Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This study presents results of a detailed geological mapping and structural analysis of auriferous quartz-vein sets of the nine current open-pit operations, of the Siguiri Mining Complex in the northeastern parts of Guinea. The Siguiri Mining Complex is hosted by a low-grade metamorphic, turbiditic succession within the larger Siguiri Basin, which forms part of the Palaeoproterozoic Birimian Supergroup of the Boualé-Mossi domain on the West African Craton. The Siguiri Mining Complex is located in a deeply weathered saprolite profile developed over the monotonous succession of interlayered metapelites and -psammites. In fresh bedrock and core samples, the host succession is mainly made up of quartz-muscovite schists, muscovite-chlorite schists and metagreywackes, with isolated occurrences of intraformational breccias. The main deformation to have affected the metasedimentary succession of the Siguiri Mining Complex can be assigned to a D2 deformational event. D2 structures comprise of north-south trending strike-slip and reverse faults anastomosing around and enveloping open- to tightly folded domains exposed over an area of 12 by 3 km. The geometry, orientation and kinematics of faults and folds suggest that D2 structures formed during progressive deformation in an overall dextral transpressive brittle-ductile shear zone. Structures within the D2 corridor record east-northeast subhorizontal shortening and north-northwest subhorizontal extension. An omnipresent carbonate alteration in form of carbonate-alteration spots testifies to the pervasive, syn-D2 hydrothermal fluid-flow within the sediments. A structurally- and fracture-controlled fluid-flow is evidenced by the abundance of auriferous quartz veins throughout the Siguiri Mining Complex. These quartz veins host the bulk of the gold mineralization. One main and, at least, three minor sets of auriferous quartz veins can be distinguished. The main quartz-vein set shows very consistent easterly to northeasterly trends and steep southerly dips throughout the Siguiri Mining Complex. This orientation is consistent with the dextral transpressive kinematics and strain within the D2 host structure and illustrates the significance of D2 strains for the mineralization. The volumetrically minor vein sets can be shown to be related to different stages of F2 folding and fold amplification. Zones of economic-grade mineralization occur in areas where competent, psammitic units are developed in structural sites of increased dilatancy. Areas of dilatancy are represented by either dilational jog geometries within the overall transpressive structure or zones of pronounced shear-zone subparallel stretch. Jog geometries could be identified in the larger Bidini-Toubani-Sanu Tinti Complex having formed as a result of the anastomosing geometry of the bounding D2 shear zones. In the large Kami Complex, F2 axial culminations and depressions correspond to zones of increased stretch within the D2 transpression zone, delineated by closer vein spacing and the formation of D2 normal faults parallel to the main vein set and normal to F2 fold hinges. The size and extent of the Siguiri Mining Complex suggests that the host D2 transpressive corridor must be assumed to have a significantly larger along-strike continuation, being part of a larger shear zone system related to the accretionary history of Palaeoproterozoic basins and arcs onto the Archaean Man Shield in West Africa. / AFRIKAANSE OPSOMMING: Hierdie studie lewer die resultate voor van 'n gedetailleerde geologiese kartering en strukturele analise van die gouddraende kwarts-aar stelle in die huidige nege oop-groef operasies van die Siguiri Myn Kompleks, in die noordoostelike deel van Guinea. Die Siguiri Myn Kompleks is geherberg deur 'n lae metamorfiese graad turbidiet suksessie in die groter Siguiri Kom, wat deel form van die Paleo-Proterosoïkum Birimian Supergroep van die Boualé-Mossi streek op die Wes Afrika Kraton. Die Siguiri Myn Kompleks is geleë in die diep veweerde saproliet profiel, wat onwikkel