This thesis describes investigations on Cu, Ag, and Au subtractive etching by H₂ and CH₄ plasmas below room temperature. Both blanket film of Cu, Ag, and Au etching and patterning studies were performed for the applications of these metals as interconnects in electronic devices and photonic devices to replace current Damascene process. The nm scale Cu patterning in H₂ plasma was demonstrated by etching Ta/Cu/Ta stacks. Also, Ag and Au etching was feasible in H₂ plasma unlike other transition metals such as Ti, Ta, Ni, Cr, Al, and Pt indicating the etching chemistry based on the similar electronic structures of group 11 metals plays important role. In addition, employing CH₄ plasma allowed the use of photoresist mask and patterned Cu, Ag, and Au with high selectivity. The overall etch mechanism is the combination of chemical reactions and physical (photon and ion) bombardment in H₂ and CH₄ plasma. However, the Cu etching mechanism is more dependent on the chemistry while Ag and Au patterning were dominated by physical bombardment. Finally, the direction for future work including further mechanistic study and process optimization is suggested.

The syenite-hosted Young-Davidson (YD) gold deposit is located at the western extension of the Cadillac-Larder-Lake deformation zone (CLLDZ), southwest of Kirkland Lake, in the southern Abitibi greenstone belt, Canada. Gold is predominantly hosted by syenite, and to a lesser extent by Timiskaming sedimentary rocks and mafic volcanic rocks in veins and/or small pervasively altered shear zones related to the CLLDZ. Historical gold production was mainly from quartz veins and disseminated pyrite hosted in altered syenite. Recent drilling by AuRico Gold Corporation (formerly Northgate Minerals Co.) has expanded the underground resource to 14.6 million tonnes (measured and indicated) at an average grade of 2.03 g/t Au and an underground reserve of 39.1 million tonnes (proven and probable) at an average grade of 2.79 g/t Au, where most of the gold is hosted in the syenite. Three generations of veins have been identified based on crosscutting relationships mapped at an underground ore crosscut: V1 boudinaged iron-carbonate veins, V2 folded quartz-pyrite veinlets and V3 planar quartz-carbonate veins. Structural characterization of the vein sets indicates that V2 and V3 extensional vein arrays developed during the D2 deformation, which generated the steeply dipping east-west striking penetrative S2 foliation that is found elsewhere along the CLLDZ. Petrographic analysis of mineralized syenite shows that native gold grains are most abundant in zones of intense potassic-hematite-pyrite alteration as inclusions and along cracks in vein-related and disseminated pyrite. Volcanic-hosted gold is mainly located in quartz-iron-carbonate veins hosted in narrow sheared and pervasively albite-iron-carbonate-pyrite altered volcanic rocks. Whole rock lithogeochemical analyses and mass balance calculations show that mineralized syenite is characterized by enrichments in K, S, Na, Ba and W whereas mineralized volcanic rocks are characterized by strong enrichments in Na, Al, Si, K, Fe, S, Ba and W. Geochemical contouring of 279 analyses of drill core along two N-S sections through the YD syenite show broad cross section scale correlation of gold mineralization with K2O, S and Ba. Sulfur is the most strongly correlated with gold mineralization; however, the most intense sulfidation is generally coincident with zones containing coarse altered feldspars and a fine-grained groundmass of iron-carbonate, Na- and K-feldspar and minor quartz. Bulk sulfur isotopic analyses of syenite-hosted pyrite grains indicate that the dominant source of sulfur is magmatic but there is also a component that has interacted with the reduced Archean atmosphere. Pyrite grains in syenite and volcanic rocks contain up to 15,000 ppm Co, 4,000 ppm Ni and 4,200 ppm As. Chemical mapping of Co, Ni and As from different vein associated pyrite grains show: 1) Arsenic in pyrite is low, < 1,000 ppm; 2) Pyrite shows Co-Ni zoning and gold in V1 vein pyrite is associated with Co-Ni rich pyrite overgrowths of earlier corroded pyrite grains; 3) gold along fractures in V2 vein pyrite is also associated with Co-Ni enrichment; and 4) gold in V3 veins crosscuts Co-Ni patterns in pyrite, which suggests that the V3 style of mineralization has precipitated by different mechanisms. Pyrite mapping combined with alteration assemblages, mineralization characteristics and mineral chemistry suggests that the syenite-hosted mineralization has formed from interaction between multiple fluids with distinct physicochemical conditions. The proposed formational model for the Young-Davidson deposit is of fluid mixing between magmatic and metamorphic fluids during the deformation events that generated the extensive veining systems at Young-Davidson.

