Made available in DSpace on 2014-10-09T12:26:04Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:49Z (GMT). No. of bitstreams: 1 12891.pdf: 1261412 bytes, checksum: 22d81b21c8b5536ef9c962a801aed517 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Quimica, Universidade de Sao Paulo - IQ/USP

Gold mineralization is hosted within gossanous quartz-haematite veins in volcano-sedimentary lithologies of the Klein Aub - Rehoboth basin of the Irumide Belt, Namibia. Mineralization and hydrothermal alteration are restricted to deformed lithologies particularly the metasediments. Lithological relationships, geochemistry and metallogenic characteristics of the Irumide Belt suggest an intra-continental rift setting. Copper mineralization is well known along the length of the belt, from Klein Aub in the southwest to Ghanzi in the northeast, whereas gold mineralization appears restricted to the Klein Aub Rehoboth basin. The gold is envisaged as having being leached initially from graben fill sequences during rift closure and basin dewatering. Location of the mineralization is strongly controlled by structure and lithological contact zones. Such zones are percieved as having acted as conduit zones for escaping mineralized fluids during basin closure and deformation. Apart from the lack of an effective mineralizing trap, all features consistent with the development of an ore deposit are present. The largest mineralization traps within the area studied are shear zones followed by lithological contact zones. The Mebi and Blanks gold mines are developed over large shear zones while the Swartmodder and Neuras gold mines are situated over mineralized lithological contacts. The Swartmodder copper mine yielded ore from a mineralized schist enclave within granite. Copper and gold occurrences are attributed to two contrasting styles of mineralization. Copper mineralization is suggested to have developed during initial rifting of the belt (ie. stratabound sedimentary exhalative type), while the gold and minor copper resulted from rift closure and basin dewatering. Although no economical orebody was realized during the course of this study a model is proposed for the development of mineralization within the Irumide basement lithologies as a working hypothesis for future exploration.

Porphyry copper and molybdenum deposits in west-central British Columbia are associated with plutons of Late Cretaceous and Tertiary age which intrude Mesozoic volcanic and sedimentary rocks of the Intermontane Tectonic Belt. The porphyry deposits are contained in an area bounded on the west by granitic rocks of the Coast Plutonic Complex, and on the east and southeast by a belt containing Mesozoic granitic stocks and an extensive area of Tertiary volcanic rocks. The porphyry intrusions take the form of small stocks, plugs , dykes, and dyke swarms generally not exceeding 1 square mile in surface area. The intrusions are commonly multiple and range in composition from quartz diorite to granite. Copper and molybdenum sulphides occur as fracture fillings and as veinlet stockworks within and adjacent to the intrusive bodies. Sulphide and alteration minerals exhibit concentric zoning patterns. Volcanic and sedimentary rocks marginal to the intrusions are thermally metamorphosed to biotite hornfels. Results of potassium-argon dating indicate four crudely parallel north to northwest-trending belts of porphyry intrusions, each being distinctive in age, rock composition, and contained metallic mineralization. From west to east these include: (1) Alice Arm intrusions - 50 m.y. molybdenum-bearing quartz monzonite and granite intrusions; (2) Bulkley intrusions - 70 to 84 m.y. copper-molybdenum and molybdenum-bearing porphyries of granodiorite to quartz monzonite composition; (3) Nanika intrusions - 50 m.y. copper-molybdenum and molybdenum-bearing intrusions of quartz monzonite composition; (4) Babine intrusions - 50 m.y. copper-bearing intrusions of quartz diorite and granodiorite composition. Potassium-argon analyses were carried out mainly on biotite separates from the mineralized porphyry phases within the deposits. Dating of inter-mineral and post-mineral porphyry phases, common at many of the deposits, yielded ages equivalent to, or 2 to 3 m.y. younger than, the mineralized phases, indicating that the age of mineralization is essentially synchronous with the age of intrusion. Limits of analytical errors in these potassium-argon analyses are within 3 per cent of the calculated ages. The distribution of potasslum-argon ages for porphyry deposits in west-central British Columbia does not fit the plate tectonic theories proposed for the origin of similar deposits elsehwere in the Cordillera of North and South America, in which deposits are progressively younger in a given direction. Here, four crudely parallel belts of porphyry intrusions display a reversal in age from 50 m.y. to 70 - 84 m.y. to 50 m.y. in an eastward direction. This distribution of ages may have been caused by periodic movement from Late Jurassic to Tertiary time along a subduction zone beneath the Coast Plutonic Complex which forms the west border of the area containing the porphyry deposits. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Ph.D. / The economically important sedimentary manganese deposits of the Paleoproterozoic Kalahari and Postmasburg manganese fields, are situated in close geographic vicinity to each other in the Griqualand West region of the Northern Cape Province, South Africa. This thesis describes aspects of mineralogy, petrography and geochemistry of the manganese ores with the purpose to establish genetic models for genesis and alteration of manganese ores of both manganese fields. The Kalahari manganese field, situated some 60 km northwest of Kuruman, is the largest known land-based manganese deposit. Manganese ores occur interbedded with iron-formations of the Hotazel Formation of the Voelwater Subgroup of the Late Archean-Paleoproterozoic Transvaal Supergroup. The sediments of the Voelwater Subgroup are preserved in five erosional relics, of which the Kalahari manganese deposit is by far the largest and the only one of economic importance. Two types of ore are mined, low-grade sedimentary Mamatwan-type ore and high-grade Wesselstype ore. Mamatwan-type ore is represented by microcrystalline laminated braunite-lutite composed of kutnahorite, Mn-calcite, braunite and hematite, modified by the occurrence of late diagenetic or metamorphic hausmannite, partridgeite, manganite and calcite. Mamatwan-type ore contains up to 38 mass % Mn and constitutes about 97 % of the ore reserves in the Kalahari manganese deposit. High-grade Wessels-type ore, with a manganese content of between 42 to 48 mass % Mn (on average), constitutes about 3 % of the ore reserves. It occurs only in the northwestern part of the main Kalahari deposit, and in small deposits at Hotazel and Langdon, in association with a system of north-south striking normal faults. The Wessels alteration event is thought to be related to the Kibaran orogenetic event (about 1.1 Ga). Fault zones are ferruginized and alongside faults sedimentary Mamatwan-type ore has been hydrothermally upgraded to Wessels-type ore. Metasomatic fronts are defined by changing mineral associations. These associations clearly illustrate that decreasing degrees of alteration relate to increasing distance from the fluid feeders. Areas of unaltered Mamatwan-type ore are preserved in the core of fault blocks. Wessels-type ore consists mostly of hausmannite, bixbyite, braunite II and manganite and subordinate gangue minerals such as clinochlore and andradite but the mineral assemblage associated with the Wessels alteration event is unusually diverse. More than 100 minerals have been identified, amongst them 8 new mineral species and an unusual, ferrimagnetic, Fe-rich variety of hausmannite. Mass balance calculations illustrate that the upgrading of the Wessels-type manganese ore is a consequence of leaching of CaO, MgO, CO 2, and Si02 from a low-grade Mamatwan-type precursor. This metasomatic process results in increasing secondary porosities, compaction of the orebody to two thirds of its original thickness and consequently residual enrichment of manganese in the ores. Three younger alteration events are observed in the Kalahari manganese deposit. These are only of minor economic importance. Wallrock alteration associated with the Mamatwan alteration event is characterized by reductive leaching of Fe and Mn around syntectonic veins and joints with pyritechalcopyrite- carbonate mineralization. The alteration is explained by infiltration of epithermal solutions that were introduced along veins or joints. The timing of the alteration event has tentatively been placed into the Pre-Karoo era. The Smartt alteration event is associated with intensive faulthosted brecciation and replacement of braunite and carbonates of the Mamatwan-type ore by todorokite and manganomelane, a process that causes considerable upgrading of the manganese ore next to a fault breccia at Mamatwan mine, and the formation of stratiform cross-fibre todorokite veins at Smartt mine. The Smartt alteration event postdates the Mamatwan alteration event and has tentatively been correlated with Pre-Kalahari groundwater circulation. Supergene alteration of the ores took place in Kalahari and Post-Kalahari times. It is characterized by the occurrence of cryptomelane, pyrolusite and other typically supergene manganese oxides along the suboutcrop of the Hotazel Formation beneath the Cenozoic Kalahari Formation. The Postmasburg manganese field is situated about 120 km to the south of the Kalahari manganese field on the Maremane dome. Two arcuate belts of deposits extend from Postmasburg in the south to Sishen in the north. Two major ore types are present. The ferruginous type of ore is composed mainly of braunite, partridgeite and bixbyite and occurs along the centre of the Gamagara Ridge, or Western belt. The siliceous type of ore consists of braunite, quartz and minor partridgeite