het oor die eentonige suksessie van metapeliete en -psammiete. In vars bodemrots en kern monsters is die herberg-gesteente opgemaak uit kwarts-muskoviet skiste, muskoviet-chloriet skiste en metagrouwakte, as ook afgesonderde voorvalle van intraformasie breksies. Die hoof deformasie fase wat die metasedimentêre suksessie van die Siguiri Myn Kompleks geaffekteer het, kan toegeken word aan 'n D2 deformasie gebeurtenis. D2 strukture bestaan uit noord-suid neigende strekkingwaartse verskuiwings en opskuiwings, wat anastomoserend oop- en steil geplooide gebiede omsluit en is oor 'n area van 12 by 3 km ontbloot. Die geometrie, oriëntasie en kinematika van verskuiwings en plooie stel voor dat D2 strukture gevorm het tydens progressiewe deformasie in 'n algemene regse transpressie skuifskeursone, onder brosheid-duktiliteit toestande. Strukture in die D2 gang wys 'n oos-noordoos subhorisontale verkorting en 'n noord-noordwes subhorisontale verlenging. Die alomteenwoordigheid van karbonaat alterasie, in die vorm van karbonaat-alterasie spikkels, getuig van die deurdringende, sin-D2 hidrotermiese vloeistof vloei in die sedimente. Die strukturele- en breuk-beheerde vloeistof vloei is ook duidelik, as gevolg van die oorvloed van gouddraende kwarts-are reg deur die Siguiri Myn Kompleks. Die kwarts-are bevat die grootmaat van die goud mineralisasie. Een hoof, en te minste drie minder belangrike stele van gouddraende kwarts-aar stelle kan uitgeken word. Die hoof kwarts-aar stel wys konstante oostelike to noordoostelike neigings en steil suidelike hellings, reg deur die Siguiri Myn Kompleks. Die oriëntasie is konstant met regse transpressie kinematika en vervorming in die D2 strukture en illustreer die belangrikheid van D2 vervorming vir mineralisasie. Die minder-belangrike aar stelle is verwant aan die verskillende staduims van F2 plooiing en plooi amplifikasie. Sones van ekonomiese graad mineralisasie kom voor in areas waar bevoegde eenhede van psammiete ontwikkel het in strukturele terreine van verhoogde dilatasie. Areas van dilatasie word verteenwoordig deur dilatasie uitwykings in die transpressie strukture of sones van skuifskeur subparalelle verlenging. Uitwykings geometrië kan geidentifiseer word in die groter Bidini-Toubani-Sanu Tinti Kompleks, waar dit gevorm het asgevolg van die anastomoserende geometrie van die D2 skuifskeur sones. In die groter Kami Kompleks kom F2 aksiale kulminerings en depressies voor in sones van verhoogde strekking binne-in die D2 transpressie sone en word uitgebeeld deur nader aar-spasiëring en die formasie van D2 afskuiwings, parallel aan die hoof kwarts-aar stel en normaal met betrekking tot die F2 plooi-skarniere. Die groote en omvang van die Siguiri Myn Kompleks stel voor dat die D2 transpressiewe gang nog n groter voorsetting het, en vorm deel van 'n groter skuifskeur sisteem en is verwant aan die anngroeings geskiedenis van die Paleo-Proterosoïese komme en boë aan die Argeïese Man Skild in Wes Afrika.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2014. / The Karasburg Basin is situated in southern Namibia and preserves a heterogeneous succession of Karoo Supergroup strata up to 1000m thick. The uppermost preserved succession in this basin is the Amibberg Formation which is 250m thick and consists of intervals of sandstone, siltstone and mudstone. This study uses facies analysis, sequence stratigraphy and petrography to determine the palaeogeography and provenance for the Amibberg Formation. This is then used to establish environmental variability across the Karasburg – Aranos – Main Karoo basins and to define an equivalent of the Amibberg Formation in the Main Karoo Basin. Detailed stratigraphic logging of five outcrop localities has led to the identification of seven distinct lithofacies and two dominant ichnofacies (Cruziana and Skolithos). These lithofacies include: 1) Massive, laminated and bioturbated mudstones interpreted as offshore deposits (OS); 2) Bioturbated siltstones and sandstones which are representative of offshore-transitional environments (OST); 3) Interbedded sandstones and siltstones