The aim of this research was to determine if strategic marketing options will grow the sales of finer grade vermiculite.

Biohydrometallurgical techniques are quite established for the treatment of certain sulphide minerals and others have been demonstrated at laboratory or pilot plant scale level, where iron and sulphuroxidising bacteria are utilised for the leaching of low grade sulphide ores and the pretreatment of gold ores and concentrates. The majority of the microorganisms which are used for bacterial leaching are autotrophic aerobes, therefore carbon dioxide and oxygen are essential nutrients for their growth and survival, adequate supplies must be ensured in order for the oxidation process to be successful through an effective gas mass transfer process from air or other sources to the gas/liquid/solids interface in the pulp which can then be readily available to the microorganisms. Gas mass transfer limitation is one of the major problems faced by the industry therefore, most commercial biooxidation plants currently operate at low pulp densities at around 20 - 25% to minimise gas mass transfer limitations. Three cultures, a mesophile (DSM 583), a moderate thermophile (Y1FI) and a extreme thermophile iSulfolobus BC65) were used to bioleach the Ok Tedi copper concentrate under optimum Ch and CO2 enriched air (30% Ch and 10% CO2) based on volume ratios. The positive effect of using oxygen and carbon dioxide enriched air to bioleach the copper mineral was clearly demonstrated where an increase in Cu leaching rate by a factor of2.8, 2.1 and 1.9 for DSM 583, YTFI and Sulfolobus respectively were observed compared with the shake flask tests. The lag phase observed with the other test conditions such as in shake flask or with air, was eliminated when leached under optimum gas enrichment and 1t;80%of the Cu was extracted in the first 120 to 150 hours of leaching for all three cultures. The average dissolved oxygen concentrations observed in the pulp for these tests were 11.8, 8.0 and 7.2 mgll for DSM 583, YTFI and Sulfolobus respectively, indicating that O2 was not limiting in these tests. The Fe released during the bioleaching of copper was non stoichiometric for a predominantly chalcopyrite concentrate and the low redox potential values (max 638mV) suggested galvanic interaction during the leaching of copper where chalcopyrite was leached preferentially due to the presence of pyrite. Bioleaching of copper under optimum gas enrichment at different pulp densities showed near total copper extraction occurred for pulp densities of 3, 10 and 20% (w/v). At high pulp densities, more so at 40% than 30% (w/v), the leaching rate decreased rapidly for tests with YTFI and Sulfolobus. Monitoring of dissolved Ch shows that O2 demand increased with increasing pulp density and the average dissolved O2 concentration observed for DSM 583, YTFl and Sulfolobus at 40% solids concentration were 3.0, 2.6 and 2.4 mgll respectively, suggesting that oxygen and carbon dioxide are not limiting. The decrease in leaching rate observed at high pulp densities (30 & 40%) under optimum gas enrichment was accompanied by low metal dissolution and low redox potential values which was attributed to shear stress due to attrition of cells by high solids concentration, toxicity of metal ions especially Ag, Fe and Cu, and the formation of precipitates and jarosites as confirmed from XRD analysis of leach residues hence impeding the leaching process rather than as a result of O2 and C~ limiting conditions. The addition of flowing air increased the overall iron release rate for the Porgera gold-bearing pyrite concentrate by a factor of AJ 2.8, 1.8 and 1.5 for DSM 583, YTFl and Sulfolobus respectively compared with the shake flask tests, and the lag time was observed to decrease by about 80% for all cultures, suggesting O2 and CO2 limiting conditions in the shake flask. The average dissolved ~ concentration observed for the pulp with the different cultures were 8.7, 5.8 and 5.0 mgll for DSM 583, YTFI and Sulfolobus respectively indicating oxygen was not limiting in these tests. Biooxidation of pyrite concentrate under optimum gas enrichment at various pulp density shows DSM 583 performing well exhibiting the highest oxidation rate for all pulp densities, followed by YTFt and Sulfolobus, except at 3% pulp density where the rates are similar for all cultures. At high pulp density, above 30%, the oxidation rate decreased rapidly for YTFt and Sulfolobus, with DSM 583 showing a moderate decrease. Monitoring of dissolved oxygen showed that oxygen demand increased with increasing pulp density and at one point the dissolved oxygen concentration for the test with YTFI at 40% and Sulfolobus at 30 and 40% solids concentration decreased below t.O mgll, suggesting oxygen and carbon dioxide limiting conditions. The decrease in leaching rate at high pulp densities above 30% under optimum gas enrichment was accompanied by low Fe dissolution and low redox potential which was attributed to shear stress due to attrition of cells by high solids concentration, toxicity of metal ions especially Ag, and Fe. and the formation of precipitate andjarosites hence impeding the leaching process. Oxygen and CO2 limiting conditions due to high pulp density and viscosity were only observed for YTFt and Sulfolobus cultures. The cyanide leaching of the pretreated pyrite concentrate shows that the extent of gold and silver recovery increased with the degree of pyrite oxidation and Au and Ag recoveries in excess of 80% were achieved compared with that of only 18.1% and 35.94'10 for gold and silver respectively, from the original. untreated concentrate by direct cyanidation.

