The stratigraphy of the late Precarnbrian upper Brachina Subgroup has been studied in detail throughout the southern and central Flinders Ranges of South Australia. Ten stratigraphically significant facies associations are readily recognisable within which 18 separate and distinct lithotypes have been defined and described. The complex regional strati - graphic arrangement has been simplified by using a Markov Chain technique of analysis. The resultant lithotype stratigraphy is used as the base upon which the palaeogeographic history of the upper Brachina Subgroup is reconstructed. A detailed sedimentologic analysis of each lithotype was undertaken in order to ascertain their individual palaeoenvironments of deposition. This involved a petrologic analysis of the arenaceous component of each lithotype, the analysis of the suite of sedimentary structures contained within each lithotype, and the analysis of all directional structures for palaeocurrent directions. For this latter analysis a new computer technique was developed whereby up to 3 individual populations can be separately analysed from any one distribution. Deposition of the upper Brachina Subgroup succession was due to a phase of uplift tectonism and minor accompanying basic volcanism. Within this succession two distinct depositional episodes are readily discernable. During the first episode a massive sand influx flowed from a westerly source region ( the Gawler Craton ) into a shallow submerged, though possibly tidally influenced mudflat as a prograding deltaic succession ( the " Alligator River Delta " ). This initial delta developed in the western region of the Adelaide ' Geosyncline ' as a fluvial and tide modified, wave dominated system which was fed by stable outlet channels, protected by barrier - bars and surrounded by a low intertidal aerobic mudflat. Preserved wi - bhin this mudflat deposit are the probable body fossils of primitive cup - shaped coelenterates ( ? ), which were possibly the ancestral organisms of the Ediacara assemblage. With, continued sediment influx and basin shallowing, this initial delta system evolved to an unbarred fluvial modified, tide - dominated delta which was fed by migrating channels and surrounded by an intertidal mudflat. This mudflat was anaerobic, possibly due to the activity of abundant microscopic organisms. The second depositional episode of the upper Brachina Subgroup developed when tectonic instability affected a portion of the basin's western margin ( Uplift I ). As a result, part of the previously deposited deltaic succession was eroded and reworked into a vast, thin intertidal sandflat which extended through the central region, and into the northern region of the Adelaide ' Geosyncline '. A second phase of tectonic instability ( Uplift II ) caused renewed activity along the basin ' s western margin, and also induced the emergence of at least two islands within the basin. Around these islands a thin, dominantly fluvial deposit was generated. The final phase of tectonic instability ( Uplift III ) affected only the western margin of the basin, and produced a narrow sand deposit of probable beach origin. Meanwhile, within the basin gradual subsidence induced the development of a shallow, possibly tidal aerobic mudflat and marked the end of the upper Brachina Subgroup phase of sedimentation. / Thesis (Ph.D.)--Department of Geology and Mineralogy, 1978.

During deposition of the mixed carbonate - clastic sequence of the Mundallio Subgroup, the " Adelaide Geosyncline " was a very shallow, elongate sedimentary basin, flanked to the west and east by older Precambrian basement. In much of the southern and northern Flinders Ranges, clastic deposition predominated in the lower Mundallio Subgroup. In the north, alternating development of shallow mudflats and sandflats ( Nankabunyana Formation ) depended on the interplay between the sediment supply and winnowing processes, while dolomite mudstones were locally deposited in the shallowest areas. In the eastern half of the Willouran Ranges, massive shales were deposited as the environment remained persistently below wave base ( Camel Flat Shale ), but a renewed sand influx led to deposition of the Tilterana Sandstone. In the southern Flinders Ranges, terrigenous clay and silt were deposited on submergent mudflats which shallowed into intermittently exposed dolomite mudflats ( Nathaltee Formation ). Dolomite mudflats were