The electronic spectra of sulfide minerals can be complex, and their features difficult to assign. Often, therefore, they are interpreted using electronic-structure models obtained from quantum-chemical calculations. The aim of this study is to provide such models for the minerals sphalerite, wurtzite, pyrite, marcasite, and chalcopyrite. All are important minerals within a mining context, either as a source for their component metals or as a gangue mineral. They are also semiconductors. Each is the structural archetype for a particular class of semiconductors, and so a knowledge of their electronic structures has wider applicability. / PhD Doctorate

The thesis is inspired by recent interests in oxide zinc ores caused by new developments in the technology of hydrometallurgy. The improved techniques turned the non-sulphide zinc ores in to attractive exploration targets due to a number of advantages such as low metal recovery costs and favorable environmental aspects such as the obvious absence of sulfur (Large, 2001). Historically extraction of zinc metal from oxide ores was not possible until recently. The metallurgical complexity resulted in a lack of interest and hence some economic oxide zinc ores might have been missed by conventional exploration techniques. The study presents a review of exploration status at Skorpion mine based on different exploration techniques and their application to sulphide and oxide zinc ore exploration. The challenge facing the mineral exploration industry today is the inability to detect mineral deposits under cover. Therefore a key to successful exploration program lies in the selection of the right exploration technique. Important parameters that should be highlighted in the exploration methodology are the geological situation of an area, equipment applicability and effectiveness, survey limitation, equipment mobilization and the safety aspects involved. The aim of this thesis is to provide a general guideline for sulphide and non-sulphide zinc ore exploration on the Skorpion area and other similar geological environments. Geochemical surveys appears to be more complimentary in exploration of non-sulphide zinc exploration. Although geochemical techniques are preferred, it is equally important to choose the right soil horizon. Furthermore, sample media may mean the difference between success and failure in geochemical exploration of non-sulphide zinc mineralization, due to high mobility of zinc in the surficial environment. On cost comparison, surface geochemical surveys programs are more cost effective except for litho-geochemical sampling which are commonly carried out through subsurface drilling. Geophysical techniques have limited application in exploration of non-sulphide zinc mineralization due to a lack of major physical properties (e.g., magnetic and electrical properties) in non-sulphides unlike their sulphide counterparts. However geophysical methods are commendable in delineating massive and disseminated sulphides mainly if they are associated with major Fe minerals (pyrrhotite or magnetite). In addition, geophysical techniques may be effective in mapping of subsurface primary and secondary structures such as basin faults which might have acted as pathways for metal-rich fluids. Terms non-sulphide and oxide zinc mineralization are used interchangeably throughout the thesis. Recommendations on regional and local target generation are presented in the thesis to give some basic guide lines on target generation strategies. The most important conclusion reached in this study is that, success in exploration for non-sulphide or sulphide zinc mineralization might be enhanced through the integrated exploration methodology.

Downhole sampling of unboiled liquid at 1350 and 1500 m depth in the seawater-dominated Reykjanes high-temperature geothermal system in Iceland shows that metal concentrations measured at surface are minimum values due to mineral precipitation in the wells; by analogy of similar tectonic setting, host rocks and fluid composition, the metal concentrations measured in many black smoker vents at the seafloor are also minima. Fluids in the Reykjanes geothermal system react with mid-ocean ridge basalt at temperatures as high as 346°C and contain Fe 9-140 ppm, Cu 14-17 ppm, Zn 5-27 ppm, Pb 120-290 ppb, 1-6 ppb Au, and 28-107 ppb Ag. Fluids discharged at surface from the same wells have orders of magnitude lower metal concentrations due to precipitation caused by boiling and vapor loss during depressurization. Upstream of the orifice plate at high pressure (40 bar, 252°C) the precipitates consist mainly of sphalerite and chalcopyrite with a trace of galena and bornite. At the orifice plate of old wells, the pressure decreased sharply to 11 bar (188°C), resulting in abundant deposition of amorphous silica together with minor sphalerite and traces of chalcopyrite. In new wells the pressure at the orifice plate decreases to 22 bar (220°C); this pressure decrease and concomitant boiling causes deposition of fine-grained bornite-digenite solid solution together with sphalerite and galena on the fluid flow control valve. In high-pressure wells (average wellhead pressure 45-35 bar) most metals (mainly as sphalerite) are deposited downstream of the orifice plate, with up to 950 ppm Au and 2.5 wt.% Ag. Bulk concentrations in the scales vary between 15-60 wt.% upstream and downstream of the orifice plate and diminish from there. Iron increases up well from 8 to ~20 wt.% and decreases downstream of the orifice plate from 6 to 2 wt.% at the separation station; Cu downhole is ~3 wt.% but increases to 25 wt.% on the fluid flow control valve and then decreases; Pb downhole 100s ppm but at the wellhead is ~3 wt.%, increasing to 15 wt.% at the fluid flow control valve, then decreasing sharply from there.

