were also measured in an effort to ascertain the possible factors which may affect the distribution and length frequency of the most common species within this area. Salinity was found to be the single most important factor affecting the species composition, and the sampling area was consequently divided into three regions, viz. river (< I ‰), head (1-4 ‰) and estuary (> 4 ‰). In addition, it was determined that river flow rate during the month prior to sampling also had a profound effect on species composition in all three regions. Based on the available evidence it is suggested that for most species this is related to conductivity levels rather than flow per se.
- Full Text:
- Date Issued: 1996
Early Cretaceous alluvial palaeosols (Kirkwood formation, Algoa Basin, South Africa) and their palaeoenvironmental and palaeoclimatological significance
- Authors: Frost, Susan
- Date: 1996
- Subjects: Paleopedology -- South Africa -- Eastern Cape , Paleoclimatology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4939 , http://hdl.handle.net/10962/d1005551 , Paleopedology -- South Africa -- Eastern Cape , Paleoclimatology -- South Africa -- Eastern Cape
- Description: The Kirkwood Formation in the Bushman's River area of the Algoa Basin is characterised by a number of fining-upward cycles. These have been interpreted as indicating deposition in a dynamic aggrading meandering river system with the channel deposits (conglomerates grading upwards into sandstones) fining upward into the overbank deposits (mudrocks). Channel, channel-margin and overbank deposits were recognised. The three mudrock sequences logged comprise compound pedofacies sequences of multistorey, simple and cumulative palaeosols. Distinctive palaeopedological features, such as root traces and pedotubules, soil horizons and structures, mottles, and iron-rich and calcareous glaebules and calcareous hardpan lenses and layers were used to identify a number of palaeosols within the mudrock sequences. Each mudrock sequence comprises multistorey entisol, inceptisol, alfisol, ultisol, aridisol and vertisol profiles at different stags of pedogenic maturity. The entisols and inceptisols are relatively immature profiles formed close to the meandering river channel and are classified as channel-margin palaeosols. The ultisols, alfisols, aridisols and vertisols are more mature and formed at some distance from the channel. They are classified as proximal floodbasin or distal floodbasin palaeosols depending on their maturity, distance from the channel and grain-size. Slickensides, desiccation cracks, and iron-rich concretions occur, indicating multiple cycles of wetting and drying. A low water-table beneath the floodplain is indicated by both the prominent maroon-brown colouration of the mudstones, caused by oxidation during deposition, and the general lack of evaporites in the sequence. Calcretes comprising calcic and petrocalcic horizons are very common in the lower mudrock sequence, rare in the middle mudrock sequence and relatively common in the upper mudrock sequence. The calcretes generally consist a nodular zone which may, in some cases, be capped by a thin hardpan layer. The calcic palaeosols commonly show stages of carbonate accumulation which indicate at least 10 000 years of formation. The lack of calcrete formation in some of the profiles may indicate frequent flooding and high sediment accretion rates or a decrease in the influx of Ca²⁺-rich aeolian dust into the depositional basin. Clay alluviation is common in many of the profiles and soil structures are commonly well developed. The palaeosols are interpreted as having formed on an aggrading floodplain in a warm to hot (25-30°C), semi-arid climate with a low but seasonal rainfall (100-500mm per annum).
- Full Text:
- Date Issued: 1996
- Authors: Frost, Susan
- Date: 1996
- Subjects: Paleopedology -- South Africa -- Eastern Cape , Paleoclimatology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4939 , http://hdl.handle.net/10962/d1005551 , Paleopedology -- South Africa -- Eastern Cape , Paleoclimatology -- South Africa -- Eastern Cape
- Description: The Kirkwood Formation in the Bushman's River area of the Algoa Basin is characterised by a number of fining-upward cycles. These have been interpreted as indicating deposition in a dynamic aggrading meandering river system with the channel deposits (conglomerates grading upwards into sandstones) fining upward into the overbank deposits (mudrocks). Channel, channel-margin and overbank deposits were recognised. The three mudrock sequences logged comprise compound pedofacies sequences of multistorey, simple and cumulative palaeosols. Distinctive palaeopedological features, such as root traces and pedotubules, soil horizons and structures, mottles, and iron-rich and calcareous glaebules and calcareous hardpan lenses and layers were used to identify a number of palaeosols within the mudrock sequences. Each mudrock sequence comprises multistorey entisol, inceptisol, alfisol, ultisol, aridisol and vertisol profiles at different stags of pedogenic maturity. The entisols and inceptisols are relatively immature profiles formed close to the meandering river channel and are classified as channel-margin palaeosols. The ultisols, alfisols, aridisols and vertisols are more mature and formed at some distance from the channel. They are classified as proximal floodbasin or distal floodbasin palaeosols depending on their maturity, distance from the channel and grain-size. Slickensides, desiccation cracks, and iron-rich concretions occur, indicating multiple cycles of wetting and drying. A low water-table beneath the floodplain is indicated by both the prominent maroon-brown colouration of the mudstones, caused by oxidation during deposition, and the general lack of evaporites in the sequence. Calcretes comprising calcic and petrocalcic horizons are very common in the lower mudrock sequence, rare in the middle mudrock sequence and relatively common in the upper mudrock sequence. The calcretes generally consist a nodular zone which may, in some cases, be capped by a thin hardpan layer. The calcic palaeosols commonly show stages of carbonate accumulation which indicate at least 10 000 years of formation. The lack of calcrete formation in some of the profiles may indicate frequent flooding and high sediment accretion rates or a decrease in the influx of Ca²⁺-rich aeolian dust into the depositional basin. Clay alluviation is common in many of the profiles and soil structures are commonly well developed. The palaeosols are interpreted as having formed on an aggrading floodplain in a warm to hot (25-30°C), semi-arid climate with a low but seasonal rainfall (100-500mm per annum).
