The Mount Fubilan Intrusion is part of a geologically young hypabyssal stock in the Star Mountains of Papua New Guinea. This stock was mapped as the Ok Tedi Intrusive Complex and divided into four separate bodies: the Mount Fubilan, Sydney Intrusion, Kalgoorlie, and Ningi Intrusions. Hydrothermal fluids caused alteration of the Mount Fubilan, and parts of the other intrusions, to potassic and propylitic mineral assemblages and deposited gold and copper. This investigation documents similarities and differences between the least-altered intrusive rocks of the complex and those that have undergone potassic metasomatism. The study involved detailed petrographic examination of more than two hundred thin-sections, major-oxide and trace element chemistry, and microprobe analyses of individual minerals. The magmas that crystallized to form the stock are shown to be intermediate in composition between andesite and latite. They were quartz-saturated, metaluminous, weakly iron-rich, and crystallized under oxidizing conditions. The principal mineral phases in the least-altered intrusive rocks are andesine, pyroxene, orthoclase, and quartz. The accessory mineral suite in least-altered rocks includes biotite, sphene, apatite, magnetite, and zircon. Hornblende is present in a few samples Magmatic pyroxene is diopsidic in composition; hornblendes is cdenitic; and biotite is annitic. Potassic alteration has converted andesine to orthoclase, or mixtures of albite and orthoclase, ferro magnesian minerals to hydrothermal biotite, sphene to rutile, and magnetite to pyrite and chalcopyrite. Hydrothermal biotite is phlogopitic in composition. Gold and copper were concentrated in the zone of potassic alteration. The mineralogical transformation of the intrusive rocks of the Mount Fubilan and associated intrusions was caused by the infiltration of hydrothermal fluids that deposited potassium, gold, and copper and that leached and removed virtually all other rock constituents. Leached components were transported away from the zone of potassic alteration and deposited in peripheral parts of the intrusive complex to form propylites, endoskarn, and massive replacement bodies or removed from the system entirely. The Mount Fubilan intrusion was closely similar in chemistry and mineralogy to the other intrusions of the complex prior to alteration. Petrochemical differences between the Mount Fubilan Intrusion and the other intrusions were produced entirely by hydrothermal alteration. / Graduation date: 2000

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 6, 2007) Includes bibliographical references.

Graduation date: 1991

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

abstract / Earth Sciences / Doctoral / Doctor of Philosophy

Stikinia is a tectonostratigraphic terrane in the Canadian Cordillera comprised of the Early Permian Asitka Group, the Late Triassic Stuhini Group and the Early to Middle Jurassic Hazelton Group. William’s Gold property which coincides with the study area is located on the east-northeast margin of the Stikine terrane within a fault mosaic of Devonian to Permian Asitka Group carbonates and volcanic and sedimentary rocks of the Stuhini Group. The primary purpose of this study is to determine the timing of mineralization and the absolute ages of the intrusions within the Williams west region of the William’s Gold property. This study attempts to correlate mesothermal gold veining and Cu-Au porphyry style mineralization from the study area with mineralization that has occurred approximately 100km southeast at Kemess Mine. U-Pb, Ar-Ar geochronology and Pb isotopic studies were used to determine the ages and isotopic signatures of rocks located within the study area. Four samples of quartz monzonite and one sample of a feldspar porphyry gave U-Pb crystallization ages ranging from 221.4 to 183.6 Ma. Two samples G090062, and G090063 contained cores that cluster between 230 and 260 Ma and 330 and 380 Ma. The oldest gave an age of 420Ma. The presence of older cores suggests that the intrusion passed through older basement rocks, possibly the Paleozic Stikine Assemblage. A sample of alteration sericite from the T-bill prospect that is believed to occur syn-mineralization was dated using the Ar-Ar method and returned an inverse isochron age of 194.6 +/-3.5 Ma. The age of the sericite alteration did not correspond to the ages of the five intrusive units analyzed during this study. This suggests that the mineralization at the T-bill prospect was likely not genetically related to any of the intrusions dated in this study.

The area of this study is a northeast trending zone which is approximately ninety miles long, extending from Casa Grande to Globe, Arizona. A number of porphyry copper deposits and barren Laramide stocks occur within this zone. Geological mapping of the various Laramide granitic stocks shows that all of the stocks are composite, epizonal granitic stocks, which are all elongate in a N45°E to N80°E direction. Sulfide bearing veins also trend N45°E to N80°E. The configuration of the stocks defines the structural framework into which they were intruded. The consistent elongation of the granitic stocks shows that the stocks were intruded into a series of parallel, regional faults that trend approximately N60°E to N80°E. Isotopic dating of the stocks shows that they become progressively younger from west to east. Typical isotopic ages are 71 m.y. on the west portion of the zone, and 61 m.y. on the east portion. The porphyry copper deposits also show a trend of decreasing age from west to east. The granitic Laramide stocks are localized where the N45°E to N80°E regional faults intersect the Precambrian granite-Pinal Schist contact. In some cases the regional faults are parallel to the Precambrian granite-Pinal Schist contact, in which case the Laramide stocks are parallel to the contact. The Laramide quartz diorite stocks only occur along the "San Pedro hinge line" and farther to the east. Although the individual quartz diorite stocks are aligned in an east-northeast direction, the overall geographical trend of the quartz diorite is north-northwest. The quartz diorite stocks may also become progressively younger proceeding to the east. The defining of the regional faults or lineaments, based upon the orientation of the Laramide granitic stocks, permits a rather precise projection of these lineaments into areas of complete post-mineral rocks. This allows a large area of post-mineral rocks to be reduced to a rather small area, where exploration for porphyry copper deposits can be intensified.