and occurs in small deposits along the Klipfontein Hills (or Eastern belt) and the northern and southern extremities of the Gamagara Ridge. Geological and geochemical evidence suggest that the manganese ores represent weakly metamorphosed wad deposits that accumulated in karst depressions during a period of lateritic weathering and karstification in a supergene, terrestrial environment during the Late Paleoproterozoic. The dolomites of the Campbellrand Group of the Transvaal Supergroup are host and source for the wad accumulations. Contrasting geological settings are suggested for the accumulation of the siliceous and the ferruginous types of ore respectively. The former originated as small pods and lenses of wad in chert breccia that accumulated in a karst cave system capped by the hematitized Manganore iron-formation of the Transvaal Supergroup. The cave system finally collapsed and the hematitized iron-formation slumped into the sinkhole structures. The ferruginous type of ore accumulated as mixed wad-clay sediment trapped in surficial sinkhole depressions in the paleokarst surface. The orebodies are conformably overlain by the Doornfontein hematite pebble conglomerate or aluminous shales belonging to the Gamagara Formation of the Late Paleoproterozoic Olifantshoek Group. Well preserved karst laterite paleosol profiles, described from the basal section of the Gamagara Formation, provide a strong argument for the terrestrial, supergene origin of the manganese ores. The manganese ores in the Postmasburg manganese field were affected by diagenesis and lower greenschist facies metamorphism. Metamorphism resulted in recrystallization to braunite in the siliceous ores of the Eastern belt, and to massive or mosaic textured braunite and idioblastic partridgeite in the ferruginous environment of the Western belt. Secondary karstification and supergene weathering are evidence for renewed subaerial exposure of the manganese ore and their host rocks. The metamorphic mineral assemblage is replaced by abundant romanechite, lithiophorite and other supergene manganese oxides. Comparison between the Kalahari- and the Postmasburg manganese field shows that sedimentary manganese accumulation took place in entirely different depositional environments and owing to different mechanisms. Their close geographic relationship appears to be coincidental. Apparent similarities arise as a consequence of regional geological events that postdate the deposition of the manganese ores. These similarities include the lower greenschist facies metamorphic overprint, an event tentatively related to thrusting and crustal thickening during the Kheis orogenetic event, and syn- to Post-Kalahari supergene alteration. The correlation of structurally controlled hydrothermal alteration events in the Kalahari manganese field and the Postmasburg manganese field remains difficult due to the absence of the necessary geochronological constraints.

Economically important Mississippi Valley type zinc-lead deposits exist in a late Proterozoic dolomite, the Society Cliffs Formation, at north Baffin Island, District of Franklin, N.W.T., Canada. The Society Cliffs Formation ranges from 1,000 to 2,000 feet in thickness and is underlain by up to 2,000 feet of black, organic-rich shale, the Arctic Bay Formation, and overlain by either black shale and limestone of the Victor Bay Formation or by red, fine- to coarse-grained clastic rocks of the Strathcona Sound Formation. Disconformities exist between each of the formations. Society Cliffs Formation has undergone at least four temporally distinct episodes of karstification since its deposition. The most important karst episode, with respect to the formation of the zinc-lead deposits, occurred during the hiatal interval between the deposition of the Victor Bay Formation and the deposition of the Strathcona Sound Formation. During this hiatal interval a holokarst developed in Society Cliffs Formation and a large integrated cave system of the Mammoth Cave-Flint Ridge Cave System type was formed; i.e. long, nearly horizontal, tubular passages were formed during initial periods of base-level stabilization, followed by the development of sub-vertical canyons beneath the tubes when the base-level dropped. After this karst episode the Society Cliffs Formation was deeply buried and the cave system was partially or completely filled with sulphide and carbonate minerals. The zinc-lead deposits are characterized by banded structure which comprises pyrite, relict marcasite, sphalerite and galena interlayered with sparry dolomite. The zinc-lead deposits contain several sedimentary structures that were formed by a chemical deposition-chemical corrosion process. These include cross-stratification, cut-and-fill and onlap. Onlap indicates the paleocaves were filled from the floor up. The meteoric waters which formed the caves did not form the zinc-lead deposits because the temperature of ore deposition was between 200°C and 150°C, the calculated oxygen isotope composition of