- Full Text:
- Date Issued: 1996
Exotic deposits derived from porphyry copper systems in Chile
- Authors: Diaz Acevedo, Nelson Simon
- Date: 1996
- Subjects: Porphyry -- Chile , Copper mines and mining -- Chile , Copper ores -- Chile
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5050 , http://hdl.handle.net/10962/d1011149 , Porphyry -- Chile , Copper mines and mining -- Chile , Copper ores -- Chile
- Description: The exotic orebodies related to cal-alkaline porphyry copper deposits. are sub-horizontal lenticular bodies of secondary copper minerals that impregnate Tertiary gravels and bedrock of different ages. They lie immediately downslope of the porphyry copper deposits, that is to say. they are related to the propylitic halo of the main deposits, and are considered to have originated with the deposition of copper minerals from solutions that overflowed during the secondary enrichment process. Supergene alteration took place between the late Oligocene and Miocene, by which time both orehodies (exotic and porphyry copper) were established. The paucity of tile denudation since the Miocene in the Andean segment from 21º to 26º latitude S. due to the dominance of a hyperarid climate explains the remarkable preservation of the shallow porphyry copper systems, supergene enriched blankets and associated deposits. This is reflected in the limonites, where the typical boxworks have been partially or totally destroyed on surface by the superleaching. As a result of the lateral migration of the copper-bearing solutions, the exotic deposits show a zonation. alteration and mineralization whose characteristics depend among other factors. on the reactivity of the bedrocks and the Cu/S ratio of the mother deposit. In these deposits three zones can be recognized: Proximal (0 to 2 km Intermediate (2 to 3) and Distal (3 to 8-14 km) with palaeodrainage control. The associations and mineralogical abundance are related to the climate (rain. temperature). In some deposits two important units are detected and they are the Cu-phosphates and Cu-lixiviable (to sulphuric acid) units. The size of tile Chilean exotic deposits varies between 100 and 3.500.000 tons of copper, with a total known resource of 8 M tons of copper. The large exotic deposits are comparable to the resources of a medium-sized porphyry copper- type deposit. The discovery of the exotic deposits is related to the exploration of porphyry copper deposits, where a mass balance of the leached column must be done. Moreover the lithology and alteration of the propylitic halo. permeability, structures, geophysics and geochemistry should be considered. The diorite model is not compatible with a supergene enrichment process, expressed by the absence of colour anomalies, exotic deposits and in the presence of secondary minerals like jarosite, which is coherent with the pyrite deficiency of the system. The projects are for exploitation of reserves by open pit methods. The projects plan to extract and to crush copper oxide ore which will he pre-treated with concentrated sulphuric acid prior to heap leaching, solvent extraction and electrowinning. The copper output varies between 10,000 and 50,000 ton per year of catilode copper. The total investment varies between 20 and 100 millions dollars. For project calculations, estimation of 65 % - 82 % copper recovery and 37 - 40 kg/ton net acid consumption can be used due to the nature of ore. The leaching time is estimated as 30 to 180 days for heaps of 4,5 to 30 metres high. As a result of this, the plant capacity is determined by an annual equivalent of 10,000 to 25,000 ton Cu per year. Pit planning has heen carried out using diverse software on the basis of 5 x 5 x 5 m and 10 x 10 x 10 m block models, evaluated using a kriging package built into the program, giving an overall waste/ore ratio (induding pre-stripping) of 0: I (in an outcrop) to 3: I. The location of the mine and plant sites are associated with the porphyry copper in production, for this the already installed facilities can be used. So there is no need to build a new mine camp or access. The environmental impact is summarized relating to the characterization of the physical, biological and socio-cuitural effects, using the framework of the Base Line study and the Impact evaluation derived from the construction and project operation phases. The conclusions and recommendations will diminish, mitigate and/or eliminate impact derived from the specific activities.
- Full Text:
- Date Issued: 1996
- Authors: Diaz Acevedo, Nelson Simon
- Date: 1996
- Subjects: Porphyry -- Chile , Copper mines and mining -- Chile , Copper ores -- Chile
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5050 , http://hdl.handle.net/10962/d1011149 , Porphyry -- Chile , Copper mines and mining -- Chile , Copper ores -- Chile
- Description: The exotic orebodies related to cal-alkaline porphyry copper deposits. are sub-horizontal lenticular bodies of secondary copper minerals that impregnate Tertiary gravels and bedrock of different ages. They lie immediately downslope of the porphyry copper deposits, that is to say. they are related to the propylitic halo of the main deposits, and are considered to have originated with the deposition of copper minerals from solutions that overflowed during the secondary enrichment process. Supergene alteration took place between the late Oligocene and Miocene, by which time both orehodies (exotic and porphyry copper) were established. The paucity of tile denudation since the Miocene in the Andean segment from 21º to 26º latitude S. due to the dominance of a hyperarid climate explains the remarkable preservation of the shallow porphyry copper systems, supergene enriched blankets and associated deposits. This is reflected in the limonites, where the typical boxworks have been partially or totally destroyed on surface by the superleaching. As a result of the lateral migration of the copper-bearing solutions, the exotic deposits show a zonation. alteration and mineralization whose characteristics depend among other factors. on the reactivity of the bedrocks and the Cu/S ratio of the mother deposit. In these deposits three zones can be recognized: Proximal (0 to 2 km Intermediate (2 to 3) and Distal (3 to 8-14 km) with palaeodrainage control. The associations and mineralogical abundance are related to the climate (rain. temperature). In some deposits two important units are detected and they are the Cu-phosphates and Cu-lixiviable (to sulphuric acid) units. The size of tile Chilean exotic deposits varies between 100 and 3.500.000 tons of copper, with a total known resource of 8 M tons of copper. The large exotic deposits are comparable to the resources of a medium-sized porphyry copper- type deposit. The discovery of the exotic deposits is related to the exploration of porphyry copper deposits, where a mass balance of the leached column must be done. Moreover the lithology and alteration of the propylitic halo. permeability, structures, geophysics and geochemistry should be considered. The diorite model is not compatible with a supergene enrichment process, expressed by the absence of colour anomalies, exotic deposits and in the presence of secondary minerals like jarosite, which is coherent with the pyrite deficiency of the system. The projects are for exploitation of reserves by open pit methods. The projects plan to extract and to crush copper oxide ore which will he pre-treated with concentrated sulphuric acid prior to heap leaching, solvent extraction and electrowinning. The copper output varies between 10,000 and 50,000 ton per year of catilode copper. The total investment varies between 20 and 100 millions dollars. For project calculations, estimation of 65 % - 82 % copper recovery and 37 - 40 kg/ton net acid consumption can be used due to the nature of ore. The leaching time is estimated as 30 to 180 days for heaps of 4,5 to 30 metres high. As a result of this, the plant capacity is determined by an annual equivalent of 10,000 to 25,000 ton Cu per year. Pit planning has heen carried out using diverse software on the basis of 5 x 5 x 5 m and 10 x 10 x 10 m block models, evaluated using a kriging package built into the program, giving an overall waste/ore ratio (induding pre-stripping) of 0: I (in an outcrop) to 3: I. The location of the mine and plant sites are associated with the porphyry copper in production, for this the already installed facilities can be used. So there is no need to build a new mine camp or access. The environmental impact is summarized relating to the characterization of the physical, biological and socio-cuitural effects, using the framework of the Base Line study and the Impact evaluation derived from the construction and project operation phases. The conclusions and recommendations will diminish, mitigate and/or eliminate impact derived from the specific activities.
