No description available.

A 20 litre experimental batch and continuous test rig and 5 litre batch and 50 litre continuous test rigs for stirred ball milling were built at the University of Natal and Mintek respectively. All the mills featured a grinding vessel with a central shaft equipped with pins and a torque measurement system. A washed chrome sand from the Bushveld Igneous Complex was used for the grinding experiments. Particle size analysis of products was performed using standard sieves and a Malvern Particle Sizer. Batch tests were run in the 20 litre stirred ball mill to achieve efficient grinding conditions. The effects of grinding conditions such as pulp density, media size, media density and shaft rotation speed and mill design parameters such as ball load, pin spacing and pin diameter on product size, power consumption and media wear were studied. It has been shown that the median size of the product can be calculated by the Charles' Energy-Size Equation. The stirred ball mill has been found to be more energy efficient than the tumbling ball mill. An energy reduction of 50% was possible for a product size of 6 microns when the stirred ball mill was employed instead of the tumbling ball mill. The energy input per ton of grinding media in the stirred ball mill could be 10 times higher than for the tumbling ball mill. Although during coarse grinds the media wear was higher in the stirred ball mill than in the tumbling mill, it became less so as grinding proceeded and for a product median size of 4.8 microns it was the same. Using a 5 litre batch mill, an experimental programme was designed to study the comminution characteristics of the stirred mill. A factorial design was prepared with the following parameters, which influence grinding in the stirred ball mill: pulp density, pin tip velocity and ball density and size. The energy required for grinding the chromite sand in the stirred ball mill was determined by the use of Charles' Equation. The findings were in agreement with the results predicted by this equation. It was shown that the Rosin-Rammler size distribution equation was a suitable procedure for presenting and comparing grinding data obtained from the stirred ball mill. The factors that had the greatest effect on grindability were, in order of importance: ball size, pin tip velocity and ball density. Interactions between grinding parameters were negligible. results implied that accurate predictions can be made to determine the grinding conditions required to achieve a desired product specification. An attempt was made to study the grinding kinetics the chromite are using the mass population·balance model. Grinding tests were performed with two mono size fractions ·53+38 and -38+25 microns and natural feed ·100 microns using various pin tip velocities, ball densities and within the normal stirred ball milling operating range. relationship between the ball diameter and the particle was explained by the "angle of nip" theory which applied for roller crushers. It was shown that the particle giving the maximum breakage rate was directly proportional to the ball diameter. Estimated grinding kinetic parameters from monosize provided a good basis for predictions of natural feed. However, the breakage rate obtained from monosize tests appeared to be lower than those from the natural feed It was found that if the selection and breakage functions were determined by monosize tests, it was possible to modify selection function parameters by back-calculation which gave the best fit to the natural feed size. A good correlation was obtained between the experimental and product distributions using a population-balance model. The links between the empirical model combining Charles' and Rosin-Rammler equations and the first-order batch grinding equation were also shown. The stirred ball mills were operated in batch and continuous mode. The median size of the products from the batch stirred ball mill experiments closely matched those of the continuous grinding experiments under similar grinding conditions. Using a salt solution as a tracer material, an attempt was made to estimate the residence time distribution based on a simplified analysis of the motion of the water in tile mill. The current scale-up methods for the stirred ball mill are discussed. A torque model was developed for given shaft geometry and ball relating the power rements of the stirred ball mill to the following prime design and operating parameters : mill diameter, mill height, pin tip velocity and effective density of the mill load. The basic assumptions underlying the model were that the mill content behaved as a fluidised bed, consequently a P effg h type model for the pressure was applied throughout the grinding media bed the effective charge velocity was proportional to the pin tip velocity. It was found that pin spacing, pin diameter and ball diameter significantly affected the mill torque. A semi-empirical torque model was derived to include these parameters. The relationships formulated from these models were shown to be in excellent agreement with experimental results. / Thesis (Ph.D.)-University of Natal, Durban, 1993.