a more persistent feature in areas more distal from the terrigenous source, and sometimes contained isolated, ephemeral lakes which were sites of magnesite deposition ( Yadlamalka Formation ). Dolomite and magnesite mudstone deposition of the Yadlamalka Formation became wide spread in the northern and southern Flinders Ranges in the upper Mundallio Subgroup, as shallowing and retreat of the basin margin led to the formation of semi - isolated lakes, separated and enclosed by exposed carbonate mudflats. The elastics deposited in association with these carbonate mudstones consisted largely of sand sized detritus, probably derived from the reworking of aeolian deposits. In the eastern Willouran Ranges, the greater influx of sand and the slightly deeper, largely submergent environments, led to the deposition of the sandstones, dolomites and siltstones of the Mirra Formation. Because of little clastic influx into the northern Mt. Lofty Ranges, shallow to occasionally exposed environments were largely sites of dolomite deposition ( Skillogalee Dolomite ). To the south, shales were deposited in slightly deeper environments ( Woolshed Flat Shale ), although local dolomite deposition occurred in the Adelaide region ( Castambul Formation, Montacute Dolomite ). In the uppermost part of the subgroup, the area of shale deposition extended northward, encroaching over the dolomite mudflats of the upper Skillogalee Dolomite. Dolomite, occurring largely as mudstones, is the major carbonate mineral present in the Mundallio Subgroup, but magnesite is also widespread. Limestones are not present. The carbonates experienced minor replacement by early diagenetic chert, initially precipitated as both crystalline and amorphous phases. Within the upper Mundallio Subgroup, the preservation of fine details of the detrital texture of dolomite mudstones and peloidal dolomites, and the high Sr contents of dolomites ( largely in the range of 400 - 650 ppm ), suggest that these sediments consisted of Ca - Mg carbonates ( protodolomite, Mg - calcite ) at the time of deposition. Slightly greater recrystallisation of dolomites in the lower Mundallio Subgroup resulted in their lower Sr and higher Mn and Fe contents. Magnesite mudstones may have initially precipitated as hydrated Mg - carbonates. Lithification of surface sediments as a result of subaerial exposure, led to the formation of micritic magnesite. Much of this magnesite was subsequently reworked into intraclastic beds. The carbonate mineralogy of this sequence, and the evidence of only rare sulphates, indicate that the carbonates were precipitated from alkaline, Mg - Ca - C03 waters, with a higher carbonate and lower sulphate content than seawater. / Thesis (Ph.D.)--Department of Geology and Mineralogy, 1980.

Pre-vegetation alluvium is unique; at the present day, plants affect multiple aspects of river functioning and deposition and so those rivers that operated before the evolution of land plants largely lack modern sedimentological analogue. However, such rivers were the norm for the first 90% of Earth history and so a better understanding of their sedimentary product enables insight into both the fundamental underlying mechanisms of river behaviour and the ways in which fluvial processes operated on ancient Earth and other rocky planets. This study presents five original fieldwork based case studies and an analysis of a holistic database of all of Earth’s pre-vegetation alluvium. Together these research strands offer perspectives on the sedimentological characteristics and stratigraphic trends of pre-vegetation alluvium and the behaviour and functioning of pre-vegetation rivers. Results show that, in pre-vegetation alluvial settings: 1) a variety of fluvial styles are represented, but diminished in comparison with syn-vegetation alluvium; 2) ‘sheet-braided’ architectures are common but may record a variety of fluvial planforms; 3) meandering planforms were less frequent, particularly in small- to moderate-sized river systems; 4) mudrock is on average 1.4 orders of magnitude less common than it is in syn-vegetation alluvium; and 5) microbial matgrounds were present, but had negligible effect on preserved architecture and facies. This thesis demonstrates that whilst the physical laws governing fluvial fluid-sediment interaction have not changed, the theatre in which they operated irrevocably evolved with the greening of the continents.