- Full Text:
- Date Issued: 1996
Geochemical exploration in tropical terrains with special reference to base metals
- Authors: Chiconela, Domingos Rubão
- Date: 1996
- Subjects: Geochemical prospecting -- Research -- Tropics , Geological mapping -- Research -- Tropics , Weathering -- Research -- Tropics , Geochemistry -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4953 , http://hdl.handle.net/10962/d1005565 , Geochemical prospecting -- Research -- Tropics , Geological mapping -- Research -- Tropics , Weathering -- Research -- Tropics , Geochemistry -- Research
- Description: In tropical areas, the high rainfall induces severe-and pervasive weathering, producing a thick soil cover. The lithologies underneath may b~ recognised using geochemical mapping, which is based on certain elements that have the ability to differentiate between various lithologic units. Elements that are independent of the weathering process are normally selected for this purpose. The chemistry of mobility of base metals is an important factor to take into account when evaluating the mobility and distribution of these elements in a soil profile. Factors such as pH, Eh, organic material, clay minerals, Fe and Mn oxides are normally key aspects to be considered. When iron-rich rocks undergo deep weathering, lateritic profiles are developed. These are widespread in a belt bordering the equatorial zone, including the Brazilian shield, West and East Africa, parts of India and Northern Australia. In these profiles, the high rainfall promotes intense leaching of the different horizons. Where the pre-existing profiles are mostly preserved, the base metals are distributed throughout the profile: in the upper ferruginous horizon, goethite and hematite can adsorb large amounts of Mo, resulting in large dispersion halo. Other base metals such as Cu and Zn are less resistant in these freely-drained profiles and, therefore, they may be partly leached from the profile. In the lower horizons, Cu, ,zn, Ni and Co are retained, hosted in kaolinite and smectite, and thus, a high geochemical contrast will be identified in this horizon at the expense of a decline in the size of the dispersion haloes. The pre-existing profiles can be truncated, with a thin stone line developing at the contact between the lateritic profile and the recent soil. The conditions in these environments favour the retention of most of the pathfinder and target elements in all soil horizons, with the B horizon showing the highest contrast. If the primary rock is rich in AI, a bauxitic profile will be developed. The world distribution of bauxites closely resembles that of laterites. The behaviour of Co and Ni is very similar to that of iron during the bauxitization. Furthermore, the factors that induce residual enrichment of Al with removal of Fe in the soil profile will cause significant depletion of Co and Ni in these profiles. These metals are then concentrated at the base of the profile because of precipitation from downward percolating solutions. Many karst bauxite deposits in Southern Europe are enriched with Ni and Co in the basal horizon. Such horizon is mined as nickel ore in the bauxites of the Lokris region in Greece. Copper and molybdenum are strongly enriched.in bauxitic profiles. Concentration ratios are 8 and 3.2 for Cu and Mo respectively. Molybdenum is closely related to goethite and hematite, and therefore, the high concentration of Mo in a bauxitic profile will be consistent with the horizon where iron is concentrated. Copper concentrates at the base of the iron rich-horizon but also appears enriched in the saprolite together with Co. When sulphide bodies occur, in this environment, deep and penetrative weathering has resulted in considerable near-surface mobilization of iron and silica. The supergene alteration commonly obscures the identity of the primary sulphides at the surface. In this case, geochemical assessment of the resulting gossan has proved to be crucial in mineral exploration. A search in the secondary mineral assemblage, volatile and precious metals may lead to the information on the composition of the primary sulphide assemblage. The conclusion that will be reached is that if the geochemical properties (mobility, affinities with Fe or Mn oxides and/or clay minerals) of each of the base metals are understood, an appropriate sampling (optimum size-depth combination) will then be done. In such cases, a subdued, weak, but significant, geochemical response will be identified in the surface horizon.
- Full Text:
- Date Issued: 1996
- Authors: Chiconela, Domingos Rubão
- Date: 1996
- Subjects: Geochemical prospecting -- Research -- Tropics , Geological mapping -- Research -- Tropics , Weathering -- Research -- Tropics , Geochemistry -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4953 , http://hdl.handle.net/10962/d1005565 , Geochemical prospecting -- Research -- Tropics , Geological mapping -- Research -- Tropics , Weathering -- Research -- Tropics , Geochemistry -- Research
- Description: In tropical areas, the high rainfall induces severe-and pervasive weathering, producing a thick soil cover. The lithologies underneath may b~ recognised using geochemical mapping, which is based on certain elements that have the ability to differentiate between various lithologic units. Elements that are independent of the weathering process are normally selected for this purpose. The chemistry of mobility of base metals is an important factor to take into account when evaluating the mobility and distribution of these elements in a soil profile. Factors such as pH, Eh, organic material, clay minerals, Fe and Mn oxides are normally key aspects to be considered. When iron-rich rocks undergo deep weathering, lateritic profiles are developed. These are widespread in a belt bordering the equatorial zone, including the Brazilian shield, West and East Africa, parts of India and Northern Australia. In these profiles, the high rainfall promotes intense leaching of the different horizons. Where the pre-existing profiles are mostly preserved, the base metals are distributed throughout the profile: in the upper ferruginous horizon, goethite and hematite can adsorb large amounts of Mo, resulting in large dispersion halo. Other base metals such as Cu and Zn are less resistant in these freely-drained profiles and, therefore, they may be partly leached from the profile. In the lower horizons, Cu, ,zn, Ni and Co are retained, hosted in kaolinite and smectite, and thus, a high geochemical contrast will be identified in this horizon at the expense of a decline in the size of the dispersion haloes. The pre-existing profiles can be truncated, with a thin stone line developing at the contact between the lateritic profile and the recent soil. The conditions in these environments favour the retention of most of the pathfinder and target elements in all soil horizons, with the B horizon showing the highest contrast. If the primary rock is rich in AI, a bauxitic profile will be developed. The world distribution of bauxites closely resembles that of laterites. The behaviour of Co and Ni is very similar to that of iron during the bauxitization. Furthermore, the factors that induce residual enrichment of Al with removal of Fe in the soil profile will cause significant depletion of Co and Ni in these profiles. These metals are then concentrated at the base of the profile because of precipitation from downward percolating solutions. Many karst bauxite deposits in Southern Europe are enriched with Ni and Co in the basal horizon. Such horizon is mined as nickel ore in the bauxites of the Lokris region in Greece. Copper and molybdenum are strongly enriched.in bauxitic profiles. Concentration ratios are 8 and 3.2 for Cu and Mo respectively. Molybdenum is closely related to goethite and hematite, and therefore, the high concentration of Mo in a bauxitic profile will be consistent with the horizon where iron is concentrated. Copper concentrates at the base of the iron rich-horizon but also appears enriched in the saprolite together with Co. When sulphide bodies occur, in this environment, deep and penetrative weathering has resulted in considerable near-surface mobilization of iron and silica. The supergene alteration commonly obscures the identity of the primary sulphides at the surface. In this case, geochemical assessment of the resulting gossan has proved to be crucial in mineral exploration. A search in the secondary mineral assemblage, volatile and precious metals may lead to the information on the composition of the primary sulphide assemblage. The conclusion that will be reached is that if the geochemical properties (mobility, affinities with Fe or Mn oxides and/or clay minerals) of each of the base metals are understood, an appropriate sampling (optimum size-depth combination) will then be done. In such cases, a subdued, weak, but significant, geochemical response will be identified in the surface horizon.