Production of platinum and associated metals is a major source of revenue for South Africa. Significant losses occur in the concentrating stage (10 to 15 per cent) and this research is focused on optimising platinum flotation. Research begins by conducting laboratory batch flotation tests. However, subsequent pilot-plant tests often produce different results. It is believed these differences arise from the artificial nature of laboratory techniques. This project was focused on improving flotation techniques in the laboratory. The largest source of platinum in South Africa is the UG2 reef and two samples of this ore were used for testing: ‘good’ and ‘bad’ ore. These had different characteristics with regards to the recovery of PGMs and the presence of talc. The latter is an unwanted floatable mineral, which must be depressed to prevent excessive recovery. The conventional laboratory test procedure makes use of batch tests in various sizes of flotation cells. The procedure was made more realistic, by using four stages of flotation, rather than just two, to mimic a typical platinum flotation plant. The use of four stages made it possible to separate the fast-floating and slow-floating stages and to control froth conditions accordingly. Attention was also given to the fact that in laboratory tests, water is often added to the ‘cleaner’ stage of flotation, to make up the level. Experiments showed that this dilution, which does not take place in practice, had a significant impact on overall efficiency. A method of measuring frother concentration was developed and used to determine the realistic level of frother in cleaning tests. Tests at these levels of frother concentration showed that significant improvements could be made to plant performance, by making use of a thickener to reduce the frother concentration in the cleaning stages. The improved test procedure was used on both good and bad ores, and the effect of regrinding was also tested. A combined solids recovery of 2 % over both cleaners was targeted for all test work. At this recovery, the regrinding of the bad ore increased the PGM recovery from 67 to 76 per cent at the cost of an additional 8 g/t depressant. An investigation of the effect of frother concentration in the cleaning stage, using good ore, demonstrated that that rejection of chromite could be improved significantly by reducing frother concentration. The tests mimicked the use of a thickener to separate some of the water with a high concentration of frother. Tests conducted on the good ore showed that use of two thickeners, as opposed to none, reduced the Cr2O3 content of the final concentrate from 4.2 to 3.2 per cent for the equivalent concentrate mass and PGM recovery. The depressant requirement was also reduced from 67 to 55 g/t. These tests provided insight on how to improve performance on a platinum flotation plant, particularly when floating the bad ore.

Die 1990 stillgelegte Grube kann auf eine 750-jährige Bergbaugeschichte zurückblicken. Im vorliegenden Band werden vor allem die Ergebnisse der umfangreichen Such- und Erkundungsarbeiten der letzten Betriebsperiode zusammenfassend dargelegt. Die Rahmengesteine bilden amphibol- bis grünschieferfaziell geprägte Metamorphite proterozoischer und kambrischer Ausgangsgesteine. Die metamorphe Schichtenfolge wird unterlagert vom mittelerzgebirgischen Teilpluton, in dem vier Granittypen unterschieden werden, die petrographisch und geochemisch eine Entwicklungsreihe bilden. Die Lagerstättentektonik wird von einer diagonalen Scherflächentektonik bestimmt. Zwischen Deformation, Magmatismus, Metasomatose und Mineralisation bestehen enge genetische Beziehungen. Zeitlich lassen sich die Zinnmineralisationen nach Altersdatierungen zwischen 288 und 302 Millionen Jahren einordnen. Unter den zinnerzführenden Strukturen erlangen Ausfüllungsstrukturen (Trümerzüge, Gangzüge) die größte Bedeutung. Bei den metasomatischen Strukturen lassen sich gangförmige (Greisengänge im Exokontakt, gangartige Greisenzonen im Endokontakt), stockwerkartige (unregelmäßige Greisenkörper im Endokontakt) und lagerförmige Strukturen (Skarne) unterscheiden. Intensive pedo- und lithogeochemische Untersuchungen führten zur Berechnung von Zonalitätsreihen und zur Ableitung von Zonalitätskoeffizienten in mehreren Teillagerstätten. Die Verteilung bestimmter Spurenelemente im Kassiterit wird, abhängig vom Chemismus der zinnführenden Lösungen, vor allem durch die räumliche Position zum Granit und durch die Lithologie des Nebengesteins bestimmt. Innerhalb des gesamten variszischen Mineralisationszyklus zeigen Temperatur und Salinität der Lösungen eine relativ gleichförmige Entwicklung von höheren zu niedrigeren Werten an. Das geomechanische Verhalten des Gebirges und mögliche Auswirkungen auf die Tagesoberfläche werden entscheidend beeinflusst von den gewählten Abbauverfahren, der Lage der Abbaue in Bezug zur Erdoberfläche und der lokalen geologischen Situation. Die älteste Abbaumethode im Festgestein ist der Strossenbau. Der Firstenstoßbau kam nur in unbedeutendem Umfang zur Anwendung. In der letzten Bergbauperiode wurde der Firstenstoßbau mit Magazinierung eingeführt. Greisenkörper wurden im Teilsohlenkammerbau, die bis 40 m mächtigen Trümerzüge des Nordwestfeldes im Teilsohlenbruchbau gewonnen. Die Bemusterung der Auffahrungen geschah durch Schlitzproben, der bergmännisch nicht aufgeschlossenen Lagerstättenbereiche durch Bohrkern- oder Bohrschlammproben. Tiefbohrungen wurden mittels Sammelsplitter- und Kernproben bemustert. Mit Einstellung des Bergbaus ist im Lagerstättendistrikt Ehrenfriedersdorf bei Trümer- und Greisenerz ein Vorratsstand von 17,1 kt zu verzeichnen. Die Hauptaltlast des Erzbergbaus stellt Arsen dar. Besondere Bedeutung erlangen anthropogen bedingte As-Anomalien (Hüttenwerke, Pochwerke, Aufbereitungsrückstände).

