Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 66-70). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 66-70). Also available on the Internet.

The Summitville high-sulfidation gold deposit is hosted by a volcanic dome consisting of the South Mountain Quartz Latite that was erupted 23 Ma ago during formation of the Platoro Caldera complex in the San Juan volcanic field of south central Colorado. Alteration and mineralization developed during or shortly after dome emplacement as a result of metal-rich magmatic fluids and vapor emanating from a crystallizing intrusion at depth. Copper, arsenic, silver and gold are enriched in the deposit with two of the last paragenetic stages, the barite-base metal sulfide and goethite stages, containing the highest gold grades. Barite contains magmatic sulfur with a range of δ34S values (19.3 – 31.8 ‰) that reflects SO42– – H2S isotopic equilibration over a temperature range of 115 to 180 °C, which is consistent a calculated temperature of 147 °C based on the sulfur isotopic fractionation between intergrown barite and galena. Barite δ18O values (19.3 – 31.8 ‰) indicate the barite fluids contained a minor component of meteoric water. Barite growth zones with acicular crystals (wires) of emplectite (CuBiS2), a mineral not previously reported from Summitville, contained primary fluid inclusions that yielded a wide range of vapor to liquid homogenization temperatures as a result of stretching but consistent freezing point depressions that infer an average salinity of 5.1 wt. % NaCl equivalent. These data indicate that the barite fluids were modestly enriched in magmatic sulfur and metals (Cu, As, Bi, Pb, Zn, Au, Ag) and that barite precipitation was likely triggered by cooling during mixing with meteoric waters. The goethite stage developed during weathering of the deposit that likely occurred during uplift and exposure around 9 to 7.7 Ma ago based on 40Ar/39Ar dates on jarosite. The assemblage goethite + hematite ± jarosite ± scorodite ± gold filled open spaces and coated barite of the barite-base metal sulfide stage. Inclusions of barite and bladed alunite in the iron oxide/hydroxide (FeOx) matrix have the texture, composition and isotopic values of their earlier formed counterparts in the deposit and therefore represent residual material that survived the weathering event. Three 40Ar/39Ar dates on the bladed alunite ranged from 23.15 to 22.88 Ma, confirming their origin as magmatic hydrothermal alteration alunite. Layers of compositionally zoned, small rhombohedral crystals of alunite were also discovered in the FeOx matrix. Although these could not be successfully dated, they had a distinct texture, chemistry and isotopic composition (δ34S = 0.8 ‰ δ18O = 4.7 ‰) that indicated they formed during the weathering event. The acidic, oxidizing supergene fluids remobilized and broadly enriched the top of the deposit in Cu and Ag and locally in native gold (5 wt. % Ag).

No description available.

No description available.

Η περιοχή του κεντρικού Αιγαίου έχει υποβληθεί σε ηπειρωτική διαστολή από το κατώτερο Μειόκαινο. Κατά το στάδιο της διαστολής είχαμε διείσδυση ενός πλουτωνίτη ο οποίος σχετίζεται με το σύστημα αποκόλλησης της Μυκόνου. Η Μύκονος κυριαρχείται από έναν μονζογρανίτη, Ι-τύπου, ηλικίας 10 Ma ο οποίος διείσδυσε μέσα σε μάρμαρα, μεταπηλίτες και μεταβασίτες της Κατώτερης Ενότητας. Τα γρανιτοειδή της Μυκόνου έχουν μορφή λακκόλιθου με μονζογρανιτική έως γρανοδιοριτική σύσταση και υπέρκειται από την αποκόλληση της Λιβάδας η οποία ήταν ενεργή ταυτόχρονα με την εκταφή του γρανίτη και έχει υποβληθεί σε έντονη μυλωνιτίωση. Η τοποθέτηση του λακκόλιθου χρονολογείται στα 13,5 +/- Ma όπως βρέθηκε από χρονολογήσεις U/Pb σε ζιρκόνιο. Η εκταφή του λακκόλιθου της Μυκόνου ήταν γρήγορη όπως υποδεικνύεται από θερμοχρονολογικά δεδομένα. Το τέλος της περιόδου δραστηριότητας της αποκόλλησης είναι ισόχρονο με την απόθεση του συστήματος των φλεβών βαρύτη το οποίο αποτέθηκε στην περιοχή του Πανόρμου. Δείγματα που συλλέχθηκαν από την περιοχή του Πανόρμου χρησιμοποιήθηκαν για την ισοτοπική ανάλυση των ρευστών εγκλεισμάτων που απομονώθηκαν από τις βαρυτικές φλέβες. Οι αναλύσεις μπορούν να μας δώσουν χρήσιμα δεδομένα για τις συνθήκες που επικρατούσαν κατά την απόθεση του βαρύτη καθώς και την προέλευση της μεταλλοφορίας του πλουτωνίτη της Μυκόνου. / The central Aegean region has undergone continental extension since at least the Early Miocene. The extensional stage was accompanied by the intrusion of granitic plutons and associated detachments such as the Mykonos detachment. Mykonos is dominated by a 10 Ma I-type monzogranite intruded into marble, metapelite and metabasite of the Lower Unit. The Mykonos granitoids form a laccolith-like intrusion with a monzogranitic to granodioritic composition and are topped by a low angle normal fault system. The top of the laccolith has been reworked by the Livada detachment which was active along with the exhumation of the granite and has undergone through intensive mylonitization and brecciation. Emplacement of the laccolith is dated at 13,5 +/- Ma using the U/Pb technique on Zircon. The exhumation of the Mykonos laccolith was very fast as indicated by thermochronological data. The end of the period of activity of the detachment is coeval with the emplacement of huge barite veins. The barite vein system which is deposited in the area of Panormos Bay is hosted in the monzogranite and consists of a set of ten major NW- to NNW- crustified tension gashes filled with barite and other minerals. Sample material that was collected from Panormos Bay was used for the study of fluid inclusions that were trapped in coarse-grained transparent minerals such as barite and quartz. Fluid inclusions can provide very useful information about the conditions existing during the formation of barite as well as the origin of the mineralization on the Mykonos pluton.