- Full Text:
- Date Issued: 1996
Glycerol production by Dunaliella species in saline waste water treatment
- Authors: Emmett, Robyn Angela
- Date: 1996
- Subjects: Dunaliella -- Growth , Glycine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4019 , http://hdl.handle.net/10962/d1004079 , Dunaliella -- Growth , Glycine
- Description: In recent years, much research has focused on Algal High Rate Oxidation Ponds as both an economic means for wastewater treatment and as a system for the mass production of algae. With the advent of these systems for the treatment of saline organic effluents, the extreme halophile, Dunaliella salina was considered. In this study, the growth and productivity of a number of Dunaliella species (and strains thereof) was evaluated in hide soak liquor tannery effluent. Hide soak liquor, diluted to 20% with water, proved to be highly suitable as a growth medium for the majority of the Dunaliella species under study and in some instances, resulted in enhanced growth rates and higher biomass yields compared to those obtained in defined inorganic medium. A few Dunaliella species failed to grow in this effluent. A correlation was observed between the lack of growth displayed by these species in this organio-rich medium and their failure to utilise organic compounds. Glycine, a major component of this effluent, possibly stimulates the growth of Dunaliella. Studies on the mechanism of growth stimulation by glycine revealed that an algal-bacterial relationship existed whereby the bacteria mineralised the amino acid, releasing ammonia which was then utilised by the alga. Results of this work revealed significant variations in the intracellular glycerol content amongst the Dunaliella species under study. Large differences were also observed between the glycerol contents of effluent-grown and control Dunaliella cells, where the effluent-grown cells were characterised by greatly reduced intracellular glycerol content. These reduced glycerol levels are assumed to have arisen from the glycine-induced stimulation of glycerol release which was observed in this study, where the high glycine content of the hide soak liquor is proposed to have induced glycerol release. This enhanced glycerol release in tatmery effluent could play a central role in the fimction of Dunaliella-based High Rate Oxidation Ponding systems, by stimulating bacterial activity. Observed glycerol productivities were therefore proposed to be a fimction of the type and concentration of the organic constituents of the medium. A similar medium-induced phenomenon was observed in the starch content of Dunaliella cells.
- Full Text:
- Date Issued: 1996
- Authors: Emmett, Robyn Angela
- Date: 1996
- Subjects: Dunaliella -- Growth , Glycine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4019 , http://hdl.handle.net/10962/d1004079 , Dunaliella -- Growth , Glycine
- Description: In recent years, much research has focused on Algal High Rate Oxidation Ponds as both an economic means for wastewater treatment and as a system for the mass production of algae. With the advent of these systems for the treatment of saline organic effluents, the extreme halophile, Dunaliella salina was considered. In this study, the growth and productivity of a number of Dunaliella species (and strains thereof) was evaluated in hide soak liquor tannery effluent. Hide soak liquor, diluted to 20% with water, proved to be highly suitable as a growth medium for the majority of the Dunaliella species under study and in some instances, resulted in enhanced growth rates and higher biomass yields compared to those obtained in defined inorganic medium. A few Dunaliella species failed to grow in this effluent. A correlation was observed between the lack of growth displayed by these species in this organio-rich medium and their failure to utilise organic compounds. Glycine, a major component of this effluent, possibly stimulates the growth of Dunaliella. Studies on the mechanism of growth stimulation by glycine revealed that an algal-bacterial relationship existed whereby the bacteria mineralised the amino acid, releasing ammonia which was then utilised by the alga. Results of this work revealed significant variations in the intracellular glycerol content amongst the Dunaliella species under study. Large differences were also observed between the glycerol contents of effluent-grown and control Dunaliella cells, where the effluent-grown cells were characterised by greatly reduced intracellular glycerol content. These reduced glycerol levels are assumed to have arisen from the glycine-induced stimulation of glycerol release which was observed in this study, where the high glycine content of the hide soak liquor is proposed to have induced glycerol release. This enhanced glycerol release in tatmery effluent could play a central role in the fimction of Dunaliella-based High Rate Oxidation Ponding systems, by stimulating bacterial activity. Observed glycerol productivities were therefore proposed to be a fimction of the type and concentration of the organic constituents of the medium. A similar medium-induced phenomenon was observed in the starch content of Dunaliella cells.
- Full Text:
- Date Issued: 1996
Gold exploration in tropical and sub-tropical terrains with special emphasis on Central and Western Africa
- Authors: Breedt, Machiel Christoffel
- Date: 1996
- Subjects: Geochemical prospecting -- Tropics , Geochemical prospecting -- Africa , Gold ores -- Geology -- Tropics , Gold ores -- Geology -- Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4966 , http://hdl.handle.net/10962/d1005578 , Geochemical prospecting -- Tropics , Geochemical prospecting -- Africa , Gold ores -- Geology -- Tropics , Gold ores -- Geology -- Africa
- Description: The aim of this dissertation is an attempt to' provide a general guide for future gold exploration in tropical and sub-tropical terrains. The dissertation includes a brief discussion of the various exploration techniques used in regional and local exploration. This provide the necessary background knowledge to discriminate between the constraints and applications and to be able to select the techniques which are more suitable for gold exploration in tropical and sub-tropical terrains. Weathering, gold geochemistry and soil formation, fields often neglected, are emphasized to illustrate the importance of the mobility and dispersion of gold in the weathering of the lateritic soil profile. A sound knowledge and experience in regolith mapping is to the advantage of the explorationist. Case studies with special emphasis on Central- and Western Africa are included to illustrate the effectiveness of some of the gold exploration techniques in tropical and sub-tropical terrains. Gold exploration is a highly complex and demanding science and to be successfull involves the full intergration of all geological, geochemical and geophysical information available. An intergrated exploration method and strategy would enhance the possibility of making viable discoveries in this highly competative environment where our mineral resources become more depleted every day. Where applicable, the reader is refered to various recommended literature sources to provide the necessary background knowledge which form an integral part of gold exploration.
- Full Text:
- Date Issued: 1996
- Authors: Breedt, Machiel Christoffel
- Date: 1996
- Subjects: Geochemical prospecting -- Tropics , Geochemical prospecting -- Africa , Gold ores -- Geology -- Tropics , Gold ores -- Geology -- Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4966 , http://hdl.handle.net/10962/d1005578 , Geochemical prospecting -- Tropics , Geochemical prospecting -- Africa , Gold ores -- Geology -- Tropics , Gold ores -- Geology -- Africa
- Description: The aim of this dissertation is an attempt to' provide a general guide for future gold exploration in tropical and sub-tropical terrains. The dissertation includes a brief discussion of the various exploration techniques used in regional and local exploration. This provide the necessary background knowledge to discriminate between the constraints and applications and to be able to select the techniques which are more suitable for gold exploration in tropical and sub-tropical terrains. Weathering, gold geochemistry and soil formation, fields often neglected, are emphasized to illustrate the importance of the mobility and dispersion of gold in the weathering of the lateritic soil profile. A sound knowledge and experience in regolith mapping is to the advantage of the explorationist. Case studies with special emphasis on Central- and Western Africa are included to illustrate the effectiveness of some of the gold exploration techniques in tropical and sub-tropical terrains. Gold exploration is a highly complex and demanding science and to be successfull involves the full intergration of all geological, geochemical and geophysical information available. An intergrated exploration method and strategy would enhance the possibility of making viable discoveries in this highly competative environment where our mineral resources become more depleted every day. Where applicable, the reader is refered to various recommended literature sources to provide the necessary background knowledge which form an integral part of gold exploration.
