Dissertations / Theses on the topic 'Fluid inclusion'

Magmatic-hydrothermal ore deposits are formed in association with aqueous fluids that exsolve from hydrous silicate melts during ascent and crystallization. These fluids are invariably trapped as inclusions in vein-filling minerals associated with hydrothermal fluid flow, and their composition may be modeled based on the H₂O-NaCl system. Thus, if we know the pressure-volume-temperature-composition (PVTX) properties of H₂O-NaCl solutions, it is possible to interpret the PTX trapping conditions, which is important for understanding the processes leading to the generation of the hydrothermal system and ore mineralization. High salinity (> 26 wt. % NaCl) fluid inclusions contain liquid, vapor, and halite at room temperature, and are common in magmatic-hydrothermal ore deposits. These inclusions homogenize in one of three ways: A) halite disappearance (Tmhalite) followed by liquid-vapor homogenization (ThL-V), B) simultaneous ThL-V and Tmhalite, or C) ThL-V followed by Tmhalite. The PVTX properties of H₂O-NaCl solutions three phase (L+V+H) and liquid-vapor (L+V) phase boundaries are well constrained, allowing researchers to interpret the minimum trapping pressure of inclusion types A and B. However, data that describe the pressure at Tmhalite for inclusion type C are limited to a composition of 40 wt. % NaCl. To resolve this problem, the synthetic fluid inclusion technique was used to determine the relationship between homogenization temperature and minimum trapping pressure for inclusions that homogenize by mode C. These results allow researchers to interpret the minimum trapping pressure of these inclusions, and by extension the depth at which the inclusions formed. The temporal and spatial distribution of fluid inclusions formed in associated with porphyry copper mineralization has been predicted using a computer model. A simple geologic model of an epizonal intrusion was developed based on a Burnham-style model for porphyry systems and thermal models of the evolution of epizonal intrusions. The phase stability fields and fluid inclusion characteristics at any location and time were predicted based on PVTX properties of H₂O-NaCl solutions. These results provide vectors towards the center of a magmatic-hydrothermal system that allow explorationists to use fluid inclusion petrography to predict position with the overall porphyry environment when other indicators of position are absent.
Ph. D.

Many geologic processes occur in association with hydrothermal fluids and some of these fluids are eventually trapped as fluid inclusions in minerals formed during the process. Fluid inclusions provide valuable information on the pressure, temperature and fluid composition (PTX) of the environment of formation, hence understanding PTX properties of the fluid inclusions is required. The most important step of a fluid inclusion study is the identification of Fluid Inclusion Assemblages (FIA) that represent the finest (shortest time duration) geologic event that can be constrained using fluid inclusions. Homogenization temperature data obtained from fluid inclusions is often used to reconstruct temperature history of a geologic event. The precision with which fluid inclusions constrain the temperatures of geologic events depends on the precision with which the temperature of a fluid inclusion assemblage can be determined. Synthetic fluid inclusions trapped in the one-fluid-phase field are formed at a known and relatively constant temperature. However, microthermometry of synthetic fluid inclusions often reveals Th variations of about ± 1- 4 degrees Centigrade, or one order of magnitude larger than the precision of the measurement for an individual inclusion. The same range in Th was observed in well-constrained natural FIAs where the inclusions are assumed to have been trapped at the same time. The observed small variations are the result of the effect of the fluid inclusion size on the bubble collapsing temperature. As inclusions are heated the vapor bubble is getting smaller until the pressure difference between the pressure of the vapor and the confining pressure reaches a critical value and the bubble collapses. It was observed that smaller inclusions reach critical bubble radius and critical pressure differences at lower temperatures than larger inclusions within the same FIA. Homogenization temperature (Th) variations depend on many factors that vary within different geological environments. In order to determine minimum and acceptable Th ranges fro FIAs formed in different environments we investigated several geologic environments including sedimentary, metamorphic, and magmatic hydrothermal environments. The observed minimum Th ranges range from 1-4 degrees Centigrade and acceptable Th range from 5-25 degrees Centigrade. The variations are mostly caused by the fluid inclusion size, natural temperature and pressure fluctuations during the formation of an FIA and reequilibration after trapping. Fluid inclusions containing H₂O-CO₂-NaCl are common in many geologic environments and knowing the salinity of these inclusions is important to interpret PVTX properties of the fluids. A technique that combines Raman spectroscopy and microthermometry of individual inclusions was developed to determine the salinity of these inclusions. In order to determine the salinity, the pressure and temperature within the inclusion must be known. The pressure within the inclusions is determined using the splitting in the Fermi diad of the Raman spectra of the CO₂ at the clathrate melting temperature. Applying the technique with to synthetic fluid inclusions with known salinity suggests that the technique is valid and useable to determine salinity of H₂O-CO₂-NaCl fluid inclusions with unknown salinity.
Ph. D.

When hydrothermal fluids flow through microfractures in quartz, they effectively heal (anneal) them to produce Fluid Inclusion Planes (FIPs). These FIPs are viewed as a three dimensional plane or array of secondary fluid inclusions and may be used to relate brittle deformation associated with tectonic, thermal and hydraulic stresses to contemporaneous hydrothermal events. In this study, FIPs have been interpreted in granitic quartz from various geological settings. Analysis of the FIPs includes recording their orientation, the morphological characteristics of both the FIPs and the inclusions contained within them, together with the thermometric properties of the inclusions. Results show that FIPs may possess a preferential orientation over a wide area, similar to the trend of macrostructures observed in the field. However, local deviations in the stress field, related to the proximity of possible second order faults, may cause local deviations in the orientation of the FIPs. The presence of high FIP abundances has also been linked to the widespread, localised development of kaolinisation (possibly linked to tectonic stresses) and greisenisation (possibly linked to thermal and hydraulic stresses). These phenomena have been identified at several localities in the field areas. It is presumed that intense microfracture networks will allow the wide-spread movement of hydrothermal fluids allowing pervasive alteration. A classification scheme for FIPs has been devised, whereby FIPs may been classified as tensile, dilatant (mode 1) and dilatant shear (mode 2) fractures. This classification is based upon the orientation of the FIPs (to macro structures), their proposed origin and their morphology (both the FIP and the inclusions contained within them). Variation in inclusion morphology has been recorded within selected FIPs. Inclusions have been observed to occur parallel and perpendicular (rare) to the length of the FIP. The presence of a preferred shape orientation in the inclusions has been attributed to a combination of fracturing and subsequent healing process, with controlling parameters including the temperature and chemistry of the fluids (affecting crack lifetimes) together with the geometry of the fracture network.

The thesis consists of 8 chapters. The first Chapter gives an introduction to carbonatites and outlines the general aims of this study. The general geology of Sukulu, the methodology used in this research, and previous work are presented in Chapter 2. Detailed descriptions and analytical results on the principal minerals are given in Chapter 3. Chapters 4 and 5 focus on aqueous and solid inclusions in apatite, and detailed descriptions, microthermometric results and interpretations are presented. Determination of oxygen and carbon stable isotope compositions and their interpretations are covered in Chapter 6. Chapter 7 describes geothermometric and geobarometric investigations and the calculation of oxygen fugacities during the deposition of apatite and carbonate. The final chapter discusses evolution of the fluids in the Sukulu carbonatite complex and presents a petrogenetic model. Aqueous inclusions in apatite from the Sukulu carbonatite consist essentially of three types: CO[sub]2-bearing, H[sub]2 0-rich and CH[sub]4-bearing. The CO[sub]2- and CH[sub]4-bearing inclusions, in general, are not present together in individual apatite crystals. It is considered that these compositionally discrete inclusions represent different fluids trapped during different stages of apatite crystallisation. The CO[sub]2-bearing fluid probably formed from an originally H[sub]2 0-rich fluid containing significant CO[sub]2 by immiscible separation under high pressure and temperature. This precursor H[sub]2 0-CO[sub]2 fluid was probably derived from a carbonatite melt, also by a possible process of liquid immiscibility. The CH[sub]4-bearing inclusions were probably formed by late stage hydrothermal processes under different P-T conditions. Many solid inclusions occur in apatite of the Sukulu carbonatite, of which the most abundant are carbonate. They can be classified into Mg-calcite. (primary) and calcite (secondary) inclusions based on their morphology, texture and chemical composition. Although such carbonate inclusions are ubiquitous in carbonatite apatite and have been described by many other workers, this study provides new insight into their genesis and petrogenetic significance. Carbon and oxygen stable isotopic composition from fluid inclusions, in both apatite and matrix carbonate, suggest that the CO[sub]2-bearing fluid was equilibrated with carbonate fluids at an early stage, but it evolved along a different path. The CO[sub]2-bearing fluids which has a stable isotopic composition close to upper-mantle values, evolved in a closed-system after being trapped by apatite, but the carbonate fluid evolved in an open-system and its isotopic composition was elevated by assimilation and contamination during ascent. The results also reveal that post-magmatic processes played an important role in the development of the Sukulu carbonatite. P-T-X isochores calculated for each type of fluid indicate that their evolution was probably from a CO[sub]2-bearing fluid, through a moderate to highly saline one, to a CH[sub]4-bearing one, and took place under temperatures and pressures varying from >1000°C and >7.4kb, through >560°C and >5kb, to about 500°C and <3 kb. This trend represents evolution of the carbonatite from a deep magmatic (carbonate melt) environment towards a shallow level hydrothermal system. This study confirms that both apatite and carbonate-can be precipitated over a wide range of temperatures and melt fluid compositions. The present findings indicate that the compositions of the fluids associated with the Sukulu carbonatite complex appear to have evolved chemically from a Mg-bearing calcite melt, through aqueous CO[sub]2-bearing and bicarbonate-rich melts (NaHC0[sub]3 daughters) to a final aqueous CH[sub]4-bearing fluid.