The wood’s Point dyke swarm, Victoria, consists of a set of abundant subparallel narrow dykes with occasional elliptical expansions (“bulges”) intruded into strongly folded Lower Palaeozoic sediments. The swarm represents a hisly differentiated calc-alkaline rock series derived by fractional crystallization of a single parent magma, possibly of periodotitic composition. The rock types present include both high and low Cr-Ni periodotites, pyroxenite, hornblendite, hornblende diorite and monzonite, biotite leucodiorite, and minor residual granophyre. Apart from this hornblende-bearing rock series, a few hornblende-free basaltic dykes of related chemical composition but intruded later, are petrographically and mineralogically distinct, displaying tholeiitic tendencies. The latter dykes appear to be genetically related to volcanics underlying the Upper Devonian Acheron and Cerberean cauldron subsidences. / Fractional crystallization, flowage differentiation, crystal accumulation and chilling were important factors in the development of the members of the dyke swarm, whilst assimilation in situ was not. The dykes are zonod, ultramafic types having more basic interiors (“cores”) whereas basic to intermediate composition bulges have more basic margins (“rims”). / Magmalic copper-nickel sulphides rich in precious metals (Pt, Pd, Au) occur in dyke bulges of all compositions, especially close to margins where they accumulated by gravitational settling or were trapped by chilling. The sulphides have high Cu/Ni (and Co/Ni) ratios indicative of a highly evolved magma and, along with Au, Pd and Ir are fractionated between dykes of different silicate compositions. The base metal contents of silicates and sulphides vary sympathetically. / The dykes have undergone pervasive hydrothermal alteration during which sulphides were largely recrystallised and Au was leached from some copper-nickel sulphides. A zonal arrangement of increasing intensity of alteration inwards was observed in one ultramefic dyke bulge. Later the dykes were deformed and the basic to intermediate composition dykes were fractured and veined, and major gold deposits formed. The veins have associated wall rock alteration which may be mineralogically subdivided into inner and out zones. / Dyke bulges, ultramafic rocks, copper nickel sulphides and Au mineralization are all concentrated along two main lineations paralleling the fold axes of the sedimentary trough. The eastern and more important trend (at the centre of the trough) marks the eastern limit of the dyke swarm except at its northern end. These lineations may represent deep-seated fractures which controlled the later upward migration of Au-bearing hydrothermal solutions from depth. The source of the Au could have been various rock types present at depth, including copper-nickel sulphides and Lower Palaeozoic sediments.

The oxidation of refractory gold concentrates containing arsenopyrite and pyrite and the simultaneous dissolution of gold in aerated alkaline solutions at ambient temperatures and pressures without the addition of cyanide has been studied. It involves the following aspects: the chemistry of the oxidation of pure arsenopyrite and pyrite minerals in aerated alkaline solutions; the kinetics of oxidation of arsenopyrite and the simultaneous dissolution of gold in such solutions; the kinetics of simultaneous dissolution of gold during the alkaline oxidation of refractory gold concentrates; the electrochemistry of gold in alkaline solutions containing thiosulfate or monothioarsenate; the effect of copper on the leaching of gold in alkaline thiosulfate solutions; and the leaching of gold in alkaline solutions with thioarsenites. The nature and proportions of the products of the oxidation of arsenopyrite in aerated alkaline solutions have been studied using high pressure ion chromatography techniques that have shown that thiosulfate and a new species, monothioarsenate, are the main oxidation products of arsenopyrite apart from arsenate and sulfite. The alkaline oxidation of pyrite primarily yields thiosulfate and sulfite. A kinetic investigation of the oxidation of arsenopyrite with air or oxygen has shown that the initial rate of arsenopyrite oxidation is proportional to the concentration of dissolved oxygen. A reaction mechanism for the oxidation of arsenopyrite has been proposed, which involves an anodic oxidation of the mineral involving hydroxyl ions coupled to a cathodic process for oxygen reduction which is partially controlled by mass transfer of dissolved oxygen to the mineral surface. Detailed studies of the dissolution behaviour of gold in aerated alkaline solutions in the presence of thiosulfate or monothioarsenate by electrochemical and leaching methods have demonstrated that the dissolution rate is very low as compared to that of gold in alkaline cyanide or ammoniacal thiosulfate solutions. It has been found that copper ions catalyze the dissolution of gold in the thiosulfate solutions in the absence of ammonia. The leaching experiments also have shown that gold may dissolve in alkaline thioarsenite solutions, which provides a possible new process option for the leaching of gold. The oxidation of refractory arsenical gold concentrates in aerated alkaline solutions results in the formation of thiosulfate, arsenate and sulfate as well as the dissolution of gold, copper and iron. It appears that the dissolution of gold is due to the complex reactions of gold with thiosulfate ions promoted by the catalytic effect of copper ions. Up to 80% of the gold may be extracted during the oxidation of selected refractory arsenical

Thesis (MSc)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.

Frankfurt (Main), Univ., Diss., 1998

Thesis (Ph. D.)--University of Nevada, Reno, 2006. / "December, 2006." Includes bibliographical references (leaves 152-157). Online version available on the World Wide Web.

Thesis (Ph.D.)--University of Western Australia, 2003.

Thesis (Ph.D.)--University of Western Australia, 2005.

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1910. / The entire thesis text is included in file. Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed March 17, 2009) Includes bibliographical references (p. 26).