Barium sulfate scaling can cause many oilfield problems leading to loss of well productivity and well abandonment. Currently, diethylene triamine pentaacetic acid (DTPA) is used, along with synergist oxalic acid and potassium hydroxide, to remove the scale by dissolution. However, the chemical factors affecting this reaction are not known fully, leading to mixed results in terms of treatment effectiveness. This thesis investigates the effect of these factors, by analyzing the change in barite dissolution due to intrinsic factors like variations in formulation composition and extrinsic factors like presence of competing ions. The dissolution reaction is carried out, by taking the barite powder and chelant solution in a teflon round bottom flask and measuring the barite dissolved periodically, with an ICP-OES. The effect of different factors is studied by varying each factor individually and plotting the changes in solubilities. These lab tests show that solubility of barite (0.01mM in water), ideally, increases with increasing concentrations of chelating agents, even going as high as 239 mM. However experimental or field constraints lead to significant decrease in dissolution, especially at higher chelant concentrations. Thus, field tests to determine most effective chelant concentrations must precede treatment design. Lab tests also show that combination of DTPA with weaker chelating agents like ethylene diamine tetraacetic acid (EDTA), L-glutamic acid, N,N-diacetic acid (GLDA) or methyl glycine diacetic acid (MGDA) reduces barite dissolution and should be avoided during treatment design. Addition of synergists to the formulations, initially improves dissolution performance, especially for moderate chelant concentrations, but proves detrimental and hence must be avoided, over longer treatments. Finally, presence of competing ions in seawater, calcium sulfate and calcium carbonate, can significantly reduce barite dissolution and must be carefully studied for each formation-fluid system before design of treatments. Thus, this project sets a framework to identify the best chelant formulation and estimate its dissolution profile to ensure, a more informed treatment design for barite scale removal.

The presence of ion-pairs in electrolyte solutions affects the activity of dissolved species as well as the solubility of minerals. The extent of ion-pairing in a system is predicted by an association constant, K[subscript A], which for sparingly soluble salts are frequently determined experimentally in binary or ternary systems. This introduces complex activity coefficient calculations that often require unavailable parameters. Barite (BaSO₄) and celestite (SrSO₄) are sparingly soluble minerals with interest in the oil and mining industry, yet the values of K[subscript A] for the ion-pairs BaSO₄(aq.) and SrSO₄(aq.) are still uncertain. Molecular dynamics simulations are used to obtain the K[subscript A] values for these two salts through potential of mean force (PMF) calculations. The molecular mechanisms involved in the association reactions are also explored, in particular the role of the association intermediates in the overall reaction as described by the Eigen mechanism. Additionally, the kinetics of water exchange around the free and paired ions is examined and the residence time of a water coordinated to the free and paired cation is calculated.

No description available.

In the past ten years, there have been 194 hurricane-damaged platforms in the Gulf of Mexico (GOM), each with many wells that have not been permanently abandonment. This could lead to disastrous environmental consequence. The wells where their platforms were destroyed by hurricanes cannot be abandoned by conventional methods. Our research showed that barite-weighted epoxy material could be potentially used for well abandonment for those wells in GOM. Shear bond strength tests showed that between two candidates epoxy systems - the bisphenol A system and the bisphenol F system, the latter was less sensitive to barite weighting material. The shear bond strength of besphenol A system was deteriorated as barite increased, while bisphenol F system showed slightly increasing trend when barite was added. The minimum bond strength given by bisphenol A system appears around 68 wt% of barite, which is around 1290 psi. The maximum value of 2200 psi comes at 0 wt% of barite. And the bisphenol F system can stand a minimum of 1010 psi bond strength at 0 wt% of barite, and a maximum of 1160 psi of bond strength with 70 wt% of barite. Moreover, mixing with seawater did influence the shear bond strength between epoxy system and low-carbon steel. The influence that seawater has on the F system is less than that of the A system. The time that the epoxy system needs to fully develop the bond is far longer than curing time determined in our parallel research. Bond strength is lower in both seawater environment and at high temperature.