Abstract In this thesis, a melt and fluid inclusion study was performed to investigate both anatectic melt and fluid phase during anatexis of metapelitic rocks, by studying samples from two different geological settings, the khondalites of the Kerala Khondalite Belt, India, and the granulitic enclaves from El Hoyazo, Neogene Volcanic Province, Spain. In khondalites (garnet-sillimanite-cordierite granulite/gneiss), melt inclusions (MI), interpreted as containing anatectic melt, were found for the first time in peritectic minerals from classic regionally metamorphosed metapelitic migmatites, partially melted at T~900°C and 6-8 kbar. A detailed study was carried out to characterize the petrographic features of MI, their chemical composition and the structures of the crystallized phases within the inclusions, by microscope observation, FESEM imaging in BSE mode, X-ray elemental mapping, EMP and Micro-Raman analyses. Peritectic garnets contain irregular clusters of hundreds of MI, from totally crystallized (nanogranites) to totally glassy, often negative-crystal in shape. Nanogranites are 5-25 μm across and contain a cryptocrystalline aggregate of Bt+Kfs+Pl+Qtz±Ap, along with trapped phases (apatite, zircon, rutile, Zn-bearing spinel and rarely ilmenite) that are likely to have favoured the entrapment of the anatectic melt during the host growth.. The grain size of crystals in nanogranite is variable, from few tens of nanometer to several microns. Partially crystallized inclusions contain a differentiated melt that occupies 60 to 20% of the inclusion area, along with Qtz, Kfs and Bt. Glassy inclusions are usually smaller (2.5–17.5 µm) than nanogranites and represent about 15% of the total amount of MI in the clusters. They contain an amorphous phase, along with the same trapped phases found in nanogranites. EMP analysis of the glass provides an ultrapotassic and rhyolitic composition, with K2O >> Na2O. The EMP totals suggest a H2O content (calculated by difference to 100%) <3 wt%. The occurrence of preserved glassy MI is an unprecedented finding, and since the mean diameter (8 μm) of glassy inclusions is smaller than those of nanogranites (13 μm), we propose that this difference in size was influential to the crystallization of melt droplets, so that most of the smaller inclusions remained glassy because of inhibited nucleation. Nanogranites were homogenized using a heating stage at controlled atmosphere, and then analyzed, to obtain a consistent set of compositional data on their bulk composition. EMP analyses on homogenized inclusions show a compositional homogeneity of the melt from all the nanogranites, with strong similarity to those of preserved glassy inclusions. Melt composition is Na-poor, and plots very far from the “minimum melt” of the haplogranitic system in the Q-Ab-Or diagram, commonly accepted as the composition of the anatectic melt produced by partial melting of metapelites. The retrieved composition, although uncommon for anatectic melts, is reported for natural rhyolites and for experimental products, and accounts for partial melting conditions with T in excess of 850°C, in agreement with the inferred PT conditions of partial melting for these rocks. Moreover, it testifies that assuming a minimum melt composition as representative of the anatectic melt is not correct in the present case study and should not be considered a general rule. The consistency of the compositional data and the careful microstructural investigation of the samples, coupled with the use of the correct techniques of MI homogenization, microchemical analyses and data correction, support for the interpretation of these data as representative of the phase trapped in MI, and the conclusion that MI in garnet from khondalites contain droplets of anatectic melt. This novel result represents therefore an important contribution to the knowledge of anatectic melt in natural rocks. In the second part of the research the granulitic enclaves of El Hoyazo are studied. These partially melted metapelites, ripped off from the basement when anatexis was still an on-going process, contain abundant rhyolitic glass both as layers and pockets, and as glassy inclusions in almost all the minerals of the assemblage. Unlike regionally, slowly cooled rocks, in this case the anatectic conditions were frozen by the rapid ascent of the samples in a uprising magma. MI-bearing garnet is the first peritectic phase produced by partial melting at ~700°C and 5-7 kbar, and contains abundant FI with no visible evidence of post-entrapment modifications, trapped in conditions of fluid-melt immiscibility. A FI study was performed on garnets from Spl-Crd and Bt-Grt-Sil enclaves by microscope investigation, microthermometric studies, Micro-Raman analyses, mass balance calculation and TEM investigation. In Spl-Crd enclaves FI are two-phase (L+V), spherical to tubular, and often contain graphite as trapped phase. Trapped fluid is a mixture of H2O+CO2+N2±H2S±CH4, with water up to 95 mol%, while in Bt-Grt-Sil enclaves FI in garnet are one phase, and contain a CO2+N2 mixtures. In both samples FI have densities that are not consistent with the inferred trapping conditions, and suggest that despite of their primary-looking features, FI re-equilibrated during uprising. TEM investigation on Bt-Grt-Sil samples showed partially healed cracks at sub-μm scale, possible escape pathways for the leakage of fluids out of the inclusions. In Spl-Crd enclaves microchemical data acquired on MI and biotite inclusions, that occur in the same cluster along with FI, demonstrate that a water-rich leucogranitic melt was trapped along with a H2O-rich, COH phase at conditions consistent with the inferred garnet growth (c. 700°C). In garnet from Bt-Grt-Sil enclaves, the almost complete decrepitation and fluid leakage suffered by the studied FI did not allow to estimate the original composition of fluids hosted in garnet. Based on the H2O content of coexisting melt inclusions, however, the fluid is inferred to have been more CO2-rich than the fluid in the Spl-Crd enclaves. This work adds further compositional constraints to the characterization of anatexis of metapelites in the lower crust: in fact, although final results clearly show that enclaves lost part of the original components, the composition of fluid trapped in garnet from Spl-Crd enclaves is probably very close to the original, and is consistent with the composition of the coexisting melt. Research on melt and fluid inclusions in peritectic minerals represents a new approach to the problem of partial melting in natural rocks, and the present study demonstrated that reliable petrological and geochemical information on anatexis can be collected from nano- to micron-scale objects. The dataset reported in this study widens the horizons in crustal petrology, because for the first time the crustal melt composition can be analyzed rather than assumed. Moreover, MI study in migmatites is likely to have large potentials of development, as confirmed by recent findings of anatectic melt trapped in inclusions in peritectic minerals from various migmatite terrains. As regard the fluid coexistent with anatectic melt, the exceptional occurrence of MI and FI in garnets from El Hoyazo enclaves allowed the identification and characterization of a H2O-rich fluid present during the first step of anatexis of these metapelites.
Nel presente lavoro di tesi sono riportati i risultati dello studio di inclusioni fluide e di fuso silicatico effettuato sulle khondaliti della Kerala Khondalite Belt, India, e sugli inclusi granulitici di El Hoyazo, Neogene Volcanic Province, Spagna meridionale, con il fine di caratterizzare l`anatessi di rocce metapelitiche. Nelle khondaliti (gneiss granulitici a granato-sillimanite-cordierite), inclusioni di fuso silicatico (inclusioni vetrose, o MI), interpretate come contenenti fuso anatettico, sono state rinvenute per la prima volta in fasi peritettiche di classiche migmatiti metapelitiche, caratterizzate da metamorfismo regionale con fusione parziale a T~900°C e 6-8 kbar. Le caratteristiche petrografiche delle MI, la loro composizione chimica e il loro fabric interno, dovuto alla presenza di fasi cristallizzate, sono state caratterizzate attraverso l`uso del microscopio ottico e di quello elettronico a scansione con emissione di campo (FESEM), l`acquisizione di mappe elementari ai raggi X e le analisi alla microsonda elettronica (EMP) e in spettroscopia Micro-Raman. I granati peritettici contengono aggregati irregolari costituiti da centinaia di MI, le quali vanno da totalmente cristallizzate (nanograniti) a vetrose, spesso con forme a cristallo negativo. I nanograniti presentano dimensioni tra 5 e 25 μm, e contengono un aggregato criptocristallino di Bt+Kfs+Pl+Qtz±Ap, oltre a fasi accessorie (apatite, zircone, rutilo, spinello e occasionalmente ilmenite) che molto probabilmente hanno favorito l`intrappolamento di porzioni di fuso durante la crescita del granato e la conseguente formazione di inclusioni. La grana delle fasi cristalline nei nanograniti è variabile, da pochi nanometri fino ad alcuni micron. Le inclusioni parzialmente cristallizzate contengono un fuso differenziato, che può occupare il 20-60% dell`area dell`inclusione, coesistente con quarzo, K-feldspato e biotite. Le inclusioni vetrose hanno solitamente dimensioni inferiori, 2.5–17.5 µm, a quelle dei nanograniti e costituiscono circa il 15 % delle inclusioni di ogni ammasso. Al loro interno è presente una fase vetrosa, solitamente coesistente con le stesse fasi accidentali riconosciute nei nanograniti. Dati microchimici sul vetro mostrano una composizione riolitica ultrapotassica, con K2O >> Na2O. Il contenuto di acqua stimato dalla differenza da 100 wt% dei totali delle analisi EMP è inferiore a 3 wt%. La presenza di inclusioni vetrose preservate in questo contesto è una scoperta senza precedenti. Il diametro medio delle inclusioni vetrose (8 μm) è inferiore a quello dei nanograniti (13 μm), e si propone che tale differenza di dimensioni abbia influito sulla cristallizzazione delle porzioni di fuso intrappolato, inibendo la nucleazione delle fasi cristalline nella maggior parte delle inclusioni più piccole. I nanograniti sono stati rifusi attraverso l`uso di un tavolino riscaldante ad atmosfera controllata, e successivamente analizzati al fine di ottenere dati sulle loro composizioni totali. Le analisi in microsonda elettronica mostrano in tutte le inclusioni rifuse una composizione molto simile a quella delle inclusioni vetrose preservate. Avendo un chimismo povero in Na, nel diagramma Q-Ab-Or per il sistema aplogranitico questo fuso si trova molto lontano dalla composizione del “minimum melt”, comunemente accettata come rappresentativa di un fuso anatettico prodotto dalla fusione parziale di metapeliti. Tale composizione, sebbene non sia comune, è segnalata in letteratura per magmi riolitici e per prodotti sperimentali, e suggerisce che la fusione parziale di sia avvenuta a temperature superiori a 850°C, in accordo con le condizioni di anatessi proposte per queste rocce. Questi dati mostrano che assumere una composizione da “minimum melt” come rappresentativa non sia corretto nel presente caso di studio, e che non dovrebbe essere considerata quindi una regola generale. La coerenza dei dati microchimici ottenuti e l`attento studio microstrutturale dei campioni, unito all’uso delle opportune tecniche di rifusione, di microanalisi e di correzione dei dati, supportano l`interpretazione delle composizioni ottenute come rappresentative della fase intrappolata nelle inclusioni, e la conclusione che le MI nei granati delle khondaliti contengano porzioni di fuso anatettico. Questo risultato originale costituisce quindi un importante contributo alla conoscenza di fusi anatettici in rocce naturali. Nella seconda parte del progetto di ricerca sono stati studiati gli inclusi granulitici di El Hoyazo. Queste metapeliti, parzialmente fuse, sono state rimosse dalla bassa crosta mentre l`anatessi stava avendo luogo, e contengono abbondante vetro riolitico in livelli e sacche, oltre che in inclusioni vetrose in quasi tutti i minerali della paragenesi. Diversamente dalle rocce sottoposte a metamorfismo regionale e raffreddate lentamente, in questo caso i caratteri microstrutturali dovuti alla fusione parziale sono stati “congelati” dalla rapida risalita dei campioni in un magma in eruzione. Il granato che contiene inclusioni vetrose è stato la prima fase solida prodotta dalla fusione parziale a ~700°C e 5-7 kbar, e, oltre alle MI, contiene numerose inclusioni fluide (FI) intrappolate in condizioni di immiscibilità fuso-fluido e che non presentano evidenze di modificazioni successive alla loro formazione. Lo studio delle FI nei granati degli inclusi a Spl-Crd e a Bt-Grt-Sil è stato condotto attraverso la loro caratterizzazione petrografica, studi microtermometrici, analisi in spettroscopia Micro-Raman, calcoli di bilanci di massa e studi al microscopio elettronico a trasmissione (TEM). Negli inclusi a Spl-Crd le FI sono bifasiche (L+V), da sferiche a tubulari, e spesso contengono grafite come fase intrappolata. Il fluido contenuto nelle inclusioni è una miscela di H2O+CO2+N2±H2S±CH4, con abbondante H2O, fino a 95 mol%. Negli inclusi a Bt-Grt-Sil, le inclusioni fluide nel granato sono monofasiche e contengono una miscela gassosa a CO2+N2. In entrambi i campioni le inclusioni fluide presentano densità in disaccordo con le proposte condizioni di intrappolamento, e suggeriscono che, nonostante il loro aspetto primario preservato, esse si siano riequilibrate durante la risalita. Lo studio al TEM dei granati negli inclusi a Bt-Grt-Sil ha mostrato, alla scala sub micrometrica, la presenza di fratture parzialmente rinsaldate, interpretabili come possibili vie di fuoriuscita di componenti dalle inclusioni fluide. Negli inclusi a Spl-Crd, i dati raccolti sulle biotiti e le inclusioni vetrose, entrambi coesistenti con le inclusioni fluide, dimostrano che un fuso leucogranitico e una fase COH, entrambi ricchi in acqua, sono stati intrappolati a condizioni di temperatura in accordo con quelle proposte per la formazione del granato (c. 700°C). Negli inclusi a Bt-Grt-Sil, invece, la quasi totale decrepitazione delle inclusioni fluide e la conseguente perdita di componenti non hanno permesso la caratterizzazione della composizione originale del fluido intrappolato nel granato. Tuttavia, sulla base dei contenuti in acqua delle inclusioni vetrose coesistenti, si ipotizza che il fluido fosse in origine più ricco in CO2 di quello presente negli inclusi a Spl-Crd. Il presente studio fornisce ulteriori dati sulla caratterizzazione della fusione parziale di metapeliti nella bassa crosta. Infatti, sebbene i risultati mostrino che gli inclusi hanno perso parte dei componenti originali, la composizione del fluido negli inclusi a Spl-Crd molto probabilmente è simile a quella primaria, in accordo con la composizione del fuso coesistente Lo studio di inclusioni fluide e di fuso silicatico in minerali peritettici rappresenta un nuovo tipo di approccio al problema della fusione parziale in rocce naturali, e questa tesi dimostra che è possibile ottenere risultati validi e rappresentativi, sia dal punto di vista petrologico che geochimico, attraverso lo studio di campioni come i nanograniti, con dimensioni micrometriche o inferiori. Il set di dati ottenuto in questo studio amplia gli orizzonti dello studio petrologico della crosta, in quanto per la prima volta la composizione dei fusi crostali può essere analizzata invece che ipotizzata. Lo studio delle MI nelle migmatiti rappresenta inoltre un campo di studio con grandi potenziali di sviluppo, come è stato recentemente confermato dall`individuazione di ulteriori esempi di nanograniti intrappolati in minerali peritettici di differenti basamenti migmatitici. Per quanto riguarda il fluido coesistente col fuso anatettico, l`eccezionale presenza di MI e FI nei granati di El Hoyazo ha permesso l`identificazione e la caratterizzazione del fluido ricco in acqua che era presente in queste metapeliti all`inizio dell`anatessi