- Full Text:
- Date Issued: 1996
Overview and comparison of Besshi-type deposits ancient and recent
- Authors: Schoeman, Philo
- Date: 1996
- Subjects: Ore deposits -- Japan , Ore deposits -- Canada , Ore deposits -- Namibia , Ore deposits -- South Africa , Ore deposits
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4983 , http://hdl.handle.net/10962/d1005595 , Ore deposits -- Japan , Ore deposits -- Canada , Ore deposits -- Namibia , Ore deposits -- South Africa , Ore deposits
- Description: Besshi-type deposits range in age from early Proterozoic to early Tertiary, of which the largest number are late Proterozoic, early Palaeozoic or Mesozoic in age. No Archaean examples of Besshi-type deposits are known, probably due to insufficient availability of sialic crust for erosion and clastic marine sedimentation before the start of the Proterozoic. All Besshi-type deposits are contained within sequences of clastic sedimentary rock and intercalated basalts in a marine environment. The basalts and amphibolites are principally tholeiitic in composition. Besshi-type deposits characteristically form stratiform 1enses and sheet-like accumulations of semi-massive to massive sulphide. The main ore assemblage consists dominantly of pyrite and/or pyrrhotite with variable amounts of chalcopyrite, sphalerite and trace galena, arsenopyrite, gold and e1ectrum, barite being absent in general. The median Besshi-type deposit (n=75) contains 1.3 million tonnes (Mt) of massive sulphide with a Cu grade running at 1.43%. It is suggested that Besshi-type deposits form by both exhalative and synsedimentary replacement processes when considering geological features and comparisons with modern analogues in the Guaymas Basin, Middle Valley and Escanaba Trough. The currently forming metalliferous sediments in the Red Sea provide for a brine pool model explaining the lack of footwall feeder zones below sheet-like deposits. Where thick sulphide lenses are contained in some Besshi-type deposits, combinations of exhalative precipitation and sub-sea-floor replacement of permeable sediments and/or volcanic rocks, take place in the upper parts of submarine hydrothermal systems.
- Full Text:
- Date Issued: 1996
- Authors: Schoeman, Philo
- Date: 1996
- Subjects: Ore deposits -- Japan , Ore deposits -- Canada , Ore deposits -- Namibia , Ore deposits -- South Africa , Ore deposits
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4983 , http://hdl.handle.net/10962/d1005595 , Ore deposits -- Japan , Ore deposits -- Canada , Ore deposits -- Namibia , Ore deposits -- South Africa , Ore deposits
- Description: Besshi-type deposits range in age from early Proterozoic to early Tertiary, of which the largest number are late Proterozoic, early Palaeozoic or Mesozoic in age. No Archaean examples of Besshi-type deposits are known, probably due to insufficient availability of sialic crust for erosion and clastic marine sedimentation before the start of the Proterozoic. All Besshi-type deposits are contained within sequences of clastic sedimentary rock and intercalated basalts in a marine environment. The basalts and amphibolites are principally tholeiitic in composition. Besshi-type deposits characteristically form stratiform 1enses and sheet-like accumulations of semi-massive to massive sulphide. The main ore assemblage consists dominantly of pyrite and/or pyrrhotite with variable amounts of chalcopyrite, sphalerite and trace galena, arsenopyrite, gold and e1ectrum, barite being absent in general. The median Besshi-type deposit (n=75) contains 1.3 million tonnes (Mt) of massive sulphide with a Cu grade running at 1.43%. It is suggested that Besshi-type deposits form by both exhalative and synsedimentary replacement processes when considering geological features and comparisons with modern analogues in the Guaymas Basin, Middle Valley and Escanaba Trough. The currently forming metalliferous sediments in the Red Sea provide for a brine pool model explaining the lack of footwall feeder zones below sheet-like deposits. Where thick sulphide lenses are contained in some Besshi-type deposits, combinations of exhalative precipitation and sub-sea-floor replacement of permeable sediments and/or volcanic rocks, take place in the upper parts of submarine hydrothermal systems.
- Full Text:
- Date Issued: 1996
Petrology and geochemistry of the basal gabbro unit, Uitkomst complex
- Strauss, Toby Anthony Lavery
- Authors: Strauss, Toby Anthony Lavery
- Date: 1996
- Subjects: Petrology -- South Africa -- Mpumalanga -- badplaas , Geochemistry -- South Africa -- Mpumalanga , Gabbro -- South Africa -- Mpumalanga
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4989 , http://hdl.handle.net/10962/d1005601 , Petrology -- South Africa -- Mpumalanga -- badplaas , Geochemistry -- South Africa -- Mpumalanga , Gabbro -- South Africa -- Mpumalanga
- Description: The Cu/(Cu+Ni) ratios associated with the Basal Gabbro also display the vertical reverse fractionation trend, supporting the supercooled margin model. The disseminated sulphides in the lowermost units, are regarded as being the result of sulphur saturation induced by contamination from the dolomitic and quartzitic xenoliths. This is supported by isotope data which indicate the high degree of contamination in the lowermost units of the Complex. The results of this study are used to propose a model for the petrogenesis and metallogenesis of the Uitkomst Complex, whereby the Complex is closely related to the Bushveld Complex. The Basal Gabbro, as supported by its chemistry and style of mineralisation (Cu-rich), represents a supercooled margin to the lowermost units of the Uitkomst Complex, which stoped upwards into the surrounding sediments, assimilating the country rock xenoliths, and precipitating sulphides. Following this was a period in which large quantities of magma moved laterally through the system before the magma flow waned, and closed system crystallisation ensued. As the body cooled, the primarily magmatic water was superceded by the hydrothermal magmatic water released from the xenoliths, and later by geothermally driven circulating meteoric water, producing the extensive alteration. This alteration was accompanied by considerable stress and the development of fractures and shears. Finally the Complex was itself intruded by diabase sills and later dolerite dykes.
- Full Text:
- Date Issued: 1996
- Authors: Strauss, Toby Anthony Lavery
- Date: 1996
- Subjects: Petrology -- South Africa -- Mpumalanga -- badplaas , Geochemistry -- South Africa -- Mpumalanga , Gabbro -- South Africa -- Mpumalanga
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4989 , http://hdl.handle.net/10962/d1005601 , Petrology -- South Africa -- Mpumalanga -- badplaas , Geochemistry -- South Africa -- Mpumalanga , Gabbro -- South Africa -- Mpumalanga
- Description: The Cu/(Cu+Ni) ratios associated with the Basal Gabbro also display the vertical reverse fractionation trend, supporting the supercooled margin model. The disseminated sulphides in the lowermost units, are regarded as being the result of sulphur saturation induced by contamination from the dolomitic and quartzitic xenoliths. This is supported by isotope data which indicate the high degree of contamination in the lowermost units of the Complex. The results of this study are used to propose a model for the petrogenesis and metallogenesis of the Uitkomst Complex, whereby the Complex is closely related to the Bushveld Complex. The Basal Gabbro, as supported by its chemistry and style of mineralisation (Cu-rich), represents a supercooled margin to the lowermost units of the Uitkomst Complex, which stoped upwards into the surrounding sediments, assimilating the country rock xenoliths, and precipitating sulphides. Following this was a period in which large quantities of magma moved laterally through the system before the magma flow waned, and closed system crystallisation ensued. As the body cooled, the primarily magmatic water was superceded by the hydrothermal magmatic water released from the xenoliths, and later by geothermally driven circulating meteoric water, producing the extensive alteration. This alteration was accompanied by considerable stress and the development of fractures and shears. Finally the Complex was itself intruded by diabase sills and later dolerite dykes.