the ore fluid is +12.8 per mil, and mineral stability and isotopic data indicate the oxygen fugacity decreased during ore deposition. The sulphide sulphur isotope composition of the zinc-lead deposits has a relatively narrow range about +26 per mil, similar to that of sulphate evaporite (+23.7 per mil) which exists locally within the Society Cliffs Formation. Lead isotope data indicate the lead in the deposits was derived by at least a two-stage process from a source with a uniform uranium-thorium ratio. The ore fluid and contained metals are postulated to have been derived from the Arctic Bay Formation during a late-stage dewatering of the shale. Sulphide deposition may have been caused by the chemical reduction of sulphate which existed in the ore fluid when the ore fluid entered hydrocarbon-filled caves. The hydrocarbons were probably expelled from the Arctic Bay Formation shale during an earlier stage of thermal metamorphism and dewatering. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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The following thesis describes part of a set of ore specimens collected by James Gilluly and the writer at Ajo, Arizona during the early summer of 1932. This field work was done for the United States Geological Survey, and while considerable geologic work was done, only passing mention will be made concerning the geology, as the conclusions reached properly belong to Mr. Gilluly and will be published by him at some future time. Mr Eldred Wilson of the Arizona Bureau of Mines has kindly put at my disposal a number of polished sections which he collected in 1923 from the semi-oxidized zone in the southwest part of the orebody. In all, about 50 polished sections were studied in detail and the conclusions reached concerning the paragenesis of the ore minerals are based entirely upon the evidence presented by these sections, as the field relations are not in my possession.

M.Sc. / This investigation is a mineralogical study of the reduction products formed during the reduction of Mamatwan manganese ore, as well as presentation of a possible reduction mechanism for this ore type. Cubes, 20 millimeter in dimensions, of Mamatwan manganese ore were reduced in a vertical tube resistance furnace at temperatures varying from 1200 to 1500°C with various reductants and retention times...

The mineralogical basis for understanding biohydrometallurgical processing of low-grade sulphide ores and means by which microwave processing improves their microbial recovery is investigated using a Nigerian low-grade complex sulphide ore as a case study. The study is approached through an applied mineralogical study of the ore and its influence on developing an optimal route for the microbial leaching of the low-grade complex ore under varying process parameters, and an investigation on the interaction between mineralogy, microwave processing and bioleaching. Bioleaching behaviour, mechanisms of bioleaching, and the interplay of mineralogy and microwave irradiation and their influence on bioleaching process were carried out using mixed cultures of Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillium ferrooxidans in a mechanically stirred glass reactor at varying bioleaching process parameters and through electrochemical studies. Mineralogical analysis of the ore revealed the presence of siderite, sphalerite, galena, quartz, and traces of pyrite and chalcopyrite, with the ore exhibiting fine to coarse grain intergrowths of the constituent crystalline phases both at the interstitials and the boundaries. Complexity in the mineralogy of the ore affected mineralogical and elemental distribution amongst varying size fractions that led to variation in the galvanic behaviour within these size fractions and influenced microbe-mineral’s reactivity and the different dissolutions behaviours. Bioleaching at optimal bioleaching parameters revealed the highest dissolution at a particle size fraction of 75 μm, while electrochemical studies revealed the highest dissolution at particle size fraction of 106 μm. This discrepancy was consistent with and attributed both to the physical and mineralogical influences. The combined effects of mineralogical variation, precipitation phenomenon as well as the physico-chemical effect of particle size, controlled bioleaching behaviour, while galvanic interaction resulting from variations in mineralogical distribution controlled the electrochemical behaviour. Ore mineralogy and microwave heating both showed dual influences on heating characteristics, size reduction, and the effectiveness of microwave treatment in improving dissolution. The increase in the dissolution rate and the overall dissolution of the microwave treated samples is attributed to phase changes in the ore which promoted galvanic interaction within the system, decrease in the amounts of sulphur contents, and an increase in electrochemical and microbial growth sites resulting from an increase in the number of cracks induced by microwave heating.