Estromatólitos foram estudados em nove localidades ao sul de Itapeva (SP), principalmente em metacalcários dolomíticos cinza-claro e, secundariamente, em metacalcários calcíticos cinza-escuro, do Grupo Itaiacoca, uma unidade vulcanossedimentar mesoproterozóica da Faixa Ribeira. Foram diferenciados em cinco formas colunares, a mais comum consistindo de colunas coniformes, não ramificadas, de diâmetros e alturas centimétricas a decimétricas, atribuídas a Conophyton. As outras quatro formas, com laminação convexa mas não coniforme, diferem em tamanho, silhueta e estilo/freqüência de ramificação. As diferenças na preservação dos estromatólitos são relacionadas ao comportamentos tectônicos distintos entre o metacalcário dolomítico (mais puro), com comportamento competente, e o calcítico (mais argiloso) que atuou de forma mais plástica. Nas melhores exposições desta área os estromatólitos estão agrupados em bioermas de Conophyton, sem indícios de exposição ou retrabalhamento sub-aéreo ou por ondas, evidenciando um ambiente calmo e relativamente profundo, provavelmente abaixo do nível de base de ondas, de talvez até algumas dezenas de metros de profundidade. Conophyton de Itapeva é semelhante a estromatólitos coniformes próximo a Abapã (PR), também no Grupo Itaiacoca, a cerca de 100 km de Itapeva, mas difere de outras formas, incluindo Conophyton cylindricum e C. metulum, de unidades proterozóicas associadas a margem oeste do Cráton do São Francisco. O Conophyton do Grupo Itaiacoca é semelhante a formas na ex-União Soviética que são geralmente encontrados no Mesoproterozóico ou Neoproterozóico inferior, que é consistente com as datações radiométricas disponíveis que colocam esta unidade próximo ao final do Mesoproterozóico. / Stromatolites were studied at nine localities south of Itapeva, São Paulo, Brazil, generally in light-gray metadolostones and secondarily in dark-gray metalimestones of the Itaiacoca Group, a Mesoproterozoic volcanosedimentary unit of the Ribeira Belt. Five columnar forms were distinguished, the most common consisting of unbranched, coniform columns, with centimetric to decimetric diameters and heights, attributed to Conophyton. The other four forms exhibit convex, but not coniform lamination and differ in size, silhouette and style/frequency of branching. Differences in stromatolite preservation are related to the differing tectonic behavious of the purer and more competent metadolostones and the more argillaceous metalimestones which behaved more plastically. In the best exposures in this area the stromatolites are grouped into Conophyton bioherms, without any evidence of subaerial exposure or reworking by waves, which suggests that they formed in a calm and relatively deep setting (perhaps up to several tens of meters in depth), probably below the base of fairweather water. Conophyton from Itapeva is similar to other coniform stromatolites in the Itaiacoca Group near Abapã (Paraná), about 100 km SW of Itapeva, but differs from other forms, including Conophyton cylindricum and C. metulum, from Proterozoic successions associated with the western margin of the São Francisco Craton. The Conophyton from the Itaiacoca Group is most similar to forms in the ex-Sovietic Union that are usually found in the Mesoproterozoic or lowest Neoproterozoic, which is consistent with available radiometric age dates that place this unit near the end of the Mesoproterozoic.

Numerosos terrenos pré-cambrianos de origem enigmática são individualizados nas regiões do vale e serrania do Rio Ribeira e Planalto Alto Turvo (SP, PR), com base em histórias evolutivas contrastantes e diferentes padrões litotectônicos, metamórficos e estruturais. Esses terrenos suspeitos formam três grandes terrenos compostos justapostos no final do Ciclo Brasiliano: Terreno Apiaí, Terreno Curitiba e Terreno Luís Alves. A evolução geotectônica de uma área que abrange estes três terrenos compostos foi investigada por meio da integração de análises petrológicas, microestruturais e estruturais, apoiadas com trabalhos de mapeamento geológico e compilação e integração de dados geocronológicos disponíveis. Os estudos foram concentrados em unidades geológicas representativas de cada um dos três terrenos compostos. Análises petrológicas, estimativas geotermobarométricas e quantificações de trajetórias PT mostram que os terrenos estudados apresentam assinaturas metamórficas contrastantes, refletindo ambientes geotectônicos distintos. O Grupo Votuverava e a Seqüência Serra das Andorinhas (Terreno Apiaí) passaram por metamorfismo barroviano com caminhamento P-T horário sob pressões e temperaturas máximas ao redor de 8 kbar e 550-650ºC. Parte do Complexo Turvo-Cajati (Terreno Curitiba) apresenta gradiente metamórfico acima do barroviano, com pico metamórfico (650-800ºC) sob pressões relativamente altas (9-12 kbar). Parte desta unidade passou por uma trajetória horária com aquecimento isobárico até atingir o pico térmico, enquanto algumas rochas passaram por descompressão praticamente isotérmica. Datações químicas em monazita indicam que o pico metamórfico do Complexo Turvo-Cajati ocorreu entre 