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on January 15, 2010). Thesis advisor: Dr. Peter Nabelek. Includes bibliographical references.

Diagenetic histories of Proterozoic and Paleozoic carbonate strata on Victoria Island, in the Canadian arctic, are poorly understood, and their potential to be associated with base metals or petroleum is unknown. Using fluid inclusion and geochemical techniques, it was determined that the diagenetic fluid compositions of two major carbonate units, the Wynniatt Formation and the “Victoria Island formation”, were largely controlled by fluid-rock reactions in reservoirs and by mixing of multiple fluids. Diagenesis of the Wynniatt Formation resulted from the progression from a shale-dominant fluid mixture to a meteoric-dominant mixture. Fluid composition of “Victoria Island formation” was a shale-dominant mixture. A change in fluid:rock from low to high was recorded during diagenesis of both units. Metals and hydrocarbons transported to the study sites were ac-quired by the fluids during interaction with the respective source reservoirs. Mixing of diagenetic fluids follows the established ‘mixing model’ used to explain many other min-eralised locations. The diagenetic fluids that affected the strata in this study were compa-rable to those that produced the Polaris Zn-Pb deposit. This similarity suggests that there is potential for mineralisation on Victoria Island.

The Otjikoto gold deposit is located within the Damara Orogenic Belt which is part of the system of Pan-African mobile belts. The Damara Belt is a northwest trending orogenic belt which formed through sequences of spreading, rifting, subduction and from continental collision between the Congo, Kalahari and Rio Delta Plata Cratons between 900 Ma and 450 Ma. Mineralisation at Otjikoto is hosted by a group of metamorphic rocks which consist of biotite schists from the Okonguarri Formation, albitites from the Oberwasser member and marble units from the Okawayo member. The gold mineralization occurs in a sheeted vein network system with veins which are positioned parallel towards the foliation of the albitites and hornfels of the Oberwasser Member. The vein types include both quartz and carbonate hosted vein types. The vein mineralogy includes magnetite, pyrite and pyrrhotite which are associated with amphibole, quartz, almandine garnets, and free gold. A fluid inclusion study carried out on the vein quartz showed the co-existence of the aqueous, carbonic and aqueouscarbonic fluid inclusions within the Okonguarri Formation. The aqueous inclusions have moderate to high salinities with salinities ranging from 30.0 to 44.5 wt. % NaCl eq. in aqueous inclusions with halite crystals and from 0.9 to 22.9 wt. % NaCl eq. in inclusions without halite crystals. The total homogenisation temperatures, Th tot (L), ranged from 151 to 488 °C in the aqueous-carbonic inclusions and from 156 to 444 °C in the aqueous inclusions. The melting temperature of CO2 (TmCO2) ranged from -60.3 to -57.5 °C in carbonic inclusions and from - 60.2 to -57.2 °C in aqueous-carbonic inclusions. It is proposed that the aqueous and carbonic inclusions (CO2-CH4) from the Okonguarri Formation are the end members of fluid immiscibility. The presence of CO2 and CH4 is indicated by the low TmCO2 values and may be justified by the decomposition of the carbonaceous metasediments which are found in the stratigraphy at Otjikoto. The δ 18O values range from of 8.35 ‰ to 8.75 ‰ for the magnetite and 17.51 ‰ to 18.47 ‰ for the vein quartz samples. Analysis of the microprobe data on the amphiboles shows that the analysed grains are made up of anthophyllites. Microprobe data of the chlorites showed that the majority of the chlorites are made up of ripidolites. Temperatures of chlorite formation were calculated to be in the range of 221°C to 358 °C by using chlorite geothermometric equations. Major element variation diagrams show a strong negative correlation of TiO2, Al2O3, MgO, Na2O and FeOt vs SiO2. Variation diagrams were also plotted for the trace elements vs Zr. The Sr, Y, La and Ce vs Zr plots show a strong positive correlation.

Les paléo-interactions fluides-roches dans les granites, plus particulièrement la formation des fentes alpines, des épisyénites, des minerais d'U épisyénitiques et leur altération ultérieure, ont été modélisées grâce au code de calcul géochimique EQ3/6. Une version d'EQ3/6 gérant les pressions élevées a servi à modéliser l'évolution des paragenèses dans les fentes alpines intragranitiques en utilisant comme contraintes, la composition chimique détaillée d'inclusions fluides (micro-analyse après écrasement). La minéralogie principale des fentes (quartz-chlorite) a été reproduite après une chute de pression à 370°C de 3 à 1kb, et leur altération ultérieure en sidérite-muscovite par l'ajout de CO₂ et un refroidissement jusqu'à 280°C. Pour les gisements d'uranium intragranitiques hercyniens, les simulations montrent qu'un fluide de bassin à caractère oxydant altérant une source d'U (intragranitique) à 150°C précipite une paragenèse à K-mica et pechblende, fréquemment rencontré dans les gisements. L’association smectite-coffinite se met en place dans des conditions plus spécifiques : température entre 70 et 120°C, teneur en silice élevée (solubilité de la silice amorphe), fluide altérant plus sale. La fO₂ influence peu la formation de coffinite dans ces conditions, mais un fluide oxydant est nécessaire pour former la fluorine et la barytine associées. Les dissolutions et précipitations dans les verses à steriles issues de l'exploitation des minerais d'uranium ont été décrites, simulées expérimentalement et numériquement. Les calculs de spéciation-saturation des fluides naturels et expérimentaux révèlent que les minéraux néoformés dans les verses (hydroxydes de fer, sulfates) contrôlent l'essentiel du stock élémentaire libérable. La chimie des fluides circulants dépend en premier lieu de la solubilité de ces phases, et de la présence de tampons minéraux (carbonates par exemple à Lodève) ce qui conduit à une spéciation de l'uranium distincte d'un site à l'autre.