The Ducktown mining district, located in the southeastern corner of Tennessee within the Blue Ridge Province of the southern Appalachians, contains some of the largest metamorphosed pyrrhotite-pyrite-rich massive sultide deposits in the Appalachian-Caledonian orogen. Oxygen isotope temperatures of 530±20°C are consistent with previous estimates based on mineral thermobarometers (540±40°C; 6-7 kb) suggesting that minerals attained oxygen isotopic equilibrium during peak metamorphism and underwent little retrograde exchange. Fluid inclusion and petrologic data do not support the previous interpretation that low δ¹⁸O zones near orebodies are synmetamorphic, rather, a premetamorphic origin is indicated. Integrated fluid/rock ratios were low enough during and after metamorphism that premetamorphic spatial variations in δ¹⁸O were retained. However, hydrogen and carbon isotopes were homogenized throughout the area during or before metamorphism. The low δ¹⁸O zones surrounding the orebodies appear to have formed during sea—fIoor hydrothermal activity associated with ore deposition. The δ¹⁸O value of the fluid responsible for ore deposition, assuming a temperature of 300°C, is calculated to be -1 to +2 per mil, consistent with the interpretation that the ore fluid was modified seawater. Calculation of theoretical C-O-H-S fluid speciation suggests that the fluid in equilibrium with clinopyroxene-bearing rocks was essentially H₂O+CO₂with XCO₂ = 0.10. However, primary fluid inclusions located in clinopyroxene contain signifticant quantities of CH₄. This discrepancy is explained by hydrogen diffusion into primary fluid inclusions and subsequent conversion of CO₂ to CH₄ during uplift in response to an fH₂ gradient between inclusion and matrix fluids. Low δD values of primary fluid inclusions are consistent with diffusive addition of isotopically light hydrogen after trapping. Secondary inclusions in metamorphic quartz record a complex uplift history involving a variety of fluids in the C-O-H-N-salt system. lsochores calculated for these inclusions constrain the uplift path to have been initially concave toward the temperature axis. Over the pressure range 2.3 to 1.0 kb the uplift path became nearly isothermal at 215±20°C. lmmiscible H₂O-CH₄-N₂-NaCl fluids present during the isothermal stage of the uplift history were derived during Alleghanian thrusting by expulsion of pore fluids and maturation of organic matter in lower plate sedimentary rocks proposed to underlie the deposits. Average uplift rates of 0.1 mm/yr are suggested by the uplift path and available geochronologic data. / Ph. D.