590 e 575 Ma, sendo consideravelmente posterior ao clímax metamórfico das unidades do Terreno Apiaí (>= 600-620 Ma). Trajetórias P-T estimadas para o Complexo Atuba (Terreno Curitiba) sugerem um caminhamento retrógrado com resfriamento praticamente isobárico de 750ºC até um reequilíbrio ao redor de 650-700ºC e 6-7 kbar; a união dos dados petrológicos, microestruturais e geocronológicos sugere que o pico metamórfico teria ocorrido no Paleoproterozóico e o reequilíbrio no Ediacarano. A Suíte Alto Turvo (Terreno Luís Alves) compreende granulitos máficos a intermediários formados no Paleoproterozóico sob temperaturas mínimas ao redor de 850ºC, parcialmente reequilibrados em condições de fácies xisto verde ainda neste período e marginalmente re-metamorfizados em condições de fácies xisto verde a anfibolito no Ediacarano, seguindo uma trajetória horária com pico metamórfico ao redor de 650ºC e 6 kbar. Os padrões estruturais do Terreno Curitiba na área estudada estão associados a uma tectônica de cavalgamentos para oeste e nappismo tardios em relação ao Ciclo Brasiliano e concomitantes com a atuação do sistema transcorrente destral regional na Faixa Ribeira. Os dados multidisciplinares disponíveis indicam que as relações espaciais atualmente observadas para os terrenos estudados não decorrem de relações genéticas e geográficas pretéritas. Os dados convergem para uma evolução geotectônica onde a acresção de diferentes terrenos suspeitos e, em alguns casos, exóticos teria ocorrido em posições diferentes das atualmente observadas, sendo que a justaposição final teria sido controlada por dispersão lateral ao longo das grandes zonas de cisalhamento transcorrentes em períodos tardi- a pós-metamórficos. / Numerous Precambrian terranes of enigmatic origin are recognized in the Ribeira Valley and Alto Turvo Plateau regions (Southeastern Brazil), based on contrasting evolutive histories and distinct lithotectonic, metamorphic and structural patterns. These suspect terranes form three major composite terranes juxtaposed during the late Brasiliano Cycle: Apiaí Terrane, Curitiba Terrane and Luís Alves Terrane. The geotectonic evolution of an area that covers these three composite units was investigated by the integration of petrological, microstructural and structural analysis supported by geological mapping and compilation and integration of available geochronological data. The studies were concentrated on representative geological units from the three composite terranes. Petrological analysis, geothermobarometric estimatives and P-T path quantifications show that the studied terranes exhibit contrasting metamorphic signatures, refleting distinct geotectonic environments. The Votuverava Group and the Serra das Andorinhas Sequence (Apiaí Terrane) underwent barrovian metamorphism with clockwise P-T paths under maximum pressures and temperatures at around of 8 kbar and 550-650ºC. A part of the Turvo-Cajati Complex (Curitiba Terrane) shows a metamorphic field gradient above the barrovian type, with metamorphic peak (650-800ºC) under relatively high pressures (9-12 kbar). A part of this unit underwent a clockwise path with isobaric heating until to reach the thermal peak, while some rocks underwent a near isothermal descompression. Chemical dating of monazite indicate that the metamorphic peak of the Turvo-Cajati Complex occurred between 590 and 575 Ma, a period significantly younger than the metamorphic climax of the Apiaí Terrane units (>= 600-620 Ma). P-T paths from rocks of the Atuba Complex (Curitiba Terrane) suggest a retrograde path following near isobaric cooling from 750ºC to a reequilibration at around of 650-700ºC and 6-7 kbar; the integration of petrological, microstructural and geochronological data suggests that the metamorphic peak would have occurred during the Paleoproterozoic and the metamorphic reequilibration during the Ediacaran. The Alto Turvo Suite (Luís Alves Terrane) comprises mafic and intermediate granulites formed in the Paleoproterozoic under minimum temperatures at about 850ºC, partially reequilibrated under greenschist facies conditions yet in the same period and marginally remetamorphosed from greenschist to amphibolite facies conditions during the Ediacaran, following a clockwise path with metamorphic peak at around of 650ºC and 6 kbar. The structural patterns of the Curitiba Terrane in the studied area are related to a thrust nappe tectonics with westward movement late in relation to the Brasiliano Cycle and concomitant with the activation of the regional dextral transcurrent system in the Ribeira Belt. The available multidisciplinary data indicates that the present spatial relationships between the studied terranes do not imply in previous genetic and geographic relations. The data suggest a geotectonic evolution where the accretion of distinct suspect terranes, and in some cases exotic terranes, would have occurred in different positions in relation to the present array, and the final terrane juxtaposition would have been controlled by lateral dispersion along the major transcurrent shear zones during late- to post-metamorphic periods.