also interpreted as offshore-transitional deposits (OST) and generated by river-fed hyperpycnal plumes; 4) Sharp based, massive sandstones interpreted as being deposited on the distal lower shoreface (dLSF); 5) Non-amalgamated hummocky cross-stratified (HCS) and wave rippled sandstones interpreted as distal lower shoreface deposits (dLSF); 6) Amalgamated HCS and wave rippled sandstones interpreted as proximal lower shoreface deposits (pLSF); and 7) Soft-sediment deformed (SSD) sandstones and siltstones occurring in close juxtaposition with dLSF and pLSF deposits. The vertical arrangement of these lithofacies shows a general coarsening and shallowing upward trend. Overall the rocks of the Amibberg Formation consist of wave-dominated shoreface deposits with significant influence by tidal processes. Petrographically, the sandstone samples fall into the class of quartz and feldspathic wackes and are sourced from craton interior provenances. Geochemical analysis of mudstones and nodules indicate high levels of microbial activity under predominantly oxic conditions during the deposition of the Amibberg Formation. Five poorly defined 4th order T-R cycles are observable within the strata of the Amibberg Formation. Large regressive intervals are capped by thin transgressive tracts and these cycles are interpreted to have formed due to eustatic processes. Overall, the Amibberg Formation represents a regressive shoreline. iii Based on the mean palaeocurrent vectors a NNE-SSW palaeoshoreline orientation is deduced and the shoreface must have occupied a palaeohigh on the northern side of the western Cargonian Highlands. This emergent highland acted as an extensive headland and assisted in the connectivity of the Karasburg and Aranos basins, with partial connectivity with the Main Karoo Basin during the Early Permian. Based on this study, the Amibberg Formation is considered an equivalent of the Waterford Formation in the Main Karoo Basin based on similar: stratigraphic position; thickness; sedimentary structures; trace fossil assemblages and stacking patterns.

This thesis reports eight measured sections and >400 new detrital zircon U-Pb SHRIMP-II ages from the Mesoproterozoic (~1.4 Ga) upper Purcell Supergroup of southeastern British Columbia, Canada. The goal of my study is to constrain the depositional, tectonic and paleogeographic setting of the upper Purcell Supergroup. Stratigraphic sections across the Purcell Anticlinorium, constructed from measured sections, reveal three syn-depositional growth faults: (1) paleo-Hall Lake, (2) paleo-Larchwood Lake, and (3) paleo-Moyie. Stratigraphic sections were combined into a fence diagram, revealing a large north-northeast trending graben bound to the east by the paleo-Larchwood Lake fault and to the west by the paleo-Hall Lake fault. Five samples were collected for detrital zircon analysis along the eastern extent of exposed Purcell strata; one sample was collected from the western limit of strata. All samples are characterized by subordinate numbers of detrital zircons that yield Paleoproterozoic and Archean ages. Detrital zircon ages from the Sheppard Formation are dominated by 1500, 1700, 1750, and 1850 Ma grains. The overlying Gateway Formation is dominated by 1400-1450, 1700, 1850, and 1900 Ma zircon grains. The overlying Phillips, Roosville (east), and Mount Nelson formations are dominated by detrital zircon ages between 1375-1450 Ma and 1650-1800 Ma. Detrital zircon ages from the Roosville Formation (west) are dominated by 1500-1625 Ma grains. Based on the margin perpendicular orientation of the long axis of syn-depositional grabens relative to Laurentia, and on the presence of syn-depositional aged zircons through the entire sedimentary succession, we interpret the upper Purcell Supergroup to have been deposited in a transpressional pull-apart basin setting, adjacent to a convergent/translational plate margin bound to the west by terranes now located in northeastern Australia.

Thesis (M.S.)--Brigham Young University. Dept. of Geology, 2006. / Includes bibliographical references (p. 42-46).