The Central Asia Orogenic Belt is one of the largest accretionary orogenic belts in the world. In this belt, many sulfide‐bearing mafic‐ultramafic intrusions occur along faults, including the Kalatongke complex in southeast Chinese Altay and the Huangshandong intrusion in east Tianshan. The Kalatongke complex is a composite body including ~308Ma dioritic intrusion and 287Ma sulfide‐bearing mafic intrusion. The dioritic intrusion consists of biotite‐hornblende gabbro, diorite and quartz diorite. This intrusion was formed from a mixture of an evolved mantle‐derived magma and a crust‐derived adakitic magma combined with fractional crystallization of clinopyroxene, amphibole and plagioclase. The mafic intrusion is dominantly made up of norite in which sulfide ores, including disseminated, massive Ni‐Cu and massive Cu‐rich ores, are hosted. This intrusion was formed from two different pulses of basaltic magmas that had different magma evolution histories. The early magma pulse reached sulfide‐saturation due to minor crustal contamination and a small amount of sulfide (<0.03%) was removed before the emplacement. The evolved magmas then entered a shallow magma chamber and assimilated crustal materials to attain sulfide‐saturation again. Sulfide liquids segregated from the magma to form massive Ni‐Cu and massive Cu‐rich ores through further fractionation and residual silicate melts formed norites. A second pulse of magma underwent removal of <0.02% sulfides with stronger crustal contamination, and re‐attained S‐saturation during the emplacement and became a phenocryst‐laden magma. This magma then intruded the earlier formed massive sulfide ores and norites, forming the disseminated sulfide ores. The Permian Huangshandong mafic‐ultramafic intrusion hosts the largest magmatic sulfide deposit in east Tianshan. It consists of a layered unit of lherzolite, gabbro and diorite and a massive unit of olivine gabbronorite and gabbronorite. Both units formed from siliceous high magnesium basaltic (SHMB) magmas derived from a hydrous, depleted mantle source. The two units of the Huangshandong intrusion formed from magmas that have undergone different processes through the evolution of the magma plumbing system. The early magma pulse gained sulfur‐saturation before the emplacement and small amounts of sulfide (<0.03%) were removed to result in a PGE‐depleted, high‐Mg magma. This magma achieved sulfide‐saturation again in a staging magma chamber through crustal contamination and fractional crystallization of olivine and Cr‐spinel (an AFC process) to form the layered unit. A second magma pulse underwent fractionation of more olivine +/‐ Cr‐spinel but less sulfide (<0.003%) removal before the emplacement and became evolved, PEG‐undepleted and low‐Mg before the injection into the magma chamber. Mixing of the two magmas triggered sulfide‐saturation to form sulfide ores with variable PGE, Ni and Cu compositions. The study suggests that SHMB‐like magmatism, produced by melting of depleted and hydrous mantle source, may be an important feature of orogenic belts. Mafic‐ultramafic intrusions formed from SHMB‐like magmas may host economic sulfide deposits, particularly sulfide Ni‐Cu sulfide deposits. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Pt mineralization within the Bushveld Complex is strikingly focused on the chromitite reefs, despite these horizons being associated with low volumes of base metal sulphide relative to Pt grade. Partitioning of Pt (Dsil/sulp) from silicate magma into immiscible sulphide liquid appears unable to explain Pt concentrations in chromitite horizons, due to the mismatch that exists between very large R factor required and the relevant silicate rock volume. Consequently, in this experimental study we attempt to gain better insight into possible Pt grade enhancement processes that may occur with the Bushveld Complex (BC) sulphide magma. We investigate the wetting properties of sulphide melt relevant to chromite and silicate minerals, as this is a key parameter controlling sulphide liquid percolation through the cumulate pile. Additionally, we have investigated how fractionation of the sulphide liquid from mono-sulphide-solid-solution (Mss) crystals formed within the overlying melanorite might affect sulphide composition and Pt