The oxidation state, reflected in the oxygen fugacity (fO2), of the lithospheric mantle is both laterally and vertically heterogeneous. Depth-fO2 profiles from kimberlite-borne peridotitic mantle xenoliths from the Bultfontein kimberlite, Kimberley, South Africa and the A154-N and A154-S kimberlites of the Diavik Mine, NWT, Canada were constructed by measuring ferric iron concentrations in garnets using the flank method. These data demonstrate that mantle metasomatic re-enrichment processes had a significant effect on fO2. In the garnet stability field, the Kaapvaal lithospheric mantle becomes progressively more reducing with increasing depth from Δlog fO2 (FMQ) of -2 at 110 km to -4 at 210 km. The lithospheric mantle beneath Diavik is vertically layered with respect to its bulk and trace-element composition. The shallow ‘ultradepleted’ layer is oxidized, to the point that carbonate rather than graphite is the anticipated carbon host. The deeper layer is more fertile and has fO2 conditions extending down to Δlog fO2 (FMQ) -3.8. Deviations from predicted depth-fO2 trends in both xenolith localities result from metasomatic re-enrichment caused by transient fluids and melts. Diamond formation in the Kaapvaal lithospheric mantle may have occurred through the infiltration of reduced fluids into relatively more oxidized mantle. Trace-element concentrations in garnets preserve evidence of two distinct melt metasomatic enrichment events. One was a craton-wide event that is commonly observed in garnet peridotite xenoliths and xenocrysts worldwide; the other was melt infiltration event, preserved as MARID xenoliths, related to the eruption of the Group 2 kimberlites in the western portion of the Kaapvaal craton. The effect of the former melt metasomatism on fO2 is unclear ambiguous whereas the MARID event was clearly oxidizing. Diavik xenoliths preserve evidence for events similar to the fluid and ‘common’ melt metasomatism seen in the Bultfontein samples. Fluid metasomatism affected the entire depth range of xenoliths sampled from Diavik and was oxidizing. A stage of melt metasomatism affected only the deeper (>140 km) portion of the lithospheric mantle and had an overall reducing effect. The observation of sharp-edged octahedral diamonds in microxenoliths affected by the fluid metasomatic event may indicate that this was a major diamond-forming event in the mantle beneath Diavik.

Thèse (M.sc.A.)-- Université du Québec à Chicoutimi, 1981. / "Thèse présentée à Chicoutimi en vue de l'obtention d'une maîtrise en science appliqué (géologie)" CaQCU Document électronique également accessible en format PDF. CaQCU

Magister Scientiae - MSc (Earth Science) / The complexity of the Platreef stratigraphy and the generic position of the Ni-Cu-PGE mineralisation is a challenge to prospecting and mining companies in the Northern Limb of the Bushveld Complex, partially, as a result of various floor rock interactions with the reef. Therefore, this study evaluated the effects of contact metasomatic fluids on the nature and style of PGE mineralisation as the main event leading to the complexity of the Platreef stratigraphy from the contact zone near the floor rock. Fifty samples from boreholes MO009 and MO019 drilled at Moordkopje 813 LR farm for Akanani Project by Lonmin Plc were used for this study. The mineralogy and geochemistry of the Platreef samples were studied and associated with their mineralisation occurrences. Major, minor and trace element contents were analysed by XRF analysis using fused beads, and PGE contents (Pt, Pd) in 11 samples were determined by Fire Assay.