Στην παρούσα διατριβή ειδίκευσης παρασκευάστηκαν πέντε νανοσύνθετα υλικά διοξειδίου του τιτανίου (στη μορφή του ανατάση) – αλλοϋσίτη σε αναλογίες 60:40, 70:30, 75:25, 80:20, 85:15 αντίστοιχα, για την περιγραφή και μελέτη των νέων βελτιωμένων χαρακτηριστικών τους και την εφαρμογή τους ως φωτοκαταλύτες στη διάσπαση αέριων ρύπων. Τα νανοσύνθετα παρήχθησαν με τη μέθοδο κολλοειδούς διαλύματος σε πήκτωμα (sol-gel) χρησιμοποιώντας αλκοξείδιο του τιτανίου (Ti(OC3H7)4) σαν διάλυμα διασποράς-επικάθισης. Οι ιδιότητες του φυσικού δείγματος αλλοϋσίτη (από τις Η.Π.Α.), καθώς επίσης και των τροποποιημένων δειγμάτων, χαρακτηρίστηκαν με τις τεχνικές περιθλασιμετρίας ακτινών Χ (XRD), υπέρυθρης φασματοσκοπίας μετασχηματισμού κατά Fourier (FTIR-ATR), ηλεκτρονικής μικροσκοπίας σάρωσης (SEM) και μέτρησης πορώδους και ειδικής επιφάνειας (BET). Επιτεύχθηκε η διασπορά των νανοσωματιδίων (3-10nm) του διοξειδίου του τιτανίου στην επιφάνεια του αλλοϋσίτη και τα αποτελέσματα της υπέρυθρης φασματοσκοπίας έδειξαν την δημιουργία δεσμών υδρογόνου μεταξύ τους. Τα τροποποιημένα δείγματα έδειξαν αύξηση της ειδικής τους επιφάνειας συγκριτικά με το φυσικό δείγμα και μεσοπορώδη δομή (5,7nm). Η μακροπορώδης δομή του αλλοϋσίτη (εσωτερικό κενό των επιμήκων κρυστάλλων) δεν ανιχνεύτηκε στα νανοσύνθετα διότι καλύφθηκε, εν μέρει, από τα νανοσωματίδια του TiO2 με αποτέλεσμα να προκύψει ένα υλικό με μικρότερο μέγεθος πόρων. Όλα τα νανοσύνθετα (και τα πέντε) έδειξαν ικανοποιητικά αποτελέσματα ως προς τη φωτοκαταλυτική τους ικανότητα στη διάσπαση αέριων ρύπων υπό την επίδραση φωτός του ορατού φάσματος αλλά και υπεριώδους ακτινοβολίας σε σύγκριση με τα αποτελέσματα που έδωσε το πρότυπο TiO2 P25. Όσον αφορά τα οξείδια του αζώτου, υπό την επίδραση της ορατής ακτινοβολίας, το νανοσύνθετο διοξειδίου του τιτανίου - αλλοϋσίτη σε αναλογία 70:30, συγκριτικά με το πρότυπο TiO2 P25, έδειξε 16,6 φορές καλύτερα αποτελέσματα ενώ υπό την υπεριώδη ακτινοβολία η φωτοκαταλυτική του ικανότητα ήταν μεγαλύτερη κατά 1,83 φορές. Στο τολουόλιο 4,8 φορές καλύτερα αποτελέσματα έδειξε το νανοσύνθετο με αναλογία 75:25. Η αυξημένη φωτοκαταλυτική δράση των νανοσύνθετων σε σχέση με τον πρότυπο φωτοκαταλύτη οφείλεται κυρίως στην καλή διασπορά των ννοκρυστάλλων ανατάση στις επιφάνειες του αλλοϋσίτη. / Five TiO2-halloysite nanocomposites (Ti-Hall 60:40, 70:30, 75:25, 80:20, 85:15) were prepared by depositing TiO2, in the form of anatase, on the halloysite surfaces using titanium isopropoxide under hydrothermal treatment at 180˚C. The nanocomposites were characterized by X-Ray diffraction (XRD), attenuated total reflection using Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and N2 specific surface area (SSA) analysis by BET method. Good dispersion of 3-10nm TiO2 particles on halloysite external surfaces was achieved in the TiO2- halloysite nanocomposites and ATR-FTIR results showed the formation of hydrogen bonding between TiO2 and the outer surfaces of halloysite tubes. After treating with TiO2, the nanocomposites largely showed interparticle mesopores of about 5.7nm. However, the macropores of halloysite (lumen or central hole in halloysite tubes) were not detected as a result of plugging of the lumens in halloysite tubes by TiO2 nanoparticles, at least partially. These nanocomposites