The South Manasan ultramafic intrusion (ca. 1880 Ma) located in the Early Proterozoic Thompson Nickel Belt (TNB) contains Ni and platinum group element (PGE) mineralization hosted by disseminated sulfide. Whole-rock Ni values range from 0.3 to 1.7 wt. % and total precious metals (TPMs) range from 0 to 1.3 ppm Pt + Pd + Au and equate to tenor values (i.e., metal in 100% sulfide) of 11-39 wt. % Ni and 8-27 ppm TPMs. The South Manasan intrusion is a steeply dipping sill-like body with a boudinaged outline having a strike length of approximately 1200 m, average width of 125 m and a minimum depth extent of 1000 m. The intrusion is composed of approximately 25% fresh dunite, 50% serpentine altered dunite and 25% tectonized and carbonate altered dunite. The most intense alteration is found near the intrusion’s margin where it is in contact with metasedimentary rocks of the Pipe Formation, part of the surrounding Ospwagan Group. In fresh dunite the sulfide assemblage characterized by an intercumulate texture is dominated by pentlandite with accessory pyrite; the latter having a symplectic-like texture. The pentlandite-pyrite assemblage in the serpentinized dunite, although still characterized overall by an intercumlate-texture, has well developed platy intergrowths with chlorite and serpentine. In the most intensely modified unit (the carbonate altered dunite) the sulfide assemblage consists primarily of pyrrhotite and pentlandite. Whole-rock geochemical data (n=360), modal mineralogy and mineral chemistry obtained on representative drill core throughout the South Manasan intrusion have been used to establish a type section in order to evaluate the relative roles of primary magmatic versus secondary (i.e., serpentinization, carbonate alteration and deformation) processes. These data indicate that the primary silicate-sulfide assemblage was systematically modified during : serpentinization, carbonate alteration and deformation of the South Manasan intrusion such that a sequence of primary versus secondary events can be established. Intrusion of the original komatiitic magma and formation of the South Manasan intrusion took place at a shallow level into consolidated Ospwagan Group sediments with subsequent contamination of this melt with crustal S. This triggered sulfide saturation and generation of an immiscible sulfide melt. Calculated Ni and TPM tenor values constrain the R factor to between 500 and 2500. The early crystallization of olivine inhibited the sulfide melt from settling to the bottom of the magma column and as a consequence, the sulfides now have a primary interstitial magmatic texture. The current sulfide association dominated by pentlandite>>pyrite>chalcopyrite has a mineral paragenesis that is consistent with subsolidus re-equilibration of a primary pentlanditepyrrhotite- chalcopyrite assemblage. The subsequent processes of serpentinization, deformation and carbonate alteration resulted in modifying the primary sulfide assemblages and their textures (i.e., to platy habits), but did not greatly alter the bulk composition, in particular metal contents, except for addition of volatiles (H2O, CO2). It is concluded therefore that the enrichment of the sulfide assemblage at South Manasan in Ni and PGEs is a consequence of a primary magmatic process involving high R factor and that the effects of later overprinting processes (alteration, deformation) are not responsible for the presently observed high-tenor sulfide association.