grades within the evolved sulphide melt. Two sets of experiments were conducted: Firstly, at 1 atm to investigate the phase relations between 900OC and 1150OC, within Pt-bearing sulphide magma relevant to the BC; Secondly, at 4 kbar, between 900OC to 1050OC, which investigated the downwards percolation of sulphide magma through several layers of silicate (melanorite) and chromitite. In addition, 1atm experiments were conducted within a chromite dominated chromite-sulphide mixture to test if interaction with chromite affects the sulphide system by ether adding or removing Fe2+. Primary observations are as follows: We found sulphide liquid to be extremely mobile, the median dihedral angles between sulphide melt and the minerals of chromitite and silicate layers are 11O and 33O respectively. This is far below the percolation threshold of 60O for natural geological systems. In silicate layers sulphide liquid forms vertical melt networks promoting percolation. In contrast, the extremely effective wetting of sulphide liquid in chromitites restricts sulphide percolation. Inter-granular capillary forces increase melt retention, thus chromitites serve as a reservoir for sulphide melt. Sulphide liquid preferentially leaches Fe2+ from chromite, increasing the Fe concentration of the sulphide liquid. The reacted chromite rims are enriched in spinel end-member. This addition of Fe2+ to the sulphide magma prompts crystallization Fe-rich Mss, decreasing the S-content of sulphide melt. This lowers Pt solubility and leads to the formation of Pt alloys within the chromitite layer. Eventually, Cu-rich sulphide melt escapes through the bottom of the chromitite layer. These observations appear directly applicable to the mineralized chromitite reefs of the Bushveld complex. We propose that sulphide magma, potentially injected from the mantle with new silicate magma injections, percolated through the silicate cumulate overlying the chromitite and crystallized a significant volume of Fe-Mss. Chromitite layers functioned as traps for percolating, evolved, Cu-, Ni- and Pt-rich sulphide liquids. This is supported by the common phenomenon that chromitites contain higher percentages of Ni, Cu and Pt relative to hanging wall silicate layers. When in contact with chromite, sulphide melt is forced to crystallize Mss as it leaches Fe2+ from the chromite, thereby further lowering the S-content of the melt. This results in precipitation, as Pt alloys, of a large proportion of the Pt dissolved in the sulphide melt. In combination, these processes explain why chromitite reefs in the Bushveld Complex have Pt/S ratios are up to an order of magnitude higher that adjacent melanorite layers. / AFRIKAANSE OPSOMMING: Pt mineralisasie in die Bosveld Kompleks is kenmerkend gefokus op die chromatiet riwwe, alhoewel die riwwe geassosieer is met lae volumes basismetaal sulfiedes relatief tot Pt graad. Verdeling van Pt (Dsil/sulp) vanaf silikaat magma in onmengbare sulfiedvloeistof is klaarblyklik onvoldoende om Pt konsentrasies in chromatiet lae te verduidelik, a.g.v. die wanverhouding wat bestaan tussen ‘n baie groot R-faktor wat benodig word en die relatiewe silikaat rots volumes. Gevolglik, in die eksperimentele studie probeer ons beter insig kry oor moontlike Pt graad verhogingsprosesse wat plaasvind in die BK sulfied magma. Ons ondersoek die benattingseienskappe van sulfied vloeistof relevant tot chromiet- en silikaat minerale, omdat dit die sleutel maatstaf is vir die beheer van sulfied vloeistof deursypeling deur die kumulaat opeenhoping. Addisioneel het ons ook ondersoek hoe die fraksionering van sulfied vloeistof vanaf MSS kristalle, gevorm binne die hangende melanoriet muur, moontlik die sulfied samestelling en Pt graad binne ontwikkelde sulfied smelt kan beïnvloed. Twee stelle van eksperimente is gedoen: Eerstens, by 1 atm om ondersoek in te stel oor fase verwantskappe tussen 900OC en 1150OC, binne ‘n Pt-verrykte sulfied magma samestelling relevant tot die BK; Tweedens, by 4 kbar, tussen 900OC tot 1050OC, wat die afwaartse deursypeling van sulfied magma deur veelvuldige lae van silikaat minerale en chromatiet. Addisionele 1 atm eksperimente is gedoen binne ‘n chromiet gedomineerde chromiet-sulfied mengsel, om te toets of interaksie met chromiet die sulfied sisteem affekteer deur