>Magister Scientiae - MSc / This study is focused on the Akanani prospect area, approximately 25 km north-west of the town of Mokopane, Limpopo Province where exploration geologists at the study area have classified the ‘pyroxenitic’ units into P1, P2, P3 and P4 units upward in order of succession with height based on their textures, mineralogy and colour. The primary aim of this study is to distinguish the distinctive geochemical and mineralogical characteristics that can be used to identify each unit (P1 to P4) and in so doing create major geochemical, petrographic and mineralogical variables that will help or facilitate the exploration for and recovery of PGE and BMS mineralisation. Geochemical and mineralogical variation studies were carried out on the cores from ZF044, ZF045, ZF048, ZF057, ZF078, ZF082 and M0023, located in the Platreef at the Akanani Prospect area on the farms Moordkopje 813LR and Zwartfontein 814LR. Using a combination of various multivariate statistical techniques (factor, cluster and discriminant analysis) and mineralogical studies (CIPW norm, microprobe analysis, petrography), the outcomes of the study have demonstrated that the Platreef at Akanani comprise at least four lithological units i.e. the basal pyroxenite portion referred to as the P1 unit comprises chromitite, pyroxenites and feldspathic pyroxenites with associated Cr, TiO2, chromite, pyroxenes, hematite and Fe2O3, the mineralized section of the P2 unit is characterized by harzburgite, serpentinized harzburgite and in places orthopyroxenites are present consistent with high MgO and LOI contents, the feldspathic portion referred here as the P3 unit is characterized by a feldspathic pyroxenite containing higher Al2O3, Na2O, K2O, albite, hypersthene and SiO2 and the top most portion of the P4 unit comprising CaO, Diopside, ilmenite, anorthite, apatite and P2O5 that can be interpreted to have formed by three separate magma pulses. Considering the possibility that the P4 unit is a hybrid melt of assimilated Platreef that interacted with intruding Main Zone magma, this reduces the number of magma pulses to two. The classification of P1, P2, P3 and P4 units of the Platreef at Akanani shows that the criteria used by mining personnel to classify the four lithological units is not definitive and therefore are not highly reliable. Although various multivariate statistical techniques were employed relatively similar elemental associations were obtained highlighiting the importance of this approach. The strongly positive correlation between sulphides, PGEs and chromite at Akanani is consistent with an orthomagmatic deposit that had been disturbed by significant hydrothermal activity, while in places a good BMS-PGE relationship is commonly associated with the main chromitite stringers in P1. Mineral and whole rock compositions of silicate rocks highlight the strongly magnesian nature of the ultramafic P2 unit. Mineral chemistry studies of chromite, orthopyroxene, olivine, clinopyroxene and plagioclase are consistent with the multi- emplacement model. Convective exchange resulted in the enrichment of iron at the bottom of the stagnant chamber, while incompatible elements migrated upwards consistent with iron depletion with stratigraphic height. Injection of P1 magma and subsequent mixing with country rocks gave rise to the formation of chromitites and addition of plagioclase component to the intruding magma. A normal fractionation trend is suggested between P2 and P3 consistent with enrichment of MgO in P2 and enrichment of Al2O3, Na2O, SiO2 and K2O in P3. The An% of 84.4 of plagioclase coupled with CaO enrichment in P4 is suggestive of some Main Zone influence and can be interpreted as resulting from partial melting and recrystallization of P3 in response to the intrusion of the Main Zone magma is suggested for the formation of the P4 unit. There exists a good correlation between the modal mineralogy and mineral chemistry as determined optically, the norm as determined by the CIPW norm and the whole-rock geochemical results as determined by multivariate statistics and conventional methods.