The polymetallic Hornkullen deposit is situated in the western part of the Bergslagen ore province, Sweden. It is hosted by an inlier of approximately 1.90-1.88 Ga Svecofennian volcanic and sedimentary metasupracrustal rocks enclosed in a significantly younger, c. 1.8 Ga TIB granitoid (Filipstad granite). Although being mined intermittently for silver during the last 100s of years in addition to been the subject for more recent exploration work, the genesis of this deposit and others in a similar geological position is poorly understood. The hypothesis is that the Hornkullen deposit represents a metamorphically overprinted, syn-volcanic Svecofennian mineralisation. The main ore assemblage comprises magnetite, pyrrhotite, galena, chalcopyrite and arsenopyrite with subordinate pyrite, sphalerite, ilmenite and löllingite. Pb-Fe-Ag-Sb sulphosalts include boulangerite, meneghinite, jamesonite, freibergite-tetrahedrite, pyrargyrite, and stephanite, which mainly occur in trace amounts. Gudmundite and molybdenite are rare accessories. Generally, galena, chalcopyrite and pyrrhotite have accommodated strain in a ductile manner. Locally, this can also be seen in boulangerite, meneghinite and sphalerite. Magnetite, arsenopyrite and pyrite frequently have been deformed in a brittle way. The contrast in competence resulted in the remobilisation of the more ductile minerals into fractures in the more competent minerals. In massive parts, this contrast also resulted in more fragmented clasts of competent minerals within a less competent matrix, similar to “ball ore” texture. Recrystallisation is particularly evident in magnetite and pyrrhotite but also seen in coarser aggregates of ilmenite. Additionally, these minerals and also pyrite and arsenopyrite frequently exhibit euhedral morphology when occurring within less ductile minerals. Inclusions of ore minerals in porphyroblastic garnet are abundant. Geothermobarometry of arsenopyrite and sphalerite suggests temperatures and pressures of 525°C (between 440°C and c. 590°C) and c. 300-400 MPa, consistent with regional Svecokarelian amphibolite facies metamorphism, albeit with some caveats. Fluid inclusion entrapment conditions were determined to c. 440°C (between 400°C and 600°C) and c. 280 MPa. The observed textures are a result of deformation and remobilisation of diverse ore minerals during the Svecokarelian orogeny. Remobilisation was possibly initiated during prograde metamorphism, followed by additional and more extensive modification during retrograde conditions, at least to temperatures below 200°C. Sulphosalt formation is considered to reflect an evolution from prograde through retrograde metamorphism, although most of them formed during the retrograde stage, including the Ag-minerals. No evidence for any additional introduction of elements from later TIB magmatism is present. The combined observations can most easily be reconciled with a metamorphically overprinted syn-volcanic Svecofennian mineralisation. / Den polymetalliska mineraliseringen vid Hornkullen är belägen i västra Bergslagen i Mellansverige. Den uppträder i ca. 1,90-1,88 miljarder år gamla Svekofenniska metavulkaniska- och sedimentära ytbergarter inneslutna i en yngre, ca. 1,8 miljarder år gammal intrusiv bergart, så kallad Filipstadsgranit. Trots att mineraliseringen ganska nyligen varit ett mål för prospektering samt tidigare brutits på silver, saknas fortfarande information om dess malmmineralogi och hur den bildats. Hypotesen är att Hornkullen utgörs av en metamorft överpräglad synvulkanisk Svekofennisk mineralisering. Den domineras av magnetit, magnetkis, blyglans, kopparkis och arsenikkis och i mindre mängd pyrit, zinkblände, ilmenit och löllingit. Pb-Fe-Ag-Sb-sulfosalter finns lokalt och inkluderar boulangerit, meneghinit, jamesonit, freibergit-tetrahedrit, pyrargyrit, och stephanit. Gudmundit och molybdenglans är andra sällsynta accessoriska malmmineral. Blyglans, kopparkis och magnetkis har deformerats plastiskt men lokalt också boulangerit, meneghinit och zinkblände. Magnetit, arsenikkis och pyrit har deformerats sprött. Denna tydliga skillnad i kompetens har resulterat i att inkompetenta mineral ommobiliserats och kommit att fylla sprickor i de mer kompetenta mineralen. I massiva delar av mineraliseringen har denna skillnad även resulterat i en textur av kulmalmstyp. Granoblastisk omkristallisering är särskilt tydligt i magnetit och magnetkis, men även i grovkorniga aggregat av ilmenit. Vidare så förekommer dessa mineral liksom pyrit och arsenikkis ofta som euhedrala kristaller i mindre kompetent matrix. Inneslutningar av malmmineral i porfyroblastisk granat är vanligt förekommande. Geotermobarometri på arsenikkis och zinkblände gav temperatur och tryck på 525°C (mellan 440°C och ca. 590°C) och ca. 300-400 MPa, vilket överensstämmer med regional Svekokarelsk amfibolitfaciesmetamorfos. Förhållandena vid infångandet av synmetamorfa vätskeinneslutningar har uppskattats till en temperatur på ca. 440°C (mellan 400 och 600°C) och tryck på ca. 280 MPa. Merparten av de observerade texturerna är resultat av deformation och ommobilisering relaterad till de förhållanden som rådde under den Svekokarelska orogenesen. Ommobiliseringen av vissa mineral startades förmodligen redan under prograd metamorfos, vilket sedan följdes av mer omfattande modifikation under retrograda förhållanden, åtminstone till temperaturer under 200°C. Bildningen av sulfosalter reflekterar en utveckling från prograd till retrograd metamorfos där de flesta bildats under den senare, retrograda fasen, däribland de olika silvermineralen. Alla observationer resulterar sammantaget i tolkningen att Hornkullen är en regional-metamorft överpräglad och deformerad synvulkanisk Svekofennisk mineralisering.