M.Sc. / The evolution of oxygen in the Earth's atmosphere during the early Precambrian has been a subject of debate for many years. Two fundamental models oppose another. The one by Cloud, Holland and co-workers suggests that the atmosphere was essentially anoxic until about 2.2Ga and then became highly oxygenated due to a sudden rise in oxygen levels. The, other advocated by Dimroth, Kimberley and Ohmoto suggests that the atmosphere was oxygenated as early as 3.5Ga. The most crucial assumption for the Cloud-Holland model for the evolution of atmospheric oxygen is that the 2.2-2.3Ga Hekpoort paleosol formed under reducing atmospheric conditions. However, regional field, drill core, petrographic and geochemical investigations of the Hekpoort paleosol during this study clearly show that the Hekpoort paleosol in fact represents an oxidised lateritic weathering profile. In addition, the Hekpoort paleosol correlates well to the oxidised saprolites below the Gamagara/Mapedi erosion surface in the Northern Cape Province. The basis for theassumption by Holland and co-workers that a dramatic rise in atmospheric oxygen levels took place at 2.2Ga thus falls away. During this study extensive red beds, belonging to the Dwaal Heuvel Formation were discovered directly above the Hekpoort paleosol in the Pretoria Group in Botswana and the western Transvaal area. The red beds show two stages of development, firstly fluvial and then deltaic. The red beds are correlated with the Gamagara/Mapedi red beds in Griqualand West. Apart from this evidence for highly oxygenated conditions immediately above the Hekpoort/Ongeluk lavas, hematitic ferricrete, pisolitic mudclast conglomerate and hematitic oolitic ironstones were also found in the Timeball Hill Formation underlying the Hekpoort lava. Oolitic ironstones are developed over an area of more than 100 000 km2. Several different types of oolites are developed within the oolitic ironstone which contains up to 73wt% Fe203. The ferricrete and hematitic pisolitic mudclast conglomerate contain oncolites. These ferricretes, pisolitic mudclast conglomerate and oolitic ironstones suggest that the atmosphere was already highly oxidising between 2.4 and 2.45Ga, prior to deposition of the Hekpoort lava. Pretoria Group rocks that were deposited in close contact with the atmosphere show no evidence for an anoxic atmosphere. It is suggested that atmospheric oxygen levels may have fluctuated through time but at the same time increased in a steplike manner during deposition of the Transvaal Supergroup. However, at this moment in time we do not have enough information available to develop a quantitative model for the evolution of atmospheric oxygen. New age data available on the Hekpoort/Ongeluk lava unit indicate that it may be 2.395Ga old i.e. some 200Ma older than thought earlier. Thus, the atmosphere could have been highly oxygenated in very early Paleoproterozoic times. Uraninite, pyrite and siderite present in older Archean sedimentary rocks do, however, argue for more reducing atmospheric conditions at that time. Both the Cloud-Holland and Dimroth-Ohmoto models of atmospheric oxygen development are therefore in need of revision.

Master of Science / Department of Geology / Mary Hubbard / The southern Sawatch Range of the Southern Rocky Mountains of south-central Colorado is composed of Precambrian crystalline igneous and metamorphic rocks that have undergone at least three major mountain building events during the Phanerozoic, the Ancestral Rockies Orogeny, the Laramide Orogeny, and Rio Grande rifting. In order to determine how the ancient basement structures might have influenced later episodes of deformation, a small area of basement terrain was mapped along the western margin of the Poncha Pass transfer zone between the San Luis and Upper Arkansas basins in the northern Rio Grande rift. The two dominant rock types in the map area, (hornblendic) amphibolite gneiss and (felsic) quartzofeldspathic gneiss, may represent interlayered metabasalt/metadiorite and metarhyolite/metagranite, with lenses of exotic lithologies throughout. Metamorphic foliations were found to be oriented predominantly N35ºW 47ºNE and to have had an influence on younger brittle structures related to the rifting episode. Lineations and fractures in the gneissic fabric also are parallel to brittle deformation structures. Apatite Fission-Track (AFT) analysis provided a means of determining when this crust was exhumed and cooled by the removal of overburden in response to erosion and/or tectonics. The resultant AFT age distribution revealed that exhumation occurred at the higher elevations during the Laramide orogeny (~299-46 Ma), and at lower elevations during Rio Grande rifting (~29-19 Ma). Although it is commonly thought that these mountains were exhumed during the rifting episode, the results of this study indicate that older events played a significant role in the exhumation.