This study investigates the ultrahigh pressure (UHP) metamorphic and metasomatic processes involved in the transient subduction-exhumation of continental crust to over 100km depths during a collisional orogeny and the implications for the evolution of the continental crust and crust-mantle interaction at depth. The study focuses on garnet websterites (orthopyroxene eclogites) and zoned, clinopyroxenite-garnetite veining features present in a range of eclogite-facies, crustal metamafic-ultramafic bodies hosted within the Western Gneiss Region (WGR), western Norway. The structural occurrences and textures of some of these crustal garnet websterites are seemingly unique to the WGR but little research has focused on their origin or from a metasomatic perspective. Based on field and petrographic observations, a metasomatic origin is attributed to vein-associated garnet websterites at Kolmannskog, Myrbærneset and Svartberget. A metamorphic origin is attributed to body domains at Nybø, Kolmannskog, Båtneset and Myrbærneset and a combined metamorphic-metasomatic origin is attributed to garnet websterite body domains at Årsheimneset and Remøysunde and inferred at Grytting and Eiksunddal. UHP P-T conditions are obtained from garnet websterites of ~3.7GPa, 740°C at Nybø, ~3.1GPa, 670°C at Grytting, ~3.5GPa, 700°C at Årsheimneset, ~3.6GPa, 815°C at Remøysunde, ~3.0GPa, 750°C at Kolmannskog and ~3.85GPa, 790°C at Svartberget. On this basis, it is proposed the Nordøyane UHP domain be extended eastwards to incorporate the Kolmannskog locality which lies outside its currently defined boundary. Constructed P-T paths suggest the northern Nordøyane UHP domain experienced ~100°C higher temperatures than the southern Nordfjord-Stadlandet UHP domain but experienced similar pressures implying a lower regional P-T gradient than previously established. P-T paths also suggest UHP, vein-forming metasomatism occurred prior to peak temperatures. U-Pb isotopic dating of zircon and monazites in garnetite vein cores dates UHP metasomatism at 414±5.6Ma at Årsheimneset and 410±2.6Ma at Svartberget. The fluid responsible for UHP metasomatism is considered to be a Si-Al-K-H2O-rich supercritical liquid produced in the surrounding country rock associated with the breakdown of phengite with a Na-LILE-LREE-HFSE-P enrichment signature. The major element composition of the fluid added to the Svartberget body is calculated to be 48-60% SiO¬2, 17-27% Al2O3, 3-11% K2O, <10% MgO, CaO and FeO, 3-6% Na2O, <4% P2O5¬, <1% TiO2 and MnO with an overall, undersaturated-saturated sialic, syenitic character hybridised through interaction with the garnet peridotite body margins. The continental fluid-mafic-ultramafic rock systems studied imply a zoned metasomatic unit forms at the interface between subducted continental crust and above mantle wedge at depths of ≥120-130km and along any fluid pathways penetrating into the mantle transferring abundant alkalis, water and trace elements into the mantle. Fluid-mantle interaction is proposed to form abundant biotite and amphibole and zones of garnet websterite, biotite websterite and biotite clinopyroxenite with lenses of eclogite and/or accessory phase (rutile, zircon, monazite, apatite, xenotime)-rich garnetite ±glimmerite selvages where residual fluids accumulate. Subcontinental mantle metasomatism may be associated with UHP, supercritical liquids derived from subducted, eclogite-facies, continental crust rather than oceanic crust as the continental crust is a greater source of the Si, alkalis, trace elements and water which characterise mantle metasomatism.