were tested for their photocatalytic activities in decomposing NOX gas under visible-light irradiation and UV-visible light irradiation compared to that of the standard commercial titania photocatalyst, P25. Generally the nanocomposites showed significantly increased photocatalytic activities, while the most effective nanocomposite in decomposing NOX gas was the Ti-Hall 70:30 (16.6 and 1.83 times in visible light and UV respectively) and for tolouene the Ti-Hall 75:25 (4.8 times) compared to the commercial titania. The enhanced photocatalytic activities observed in the nanocomposites are a result of the good dispersion of the TiO2 nanocrystals on the surface of the halloysite.

Studies of the metallogeny of northwestern Mexico (Baja California to Chihuahua to Durango) at the mining district, geologic province, and regional scale, show that deposit formation and preservation is an intricate interrelationship between magmatism, tectonism, and hydrothermal activity. These are not only complicated by superimposed factors including erosion, enrichment, and cover, but in northern Mexico, tectonic translation as well. Using palinspastic reconstructions the relative positions of geologic units are restored to their pre-extensional configuration. Metallic "belts" are heterogeneous with numerous metal associations and deposit types superimposed in the same area. The reconstructions show that magmatism and mineralization were coeval and coincident. Superimposed environments and processes cover, erode, enrich, and preserve mineralization thus substantially affecting perceived metal distribution. Cover sequences including mid-Tertiary ignimbrites and late Tertiary clastic sediments preserve and commonly conceal mineralization. Mid-Tertiary and older extensional events preserve near surface deposit types (e.g, supergene blankets, Jurassic rift-related deposits). At the Sierra Madre Occidental (SMO) province scale, ore deposit types exhibit enormous variation from adularia sericite-dominated to advanced argillic to closely pluton related. The advanced argillic alteration with gold+/-copper+/-silver deposit types appears related to magmatic centers occurring in both the older (pre-Oligocene) and younger (Oligocene) volcanic sections and is a major focus of this dissertation. Acidic alteration-related deposits make up some of the largest Au occurrences including the Mulatos >2 million ounce gold district. Extensive kaolinitic alteration halos (>8 km²) zoned around a core of vuggy silica and quartz+/-pyrophyllite host enargite-pyrite ores. Sulfide isotopes are near zero δ³⁴S(pyrite) = -5 to -3%; δ³⁴S(enargite) = -6 to -4%) with corresponding barite (δ³⁴S = +18-22%). Phase equilibria and isotopes indicate early pyrophyllite-pyrite ores formed at ∼ 300°C with later barite-pyrite-dickite ores deposited at T = ∼ 260°C. Oxygen and hydrogen isotopes show possible mixing between magmatic and meteoric waters with a late (shallow) meteoric (heavier D, lighter δ¹⁸O) overprint. District tilting (∼ 25°NE) exposes >1.5 km altered section containing two separate centers. Alunite occurs late, rarely and is above pyrophyllite, suggesting a vertical transition in acid sulfate systems.

No description available.

No description available.