Fe2+ te verwyder of by te dra. Primêre observasies is soos volg: Ons het bevind sulfiedsmelt is uiters mobiel, die mediaan dihedrale hoek tussen sulfiedsmelt en minerale van chromiet en silikaat lae is 11O en 33O onderskydelik. Dit is ver onder die deursypelings drumpel van 60O vir natuurlike geologiese stelsels. In silikaatlae vorm die sulfiedsmelt vertikale netwerke wat deursypeling bevorder. Inteendeel, uiters effektiewe benatting van sulfiedsmelt binne chromatiete vertraag sulfied deusypeling. Tussen kristal kapilêre kragte verhoog smelt retensie, dus dien chromatiete as ‘n opgaarmedium vir sulfiedsmelt. S oorversadigte sulfied vloeistof loogsif Fe2+ vanuit chromiet en veroorsaak ‘n verhoging in Fe-konsentraie. Die gereageerde chromiet buiterante is daarvolgens verryk in Cr-spinêl eind-ledemaat. Die addisionele byvoeging van Fe2+ aan sulfied magma veroorsaak die kristalisasie van Fe-ryke Mss en verlaag dus die S-konsentrasie van die sulfied smelt. Dit verlaag Pt oplosbaarheid en lei tot die formasie van Py allooie binne-in chromatiete. Ten einde, ontsnap Cu-ryke sulfied smelt deur die onderkant van die chromatiet lae. Die observasies is direk van toepassing op die gemineraliseerde chromatiet riwwe van die Bosveld Kompleks. Ons stel voor dat sulfied magma, potensiaal ingespuit vanuit die mantel saam nuwe inspuitings van silikaat magma, deur die hangende silikaat kumulaat bo chromatiet lae deurgesypel het en ‘n betekenisvolle volume Fe-Mss gekristalliseer het. Chromatiet lae het gefunksioneer as lokvalle vir afwaartsbewegende, ontwikkelde, Cu-, Ni-, en Pt-ryke sulfied vloeistowwe. Dit word ondersteun deur die algemene verskynsel dat chromatiete hoër persentasies van Ni, Cu en Pt relatief teenoor die hangende muur silikaat lae het. Wanneer sulfied smelt in kontak is met chromiet, word dit geforseer om Mss te kristalliseer soos Fe2+ geloogsif word, waarvolgens die smelt se S konsentrasie verder verlaag word. Dit veroorsaak die presipitasie, as Pt allooie, van groot proporsies opgeloste Pt vanuit sulfied smelt. Deur die prosesse te kombineer, kan dit moontlik verduidelik word hoekom chromatiet riwwe in die Bosveld Kompleks Pt/S verhoudings veel hoër is as aanrakende melanoriet lae.

No description available.

No description available.

The main magnetite seam of the Upper Zone of the Rustenburg Layered Suite (SACS, 1980) on the Bushveld Complex is known to host the world‘s largest vanadium bearing titaniferous iron ores. The vanadiferous titanomagnetites, contain vanadium in sufficient concentrations (1.2 - 2.2 per cent V₂O₅) to be considered as resources and vanadium has been mined historically by a number of companies among them Anglo-American, Highveld Steel and Vanadium and VanMag Resources as well as currently by Evraz Highveld Steel and Vanadium Limited of South Africa. The titanomagnetites contain iron ore in the form of magnetite and titanium with concentrations averaging 50-75 per cent FeO and 12-21 per cent TiO₂. The titaniferous iron ores have been historically dismissed as a source of iron and titanium, due to the known difficulties of using iron ore with high titania content in blast furnaces. The economic potential for the extractability of the titaniferous magnetites lies in the capacity of the ores to be separated into iron rich and titanium rich concentrates usually through, crushing, grinding and magnetic separation. The separatability of iron oxides and titanium oxides, is dependent on the nature in which the titanium oxide occurs, with granular ilmenite being the most favourable since it can be separated from magnetite via magnetic separation. Titanium that occurs as finely exsolved lamellae or as iron-titanium oxides with low titania content such as ulvospinel render the potential recoverability of titanium poor. The Upper Zone vanadiferous titanomagnetites contain titanium in various forms varying from discrete granular ilmenite to finely exsolved lamellae as well as occurring as part of the minerals ulvospinel (Fe₂TiO₄) and titanomagnetite (a solid solution series between ulvospinel and magnetite) . Discrete ilmenite constitutes between 3-5 per cent by volume of the massive titanomagnetite ores, and between 5-10 per cent by volume of the magnetite-plagioclase cumulates with more than 50 per cent opaque oxide minerals. The