Thesis (PhD)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Different generalized Newtonian fluids (where the normal stresses were neglected) were considered in this study. Analytical expressions were derived for time independent, fully developed velocity profiles of Herschel-Bulkley fluids (including the simplifications thereof: Newtonian, power law and Bingham plastic fluids) and Casson fluids through open channel sections. Both flow through cylindrical pipes (Hagen-Poiseuille flow) and parallel plates (plane Poiseuille flow) were brought under consideration. Equations were derived for the wall shear stresses in terms of the average channel velocities. These expressions for plane Poiseuille flow were then utilized in the modelling of flow through homogeneous, isotropic porous media. Flow through parallel plates was extended and a possibility of a moving lower wall (plane Couette-Poiseuille flow) was included for Herschel-Bulkley fluids (and the simplifications thereof). The velocity of the wall was assumed to be opposite to the pressure gradient (thus in the streamwise direction) yielding three different possible flow scenarios. These equations were again revisited in the study on flow over porous structures. Averaging of the microscopic momentum transport equation was carried out by means of volume averaging over an REV (Representative Elementary Volume). Flow through parallel plates enclosing a homogeneous porous medium (assumed homogeneous up to the external boundary) was studied at the hand of Brinkman’s equation. It was as- sumed (also for non-Newtonian fluids) that the term dominating outside the external boundary layer area is directly proportional to the superficial velocity that is, since only the viscous flow regime was considered, referred to as the ‘Darcy’ velocity if the diffusive Brinkman term is completely neglected. For a shear thinning or shear thickening fluid, the excess superficial velocity term was included in the proportionality coefficient that is constant for a particular fluid traversing a particular porous medium subjected to a specific pressure gradient. For such fluids only the inverse functions could be solved. If the ‘Darcy’ velocity is not reached within the considered domain, Gauss’s hypergeo- metric function had to be utilized. For Newtonian and Bingham plastic fluids, direct solutions were obtained. The effect of the constant yield stress was embedded in the proportionality coefficient. For linear flow, the proportionality coefficient consists of both a Darcy and a Forch- heimer term applicable to the viscous and inertial flow regimes respectively. Secondary averaging for different types of porous media was accomplished by using an RUC (Representative Unit Cell) to estimate average interstitial properties. Only homoge- neous, isotropic media were considered. Expressions for the apparent permeability as well as the passability in the Forchheimer regime (also sometimes referred to as the non-Darcian permeability) were derived for the various fluid types. Finally fluid flow in a domain consisting of an open channel adjacent to an infinite porous domain is considered. The analytically derived velocity profiles for both plane Couette- Poiseuille flow and the Brinkman equation were matched by assuming continuity in the shear stress at the porosity jump between the two domains. An in-house code was developed to simulate such a composite domain numerically. The difference between the analytically assumed constant apparent permeability in a macro- scopic boundary layer region as opposed to a dependency of the varying superficial velocity was discussed. This code included the possibility to alter the construction of the domain and to simulate axisymmetrical flow in a cylinder.
AFRIKAANSE OPSOMMING: Verskeie veralgemeende Newtoniese vloeistowwe (waarvan die normaalspannings ignoreer- baar is) word in hierdie studie beskou. Analitiese uitdrukkings vir tyd-onafhanklike, ten volle ontwikkelde snelheidsprofiele vir Herschel-Bulkley vloeistowwe (wat die vereen- voudigde weergawes daarvan insluit: Newtoniese, magswet- en Bingham-plastiek vloei- stowwe), sowel as Casson vloeistowwe, is afgelei vir vloei deur ‘n oop kanaal. Beide vloei deur silindriese pype (Hagen-Poiseuille vloei) en parallelle plate (vlak-Poiseuille vloei) is oorweeg. Vergelykings vir die skuifspannings op ‘n wand in terme van die gemiddelde snelhede is afgelei. Hierdie uitdrukking wat vir vlak-Poiseuille vloei verkry is, is in die modellering van vloei deur homogene, isotropiese poreuse media ook gebruik. Vloei deur parallelle plate is uitgebrei en die moontlikheid van ‘n bewegende onderste wand (vlak-Couette-Poiseuille vloei) is ondersoek vir Herschel-Bulkley vloeistowwe (en die vereenvoudigings daarvan). Dit word aangeneem dat die snelheid van die wand in die teenoorgestelde rigting as die drukgradiënt georiënteer is (dus in die stroomgewyse rigting) wat dan tot drie verskillende moontlike vloeigevalle lei. Hierdie vergelykings is weer in die studie van vloei oor poreuse strukture gebruik. Die gemiddelde van die mikroskopiese momentum transportvergelyking is bereken oor die volume van ‘n REV (“Representative Elementary Volume”). Vloei deur parallelle plate wat ‘n homogene poreuse medium omsluit (waar die medium homogeen aanvaar word tot by die eksterne grens) is bestudeer aan die hand van Brinkman se vergelyking. Daar is aanvaar (ook vir nie-Newtoniese vloeistowwe) dat die dominante term buite die eksterne grenslaaggebied direk eweredig is aan die oppervlaksnelheid en, aangesien slegs vloei in die viskeuse gebied oorweeg word, daarna verwys word as die “Darcy”- snelheid, indien die diffusiewe Brinkman-term heeltemal weglaatbaar is. Vir ‘n span-ningsverdunnende of -verdikkende vloeistof, word die oortollige oppervlaksnelheidsterm ingesluit by die proporsionaliteitskoëffisiënt wat konstant is vir ‘n spesifieke vloeistof wat deur ‘n sekere poreuse medium, onderhewig aan ‘n spesifieke drukgradiënt, vloei. Vir sulke vloeistowwe kon slegs die inverse funksies opgelos word. As die “Darcy”- snelheid nie binne die betrokke gebied bereik word nie, is daar van Gauss se hipergeometriese funksie gebruik gemaak. Vir Newtoniese en Bingham-plastiek vloeistowwe is egter direkte oplossings verkry. Die effek van die konstante toegeespanning is ingebed in die proporsionaliteitskoëffisiënt. Vir lineêre vloei bestaan die proporsionaliteitskoëffisiënt uit beide ‘n Darcy- en ‘n Forch- heimer-term wat van toepassing is in die viskeuse- en traagheidsvloeigebiede onder- skeidelik. Sekondˆere gemiddeldes vir verskillende tipes poreuse media is verkry; deur gebruik te maak van ‘n RUC (“Representative Unit Cell”) kan interstisiële gemiddelde eienskappe geskat word. Slegs homogene, isotrope media is in oorweging gebring. Uit- drukkings vir die o¨enskynlike deurlaatbaarheid sowel as die deurdringbaarheid in die Forchheimer-gebied (ook soms na verwys as die nie-Darcy deurlaatbaarheid) is afgelei vir die verskillende vloeistoftipes. Ten slotte is vloeistofvloei in ‘n gebied wat bestaan uit ‘n oop kanaal aangrensend aan ‘n oneindige poreuse domein ondersoek. Die analities-afgeleide snelheidsprofiele vir beide vlak-Couette-Poiseuille vloei en die Brinkman-vergelyking is gekoppel deur ‘n kontinu¨ıteit in die skuifspanning by die poreuse-sprong tussen die twee gebiede te aanvaar. ‘n Interne numeriese kode is ontwikkel om so ‘n saamgestelde domein numeries te simuleer. Die verskil tussen die analities konstant-aanvaarde deurlaatbaarheid in ‘n makroskopiese grenslaagstreek, eerder as ‘n afhanklikheid met die veranderende opper- vlaksnelheid, is bespreek. Hierdie kode sluit ook die moontlikheid in om die domein te herkonstrueer, asook om die simulasie van aksiaal-simmetriese vloei in ‘n silinder te ondersoek.

When and how life first emerged on the Earth is an area of intense research. Signs of the first life on Earth, including morphological fossils, are scarce and hard to interpret. An alternative approach is to study organic biomarkers, which are molecular fossils commonly considered as bona fide biosignatures. The main objective of the project is to develop an approach for analysis of single oil-bearing fluid inclusions and most importantly the detection of organic biomarkers in these inclusions. Analysis of oil-bearing fluid inclusions is advantageous since the inclusions may provide an uncontaminated sample source of Precambrian hopanes and steranes, which are key biomarkers for tracing the early evolution of life on Earth. Due to the presence of several inclusion generations, single inclusion analysis is desired in order to constrain biomarkers to specific inclusions. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) could be an excellent tool for analysis of these types of samples. The development of the approach for analysis of single oil-bearing inclusions was done in a two-step process; i) a number of crude oils were analysed with ToF-SIMS and gas chromatography mass-spectrometry (GC-MS) to facilitate interpretation of ToF-SIMS spectra of these types of samples and, ii) a procedure that combines micrographs with ion etching and ToF-SIMS analysis was developed for analysis of inclusions. The feasibility of the technique was demonstrated for oil inclusions from the Siljan impact crater in which hopanes and steranes where detected. Single oil-bearing fluid inclusions trapped in mid-Proterozoic sandstones from Northern Australia were subsequently analyzed, and steranes and hopanes were detected in these inclusions. If applied on older inclusions this approach may help answer some of the questions regarding the emergence and evolution of life on Earth, and if applied on extraterrestrial samples, also the possibility of life on other planets and moons.
Livets uppkomst och tidiga utveckling på jorden är ett hett forskningsfält. Hur och när livet och dess olika domäner (arkéer, bakterier och eukaryoter) uppstod på jorden är fortfarande oklart vilket beror på att de första tecknen på liv, vilka inkluderar morfologiska fossil, spårfossil och isotoper, är få och svåra att tolka. Ett alternativt sätt att studera det tidiga livet är att studera organiska biomarkörer som är organiska molekyler som anses unika för liv. Huvudmålet med projektet är att utveckla en metod som kan detektera organiska biomarkörer i enskilda oljebärande vätskeinneslutningar. Vätskeinneslutningar, som är små mängder vätska (picoliter) infångad in en sten, är intressanta då de är en potentiell provkälla för prekambriska (äldre än 500 miljoner år) biomarkörer, som hopaner och steraner, vilka används för att utforska livets tidiga utveckling på jorden. Analys av enskilda inneslutningar är emellertid oftast nödvändigt för att kunna tidsavgränsa biomarkörer. På grund av att de flesta inneslutningar är små (10 µm i diameter) är det inte möjligt att analysera en enskild vätskeinneslutning med standardtekniken gaskromatografi-masspektrometri (GC-MS). Time-of-flight secondary ion mass spektrometri (ToF-SIMS) med sin höga känslighet, höga massupplösning och kapacitet för 2D-representation av analysdata och djupprofilering av prover är en utmärkt teknik för analys av enskilda inneslutningar. Metoden för analys av enskilda inneslutningar utvecklades i två steg. Först analyserades ett antal råoljor med ToF-SIMS och GC-MS för att underlätta förståelsen av ToF-SIMS-spektra från dessa typer av prover. Därefter utvecklades en metod som bestod av mikroskopering för att lokalisera inneslutningen, jonetsning för att öppna inneslutningen och ToF-SIMS analys av det exponerade innehållet. Metoden testades framgångsrikt på enskilda inneslutningar i hydrotermala vener av flusspat och kalcit i ordovicisk (488-443 miljoner år sedan) kalksten. Därefter användes den utvecklade metoden för att analysera enskilda vätskeinneslutningar i 1,43 miljarder år gammal sandsten från norra Australien, i vilka hopaner och steraner detekterades. De detekterade steranerna visar att trots att havet under denna tid var syrefritt existerade det lokala syrerika miljöer där eukaryoter kunde överleva. Om den utvecklade metoden används på ännu äldre inneslutningar, vilka har daterats till 3,2 miljarder år, kan den komma att svara på några de mest fundamentala frågorna kring livets uppkomst och tidiga utveckling. Om metoden används på utomjordiska prover kan den svara på frågan om det finns liv på andra planeter eller månar.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Submitted.