>Magister Scientiae - MSc / The Platreef is known for its complexity and its heterogeneous lithologies, coupled with an unpredictable PGE and BMS mineralisation. The motivation behind this study was to aid mining geologists in targeting mineralisation irrespective of the farm. It is known that the Platreef generally overlies different footwall lithologies at individual farms. Thus, the aims of this study were firstly to investigate the potential of chemostratigraphy by delineating indices indicative of distinctive lithological layers. These indices were then tied to the second aim; which were to use geochemical vectoring, which is process-based, to target the PGEs at two different farms. This study included three drillcores: from the farms Sandsloot (SS339) and Tweefontein (TN754 and TN200). The footwall units at Tweefontein are shales of the Duitschland Formation and the Penge banded iron formation; and at Sandsloot it is the Malmani Subgroup dolomites. Samples included 121 quarter cores, used for petrographical and geochemical studies. The elemental rock composition was determined by XRF and ICP-OES analyses. The approach also included statistical and mass balance methods to understand the geological and geochemical controlling processes. Initially, the Platreef package at both farms was petrographically divided into three main layers: pyroxenite, and two distinctive feldspathic pyroxenites (FP-I and FP-II). However, the pyroxenites were also further separated as P-I and P-II, because of a higher notable difference in the degree of alteration within P-I. Progressive degrees of metasomatism were further observed in the lithologies, e.g. within the Platreef package, where feldspathisation was potentially the main metasomatic process. Many geochemical plots (corroborated by the petrographical and mass balance results) illustrated that the feldspathisation were linked to an increase in the content of Al₂O₃ and CaO, and coupled with a decrease in content of Fe₂O₃ and MgO. Together with other geochemical trends, geochemically distinct units of the Platreef package could be discriminated with a metasomatism index (MI; CaO + 10Na₂O / CaO + 10Na₂O + Fe₂O₃ + MgO). The ensuing MI is lowest for the P-II pyroxenite and shows a progressive increase through FP-I, P-I to the highest values in FP-II. Geochemical layering were also observed in the calcsilicates and hornfels; e.g. a progressive decrease in the content of Fe₂O₃, Al₂O₃, Ce, Co, Cu, Ni, Zn, Zr, Au, Pd and Pt from the hornfels subunits H-I, H-II to H-III and an increase in of SiO₂, Fe₂O₃, TiO₂, SO₃, Co, Cu, Ni, Rb, V and Zn content from CS-I, CS-II to CS-III. Correlating the pyroxenites and feldspathic pyroxenites spatially from one drillcore to another were hindered, hence, chemostratigraphy were not completed. In terms of vectoring, it was essential to establish a possible link between the metasomatism index and the nature and style of the PGE and/or BMS mineralisation. The Hornfels subunit H-I and calcsilicate subunit CS-III were the main carriers of BMS and PGE. The Platreef package were more complicated: P-I (low PGE, low BMS); P-II (low PGE, high BMS); FP-II (high PGE, low BMS); and FP-I (high PGE, high BMS). Element indices (e.g. Cu+Ni and Co+Zn) were developed to define a consistent gradient indicative of these ore subunits. A validation process to assess the metasomatism index (MI), base metal indices and PGE distribution within the individual drillcores (TN754, TN200 and SS339) were then undertaken. The results were that the MI ranges were similar in all drillcores, and discriminated the subunits of the Platreef package, gabbronorites and even the calcsilicates. The base metal ratios (e.g. Ni/Co and Cu/Co) were indicative of the PGE rich zones. Trends of the base metal ratios reflected a strong positive relationship with the MI within the Platreef package and the calcsilicates. However, the opposite trend is observed with the hornfels. In conclusion, the MI could potentially be a strong vector of high PGE and BMS mineralisation. It is also possible to discriminate lithologies within the Platreef package with the MI. However, it should be noted that the limitation of this study is that the results are based on three drillcores. The Platreef is heterogeneous at individual farms and extremely diverse across the northern limb. Therefore, future research could be undertaken to validate these findings, by using a bigger drillcore database. / National Research Foundation

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19511号 / 理博第4171号 / 新制||理||1599(附属図書館) / 32547 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 河上 哲生, 教授 平島 崇男, 教授 山 明 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

No description available.