Submitted by Aline de Cassia Carlin null (alinecarlin@yahoo.com.br) on 2016-11-23T10:59:57Z No. of bitstreams: 1 Mestrado_AlineCarlin.pdf: 8299590 bytes, checksum: 2fccc8ef8565c36ad917cbdc0c96c8e3 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-11-25T17:30:28Z (GMT) No. of bitstreams: 1 carlin_ac_me_rcla.pdf: 8299590 bytes, checksum: 2fccc8ef8565c36ad917cbdc0c96c8e3 (MD5) / Made available in DSpace on 2016-11-25T17:30:28Z (GMT). No. of bitstreams: 1 carlin_ac_me_rcla.pdf: 8299590 bytes, checksum: 2fccc8ef8565c36ad917cbdc0c96c8e3 (MD5) Previous issue date: 2016-10-10 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O depósito de ouro Lavra Velha, que pertence ao Alvo de Prospecção Lavra Velha, da empresa Yamana Gold, localiza-se na cidade de Ibitiara, centro-oeste do Estado da Bahia e borda oeste do domínio fisiográfico da Chapada Diamantina, situado no Aulacógeno do Paramirim, na região norte do Cráton São Francisco. O depósito foi recentemente inserido na classe de modelo IOCG (Iron Oxide Cooper Gold), onde a mineralização de ouro se hospeda em brechas hematíticas sericitizadas. O principal objetivo do trabalho foi caracterizar química e petrograficamente as rochas encaixantes do depósito Lavra Velha, cujas litologias predominantes são metatonalitos e meta-quartzo diorito. Estas rochas encontram-se completamente alteradas, com atuação dos processos hidrotermais predominando sobre a deformação de baixo strain, resultando em intensa sericitização e formação de óxidos de ferro, além de cloritização, epidotização, carbonatação e, localmente, albitização. A análise petrográfica, suportada pela análise química, sugere que as rochas encaixantes são correspondentes alteradas do Granitoide Ibitiara, metamorfizadas, deformadas e alteradas hidrotermalmente. O Granitoide Ibitiara e o Granito Matinos apresentam comportamento de magmatismo misto e afinidade para ambiente de arco magmático (sin-colisional) ou orogênico, com idades correlatas ao ciclo orogênico Transamazônico. A intrusão do Granitoide Ibitiara ocorre, provavelmente, em ambiente mais raso da crosta, sugerindo que fluidos hidrotermais e mineralizantes sejam mais tardios. Apesar de integrado até o momento à classe de depósitos IOCG, a análise tectono-estrutural e hidrotermal do depósito Lavra Velha sugere que a mineralização de ouro tenha origem relacionada à fase mais tardia de evolução da bacia do Espinhaço, relacionada à inversão do aulacógeno do Paramirim. / The Lavra Velha gold deposit, which belongs to the prospecting target “Lavra Velha” of the Yamana Gold Company, is located in Ibitiara, Bahia’s central west and the western edge of the physiographic domain of the Chapada Diamantina, situated in Paramirim aulaconge, in northern of São Francisco Craton. The deposit was recently insert into the IOCG model class (Iron Oxide Cooper Gold), where the gold mineralization is hosted at hematite sericitic breccias. The main objective of the study was the chemical and petrographic characterization of the host rocks of the Lavra Velha deposit, whose predominant lithologies are meta-tonalites and metaquartz diorite. These rocks are completely altered due to hydrothermal process, that predominates under the deformation at low-strain rate, resulting in intense sericitization and iron oxide formation, also chloritization, epidotization, carbonatation and, locally, albitization. The petrographic analysis, supported by chemical analysis, suggests that the host rocks correspond to metamorphosed, deformed and hydrothermalized portion of Ibitiara Granitoid. The Ibitiara Granitoid and Matinos Granite show behaviors of mixed magmatism and also affinity for arc magmatic (syn-collisional) or orogenic ambient with correlative age to the Transamazônico Cycle. The Ibitiara Granitoid intrusion probably occurs at a shallower crust environment, suggesting that the hydrothermal and mineralizer fluids are later. In spite of the Lavra Velha deposit has being classified as IOCG’s class, the tectonic, structural and hydrothermal analysis suggests that the gold mineralization has originated during Espinhaço basin later deformation stage, related to inversion of the Paramirim aulacogen.