This thesis focuses on heavy mineral species found in a unique carbonate assemblage in the Mt. Mica pegmatite in order to determine the conditions of their formation and their mineral paragenesis as well as to gain insight on the origin of this very unusual carbonate-rich unit.

The Platreef occurs at the base of the Northern Limb of the Bushveld Complex and is variably mineralised with PGE, Cu, and Ni. The Platreef varies in thickness from a few meters to a few hundred meters and rests on progressively older sediments of the Transvaal Supergroup and Archaean granite basement northwards. Recent studies have highlighted the importance of magmatic processes, contamination of the magma by footwall rocks and syn- and post metasomatic fluid activity on the observed mineralisation. Along the Platreef strike, the PGE grade profiles are generally top-loaded from Overysel to Tweefontein North and more variable and bottom loaded from Tweefontein Hill southwards emphasizing the importance of the change in mineralisation style at Tweefontein in relation to the whole Platreef. This study presents the first significant PGM data on the Tweefontein farm, including ten boreholes along strike, providing insight into the distinctly different PGE mineralisation styles observed. Samples were selected based on assay data, varying rock types, stratigraphic position and proximity to geological features. The selected samples were investigated using petrography, geochemistry and the automated SEM techniques of QEMSCAN and MLA. Over 9000 PGM were analysed forming one of the most comprehensive PGM studies on the Platreef to date. The lowermost footwall intersected along the Tweefontein strike is banded ironstone of the Penge Formation. This is overlain by a metasedimentary footwall package, of variable thickness, derived from the shales and dolomites of the Duitschland Formation. Iron-rich, recrystallised, noritic sills occur at the base of the Platreef and are thought to represent sills which intruded prior to the emplacement of the Platreef. A pre- and possibly syn-Bushveld structural control resulted in irregular floor topography defined by a topographic footwall high in the central Tweefontein area and topographic depressions at Tweefontein North and Tweefontein Hill. The depression areas at Tweefontein are similar to the footwall basins at Turfspruit to the south, in which the Platreef is more lithologically complex compared to the footwall high areas. The footwall basins at Tweefontein and Turfspruit contain basal massive and submassive sulphides, which may not necessarily carry significant PGE grade. The Platreef lithologies at Tweefontein are composed of pyroxenites and norites with minor harzburgitic lithologies and contain numerous cross-cutting granitic veins. Xenoliths/interlayers of metamorphosed Duitschland lithologies occur primarily near the base of the Platreef, but also in the middle and upper Platreef sequence reflecting roof pendants. Unlike the Platreef on the farms adjacent to Tweefontein, the Platreef and footwall lithologies are relatively unaltered, but localised serpentinisation and chloritisation occur within harzburgitic lithologies and metasedimentary interlayers. Based on the stratigraphy and geochemical characteristics, the Platreef at Tweefontein can be subdivided into the upper and lower Platreef. The upper Platreef subdivision occurs in the top 20-40 m of the sequence and is defined by higher Mg#, Cr, Cr (ppm)/MgO and Pt/Pd values compared to the lower Platreef. In addition, the majority of the grade and base metal sulphide (BMS) content is enriched in the upper versus the lower Platreef, particularly for the northern and central parts of Tweefontein. The upper and lower Platreef may have been derived from different magma sources based on the “R Factor” concept proposed by Campbell and Naldrett in 1979 whereby the abundance of the PGE relative to the BMS content is linked to the proportion of magma with which the sulphide ore equilibrated (Naldrett, 2005b). Previous detailed geochemical studies from Tweefontein Hill southwards highlighted compositional breaks in the Platreef sequence thought to represent distinct sill-like intrusions (Hutchinson and Kinnaird, 2005; Kinnaird, 2005; Manyeruke et al., 2005; Nyama et al., 2006). They reported a more primitive sill at the top of the Platreef, which correlates to the upper Platreef at Tweefontein. The lower Platreef is therefore likely to represent a different sill intrusion. A relatively homogenous pyroxenitic package characterises the upper Platreef, although a more heterogeneous package is observed close to and at Tweefontein Hill. At Tweefontein North, the base of the upper Platreef is often marked by a chromitiferous package comprising a pegmatoidal feldspathic pyroxenite unit, up to 6 m thick, capped by a chromitite layer. Due to similar stratigraphy and high PGE grades, this distinct horizon has been compared to the Merensky Reef found elsewhere in the Bushveld Complex. The