Etudes methodologiques concernant l'analyse non destructive des fractions volatiles et des hydrocarbures liquides pieges dans les inclusions fluides par des methodes ponctuelles et non destructives comme la microspectrometrie infra-rouge et raman et la microfluorometrie, et d'autre part la mesure des changements de volume et de composition lors de surchauffes sous pression de confinement dans les inclusions de la fluorine. Les apports originaux des etudes d'inclusions fluides a la connaissance des circulations de fluides dans les bassins sedimentaires et pour la definition des conditions de depot des gites mineraux dans des contextes geologiques differents sont montres. Trois principaux types de solutions peuvent etre definis: les eaux connees de la diagenese faible a moyennement salines; les saumures d'origine diapirique; les solutions qui resultent d'un melange entre eaux connees et solutions hydrothermales

i) L’eterogeneità geochimica della litosfera al di sotto di El Hierro Studi geochimica dei basalti di isola oceanica (OIB) offrono I mezzi principali per la comprensione dell’etogeneità del mantello attraverso la segnatura di isotopi di Sr-Nd-Pb a lungo termine (> 1 Ga) e definiscono i relativi arricchimenti di elementi incompatibili dei basalti medio oceanici. Precedenti studi riportano dati relativi a isotopi radiogenici per basalti alcalini delle isole di La Palma ed El Hierro, e più in generale delle isole Canarie. I dati raccolti con caratterizzazione petrografica, spettroscopia Raman e spettroscopia di massa per le xenoliti di mantello, permettono di delineare le caratteristiche geochimiche e petrologiche del mantello litosferico di El Hierro nella visione dei modelli esistenti per la genesi del vulcanismo. Una harzburgite ed una dunite sono state analizzate. La petrografia ha permesso di investigare una associazione precoce di melt/inclusioni fluide contenenti carbonati/solfati/vetri silicatici evoluti ad aggregati di carbonati, solfati, fosfati e spinelli, e di caratterizzare una fase gassosa mista di CO2±N2. La caratterizzazione degli alogeni nelle inclusioni fluide è stata fatte tramite irradiazione dei campioni e misurando le anomalie degli isotopi dei gas nobili con uno spettrometro di massa (mass spectroscopy-Noble Gas Method). I rapporti di Br/Cl, I/Cl e Ba/Br sono stati calcolati, e si distinguono dai rapporti usuali di MORB/OIB. Il rapporto Br/Cl è più basso di circa il 30% e quello I/Cl è più alto di almeno 30 volte rispetto a quelli che sono considerati i tipici basalti oceanici. I dati supportano l’anomalia geochimica proposta per il mantello superiore al di sotto delle Isole Canarie, relativi alla “tipicità” del mantello litosferico. Questa anomalia potrebbe essere stata indotta da fluidi metasomatici che si sono originati da porzioni di vecchia crosta oceanica riciclata a profondità litosferiche. Questi dati possono aiutare nell’elaborazione di futuri modelli caratterizzanti i processi che originano i fluidi metasomatici nel mantello. ii) Il sistema di alimentazione dell’isola di El Hierro La geo-termobarometria delle inclusioni fluidi e la caratterizazione petrologica di rocce xenolitiche di mantello permettono di definire profondità e stazionamenti del magma e di proporre un modello caratterizzante il sistema di alimentazione della fase attività di Rift Volcanism (158 ka-presente) dell’isola di El Hierro. Xenoliti ultramafiche sono state campionate in una colata di lava nella scogliera della valle di El Julan. Gli studi petrografici hanno caratterizzato le peridotiti in “type I olivine-orthopyroxene-spinel series”, con tessiture da protogranulari a porfiroblastiche. Per sedici campioni è stata definita la composizione modale; otto sono stati analizzati per la composizione delle fasi minerali con microsonda WDS. Sulla base della chimica dei minerali sono state calcolate le condizioni di pressione di equilibrio a profondità litosferiche per le rocce lherzoliti e harzburgiti a spinello. Utilizzando il barometro K&B sono state ottenute pressioni tra 1.5 e 2.0 GPa. Utilizzando i termometri di We e B&K sono state definite differenti temperature di equilibrio per due gruppi di campioni: LT-type T=800–950 °C e HT-type T=900–1100 °C. Due differenti tipologie di inclusioni fluide sono state identificate: i) Type I, early multiphase CO2+N2ntrappolate prima della risalita nel magma e ii) Type II, late pure CO2 intrappolate durante la risalita. Sulla base di questi dati viene proposto un modello di risalita verticale attraverso piccolo porzioni di magma, identificato tra 22 e 36 km e seguito da un più superficiale livello di stazionamento nella crosta. I risultati ottenuti sono stati confrontati con le dinamiche dell’ultima eruzione del 2011-2012, al fine di comprendere se il sistema di alimentazione dell’ isola di El Hierro si è evoluto durante gli ultimi 158 ka.
i) Geochemical heterogeneity of the lithosphere beneath El Hierro: Geochemical studies of ocean island basalts (OIB) offer primary means for understanding mantle heterogeneity with OIB Sr–Nd–Pb isotope systematics defining mantle components with long-term (>1 Ga) incompatible element enrichment relative to depleted mid-ocean ridge basalt source mantle. Previous studies reported radiogenic isotope data in alkali-basalts from La Palma and El Hierro, and more generally for the Canary Islands. Data collected from petrography, Raman microspectroscopy and mass spectroscopy characterization of mantle xenoliths rocks allow to better delineate geochemical and petrological characteristics of the lithospheric mantle beneath El Hierro in the frame of existing models for the genesis of volcanism. Sample analysed were one spinel harzburgite and one dunite. Petrography characterization allow to investigate an early association of melt/fluid inclusions containing dominantly carbonate/sulfate/silicate glass, evolving to carbonate, sulfate, phosphate, spinel aggregates, and identifies a mixture gas of CO2±N2 trapped. The investigation about the halogens in fluid inclusions has performed by irradiating samples with neutrons and measuring artificial noble gas isotope anomalies in a noble gas mass spectrometer (mass spectroscopy-Noble Gas Method). Br/Cl, I/Cl and Ba/Br ratio have been calculated. The halogen patterns obtained in fluid inclusions are distinct from MORB/OIB. Their Br/Cl ratio is lower by ca. 30%, and the I/Cl ratio higher by a factor of at least 30, than what is presently considered the “typical" oceanic basalt”. The data support the proposed geochemical anomaly of the upper mantle beneath the Canary Islands, relative to the "typical" oceanic lithospheric mantle. This anomaly could have been induced by metasomatic fluids originating from portions of recycled old oceanic crust at lithospheric depths. This may constrain future models that attempt to characterise the processes giving rise to the metasomatising fluids in the lithospheric mantle. 
 ii) Magma plumbing system beneath El Hierro Island. Geothermobarometry of fluid inclusions combined with petrological characterization of mantle xenoliths rocks allows to define the depths and conditions of magma storage, and to propose a magma plumbing system for the Rift volcanism activity (158-present) of El Hierro island. Ultramafic xenoliths were collected in a lava flow El Julan cliff valley. Petrographic studies allow to classify peridotites in type I olivine-orthopyroxene-spinel series, with texture from protogranular to porphyroclastic. For 16 among the best preserved samples modal compositions have been performed. Eight peridotites were analyzed for mineral phase composition by electron microprobe analyses (WDS). Based on mineral chemistry, geobarometry of spinel lherzolite, and spinel harzburgite equilibration at lithospheric depths has been calculated using K&B barometer. Pressures are defined from 1.5 to 2.0 GPa. The geo-thermometers by We and B&K provide the presence of two groups of xenoliths with different equilibrium temperature: LT-type T=800–950 °C and HT-type T=900–1100 °C. Two fluid inclusions groups have been observed: i) Type I, early multiphase CO2+N2-rich fluid inclusions, trapped prior to the ascent of the host xenoliths; ii) Type II, late pure CO2 fluid inclusions trapped during the ascent into the host magma. From the data obtained I propose a model where the eruptive dynamics originate from a vertically stacked reservoir in the lithosphere, which has been identified from 22–36 km depth and followed by local magma accumulation at crustal levels. The results we obtained have also been compared with the dynamics of magma ascent of the last eruption of 2011-2012 of the island, in order to understand whether the magma plumbing system beneath El Hierro island was involved during the last 158 ka.