purpose of this research was to investigate the mineralogical setting and distribution of the iron and titanium oxides within the magnetitite layers from top to bottom as well as spatially along a strike length of 2 000m to determine the potential for the titanium to be extracted from the titanomagnetite ores. The titanomagnetites of the Upper Zone of the Bushveld Complex with particular reference to the Northern Limb where this research was conducted contains titanium oxides as discrete ilmenite grains but in low concentrations whose potential for separate economic extraction will be challenging. The highest concentration of titanium in the magnetite ores is not contained in the granular ilmenite, but rather in ulvospinel and titanomagnetite as illustrated by the marked higher concentration of TiO₂ in the massive ores which contain less granular ilmenite in comparison to the disseminated ores which contain 3 to 8 percentage points higher granular ilmenite than the massive ores. On the scale of the main magnetite seam, the TiO₂ content increases with increasing stratigraphic height from being completely absent in the footwall anorthosite. The V₂2O₅ content also increases with stratigraphic height except for in one of the 3 boreholes where it drops with increasing height. The decrease or increase patterns are repeated in every seam. The titanomagnetites of the main magnetite seam display a variety of textures from coarse granular magnetite and ilmenite, to trellis ilmenite lamellae, intergranular ilmenite and magnesian spinels and fine exsolution lamellae of ulvospinel and ferro-magnesian spinels parallel to the magnetite cleavage. The bottom contact of the main magnetite seam is very sharp and there is no titanium or vanadium in the footwall barely 10cm below the contact. Chromium is present in the bottom of the 4 layers that constitute the main magnetite seam and it upwards decreases rapidly. In boreholes P21 and P55, there are slight reversals in the TiO₂ and V₂O₅ content towards the top of the magnetite seams.

Kansanshi mine sulphide ore circuit did not achieve target flotation recovery in 2016, hence it was deemed necessary to carry out a research aimed at optimizing this circuit. The objective of the research was to optimise the Kansanshi milling and flotation circuit processing a copper sulphide ore. In line with this, samples were obtained around the circuit and processed in the laboratory for moisture content, slurry concentration, particle size distribution, and flotation response. This information was then used to build a computer-based model of the Kansanshi milling and flotation circuit. This was done in MODSIM®, a software package specialising in the design and simulation of mineral processing operations. After careful appraisal, appropriate models were selected for the semi autogenous grinding (SAG) and ball mills, SAG mill discharge screen, hydrocyclones, pebble crusher, and the flotation cells. The calibrated model was then used to simulate the effects of key operating parameters on flotation recovery. Analysis using the attainable region technique revealed that the SAG mill feed-rate should be adjusted from 1719 tph to 2090 tph. This would lead to a better utilisation of the pebble crusher that can process 358 tph of pebbles from the current 198 tph. From the simulation work, it was established that rougher flotation recovery can be improved from the current 80.0 % to 82.3 %. The technoeconomic benefits of the proposition are yet to be investigated. Findings from the research concluded that the milling circuit optimum operating parameter; which generated a final product falling predominantly in the range - 150 +38 μm were SAG and ball mills conditions of ball sizes 200 and 40mm respectively, ball mill ball filling 32% and rotational speed between 75 and 80% for both SAG and ball mills. The optimum hydrocyclone feed slurry concentration was found to be 62% solids. Additionally, the SAG mill discharge screen aperture size of 6 mm was the optimum. It must be noted that slurry concentration did not show any impact on both the SAG and ball mills performance. The SAG mill ball filling did not show any significant improvement on performance. / College of Engineering, Science and Technology / M. Tech. (Chemical Engineering)