- Full Text:
- Date Issued: 1996
Reduction of tungsten oxides with carbon and hydrogen
- Authors: Venables, Dean Stuart
- Date: 1996
- Subjects: Oxidation-reduction reaction , Tungsten , Hydrogen , Carbon
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4342 , http://hdl.handle.net/10962/d1005004 , Oxidation-reduction reaction , Tungsten , Hydrogen , Carbon
- Description: The reductions of WO₃ with hydrogen, with CO, and with carbon, as well as the reduction of WO₃/graphite mixtures with hydrogen, were studied using thermogravimetry, evolved gas analysis, X-ray powder diffraction, and scanning electron microscopy. The intermediate phases W₂₀O₅₈, W₁₈O₄₉ and WO₂, were observed in the reductions. The final product of the reductions with hydrogen and carbon was tungsten, and we was formed in the reduction with CO. The reaction paths in the overall processes were determined. The reactant/product gas ratio had a considerable influence on which reactions took place. The morphology of the sample was characterised at different stages of the reduction. The shape of the WO₃ particles was retained during the reduction. Particle growth was observed in the reduction with hydrogen and was attributed to the formation of WO₂(OH)₂(g). The kinetics of the reductions were investigated , and the reaction mechanisms determined. The reduction of WO₃ with CO was studied from 650 to 900°C, and occurred at a phase boundary with an activation energy of 40 kJ mol⁻¹ . The reduction of WO₂, was studied under the same conditions. The reaction also occurred at a phase boundary and had an activation energy of 62 kJ mol⁻¹. The reduction of WO₃ with carbon was studied from 935 to 1100°C and took place via CO and CO₂. Two stages were observed in the reduction . The first stage, which corresponded approximately to the formation of WO₂ had an activation energy of 66 kJ mol⁻¹ and was limited by diffusion through the porous reacting particles. The second stage was first order and had an activation energy of 40 kJ mol⁻¹. The reduction of WO₃ and WO₃ graphite mixtures with hydrogen were studied from 575 to 975 °C. The reactions were controlled by mass-transfer under the conditions investigated. The addition of carbon increased the rate of the reduction process , but did not affect the phases formed in the system. CO₂ was evolved mainly at the start, and CO mainly at the end of the process.
- Full Text:
- Date Issued: 1996
- Authors: Venables, Dean Stuart
- Date: 1996
- Subjects: Oxidation-reduction reaction , Tungsten , Hydrogen , Carbon
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4342 , http://hdl.handle.net/10962/d1005004 , Oxidation-reduction reaction , Tungsten , Hydrogen , Carbon
- Description: The reductions of WO₃ with hydrogen, with CO, and with carbon, as well as the reduction of WO₃/graphite mixtures with hydrogen, were studied using thermogravimetry, evolved gas analysis, X-ray powder diffraction, and scanning electron microscopy. The intermediate phases W₂₀O₅₈, W₁₈O₄₉ and WO₂, were observed in the reductions. The final product of the reductions with hydrogen and carbon was tungsten, and we was formed in the reduction with CO. The reaction paths in the overall processes were determined. The reactant/product gas ratio had a considerable influence on which reactions took place. The morphology of the sample was characterised at different stages of the reduction. The shape of the WO₃ particles was retained during the reduction. Particle growth was observed in the reduction with hydrogen and was attributed to the formation of WO₂(OH)₂(g). The kinetics of the reductions were investigated , and the reaction mechanisms determined. The reduction of WO₃ with CO was studied from 650 to 900°C, and occurred at a phase boundary with an activation energy of 40 kJ mol⁻¹ . The reduction of WO₂, was studied under the same conditions. The reaction also occurred at a phase boundary and had an activation energy of 62 kJ mol⁻¹. The reduction of WO₃ with carbon was studied from 935 to 1100°C and took place via CO and CO₂. Two stages were observed in the reduction . The first stage, which corresponded approximately to the formation of WO₂ had an activation energy of 66 kJ mol⁻¹ and was limited by diffusion through the porous reacting particles. The second stage was first order and had an activation energy of 40 kJ mol⁻¹. The reduction of WO₃ and WO₃ graphite mixtures with hydrogen were studied from 575 to 975 °C. The reactions were controlled by mass-transfer under the conditions investigated. The addition of carbon increased the rate of the reduction process , but did not affect the phases formed in the system. CO₂ was evolved mainly at the start, and CO mainly at the end of the process.
- Full Text:
- Date Issued: 1996
Semi-automated extraction of structural orientation data from aerospace imagery combined with digital elevation models
- Authors: Slabber, Frans Bresler
- Date: 1996
- Subjects: Image processing , Geographic information systems , Information storage and retrieval systems -- Geology , Geology -- Data processing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5001 , http://hdl.handle.net/10962/d1005614 , Image processing , Geographic information systems , Information storage and retrieval systems -- Geology , Geology -- Data processing
- Description: A computer-based method for determining the orientation of planar geological structures from remotely sensed images, utilizing digital geological images and digital elevation models (DEMs), is developed and assessed. The method relies on operator skill and experience to recognize geological structure traces on images, and then employs software routines (GEOSTRUC©) to calculate the orientation of selected structures. The operator selects three points on the trace of a planar geological feature as seen on a digital geological image that is co registered with a DEM of the same area. The orientation of the plane that contains the three points is determined using vector algebra equations. The program generates an ASCII data file which contains the orientation data as well as the geographical location of the measurements. This ASCII file can then be utilized in further analysis of the orientation data. The software development kit (SDK) for TNTmips v5.00, from MicroImages Inc. and operating in the X Windows environment, was employed to construct the software. The Watcom C\C++ Development Environment was used to generate the executable program, GEOSTRUC© . GEOSTRUC© was tested in two case studies. The case studies utilized digital data derived from the use of different techniques and from different sources which varied in scale and resolution. This was done to illustrate the versatility of the program and its application to a wide range of data types. On the whole, the results obtained using the GEOSTRUC© analyses compare favourably to field data from each test area. Use of the method to determine the orientation of axial planes in the case study revealed the usefulness of the method as a powerful analytic tool for use on a macroscopic scale. The method should not he applied in area with low variation in relief as the method proved to be less accurate in these areas. Advancements in imaging technology will serve to create images with better resolution, which will, in turn, improve the overall accuracy of the method.