The results of a combined mineral equilibria and fluid inclusion study show that the Manhattan Prong, southeastern New York, has experienced multiple metamorphic events. Two episodes of intrusion, separated by approximately 100 million years, have superimposed contact aureoles on the Taconic regional metamorphic gradient in the northeastern Manhattan Prong and have modified the regional assemblage to different degrees. The assemblage Sil-Bt-Grt-Qtz-Pl+Ksp+Ms in regionally metamorphosed Manhattan Schist records P-T conditions of 4-5 kbar and 650-700 oC. Garnet porphyroblasts, homogenous with respect to major elements but zoned with respect to P and Y, contain ubiquitous, primary, CO2-rich fluid inclusions which have a Th = 10-24 oC. Manhattan Schist collected adjacent to the Croton Falls and Peach Lake mafic complexes, intrusions thought to be related to the Late Ordovician Cortlandt Complex, record P-T estimates of 4 kbar and 700 oC and 4.2 kbar and 550-600 oC respectively. The lack of fluid inclusions in garnet porphyroblasts indicates that the regional metamorphic assemblage has been completely modified by the contact effects of the mafic intrusions. However, the presence of Ky+Sta along with the slight compositional zoning of garnets in Peach Lake samples suggests that the contact assemblage may have been modified by a later metamorphism. Manhattan Schist collected adjacent to ~350 Ma granites (Brock, 1993) has been partially modified by contact metamorphism and shearing but vestiges of the regional metamorphic assemblage remain. Garnet porphyroblasts contain abundant CO2-rich fluid inclusions and P-T estimates using Bt and Pl inclusions and garnet core compositions are similar to estimates of regional metamorphic conditions. Evidence of modification includes garnet overgrowths that are elevated in Ca and depleted in Mn, Y and Sc, and CO2-rich fluid inclusions that have reequilibrated to higher density (Th = 2-18 oC). Rim compositions of porphyroblasts yield P-T estimates of 5-6 kbar and 550-600 oC. The elevated Ca content of the overgrowths along with the presence of Ky in the matrix suggests that the reaction An = Ky + Grs + Qtz may have been active during the overprinting metamorphism. The increase in pressure recorded in the granite aureoles in the Manhattan Prong is inconsistent with the results of P-T studies of the Rowe-Hawley belt, approximately 20 km to the east across Cameron's Line. This suggests that these two terranes may have been separated in the Devonian.
Master of Science

Philosophiae Doctor - PhD
The Sandamap gold prospect is a metaturbidite shear zone-hosted gold mineralization located in the Neoproterozoic Damara Orogen 30 km northwest of the town of Usakos in Namibia with an estimated gold content of 240 000 t at 3.6 g/t up to 40 m below surface. This research project was aimed at constraining the age, crustal level of formation, pressure-temperature conditions during formation, sources of the mineralizing fluids, and by implication, the metal sources of the Sandamap gold mineralization. Fluid inclusion, geochronological and isotopic studies were carried out on quartz veins hosting the ore. The presence of kaolinite, alunite and jarosite suggest post-hydrothermal weathering of sulfides. Various sources of data from this study, giving rise to depths of entrapment of 4 to 14 km, temperature range of entrapment of fluids of 187 – 594 °C, stable isotope data (δ13C and δ18O), δD values and a δD vs. δ18OH2O plot are all in favour of an orogenic gold deposit. Additionally, the dominant CO2-rich and CH4-rich fluids observed at Sandamap do not contradict this interpretation. The calculated depth of entrapment of mineralization covers the lower portion of the epizonal zone to the upper portion of the hypozonal zone of gold deposits. The Sandamap mineralization’s δD values of -35‰ to -49‰ fall within the range of most published data for typical orogenic gold deposits which varies from -20 to -80‰. Moreover, the calculated δ18Owater values of the ore-fluids (+6.6 to +11.3‰) of the higher temperature aqueous group from the Sandamap mineralization fall within the range observed in typical orogenic gold deposits found in Phanerozoic terrains (+7 to +13‰). The schist hosting the mineralized shear zone with a gold content of 0.05 ppm Au or its higher grade equivalent at depth, is a possible gold source candidate. Two mechanisms of deposition were possibly at play: (i) the cooling below 500 °C and possible sulfidation (resulting from fluid-rock interaction), lowered the solubility of pyrite causing S3- and Au(HS)S3- (possible main Au carriers) to breakdown resulting in decreased Au solubility and its subsequent deposition and (ii) the elevated amount of CO2 (e.g. trench 14 where CO2-rich fluid inclusions are dominant) led to a sharp decrease in the Au(HS)2- and Au(HS)S3- concentrations, causing decreased Au solubility and its subsequent deposition. The age of mineralization obtained from 40Ar/39Ar dating of the muscovite associated with the ore-hosting quartz veins is placed at 472 ± 3 Ma. The mineralization is younger than the shear zone, which acted as a conduit for ore-fluid migration and it has no age relationship with proximal plutonic bodies. The mineralization is younger than the foliated granite (FG), which exhibits a metamorphic fabric in the form of mineral segregation, but older than the non-foliated granite (GT) which hosts a mineralized xenolith.

Syn-tectonic quartz veins formed along faults, folds and tension gashes in rocks of the Cape Supergroup (CSG) of the central Cape Fold Belt (CFB) comprise mainly hydrous saline fluids. These veins may also contain CO₂ Syn-tectonic quartz veins formed along faults, folds and tension gashes in rocks of the Cape Supergroup CO₂ , or CH4 and CO₂, or neither CO₂ nor CH4. The majority of inclusions are two-phase and fluid rich, and the most common fluid composition is H2O-NaCl. The final melting temperature, and therefore salinity, differs very little across different structures (fluids in all structures show maximum salinities between 2.5 and 6 wt% NaCl equivalent). Thrusts, reverse faults, strike- and oblique-slip faults, and folds all have similar homogenization temperatures (Th). Primary H2O-NaCl inclusions show Th between ~130 and 200 °C, and H2O-NaCl-CO₂ inclusions have slightly higher Th, between ~140 and 240 °C. Secondary inclusions in all structures have a similar Th range to primary inclusions, but have a lower maximum Th (~130-180 °C). Inclusions containing CH4 have the highest Th (~210 - 300 °C). Microthermobarometry indicates that fluids associated with contractional structures, such as thrust faults or folds, from the Ordovician lower Table Mountain Group (TMG) show lower greenschist facies trapping conditions (~170-175 MPa and ~240-300 °C). These veins also show a plastic deformation overprint (recrystallization of quartz and foam textures), at temperatures higher than the trapping conditions (~ ≥300 °C), indicating that temperatures increased subsequent to hydraulic fracturing, quartz precipitation and thrust slip. These structures formed on a prograde path, at approximately 335 Ma, at a time when the overlying CSG rock column was approximately 6800 m thick. This event pre-dated the thermal peak of the Cape Orogeny at ~276-261 Ma by ~60 million years. Further up in the stratigraphy of the CFB, in the Devonian upper Bokkeveld Group, fluid inclusions in quartz veins associated with a thrust fault show similar trapping pressure (~200 MPa) to the structures in the lower CFB. At 335 Ma, the stratigraphic overburden on this sample locality would not have been sufficiently thick to exert the calculated pressure. This fault may have formed at a later time. The observed pressure of ~200 MPa may have been created either by the higher Bokkeveld Group, the entire Witteberg Group, and further CSG rocks that were eroded prior to the deposition of the Permo-Triassic Karoo Supergroup, or by tectonic thickening of the CSG by prograde thrusting. Still further up in the CSG, fluids from a fold sample from the Witteberg Group record quartz precipitation at lower greenschist facies conditions and subsequent plastic deformation during folding. The formation of this fold postdates the thrusting in the lower TMG, and may correlate in time with deformation during the thermal peak in Middle Permian time (~276-261 Ma).