Mechanisms of sill and dyke intrusion require an understanding of fracture growth,stress distributions and intensities, dilation,intrusion rates, hydraulic pressure,host-rock effects,en echelon fracture arrays,and flow direction. The methods of previous studies have been applied to natural sill and dyke examples of the Karoo Igneous Province in northern Natal . An en echelon array of Jurassic dolerite sills occurs within Permian Ecca sediments along the Mhlatuze River, west of Empangeni. Dolerite emplacement occurred as two intrusive phases. The first phase resulted in thick, . coarse-grained dolerite sills. The second phase produced relatively thinner, fme-grained sills. The intrusion of fmegrained dolerite into older sills is demonstrated by abrupt variations in the whole-rock and mineral geochemistry profiles across the sills. Syn-crystallisation effects such as crystal settling and fractionation, and post-crystallisation hydrothermal activity is also manifested in the mineralogical and geochemical changes across the sills. The fine grained doleriteis associated with xenolithic dolerite which represents a contaminated magma propagation front of the fine-grained dolerite. The higher viscosity of the xenolithic dolerite hindered propagation, and was thus overtaken and engulfedby the mainmagmapulse. Consistent sinistral off setting of sill segments is interpreted to be the result of a fingered sill periphery intruding an en echelon fracture array. Dilation of individual segments, or fingers, occurred simultaneously. Subsequent interaction of near-tip stresses induced inwardly propagating curvature of adjacent segmentsin the array.Resultant linkage has produced a stepped-sill geometry; sill propagation and flow directions were orthogonal to the plane of linkage. The flow direction is confirmed by shape preferred-orientations of acicular mineral grains within the chilled margins of the sills, indicating the direction of flow to be perpendicular to the plane of the en echelon array, and parallel to strike directions of offset surfaces that link adjacent sill segments. Multiple dyke intrusion is examinedat an outcrop of the Rooi Rand Dyke Swarm, along the Pongola River. Individual intrusive episodes are identifiable on the basis of chill-zone relationships. The pattern along the Pongola River suggests that younger intrusive episodes frequently intrude through the centres of older dykes. A three dimensional analysis of en echelon dyke let segments allows a re-construction of the dilation history,and provides an explanation for the development of blunt-ended intrusion segments. Mineral geochemistry anomalies around dyke tips suggests possible facilitation of incipient fracture via decreases in mineral strengths manifested by geochemical changes. A statistical digital analysis of micro-phenocryst orientations within chilled dyke margins is shown to provide a viable method to ascertain magma flow directions within dykes, and may thus be a useful tool for future investigations. / Thesis (M.Sc.)-University of Natal, 1994.

The Jurassic Rooi Rand dolerite dyke swarm was emplaced sub-parallel to the Lebombo Monocline during the initial stages of Gondwana breakup. The dykes extend northwards from the southern Lebombo region in northern KwaZulu-Natal, into central Swaziland, spanning a distance of approximately 200 kilometres with a width between 10 and 22 kilometres. Detailed mapping of a 600m-Iong section on the Pongolo River, established at least eleven phases of intrusion. Each dyke age was systematically sampled and analysed for whole-rock major, trace and rare earth element composition, as well as mineral chemistry. Selected samples were analysed for stable isotopes. In addition to notable intra-dyke chemical variations, there is also a high degree of inter-dyke mineralogical and geochemical variation, each dyke age bearing distinct geochemical characteristics. The apparent geochemical trend is not one of simple fractionation with time. Dyke chemistries are closely linked to magma genesis and magma volumes with time. Evolution of the magmas may be described in terms of varying degrees of partial melting and fractional crystallization, with a small degree of crustal contamination. Major, trace and rare earth element data indicate a lithospheric mantle source for the majority of dyke phases, and an asthenospheric source for only two of the eleven ages. Contrary to this, isotopic data (oxygen and radiogenic) indicate an enriched asthenospheric source for all the dolerites. This suggests that all ages may have originally been derived from the asthenosphere, with the majority of ages being intruded into the lithospheric mantle to later undergo partial melting and fractional crystallization, with some contamination. Previous studies assumed an asthenospheric source with depleted MORB-like rare earth element profiles to be representative for the majority of Rooi Rand dolerites. The Rooi Rand dolerites appear to display a geochemical link with the southern Sabie River Basalt Formation, as well as the Lebombo rhyolites. Magmatic evolution of the dykes was intimately linked to the initial rifting processes of lithospheric stretching and asthenospheric upwelling, which in this case concluded in a classic failed rift situation. / Thesis (M.Sc.)-University of Natal, 1996.

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