- Full Text:
- Date Issued: 1996
- Authors: Slabber, Frans Bresler
- Date: 1996
- Subjects: Image processing , Geographic information systems , Information storage and retrieval systems -- Geology , Geology -- Data processing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5001 , http://hdl.handle.net/10962/d1005614 , Image processing , Geographic information systems , Information storage and retrieval systems -- Geology , Geology -- Data processing
- Description: A computer-based method for determining the orientation of planar geological structures from remotely sensed images, utilizing digital geological images and digital elevation models (DEMs), is developed and assessed. The method relies on operator skill and experience to recognize geological structure traces on images, and then employs software routines (GEOSTRUC©) to calculate the orientation of selected structures. The operator selects three points on the trace of a planar geological feature as seen on a digital geological image that is co registered with a DEM of the same area. The orientation of the plane that contains the three points is determined using vector algebra equations. The program generates an ASCII data file which contains the orientation data as well as the geographical location of the measurements. This ASCII file can then be utilized in further analysis of the orientation data. The software development kit (SDK) for TNTmips v5.00, from MicroImages Inc. and operating in the X Windows environment, was employed to construct the software. The Watcom C\C++ Development Environment was used to generate the executable program, GEOSTRUC© . GEOSTRUC© was tested in two case studies. The case studies utilized digital data derived from the use of different techniques and from different sources which varied in scale and resolution. This was done to illustrate the versatility of the program and its application to a wide range of data types. On the whole, the results obtained using the GEOSTRUC© analyses compare favourably to field data from each test area. Use of the method to determine the orientation of axial planes in the case study revealed the usefulness of the method as a powerful analytic tool for use on a macroscopic scale. The method should not he applied in area with low variation in relief as the method proved to be less accurate in these areas. Advancements in imaging technology will serve to create images with better resolution, which will, in turn, improve the overall accuracy of the method.
- Full Text:
- Date Issued: 1996
Structures and thermal behaviour of some monooxalato and dioxalato metal complexes
- Authors: Bacsa, John
- Date: 1996
- Subjects: Oxalates -- Research , Crystallography -- Research , Chemistry, Inorganic -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4351 , http://hdl.handle.net/10962/d1005016 , Oxalates -- Research , Crystallography -- Research , Chemistry, Inorganic -- Research
- Description: The crystal structure of Ba [Cu(C₂0₄)₂(H₂O)].5H₂O has been determined using single crystal X-ray diffractometry. It crystallises in the triclinic system, space group Pī , with a = 6.539(2) Å, b = 9.211(3) Å, c = 10.928(3) Å, a = 85.42(3)°, β = 79.22(3)° , γ = 80.30(3)°, V = 636.08(8)ų and Z = 2. The structure consists of [Cu(C₂0₄)₂(H₂O)]²⁻ ions weakly bridged by barium ions and water molecules. The copper(II) ions are in a tetragonally elongated square-pyramidal environment with some trigonal distortion. The two oxalate groups occupy the equatorial positions and a water molecule occupies the axial position. The barium ion is surrounded by nine oxygens: five oxygens from water molecules and four oxygens from oxalate groups. The thermal behaviour of Ba [Cu(C₂0₄)₂(H₂O)].5H₂0 in N₂ has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively low temperatures (~80°C), but continues until the onset of the decomposition (~280°C). The decomposition takes place in two major stages. The mass of the intermediate after the first stage corresponded to the formation of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The enthalpy for the dehydration was found to be 311 ±30 kJ mol⁻¹. The overall enthalpy change for the decomposition of Ba[Cu(C₂0₄)₂]in N₂ was estimated from the combined area of the peaks of the DSC curve as -347 kJ mol⁻¹. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly deceleratory and the α-time curves could be described by the three-dimensional diffusion (D3) model. The values of the activation energy and the pre-exponential factor for the dehydration were 125 ±4 kJ mol⁻¹ and (1.38 ±0.08)x10¹⁵ min⁻¹, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry model with n = 5. The other process was slow and could also be described by the contracting-geometry model , but with n = 2. The values of Eₐ and A were 206 ±23 kJ mol⁻¹ and (2.2 ±O.5)xl0¹⁹min⁻¹, respectively, for the fast process, and 259 ±37 kJ mol⁻¹ and (6.3 ±1.8)x10²³min⁻¹, respectively, for the slow process.The crystal structure of zinc oxalate dihydrate ([Zn(C₂0₄)(H₂O)₂]n) has also been determined by X-ray diffraction methods. It crystallises in the monoclinic system, space group C2/c with a = 11.786(2) Å, b = 5.397(1)Å, c = 9.712(1) Å, B = 126.19(5)°, V = 498.58(8)ų, Z = 4 and R = 0.037 for 435 absorption-corrected independent reflections and 50 parameters. The asymmetric unit consists of half the monomeric unit [Zn(C₂0₄)(H₂O)₂). The structure consists of infinite, linear chains of zinc ions bridged by oxalate groups. The geometry of the coordination polyhedron surrounding the zinc ion is octahedral, with the oxalate oxygens occupying the equatorial positions and water molecules occupying the axial positions.
- Full Text:
- Date Issued: 1996
- Authors: Bacsa, John
- Date: 1996
- Subjects: Oxalates -- Research , Crystallography -- Research , Chemistry, Inorganic -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4351 , http://hdl.handle.net/10962/d1005016 , Oxalates -- Research , Crystallography -- Research , Chemistry, Inorganic -- Research
- Description: The crystal structure of Ba [Cu(C₂0₄)₂(H₂O)].5H₂O has been determined using single crystal X-ray diffractometry. It crystallises in the triclinic system, space group Pī , with a = 6.539(2) Å, b = 9.211(3) Å, c = 10.928(3) Å, a = 85.42(3)°, β = 79.22(3)° , γ = 80.30(3)°, V = 636.08(8)ų and Z = 2. The structure consists of [Cu(C₂0₄)₂(H₂O)]²⁻ ions weakly bridged by barium ions and water molecules. The copper(II) ions are in a tetragonally elongated square-pyramidal environment with some trigonal distortion. The two oxalate groups occupy the equatorial positions and a water molecule occupies the axial position. The barium ion is surrounded by nine oxygens: five oxygens from water molecules and four oxygens from oxalate groups. The thermal behaviour of Ba [Cu(C₂0₄)₂(H₂O)].5H₂0 in N₂ has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively low temperatures (~80°C), but continues until the onset of the decomposition (~280°C). The decomposition takes place in two major stages. The mass of the intermediate after the first stage corresponded to the formation of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The enthalpy for the dehydration was found to be 311 ±30 kJ mol⁻¹. The overall enthalpy change for the decomposition of Ba[Cu(C₂0₄)₂]in N₂ was estimated from the combined area of the peaks of the DSC curve as -347 kJ mol⁻¹. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly deceleratory and the α-time curves could be described by the three-dimensional diffusion (D3) model. The values of the activation energy and the pre-exponential factor for the dehydration were 125 ±4 kJ mol⁻¹ and (1.38 ±0.08)x10¹⁵ min⁻¹, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry model with n = 5. The other process was slow and could also be described by the contracting-geometry model , but with n = 2. The values of Eₐ and A were 206 ±23 kJ mol⁻¹ and (2.2 ±O.5)xl0¹⁹min⁻¹, respectively, for the fast process, and 259 ±37 kJ mol⁻¹ and (6.3 ±1.8)x10²³min⁻¹, respectively, for the slow process.The crystal structure of zinc oxalate dihydrate ([Zn(C₂0₄)(H₂O)₂]n) has also been determined by X-ray diffraction methods. It crystallises in the monoclinic system, space group C2/c with a = 11.786(2) Å, b = 5.397(1)Å, c = 9.712(1) Å, B = 126.19(5)°, V = 498.58(8)ų, Z = 4 and R = 0.037 for 435 absorption-corrected independent reflections and 50 parameters. The asymmetric unit consists of half the monomeric unit [Zn(C₂0₄)(H₂O)₂). The structure consists of infinite, linear chains of zinc ions bridged by oxalate groups. The geometry of the coordination polyhedron surrounding the zinc ion is octahedral, with the oxalate oxygens occupying the equatorial positions and water molecules occupying the axial positions.