Ce travail porte sur la caractérisation de la source et de la dynamique des fluides de bassin au cours de leur chargement à travers deux exemples complémentaires de demi-grabens tardi-orogéniques pétroliers : Le Bassin Permien de Lodève, aujourd'hui à l'affleurement et un bassin jurassique enfouis dans le North Viking Graben (Mer du Nord). Le cœur de la thèse concerne le Bassin de Lodève où, à partir d'une approche pluridisciplinaire intégrée, nous avons caractérisé l'architecture des minéralisations (Ba, F, Cu, Pb) piégées dans un réseau paléokarstique alimenté par les failles syn-rift, dans le substratum carbonaté à l'apex du roll-over. La source, le calendrier et les conditions de migration des fluides ont été approchés à partir de l'analyse de la micro-fabrique, la microthermométrie sur inclusions fluides, les analyses isotopiques (Sr, S, O, H) et de Terres Rares. Les résultats analytiques ont été enfin croisés avec un modèle thermique et structural du bassin qui conforte la séquence et la dynamique du système fluide en cours d'enfouissement. Une démarche similaire, mais plus limitée, a été conduite dans le bassin du North Viking Graben où l'accès aux marqueurs fluides est restreint aux données de sismique 3D et de carottes. Comme à Lodève, les minéralisations Ba-Pb-Zn colmatent un réservoir dans le substratum à l'apex du roll-over. Elles se présentent sous forme de ciments dans des grès ou des fractures. Cette analyse apporte des contraintes complémentaires et permet de proposer un modèle dynamique général avec des variantes en fonction de la nature des fluides et des réservoirs. On retiendra donc la séquence fluide suivante :(a) Dans le cas du bassin de Lodève sur substratum carbonaté, les chemins préférentiels de drainage se développent dans des paléocanyons N-S couplés à un réseau de fractures et d'endokarsts météoriques. Ces derniers sont élargis en début de rifting par la dissolution hypogène sulfurique produite par l'oxydation bactérienne de la pyrite des blackshales, au contact de l'aquifère oxydant du Cambien.(b) Le déséquilibre de compaction initie la migration des fluides interstitiels en surpression vers les marges avec des températures autour de 150-180°C et des salinités entre 9 et 18wt%eq.NaCl. Les analyses isotopiques (Sr, S, O) révèlent que la majorité des fluides provient de l'altération diagénétique des blackshales riches en métaux. Des interactions sont également mises en évidence avec des fluides profonds (entre 240°C et 260°C ; salinités > à 20wt%eq.NaCl), qui lessivent les granites tardi-hercyniens.(c) Pendant le syn-rift, les conditions de surpression de fluide permettent la réactivation cyclique des failles, les décollements stratigraphiques et la formation de brèches hydrauliques, favorisant la mise en connexions avec les réservoirs superficiels à l'apex du roll-over. Le modèle de Sibson ajusté aux fluides de bassins est alors le moteur de la migration verticale.(d) Les fluides thermogéniques commencent à être expulsés avec les derniers fluides de compaction au cours d'un stade plus évolué de l'enfouissement en empruntant les mêmes chemins jusqu'à l'apex du roll over. Ils sont alors partiellement freinés et déviés par les colmatages minéralisés antérieurs.(e) A Lodève, la continentalisation des minéralisations antérieures au cours de l'exhumation post-rift conduit à leur remaniement partiel au niveau de la transition sulfate-méthane induite par l'interaction entre une playa évaporitique et la dysmigration des hydrocarbures. Des barytines secondaires de basse température, déprimées en Sr sont alors précipitées de manière synsédimentaire dans des karsts météoriques du socle.Outre l'illustration d'un modèle complet (source to sink) de dynamique des fluides dans un bassin, ce travail apporte de nouvelles contraintes dans l'approche du colmatage des réservoirs à hydrocarbures sur les têtes de blocs basculés et sur la genèse des gîtes miniers de type Mississippi Valley-Type
This work focus on the characterization of the source and dynamic of compactional fluids during sedimentary burial, through two complementary examples of late orogenic oil-field half-grabens: The exhumed Lodève Permian Basin and a deep buried Jurassic basin in the North Viking Graben (North Sea).Constituting the main part of the thesis, a multi-disciplinary approach was conducted in the Lodève Basin where Ba-F-Cu-Pb polymetalic mineralized systems are trapped into synrift faults and paleokarsts in the carbonate basement at the hinge point of the roll-over. The source, timing and P/T conditions of fluid migration were deduced from the analysis of the microfabric, the fluid inclusions microthermometry, and the isotopic (Sr, S, O, H) and Rare Earth Element (REE) signature. Results are then crossed with a structural and thermal modeling that consolidates the sequence and dynamics of fluid during burial.A similar approach was conducted in the North Viking Graben where fluid markers are restricted to 3D seismic and well core data. Comparable Ba-Pb-Zn veins are reported in basin margin, plugging one of the most important siliciclastic hydrocarbon reservoir in the substratum. This analysis provides additional constraints on basinal fluid behavior and allows us to propose a global dynamic model for various compositions of fluids and reservoirs.We conclude to a polyphase fluid sequence history including:(a) In the carbonate basement of the Lodève Basin, karstic paleocanyon incisions and associated cavities coupled to synrift fault, act as major drain for fluids. These structures are early affected by hypogen-sulfuric karstification in response to the interaction between bacterial oxidation of sulfides entrapped within Lower Permian blackshales and the basement oxidizing aquifer.(b) Disequilibrium compaction initiates overpressure-driven basinal fluid migration towards basin margins, characterized by temperatures around 150-180°C and salinities between 9 et 18wt%eq.NaCl. Isotopic (Sr, S, O) and REE analyses reveal that Ba-M+-rich mineralizing fluids derived mainly from buried blackshales diagenesis. External Fluids coming from the lower crust are also identified that play a key role in fluorite precipitation by the leaching of late hercynian granites (mean temperature of 250°C and salinity > 20wt%eq.NaCl).(c) During the synrift period, fluid overpressure is responsible for the periodic reactivation of fault plane according to seismic-valve process, bedded-control shearing and hydraulic brecciation at the basement-seal interface. These mechanisms induce cyclic polymetallic mineralization by the mixing between in situ formation water and deep ascending basinal fluids.(d) Thermogenic fluids expulsion starts with last basinal fluids during late burial stage. Hydrocarbons thus migrate along the same regional pathways up to the rollover crest, where they are partly rerouted by the previous mineralized baffle.(e) In the Lodève basin, post-rift exhumation of the margins led to the remobilization of synrift deposits by subaerial biochemical processes at the sulfate-methane transition. The latter results from the interaction between the still active hydrocarbon dysmigration with a playa lake sulfate-rich aquifer. Secondary low-temperature barite fronts precipitate then within basement meteoric karsts.In addition to the « source to sink » model of basinal fluids, this work provides new insights on the early plugging of hydrocarbon reservoirs and for the metallogenesis of Mississippi Valley-Type deposits

Oxide inclusions are among the most commonly reported defects in ferrous and non-ferrous castings. They affect the surface quality, machinability, and mechanical performance of a cast part. Air entrainment during mold filling is the main source of the oxygen that is consumed in inclusion formation. A quantitative understanding of the formation mechanisms or the prediction of final amounts and locations of oxide inclusions in metal castings is not available. Ductile iron experiments are conducted to study the formation of oxide inclusions during pouring. Oxide inclusions are measured by serial sectioning of the solidified castings. The effect of different gating systems, section thicknesses, and surface orientations on the inclusion formation and final distribution is studied. In addition, a computational model is developed for predicting the formation, motion and final location of oxide inclusions during pouring of metal castings, with the focus on the important mechanism of generation of oxide inclusions due to air entrainment during mold filling. The developed model calculates the local air entrainment rate as a function of the turbulent kinetic energy and the magnitude of the normal velocity gradient of the liquid metal at the liquid-air interface. The turbulent kinetic energy is estimated from the sum of the squares of the fluctuating velocity components relative to a spatially averaged mean velocity. The air entrainment model is implemented in a casting simulation software and validated by comparing its predictions to experimental air entrainment measurements for a circular water jet plunging into a quiescent pool. The liquid velocity, diameter and the turbulence intensity dependence is determined by a single entrainment coefficient. Oxide inclusions are then generated at the liquid-air interface, transported with the melt flow under the combined influences of drag and buoyancy, and captured by the solidifying casting surface. The developed model provides a powerful technique for predicting the oxide inclusion formation and final location.

In this study is presented the work I have done during the 4 years of a PhD program that was part of the internationalization programme of the Italian research system approved by the Ministero della Ricerca e dell’Università (MIUR) between the Università degli Studi di Napoli “Federico II”, (Dipartimento di Scinze della Terra) and the Virginia Polytechnic Institute and State University (Department of Geosciences). 107 selected MI, 77 open glasses, 80 olivines and 7 bulk rocks (from 4 representative samples of Solchiaro eruption) were analyzed for major/trace element and volatiles. Mostly, olivine compositions vary from Fo82 to Fo88 with one maximum value of Fo90. 2 group of MI were recognized based on major element composition: 1) K2O-rich MI with composition that is the same of bulk rock in the literature and 2) K2O-poor MI that instead have been never reported from previous study of the PVD (Phlegrean Volcanic District). The first group consists of 95% of the melt and relates mostly to within plate setting whereas the second group consists of around 5% of the melt and relates to subduction setting. Magma associated with Solchiaro eruption evolved under open system processes as suggested by petrographic evidence and glass compositions. H2O-CO2 concentrations dissolved in glass suggest that magma was saturated in volatiles at least at 12.5 km depth and continuously degassed during the Solchiaro eruption. Maximum depths are in agreement with other studies based on different approaches. Volatile correlations suggest that during closed system degassing, as the Solchiaro eruption progressed, maximum S contents decreased and minimum Cl and F contents increased. The major, trace and volatile evolution of crystals, glass, and MI is consistent with a model that involves either continuous or episodic recharge of the magma chamber ponded at least at 12.5 km depth

La capture et le stockage géologique du CO2 constituent une option importante de limitation des émissions de gaz à effet de serre au niveau des pôles industriels et des centrales de production d’énergie. Les gaz capturés à l’issu de ces chaînes de production ne sont pas constitués de CO2 pur mais contiennent une fraction (jusqu’à 10 %) de gaz annexes qui sont essentiellement Ar, N2, SOx et NOx. Ces gaz étant pour la plupart très réactifs il est essentiel de connaître leur impact sur les conditions physico-chimiques du réservoir géologique d’accueil, ainsi que sur l’environnement dans le cas d’une de contamination des aquifères voisins du stockage. Des expérimentations en laboratoire ont simulé le vieillissement de roches de réservoir et couverture en provenance d’un réservoir carbonaté du Bassin aquitain et d’assemblages minéralogiques synthétiques dans des conditions de séquestration géologique. Les roches associées à une saumure sont altérées au contact de divers composés gazeux à 100 bar et 150°C sur une durée d’un mois : CO2 pur, SO2, NO pur et un mélange contenant majoritairement du CO2 et des fractions de Ar, N2, SO2, O2. Chaque expérience est comparée à une expérience témoin où le composé gazeux est remplacé par de l’azote. Le CO2 ne montre qu’une réactivité limitée sur les minéraux des roches. Le NO et le SO2 montrent une réactivité intrinsèque passant par des dismutations en phase aqueuse ou vapeur induisant une forte altération de la roche par une attaque acide couplée à une oxydation poussée des minéraux constitutifs des roches. Le mélange de gaz montre de la même façon une réactivité double : le S02 s’oxyde en acide sulfurique s’attaquant aux carbonates et minéraux argileux et l’O2 oxyde tous les minéraux possédant du fer ou du soufre réduit. Les gaz annexes contrôlent donc la réactivité des roches en grande profondeur. Leur présence pourrait complètement changer le comportement des roches (porosité, rhéologique) lors du stockage. Leur implication devra être anticipée dans chaque cas concret de stockage en fonction de la composition du gaz d’injection, de la minéralogie et des propriétés pétrophysiques des roches
Capture and geological storage of CO2 are an main option to limit GHEG emissions of industrial poles and power plants. The captured gases are not constituted by pure CO2 but contain a fraction (until 10 %) of other gases : Ar, N2, SOx and NOx. Most of these gases are highly reactive and could have a strong influence on physical and chemical conditions of the milieu and on the environmement if contamination of neighbour aquifers occurs by leakages. Several laboratory experiments investigated the reactivity of carbonated reservoir and cap rocks from the Aquitaine Basin as well as the reactivity of synthetic mineralogical blends in geologically relevant P-T conditions. The rocks, associated to brine, were altered in presence of various gaseous components at 100 bar and 150°C during one month : pure CO2, pure SO2, pure NO and a CO2 mixture containing fractions of Ar, N2, SO2 and O2. Each experiment was compared with a blank in which the initial gas was replaced with pure N2. Pure CO2 show a limited reactivity on the rocks. NO and SO2 show a intrinsic reactivity by disproportionations in aqueous or vapour phases implying a high alteration of rocks by compled acid – base and oxidation mechanisms. The gas mixture show also a double reactivity : SO2 is oxidized in sulphuric acid dissolving carbonates and clay minerals and O2 oxidizes all reduced mineralogical phases. These gases even in limited fractions control the reactivity of rocks. Their presence could change the behaviour of the rock toward gas and induce positive as well as negative transformations. Their implication must be checked for each geological storage as a function of gas composition, mineralogy and petrophysical