predominant base metal sulphides (BMS) in the Platreef at Tweefontein are pyrrhotite, pentlandite, chalcopyrite with minor pyrite aligned with that found elsewhere along the Platreef strike. There is an increase in BMS content, primarily pyrrhotite, towards the base of the Platreef with massive and submassive sulphide development near the base and in the footwall, particularly at Tweefontein Hill. Sulphur isotopes and detailed mineralogical studies at Turfspruit have shown that the addition of S, As and Sb into the magma from the Duitschland footwall triggered the development of a PGE-poor sulphide liquid which was then able to mix, modify and dilute the magmatic sulphides (Hutchinson and McDonald, 2008). Due to the similarity in footwall between Turfspruit and Tweefontein, these proposed processes help to explain the increase in BMS towards the base and the development of basal massive and submassive sulphides, which are not necessarily associated with significant PGE grade. At Tweefontein North, the processes dominating the top-loaded PGE mineralisation were primarily magmatic. The PGM assemblage, hosted by base metal sulphides and magmatic silicates, is dominated by Pt-and Pd-bismuthides and -tellurides with minor PGE-sulphides and Pt-arsenides. PGE-sulphides occur in the Platreef where the chromitiferous horizon is developed, which may indicate an environment low in volatile activity and one of the most primary mineralisation styles along the Platreef strike. The footwall high, which separates the depressions at Tweefontein North and Tweefontein Hill may have kept the Platreef at Tweefontein North relatively protected from additional processes affecting Tweefontein Hill. In contrast, assimilation of the Duitschland footwall is thought to play a key role in the development of the variable but predominantly bottom-loaded PGE mineralisation at Tweefontein Hill. The PGM assemblage is Pd-dominant characterised by Sb-, As- and Bi-bearing PGM, reflecting the incorporation of Sb, As and Bi from the Duitschland footwall. The association of the PGE mineralisation with the extensive basal sulphide development implies that the mineralisation at Tweefontein Hill probably occurred due to the gravitational settling of a sulphide liquid containing a mix of sedimentary and PGE-hosting magmatic components. Due to a significant PGM-BMS association in the mineralised footwall and metasedimentary interlayers/xenoliths, a downward migrating sulphide melt is believed to be the main mechanism responsible for the redistribution of PGE, predominantly Pd, into the mineralised metasedimentary lithologies. Finally, the Platreef and footwall lithologies may be locally modified by late-stage felsic and hydrothermal fluids to form bismuthide- and arsenide-dominant PGM assemblages, primarily hosted in quartz and serpentine respectively. This study shows the PGM and sulphide mineralisation at Tweefontein to be multifaceted, involving magmatic processes, assimilation of the Duitchland footwall into the Platreef magma and late-stage hydrothermal and felsic fluid activity. Footwall composition and irregular floor topography, resulting in depression areas at Tweefontein North and Tweefontein Hill, are believed to play a key role in what processes become significant along the Tweefontein strike. This research represents a significant contribution to the understanding of the distinctly different PGE mineralisation styles at Tweefontein and allows for a complete comparison of the Platreef PGE mineralisation from Overysel to Turfspruit.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 1994 / A quantitative description of galvanic interactions between sulphide minerals based on thermodynamic and kinetic parameters has been developed. The basis for quantitative description involves conducting a voltage balance over the galvanic couple. The contributions to the voltage balance include the galvanic couple cell emf, kinetic descriptions of the anodic and cathodic half reactions, the voltage characteristics 'of mineral-mineral contacts and solution voltage losses. The rates of the anodic and cathodic half' reactions were modelled by the Butler-Volmer equation and ti1ediffusion equation. A potentiostat was used to vary the voltages losses across mineral-mineral contacts. TIle galvanic couples were constructed. as rotating ring disc electrodes and hence electrolyte voltage losses were negligible. Three galvanic couples, copper-platinum, copper-pyrite and galena-pyrite, were electrochemically characterised under different conditions of ferric concentration, electrode rotation rate and temperature. The effect of illumination on the anodic dissolution of galena was investigated. The electrochemical model is in good agreement with experimentally measured galvanic currents. Galvanic interaction is a dynamic function and various models are developed which account for dynamic behaviour in galvanic cells. / MT2017

Não consta resumo na publicação. / Abstract not available.