- Full Text:
- Date Issued: 1996
Synthetic and mechanistic studies of heterocyclic systems
- Authors: Deane, Philip O'Grady
- Date: 1996
- Subjects: Heterocyclic chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4379 , http://hdl.handle.net/10962/d1005044 , Heterocyclic chemistry
- Description: A series of acrylate esters and selected analogues have been reacted with pyridine-2-,pyridine-3-, and pyridine-4-carboxaldehydes in the presence of diazabicyclo[2,2,2]octane (DARCO) to afford a range of Baylis-Hillman products. The pyridine-2-carboxaldehyde-derived products have been acetylated using acetic anhydride and the kinetics of the thermal cyclisation of the acetylated compounds to indolizines was investigated using proton NMR spectroscopy. The first-order kinetics of the cyclisation has been confirmed and the influence of substituents on the first-order rate constant, kₒbs has been examined. The kinetic data has been shown to be consistent with the previously proposed mechanism in which loss of the acetate group is ratedetermining. Each of the cyclisations was also monitored at three different temperatures permitting evaluation of the activation parameters. The Baylis-Hillman products and related acetylated derivatives were treated at room temperature with sodium methylthiolate; the hydroxy precursors were observed to undergo conjugate addition with a degree of diastereocontrol but the acetylated derivatives favoured an apparent SN¹ displacement of the acetate group.
- Full Text:
- Date Issued: 1996
- Authors: Deane, Philip O'Grady
- Date: 1996
- Subjects: Heterocyclic chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4379 , http://hdl.handle.net/10962/d1005044 , Heterocyclic chemistry
- Description: A series of acrylate esters and selected analogues have been reacted with pyridine-2-,pyridine-3-, and pyridine-4-carboxaldehydes in the presence of diazabicyclo[2,2,2]octane (DARCO) to afford a range of Baylis-Hillman products. The pyridine-2-carboxaldehyde-derived products have been acetylated using acetic anhydride and the kinetics of the thermal cyclisation of the acetylated compounds to indolizines was investigated using proton NMR spectroscopy. The first-order kinetics of the cyclisation has been confirmed and the influence of substituents on the first-order rate constant, kₒbs has been examined. The kinetic data has been shown to be consistent with the previously proposed mechanism in which loss of the acetate group is ratedetermining. Each of the cyclisations was also monitored at three different temperatures permitting evaluation of the activation parameters. The Baylis-Hillman products and related acetylated derivatives were treated at room temperature with sodium methylthiolate; the hydroxy precursors were observed to undergo conjugate addition with a degree of diastereocontrol but the acetylated derivatives favoured an apparent SN¹ displacement of the acetate group.
- Full Text:
- Date Issued: 1996
The development of an ecological model to determine flood release options for the management of the Phongolo floodplain in Kwazulu/Natal (South Africa)
- Authors: Weldrick, Sarah Katharine
- Date: 1996
- Subjects: Flood control -- Environmental aspects -- South Africa -- KwaZulu-Natal -- Pongolo floodplain , Fishes -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5258 , http://hdl.handle.net/10962/d1005102 , Flood control -- Environmental aspects -- South Africa -- KwaZulu-Natal -- Pongolo floodplain , Fishes -- Behavior
- Description: The Phongolo River floodplain in KwaZulu/Natal is a river-associated wetland which was subject to regular cycles of flooding in the past. The floods were associated with seasonal summer rainfall. Through the wet and dry cycles on the floodplain there was an alternation between the aquatic and terrestrial biomes. Many of the fishes on the floodplain are dependent on this cycle for their survival. The construction of the Pongolapoort Dam in 1969 has resulted in alterations to the timing, magnitudes and duration of the natural flooding events of the Phongolo River. This alteration has affected the fisheries. It is now necessary to simulate natural floods by artificial water releases from the dam. There are several demands on the water supply, so it has not always been possible to adhere to the natural flood regime. This necessitated the need for an integrated management programme to ensure the sustainability of the natural resources. A practical ecological model of the fishery was developed to determine an optimum flood release scenario for the floodplain. The relative abundances, distribution and species richness of the fishes were determined at various lakes and rivers on the floodplain. A community classification of the fishes was determined using TWINSPAN ordination. The potential yield of the fish at each site was calculated. Flood releases of varying magnitudes were simulated using Geographic Information Systems (GIS). This information was combined in a model which can be used by resource managers to estimate the percentage species compositions of fishes at each of the lakes, and to compare the actual harvest to the potential calculated sustainable yields of fishes for various flood release regimes. Subsistence agriculture and other beneficial ecological information can be incorporated into the model to determine the effect of different flood release options for the Phongolo floodplain.
- Full Text:
- Date Issued: 1996
- Authors: Weldrick, Sarah Katharine
- Date: 1996
- Subjects: Flood control -- Environmental aspects -- South Africa -- KwaZulu-Natal -- Pongolo floodplain , Fishes -- Behavior
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5258 , http://hdl.handle.net/10962/d1005102 , Flood control -- Environmental aspects -- South Africa -- KwaZulu-Natal -- Pongolo floodplain , Fishes -- Behavior
- Description: The Phongolo River floodplain in KwaZulu/Natal is a river-associated wetland which was subject to regular cycles of flooding in the past. The floods were associated with seasonal summer rainfall. Through the wet and dry cycles on the floodplain there was an alternation between the aquatic and terrestrial biomes. Many of the fishes on the floodplain are dependent on this cycle for their survival. The construction of the Pongolapoort Dam in 1969 has resulted in alterations to the timing, magnitudes and duration of the natural flooding events of the Phongolo River. This alteration has affected the fisheries. It is now necessary to simulate natural floods by artificial water releases from the dam. There are several demands on the water supply, so it has not always been possible to adhere to the natural flood regime. This necessitated the need for an integrated management programme to ensure the sustainability of the natural resources. A practical ecological model of the fishery was developed to determine an optimum flood release scenario for the floodplain. The relative abundances, distribution and species richness of the fishes were determined at various lakes and rivers on the floodplain. A community classification of the fishes was determined using TWINSPAN ordination. The potential yield of the fish at each site was calculated. Flood releases of varying magnitudes were simulated using Geographic Information Systems (GIS). This information was combined in a model which can be used by resource managers to estimate the percentage species compositions of fishes at each of the lakes, and to compare the actual harvest to the potential calculated sustainable yields of fishes for various flood release regimes. Subsistence agriculture and other beneficial ecological information can be incorporated into the model to determine the effect of different flood release options for the Phongolo floodplain.
- Full Text:
- Date Issued: 1996