The Peña del Seo tungsten deposit in northwestern Spain is situated in the tin (Sn)-tungsten (W) metallogenic province of Europe − one of the richest tin-tungsten (tantalum-lithium) mineral provinces in the world. The European Union’s current goal is to become self-sufficient of these commodities in the near future and the iTARG3T project was launched in order to improve the understanding and provide innovative exploration methods of these types of deposits. This master thesis will contribute to the iTARG3T project. The aim was to determine which physico-chemical conditions (temperature, pressure, salinity) that prevailed during the emplacement of the Peña del Seo deposit. A geochemical study was done consisting of a fluid inclusion study on the quartz veins from the deposit, and a whole-rock geochemistry analyse of the granitic rock. Homogenisation temperatures ranged between 97,6° C to 325,6° C and salinities (NaCl % equiv.) between 0,2% to 21,3%. The fluid was determined to consist of a two-component system of H2O and NaCl based on eutectic temperature. Based on its geochemical classification the granitic rock was considered to be an alkali granite, strongly peraluminous with S-type characteristics. At least two different types of fluids were present during the emplacement of the Peña del Seo deposit, one that was hot and with a moderate salinity, and one that had a lower temperature than the other fluid and a lower salinity, possibly meteoric water. The depositional mechanism of tungsten is thought to be caused by a combination between mixing between two fluids and cooling of the fluids, with the main depositional mechanism being cooling since the change in salinity was not of such magnitude that it would change the fluid chemical composition, while the decrease in temperature was. It is uncertain whether the granitic rock found at Peña del Seo is part of the granitic cupola of the greisen system. The granitic rock has similar characteristics as the leucogranites of the West Asturian-Leonese Zone and based on quartz vein morphology, which cut the D2 foliation, time of emplacement of the deposit could be linked to the syntectonic event at 320-310 Ma. If the relation between the granitic rock and the greisen system can be determined the time of emplacement would be possible.

Exploration on Florida Mountain in southwestern Owyhee County, Idaho has defined four separate Au-Ag-Se orebodies. These deposits differ greatly in size, shape, grade, and metal ratios. However, all four are related to the same episode of epithermal vein mineralization. Ore deposition was associated with an active geothermal field related to a series of Mid-Miocene (15.2 to 16.6 m.y.a.) silicic domes and flows. Hydrothermal fluids of meteoric origin were localized along NW-trending faults and leached their constituents from the surrounding rocks. Metals were transported as complexes of sulfur and selenium in a 1% NaCl equivalent solution at 260$\sp\circ$C. Ore deposition occurred some 400m below the paleo-surface as the result of boiling and fluid mixing. The major ore minerals are aguilarite, acanthite, and electrum. The gangue is predominantly quartz and adularia. Hydrothermal alteration includes propylitic, sericitic, kaolinitic, and potassic assemblages. Supergene effects in the deposits are minimal.

Philosophiae Doctor - PhD
The use of integrated approach to evaluate the quality of reservoir rocks is increasingly becoming vital in petroleum geoscience. This approach was employed to unravel the reason for the erratic reservoir quality of sandstones of the F-O gas field with the aim of predicting reservoir quality, evaluate the samples for presence, distribution and character of hydrocarbon inclusions so as to gain a better understanding of the fluid history. Information on the chemical conditions of diagenetic processes is commonly preserved in aqueous and oil fluid inclusion occurring in petroleum reservoir cements. Diagenesis plays a vital role in preserving, creating, or destroying porosity and permeability, while the awareness of the type of trap(s) prior to drilling serves as input for appropriate drilling designs. Thus an in-depth understanding of diagenetic histories and trap mechanisms of potential reservoirs are of paramount interest during exploration stage.This research work focused on the F-O tract located in the eastern part of Block 9 on the north-eastern flank of the Bredasdorp Basin, a sub-basin of Outeniqua Basin on the southern continental shelf, offshore South Africa. The Bredasdorp Basin experienced an onset of rifting during the Middle-Late Jurassic as a result of dextral trans-tensional stress produced by the breakup of Gondwanaland that occurred in the east of the Falkland Plateau and the Mozambique Ridge. This phenomenon initiated a normal faulting, north of the Agulhas-Falkland fracture zone followed by a widespread uplift of major bounding arches within the horst blocks in the region that enhanced an erosion of lower Valanginian drift to onset second order unconformity.This study considered 52 selected reservoir core samples from six wells(F-O1, F-O2, F-O3, F-O4, F-R1 and F-S1) in the F-O field of Bredasdorp Basin with attention on the Valanginian age sandstone. An integrated approach incorporating detailed core descriptions, wireline log analysis (using Interactive petrophysics), structural interpretation from 2D seismic lines (using SMT software) cutting across all the six wells, multi-mineral (thin section, SEM,XRD) analyses, geochemical (immobile fluid and XRF) and fluid inclusion(fluid inclusion petrography and bulk volatile) analyses were deployed for the execution of this study. Core description revealed six facies from the six wells grading from pure shale (Facies 1), through progressively coarsening interbedded sand-shale “heterolithic facies (Facies 2 - 4), to cross bedded and minor massive sandstone (Facies 5 - 6). Sedimentary structures and mineral patches varies from well to well with bioturbation, synaeresis crack, echinoid fragments, fossil burrow, foreset mudrapes, glauconite and siderite as the main observed features. All these indicate that the Valanginian reservoir section in the studied wells was deposited in the upper shallow marine settings. A combination of wireline logs were used to delineate the reservoir zone prior to core description. The principal reservoirs are tight, highly faulted Valanginian shallow-marine sandstones beneath the drift-onset unconformity, 1At1 and were deposited as an extensive sandstone “sheet” within a tidal setting. The top and base of the reservoir are defined by the 13At1 and 1At1 seismic events,respectively. This heterogeneous reservoir sandstones present low-fair porosity of between 2 to 18 % and a low-fair permeability value greater than 0.1 to 10 mD. The evolution of the F-O field was found to be controlled by extensional events owing to series of interpreted listric normal faults and rifting or graben generated possibly by the opening of the Atlantic. The field is on a well-defined structural high at the level of the regional drift-onset unconformity, 1At1.Multi-mineral analysis reveals the presence of quartz and kaolinite as the major porosity and permeability constraint respectively along with micaceous phases. The distribution of quartz and feldspar overgrowth and crystals vary from formation to formation and from bed to bed within the same structure. The increase in temperature that led to kaolinite formation could have triggered the low-porosity observed. Three types of kaolinite were recognized in the sandstone, (1) kaolinite growing in between expanded mica flakes; (2)vermiform kaolinite; and (3) euhedral kaolinite crystals forming matrix.Compositional study of the upper shallow marine sandstones in the Valanginian age indicates that the sandstones are geochemically classified as majorly litharenite having few F-O2 samples as subarkose with all F-O1 samples classified as sub-litharenite sandstone.Most of the studied wells are more of wet gas, characterized by strong response of C2 – C5 with F-O1 well showing more of gas condensate with oil shows (C7 – C11) based on the number of carbon atom present. In some cases,sulphur species (characterized by the presence of H2S, S2, CS2 and SO2) of probably thermal origin were identified while some log signatures revealed aromatic enriched sandstones possibly detecting nearby gas charges. The studied wells in the F-O field, based on fluid inclusion bulk volatile analysis are classified as gas discoveries except for F-O1 with gas condensate and oil shows.The integration of multi-mineral results and fluid inclusion studies show a dead oil stain with no visible liquid petroleum inclusion in the samples indicating the presence of quartz, kaolinite and stylolite as a major poro-perm constraint.

Evidence from fluid inclusion microthermometry in Pb-Zn-Cu-(Ag-Au) veins and district scale metal ratio zonation analysis indicate that the Cordilleran veins of the Montezuma mining district Summit County, Colorado, USA are indicative of subepithermal setting about a central hydrothermal source. Cordilleran-type polymetallic mineralization is a class of ore deposits that are spatially and temporally related to felsic igneous centers and can also be genetically related to porphyry mineralization (Fontboté and Bendezú, 2009). At Montezuma, the Teritary-aged Montezuma Stock is cross cut by several Cordilleran-type veins and is spatially related to over 80 additional veins hosted in Precambrian country rock.

Five stages of mineralization in veins are identified: Stage 1. early quartz-pyrite, Stage 2. barite-incipient base metals Stage 3. base metals, Stage 4. carbonates and Stage 5. late quartz-lead-silver. There is a systematic decline in precipitation temperatures from 341 to 156°C along the progression of the paragenetic sequence, which suggests the waning of a source pluton. District scale metal ratio zonation maps from historical production data support the interpretation of a central magmatic source and that thermal decline is the primary control on ore deposition. Two district scale zones are identified: a copper rich zone (CRZ) in the center of the district, which is surrounded by a copper poor zone (CPZ). With distance from the inferred center of the district, there is a general decline in copper abundance relative to lead and silver. Thermal gradients accompanied by a decrease in metal solubilities are the mechanism for this zonation pattern, but developed late in the paragenesis. Other chemical and physical controls of phase separation, ligand removal, dilution and pH increase are likely present during vein mineralization as well. Approximate salinities ranged from 11.69 to 3.70 wt.% equivalent NaCl and showed less systematic patterns, and may reflect these additional processes. Temperature decline and variable additional depositional processes are consistent with analogous Cordilleran-type vein fields, which have proven links to a magmatic source and possible underlying stockwork porphyry base metal mineralization. Therefore, data from this study indicates that there is most likely porphyry Mo mineralization under the copper rich zone, but this may be sub economic in nature.