A common driving mechanism of metamorphic processes, from which secondary mineralizations and structures develop in a protolith, is known to be a change of the immediate P-T environment that a rock resides in. A factor in this process, which is poorly understood, however, is how the presence of metamorphic fluids in a system, influences the alteration of primary igneous rocks. How these volatile solutions interact with the solid mediums of the crust is thereby a topic which requires further research to unravel.    Incidentally, an opportunity to study the result of these interactions, has presented itself in the southern part (59o80’92”N, 17o59’91”E) of Hågadalen-Nåsten nature reserve in Uppsala, Sweden. In this area, a green mineral assemblage, believed to belong to the epidote group, has been observed. This mineral is theorized to have formed as a result of fluid-rock interactions that have occurred in the region and is therefore a subject of interest. A detailed study of the origin of this mineral assemblage could possibly shed light on the finer aspects of the fluid-rocks interactions that have occurred, and also provide and account of the transport of fluids throughout the local bedrock. The aim of this project was to identify the minerology and formation process of this green mineral, which occupies the joints in a cliff of granitic composition. The determination of how and when this mineral assemblage formed is believed to grant a more in depth understanding of the metamorphic and metasomatic processes that have transpired at this location, in addition to providing an account of the fluid transport and fluid-rock interactions in the area.   Through fieldwork and sampling, combined with descriptions of the regional bedrock provided by SGU, the local lithology was determined. With this information, in addition to data collected from optic microscopy and an EMP analysis, the mineral was identified to be an iron rich epidote, showing signs of weak zoning. The formation of this secondary mineralization can be determined to be the result of the alteration of anorthite to saussurite (saussuritization of plagioclase) in addition to the direct precipitation of epidote from the liquid medium onto joint surfaces. Through the use of BSEM, it could also be determined that a majority of the fluids migrated through open fracture systems in the bedrock. / Förändringar av de tryck och temperaturregimer som bergarter befinner sig inom, har sedan länge varit en känd orsak bakom de metamorfa processer, ur vilket sekundära mineraliseringar och strukturer uppstår i protoliten. Något som inte är lika väl studerat är dock rollen som fluider spelar i dessa förändringsprocesser, samt hur dessa volatila lösningar interagerar med skorpans solida faser.   I södra delen av Hågadalen-Nåstens naturreservat (59o80’92”N, 17o59’91”E2) har dock möjligheten till att studera resultatet av dessa interaktioner uppstått. Detta då en grön mineralsammansättning troligen tillhörande epidot gruppen, har upptäckts, vars ursprung tros komma ur fluid- och bergarts interaktioner i området. En studie av detta mineral är därav av intresse, eftersom det skulle ge en inblick i hur dessa fluider har transporterats genom den lokala berggrunden, samt vilken påverkan dessa fluid-interaktioner har haft på områdets bergarter.   Detta projekt syftade mot att identifiera mineralogin samt bildningsprocessen av detta gröna mineral som fyller ut sprickor i en vertikal klippvägg, av överhängande granitisk karaktär. En utredning kring hur och när detta mineral har bildats tros kunna ge en fördjupad förståelse kring de metamorfa och metasomatiska processer som har ägt rum i närområdet, samt antyda hur dessa fluider har migrerat genom den tidigorogena berggrunden och vilken påverkan detta har haft på bergsmassivet.      Genom observationer och provtagning i fällt, samt en studie av SGU:s beskrivning av berggrunden i området 11I Uppsala NV, har de den lokala litologin samt de geologiska processerna som påverkat närområdet utretts. Denna information, i kombination med optisk mikroskopi och en EMP analys, användes för att fastställa mineralets kemiska karaktär och kristallsystemstillhörighet. Resultaten från dessa analysmetoder lade grunden för att identifiera mineralet som en järn-rik, svagt zonerad, epidot.       Troliga processer som har legat bakom bildandet av denna sekundära mineralisering bedöms vara omvandlingen av anortit till saussurit (saussuritisering av plagioklas) samt kristallisering av epidot direkt ur fluider som cirkulerat i området. Genom observationer av BSE bilder från tunnslip, fastställdes även att majoriteten av dessa fluider har transporterats genom redan befintliga spricksystem i berggrunden.

The garnet line is a planar fabric occuring within the intermediate and core zone in many of the Oxford County, Maine pegmatites. This study focuses primarily on the textural and chemical characteristics of the garnet line within the Mt. Mica and western Mt. Apatite quarries. Smaller, but similarly textured garnet line analogs from the Bennett, Emmons, Havey and Tamminen quarries are also investigated. All of these textures represent specific fractionation events within their respective dikes. In some of these locations, multiple stages of crystallization occur and appear to be post-magmatic, related to late stage metasomatism. These late stage fluids are believed to have migrated from localized and highly evolved regions within these pegmatites. The garnet line at Mt. Mica has the greatest diversity of secondary mineral assemblages, e.g. tourmaline and/or muscovite rims around garnets and ferric pollucite. None of these late stage textures have ever been described before.