The Haveri Au-Cu deposit is located in southern Finland about 175 km north of Helsinki. It occurs on the northern edge of the continental island arc-type, volcano-sedimentary Tampere Schist Belt (TSB) within the Palaeoproterozoic Svecofennian Domain (2.0 – 1.75 Ga) of the Fennoscandian Shield. The 1.99 Ga Haveri Formation forms the base of the supracrustal stratigraphy consisting of metavolcanic pillow lavas and breccias passing upwards into intercalated metatuffs and metatuffites. There is a continuous gradation upwards from the predominantly volcaniclastic Haveri Formation into the overlying epiclastic meta-greywackes of the Osara Formation. The Haveri deposit is hosted in this contact zone. This supracrustal sequence has been intruded concordantly by quartz-feldspar porphyries. Approximately 1.89 Ga ago, high crustal heat flow led to the generation and emplacement of voluminous synkinematic, I-type, magnetite-series granitoids of the Central Finland Granitoid Complex (CFGC), resulting in coeval high-T/low-P metamorphism (hornfelsic textures), and D₁ deformation. During the crystallisation and cooling of the granitoids, a magmatic-dominated hydrothermal system caused extensive hydrothermal alteration and Cu-Au mineralisation through the late-D₁ to early-D₂ deformation. Initially, a pre-ore Na-Ca alteration phase caused albitisation of the host rock. This was closely followed by strong Ca-Fe alteration, responsible for widespread amphibolitisation and quartz veining and associated with abundant pyrrhotite, magnetite, chalcopyrite and gold mineralisation. More localised calcic-skarn alteration is also present as zoned garnetpyroxene- epidote skarn assemblages with associated pyrrhotite and minor sphalerite, centred on quartzcalcite± scapolite veinlets. Post-ore alteration includes an evolution to more K-rich alteration (biotitisation). Late D₂-retrograde chlorite began to replace the earlier high-T assemblage. Late emanations (post-D₂ and pre-D₃) from the cooling granitoids, under lower temperatures and oxidising conditions, are represented by carbonate-barite veins and epidote veinlets. Later, narrow dolerite dykes were emplaced followed by a weak D₃ deformation, resulting in shearing and structural reactivation along the carbonate-barite bands. This phase was accompanied by pyrite deposition. Both sulphides and oxides are common at Haveri, with ore types varying from massive sulphide and/or magnetite, to networks of veinlets and disseminations of oxides and/or sulphides. Cataclastites, consisting of deformed, brecciated bands of sulphide, with rounded and angular clasts of quartz vein material and altered host-rock are an economically important ore type. Ore minerals are principally pyrrhotite, magnetite and chalcopyrite with lesser amounts of pyrite, molybdenite and sphalerite. There is a general progression from early magnetite, through pyrrhotite to pyrite indicating increasing sulphidation with time. Gold is typically found as free gold within quartz veins and within intense zones of amphibolitisation. Considerable gold is also found in the cataclastite ore type either as invisible gold within the sulphides and/or as free gold within the breccia fragments. The unaltered amphibolites of the Haveri Formation can be classified as medium-K basalts of the tholeiitic trend. Trace and REE support an interpretation of formation in a back-arc basin setting. The unaltered porphyritic rocks are calc-alkaline dacites, and are interpreted, along with the granitoids as having an arc-type origin. This is consistent with the evolution from an initial back-arc basin, through a period of passive margin and/or fore-arc deposition represented by the Osara Formation greywackes and the basal stratigraphy of the TSB, prior to the onset of arc-related volcanic activity characteristic of the TSB and the Svecofennian proper. Using a combination of petrogenetic grids, mineral compositions (garnet-biotite and hornblendeplagioclase thermometers) and oxygen isotope thermometry, peak metamorphism can be constrained to a maximum of approximately 600 °C and 1.5 kbars pressure. Furthermore, the petrogenetic grids indicate that the REDOX conditions can be constrained at 600°C to log f(O₂) values of approximately - 21.0 to -26.0 and -14.5 to -17.5 for the metasedimentary rocks and mafic metavolcanic rocks respectively, thus indicating the presence of a significant REDOX boundary. Amphibole compositions from the Ca-Fe alteration phase (amphibolitisation) indicate iron enrichment with increasing alteration corresponding to higher temperatures of formation. Oxygen isotope studies combined with limited fluid inclusion studies indicate that the Ca-Fe alteration and associated quartz veins formed at high temperatures (530 – 610°C) from low