No description available.

The Giant and Con deposits, Yellowknife, Northwest Territories, represent a classic Archean lode-gold deposit now offset by a major Proterozoic fault (West Bay Fault). The link between the Giant and Con deposits is supported by their similarities. However, there are distinct differences between the two deposits in terms of the offset of stratigraphy, response to D2 deformation, geometry, gold mineralization styles, and depth of gold mineralization. Gold mineralization in the Giant-Con system formed over a protracted history of deformation and hydrothermal activity. Early D1 extension resulted in offset and excision of stratigraphy and the formation of refractory gold mineralization within strongly deformed schistose zones and quartz-carbonate veins. The main D2 deformation in the district resulted in the strong overprint of D1 refractory gold mineralization and was associated with the northwest-southeast flattening of the Giant deposit and progressive reverse-dextral shear of the Con deposit. Free-milling gold mineralization is associated with the D2 event, forming deeper in the Giant-Con system, creating a vertical zonation of free-milling quartz-carbonate veins overprinting earlier refractory gold mineralization that formed higher in the system. Ore plunge in the Giant deposit is controlled by the interaction of the original geometry of D1 deformation zones with the effects of D2 flattening. Ore plunge in the Con deposit is controlled by the orientation of F2 fold and B2 boudin axes in auriferous quartz-carbonate veins. D3 reactivation of the deformation zones (probably related to the end of the D2 compressive event) caused local reactivation of structures and is not associated with gold mineralization. D4 Proterozoic faulting offset and segmented the two deposits, including the major offset by the West Bay Fault. A new reconstruction of the West Bay Fault shows that the Con deformation zone is the down dip extension of the Giant deposit and not the Campbell deformation zone as previously thought.

The effect of physical, chemical and mineralogical properties on reducibility of iron containing raw materials were studied with the use of two pellets, one sinter and one lump iron ore sample provided by Erdemir integrated iron and steel works. Although Erdemir lump iron ore contained hematite, it was found to be less reducible than Erdemir sinter since porous structures are easier to reduce and in general sinters have a higher porosity as compared to lump ores. Experimental findings indicated that Erdemir pellet with a code B had the highest reducibility. On the other hand, the results of Erdemir samples were compared with those results obtained from the projects carried out in the Metallurgical and Materials Engineering Department of METU in 1980&rsquo / s. In mentioned projects, samples of various lump iron ores and a concentrate, pellet and sinter from Turkish sources and imported lump iron ores of CVRD from Brazil and ISCOR from the Republic of South Africa were tested. Within the context of this thesis, a mathematical model that would fit to the reduction kinetics was studied and the porous solid model was found to be the best for Erdemir samples.

Pelletizing is a size enlargement technique employed to process fine-grained iron-bearing concentrates and powder ores. Mechanical strength of fired pellets is important for handling. When the pellets undergo metallurgical processing, their mechanical strength is a measure of their resistance to degradation by breakage due to impacts and abrasion to which they are exposed in the upper part of the blast furnace. In this study, heat treatment of iron ore agglomerates with microwave energy is investigated. First drying and then heat hardening tests were performed. Two main properties of pellets were taken into consideration: percent moisture and magnetite content for the dried pellets and compressive strength and also magnetite content for the fired pellets. The tests were conducted with different particle sized pellets, in different durations. In order to increase the oxidation rate in heat hardening tests, Na2O2 is also added in different percentages. The results of the study showed that, magnetite pellets can indeed be dried and heated with microwave energy. However, the attained compressive strength and v the oxidation of the fired pellets were not sufficient as compared to pellets produced by conventional heating