Fundação de Apoio a Pesquisa e à Inovação Tecnológica do Estado de Sergipe - FAPITEC/SE / The studied acid metavolcanic rocks outcrop at Estrada Real, Rio de Contas (BA), SW of Bahia State. Those rocks represent the Novo Horizonte Formation, basal portion of Rio dos Remédios Group (Espinhaço Supergroup) and are associated to development of sin-rift phase at Oriental Espinhaço basin, at Chapada Diamantina. The methodology used to make this work consisted of fieldstrip, petrography and geochemistry. Twenty-one samples have selected to petrographic analyses and ten to whole rock chemical analyses. The rocks show grey to dark-grey color, are aphanitic and show incipient to well-marked foliation. Petrographically, the rocks present porphyroblastic, lepidoblastic and blast-porphyritic textures. The mineralogy consists of quartz blasto-porphyries, andaluzite and kyanite porphyroblasts, garnet pseudomorphs, feldspars, biotite, muscovite, sericite, chlorite, epidote, monazite, zircon and opaque minerals immersed in a quartz-feldspar matrix. The trace elements spiderdiagram shows enrichment of LILEs in relation to HFSEs. The negative anomalies of Sr, P, Nb-Ta and Ti are notable. The distribution patterns of the Rare Earth Elements show enrichment in ETRL in relation to ETRP and negative anomaly in Eu. It suggests the formation of these rocks in a continental rift environment, from a mantle previously modified by subduction. / As rochas metavulcânicas ácidas estudadas afloram na Estrada Real, Rio de Contas (BA), sudoeste do Estado da Bahia. Estas rochas representam a Formação Novo Horizonte, porção basal do Grupo Rio dos Remédios (Supergrupo Espinhaço) e estão associados ao desenvolvimento da fase sin-rifte na Bacia Espinhaço Oriental, na Chapada Diamantina. A metodologia utilizada para a realização deste estudo consistiu no trabalho de campo, petrografia e geoquímica. Vinte e uma amostras foram selecionadas para análise petrográfica e sete amostras para análise química de rocha total. As rochas possuem tonalidade cinza a cinza escuro, são afaníticas e apresentam foliação incipiente a bem marcada. Petrograficamente, apresentam textura porfiroblástica, lepidoblástica e blasto-porfirítica. A mineralogia é constituída por blasto-pórfiros de quartzo, porfiroblastos de andaluzita e cianita, pseudomorfos de granada, feldspatos, biotita, muscovita, sericita, clorita, epidoto, monazita, zircão e minerais opacos imersos em uma matriz quartzo-feldspática. As metavulcânicas foram classificadas como riolitos. O diagrama multi-elementar de elementos-traço mostra enriquecimento de LILEs em relação aos HFSEs. As anomalias negativas de Sr, P, Nb-Ta e Ti são notáveis. Os padrões de distribuição dos Elementos Terras Raras evidenciam enriquecimento em ETRL em relação aos ETRP e anomalia negativa de Eu. A formação dessas rochas em um ambiente de rifte continental é sugerida, a partir de um manto previamente modificado por subducção.

M.Sc. (Geology) / The Mzimvubu River, situated in the Eastern Cape Province of South Africa, drains essentially strata of the Late Carboniferous to Jurassic Karoo Supergroup with minor intersection of the underlying Devonian Msikaba Formation near the mouth of the river at Port St. Johns. Rock- and river sediment samples were collected at specific points from within the Mzimvubu River drainage basin, based on changes in the geology through which the rivers flow. Detrital zircon age population data was obtained by LA-ICP-MS for each sample in order to meet the two-fold objective of the study; firstly to investigate the reliability of using detrital zircon grains as indicators of sedimentary provenance and secondly to determine possible source areas for the Karoo strata and underlying Msikaba Formation. Through the comparison of detrital zircon age population data for the rock units of the Karoo Supergroup and Msikaba Formation to that of the river sediment, it is concluded that detrital zircon grains hold value in deciphering the geological history of a sedimentary basin. This interpretation is based on similar distributions and trends that are present in both the zircon age populations of the rock- and sediment samples. However, complexities associated with detrital zircon analysis pertaining to rock type and depositional settings are noted and therefore certain procedures that can be implemented during field sampling have been suggested in this study so as to ensure accurate results are obtained. This will further ensure that reliable interpretations of the geological history of a sedimentary basin are achieved. Additionally, by utilising the detrital zircon population data obtained in the first part of the study in conjunction with published scientific data, the provenance of the Karoo Supergroup in the southeastern part of the Main Karoo Basin has been determined. From this data it was determined that, especially the upper part of the Karoo Supergroup in the Eastern Cape Province of South Africa, was deposited much later than previously thought and that many of the stratigraphic layers in the Karoo Basin were deposited coevally in different parts of the basin with lithostratigraphic boundaries being time-transgressive. Ultimately the data allowed for the construction of a tectono-sedimentary model to explain the deposition of the upper Cape- and Karoo Supergroups that started with the deposition of the Msikaba Formation in a passive continental margin setting, to deposition of the lower part of the Karoo Supergroup in an Andean type of foreland basin, with rifting starting during the times of deposition of the Molteno Formation. The deposition of the Molteno-, Elliot- and Clarens Formations took place as Gondwanaland was breaking apart coeval with the formation of the Karoo Igneous Province.