CO₂, low- to moderately saline (<10 eq. wt% NaCl), magmatic-dominated fluids. Fluid inclusion decrepitation textures in the quartz veins suggest isobaric decompression. This is compatible with formation in high-T/low-P environments such as contact aureoles and island arcs. The calcic-skarn assemblage, combined with phase equilibria and sphalerite geothermometry, are indicative of formation at high temperatures (500 – 600 °C) from fluids with higher CO₂ contents and more saline compositions than those responsible for the Fe-Ca alteration. Limited fluid inclusion studies have identified hypersaline inclusions in secondary inclusion trails within quartz. The presence of calcite and scapolite also support formation from CO₂-rich saline fluids. It is suggested that the calcic-skarn alteration and the amphibolitisation evolved from the same fluids, and that P-T changes led to fluid unmixing resulting in two fluid types responsible for the observed alteration variations. Chlorite geothermometry on retrograde chlorite indicates temperatures of 309 – 368 °C. As chlorite represents the latest hydrothermal event, this can be taken as a lower temperature limit for hydrothermal alteration and mineralisation at Haveri.The gold mineralisation at Haveri is related primarily to the Ca-Fe alteration. Under such P-T-X conditions gold was transported as chloride complexes. Ore was localised by a combination of structural controls (shears and folds) and REDOX reactions along the boundary between the oxidised metavolcanics and the reduced metasediments. In addition, fluid unmixing caused an increase in pH, and thus further augmented the precipitation of Cu and Au. During the late D₂-event, temperatures fell below 400 °C, and fluids may have remobilised Au and Cu as bisulphide complexes into the shearcontrolled cataclastites and massive sulphides. The Haveri deposit has many similarities with ore deposit models that include orogenic lode-gold deposits, certain Au-skarn deposits and Fe-oxide Cu-Au deposits. However, many characteristics of the Haveri deposit, including tectonic setting, host lithologies, alteration types, proximity to I-type granitoids and P-T-X conditions of formation, compare favourably with other Early Proterozoic deposits within the TSB and Fennoscandia, as well as many of the deposits in the Cloncurry district of Australia. Consequently, the Haveri deposit can be seen to represent a high-T, Ca-rich member of the recently recognised Fe-oxide Cu-Au group of deposits.

The Precambrian rocks of KwaZulu-Natal comprise the Archaean granite-greenstone remnants of . the Kaapvaal craton and Late Archaean volcanics and sediments of the supracratonic Pongola Supergroup. These Archaean rocks have been intruded by numerous mafic/ultramafic complexes and voluminous granitoid intrusives of various ages. To the south, the basement rocks are represented by the Mid- to Late-Proterozoic Natal Metamorphic Province (NMP). The NMP comprises three discontinuity-bound tectonostratigraphic terranes. These are, from north to south, the Tugela, Mzumbe and Margate Terranes. The Tugela Terrane has been interpreted as an ophiolite suite that was thrust northwards onto the stable Archaean craton as four nappe structures. Continued thrusting resulted in the two southern terranes being thrust northwards over each other, resulting in numerous sinistral transcurrent shear zones and mylonite belts. The greenschist facies Tugela terrane has been intruded by mafic-ultramafic complexes, alpine serpentinites, plagiogranites and a number of alkaline to peralkaline granitoids. The Mzumbe and Margate Terranes comprise arc-related, felsic to mafic supracrustal gneisses and metasediments that were intruded by syn-, late- and post-tectonic granitoids. Mineralisation in the granite-greenstones consists of structurally-hosted lode-gold deposits. These deposits have many characteristics in common with lode-gold deposits found in other granitegreenstone terranes throughout the world. The Nondweni greenstones also contain volcanogenicrelated massive sulphide deposits. The Pongola Supergroup is host to lode-gold mineralisation and placer gold mineralisation. These placer deposits have been correlated with deposits found in the similarly-aged Witwatersrand Basin in an adjacent part of the craton. The metallogeny of the NMP can be described in relation to the various stages in the tectonic evolution of the belt. The initial, rifting and extension-related stage was characterised by arcrelated magmatism and volcanic arc activity. Alkali basalt magmatism due to hot-spot activity in the oceanic basin in which the Tugela Terrane initially accumulated, produced magmatic segregation deposits, while volcanic-arc activity is responsible for the submarine-exhalative massive