[Truncated abstract] The realization in 1999 that the authigenic phosphate, xenotime, could be used in geochronological studies to place age constraints on burial events that affected sedimentary basins has opened numerous opportunities for establishing timeframes for sedimentary basin analysis. Since then, the mineral has been used to place new and novel age constraints on diagenesis, metamorphism, and hydrothermal alteration and mineralization events. Whilst these studies were successful, they identified many complexities in xenotime growth and were restricted to specific areas or single basins: they do not convey, demonstrate or explore the immense variety of geological applications in which xenotime may provide unique geochronological constraints. This thesis explores the nature of authigenic xenotime, utilizing studies in three different Proterozoic sedimentary basins: two in Australia, southwestern Australia and the Northern Territory, and the third in the United States of America. The thesis includes a number of discrete studies demonstrating different aspects of xenotime growth, elucidated from detailed petrography, geochronology and geochemistry of authigenic xenotime. An integrated textural, geochemical and geochronological study of authigenic xenotime from the Mt Barren Group, SW Australia, establishes an absolute timescale on some of the many processes involved during the diagenesis of siliciclastic units. ... positions and trends and broadly confirm the chemical discrimination criteria established for an Archaean basin. However, the Proterozoic data are shifted to lower Gd-Dy values and extend beyond the original field outlines, causing more overlap between fields intended to discriminate xenotimes of different origin. The plots were revised to encompass the new data. This study has significantly extended our knowledge of the nature of authigenic xenotime. It was found that xenotime may form in (meta)sediments in response to a large number of post-depositional processes, including early- and latediagenesis, (multiple) basinal hydrothermal events and low-grade metamorphism. A combination of detailed petrography and in situ geochronology provides the best avenue to decipher complex growth histories in xenotime. With further development, it is likely that xenotime geochemistry will also prove diagnostic of origin and can be incorporated into the interpretation of age data. The number of potential applications for xenotime geochronology has been expanded by this study.

The Paleoproterozoic Transvaal Supergroup in the Northern Cape Province of South Africa is host to high-grade BIF-hosted hematite iron-ore deposits and is the country’s most important source of iron to date. Previous work has failed to provide a robust and all-inclusive genetic model for such deposits in the Transvaal Supergroup; in particular, the role of hydrothermal processes in ore-genesis has not been adequately clarified. Recent studies by the author have produced evidence for hydrothermal alteration in shales (Olifantshoek Supergroup) stratigraphically overlying the iron-ore intervals; this has highlighted the need to reassess current ore-forming models which place residual supergene processes at the core of oregenesis. This thesis focuses on providing new insights into the processes responsible for the genesis of hematite iron ores in the Maremane anticline through the use of newly available exploration drill-core material from the centre of the anticline. The study involved standard mineralogical investigations using transmitted/reflected light microscopy as well as instrumental techniques (XRD, EPMA); and the employment of traditional whole-rock geochemical analysis on samples collected from two boreholes drilled in the centre of the Maremane anticline, Northern Cape Province. Rare earth element analysis (via ICP-MS) and oxygen isotope data from hematite separates complement the whole-rock data. Iron-ore mineralisation examined in this thesis is typified by the dominance of Fe-oxide (as hematite), which reaches whole-rock abundances of up to 98 wt. % Fe₂O₃. Textural and whole-rock geochemical variations in the ores likely reflect a variable protolith, from BIF to Fe-bearing shale. A standard supergene model invoking immobility and residual enrichment of iron is called into question on the basis of the relative degrees of enrichment recorded in the ores with respect to other, traditionally immobile elements during chemical weathering, such as Al₂O₃ and TiO₂. Furthermore, the apparently conservative behaviour of REE in the Fe ore (i.e. low-grade and high-grade iron ore) further emphasises the variable protolith theory. Hydrothermally-induced ferruginisation is suggested to post-date the deposition of the post-Transvaal Olifantshoek shales, and is likely to be linked to a sub-surface transgressive hydrothermal event which indiscriminately transforms both shale and BIF into Fe-ore. A revised, hydrothermal model for the formation of BIF-hosted high-grade hematite iron ore deposits in the central part of the Maremane anticline is proposed, and some ideas of the author for further follow-up research are presented.