sulphide mineralisation. All the mineralisation within the NMP is structurally-related. These thrusts and shear zones were developed during obduction and thrusting during the NMP event, and created the paths necessary for the migration of mineralising fluids. Alpine-type ophiolite deposits were also emplaced along these zones. Epigenetic, shear zone-hosted gold mineralisation occurs in the Tugela and Mzumbe Terranes. Mineralisation occurs within quartz veins and is also disseminated within the sheared host-rocks. The Mzumbe Terrane also contains small showings of massive sulphide deposits that were related to volcanogenic exhalative processes during the formation of this terrane. Potential for finding further mineralisation of this type appears to be good. The massive sulphide deposits formed early in the evolution of the belt, and were deformed and metamorphosed during the later accretionary processes. The southernmost Margate Terrane is characterised by a lack of metalliferous mineralisation, but hosts the extensive, and economically important, limestone deposits of the Marble Delta. The recently discovered spodumene-rich pegmatite deposits of this terrane may also be considered for exploitation. Post-collisional magmatism and metamorphism resulted in extensive rapakivi-type granite/charnockite plutons

The Precambrian-Cambrian Athel Silicilyte is an enigmatic chert unit of up to 390 m thick found as slabs (each slab typically 2 × 6 km across) entrapped within salt domes at a depth of 4-5 km in the South Oman Salt Basin. This formation is a prolific self-charged reservoir with high porosity (up to 34 %) and high oil saturation (80 %). Despite its economic value, the origin and the variability of this formation are not fully understood. This study therefore aims to investigate the variability and the origin (silica source and precipitation mechanism) of the Athel Silicilyte. Data obtained from core, wireline log and petrographical analysis were employed to establish the vertical and the lateral variability and, with the assistance of geochemical data, the likely source and precipitation mechanism of silica was determined.The Athel Silicilyte is only present in the deepest parts of the South Oman Salt Basin within the fault-bounded Athel Basin, bounded by two silt-rich mudstone units. Six lithofacies were recognised in the Athel Silicilyte that reflect variability in detrital material contents (three silica-rich facies), sediment remobilisation (slumped and brecciated lithofacies) and diagenetic modification (carbonate-bearing lithofacies), with the silica-rich facies being the most abundant (> 97 % of the total thickness). The Athel Silicilyte exhibits wavy discontinuous lamination and it is predominately (silica-rich facies average = 80 wt. %) composed of connected-networks of microcrystalline quartz (1-5 µm). Other constituent components are detrital quartz (3 wt. %), illite (10 wt. %), pyrite (4 wt. %) and organic carbon (TOC = 3 wt. %). The detrital contents increase towards the Upper Athel Silicilyte and towards the basin margins (ranging from 3 to 30 wt. %). The wavy laminations are interpreted to have a microbial origin. The homogeneity, loose packing of detrital grains and preservation of 390 m thick laminated fabric suggest that the Athel Silicilyte precipitated syndepositionally in microbial layers during low detrital input. The intense detrital input during bounding mudstones sedimentation inhibited Athel Silicilyte precipitation as a result of the rapid burial of microbial layers. The Athel Silicilyte shows strong enrichments of redox-sensitive elements (U, V and Mo), Mn-depletion, positive Ce anomalies, and small framboidal pyrites (3.6-4.0 µm), suggesting that the water column was euxinic during precipitation.Based on the petrographical evidence for the Athel Silicilyte forming as a syndepositional precipitate alongside seawater-like rare earth element (REE) characteristics, silica is interpreted to have been sourced directly from seawater. Mass balance calculations support this interpretation, indicating that silica-rich Precambrian seawater provided the significant silica mass in the Athel Silicilyte. The ability of dissolved silica to form hydrogen bonds with the functional groups (e.g. carboxyl and hydroxyl) in microbial layers was the key for Athel Silicilyte precipitation. The formation of hydrogen bonds was made possible under euxinic conditions, where the pH values were probably lower (< 7) than for the normal seawater as a result of HS- and H+ production by sulphate reducing bacteria and HS- oxidation at the redox boundary by sulphur oxidising bacteria. Consequently, dissolved silica was concentrated in microbial layer microenvironemnts, resulting in silica nucleation and polymerisation.