Abstract Mineralogical-mineral chemical characterisation of Nb-Ta-bearingassemblages from the Stripåsen granitic pegmatite, NorbergJens Henriksson The occurrence of Nb-Ta-bearing minerals has earlier been briefly documented inthe Stripåsen granitic pegmatite, Norberg, central Bergslagen. This report describesthe background, preparation and basic characterisation of sampled Nb-Ta-bearingmineral assemblages from this pegmatite. These comprise (Y,REE,U,Th)-(Nb,Ta,Ti)-oxides of mainly a tantalum-dominated A 2-m B 2 X 6-w Y 1-n -type, belonging to the pyrochloresupergroup. The major primary mineral is suggested to have been afluorcalciomicrolite, ideally (Ca,Na,☐) 2 Ta 2 O 6 F. In association with abundant fractureformation related to metamictisation of the microlite minerals, they are interpreted tohave been variably altered by late-stage fluids. Thus, the system has beenextensively modified after the primary crystallisation of the pegmatite melt. Besidesthese (Y,REE,U,Th)-(Nb,Ta,Ti)-oxides, monazite-(Ce) ((Ce, LREE)PO 4 ), nativebismuth (Bi) and presumably radiogenic galena (PbS) were identified. The sampleshave mainly been studied by means of scanning-electron-microscopy with energydispersive spectroscopy (SEM-EDS), utilising reflected polarised light microscopy asa complementary tool. The study was done within the framework of the EU-supported FRAME-project which is focused on a selection of metals and minerals,among others niobium (Nb) and tantalum (Ta). / Sammanfattning Mineralogisk-mineralkemisk karakterisering av Nb-Ta-förande associationerfrån Stripåsenpegmatiten, NorbergJens Henriksson Förekomsten av Nb-Ta-förande mineral har tidigare dokumenteras iStripåsenpegmatiten, Norberg, centrala Bergslagen. Här redogörs för bakgrund,provförberedelse och grundläggande karakterisering av provtagna Nb-Ta-förandemineralassociationer från denna pegmatit. Proven som undersökts innehåller(Y,REE,U,Th)-(Nb,Ta,Ti)-oxider av främst tantaldominerad A 2-m B 2 X 6-w Y 1-n -typtillhörande pyroklorsupergruppen. Den huvudsakliga primära fasen tolkas ha varit enfluorkalciomikrolit, idealiskt (Ca,Na,☐) 2 Ta 2 O 6 F. I anslutning till rikligt förekommandesprickor som är relaterade till omfattande metamiktisering har mikroliternaomvandlats i varierande grad av sena fluider. Systemet har alltså förändrats kraftigtefter den primära kristallisationen av pegmatitsmältan. Förutom (Y,REE,U,Th)-(Nb,Ta,Ti)-oxider identifierades monazit-(Ce) ((Ce,LREE)PO 4 ), gedigen vismut (Bi)och vad som sannolikt är radiogen blyglans (PbS). Provmaterialet har huvudsakligenundersökts med genom svepelektronmikroskopi med energidispersiv spektroskopi(SEM-EDS), varvid malmmikroskopi har använts som ett kompletterande verktyg.Studien gjordes inom ramverket för det EU-stödda FRAME-projektet som blandannat fokuserar på förekomster av de kritiska och konfliktrelaterade metallerna niob(Nb) och tantal (Ta).