Mafic volcanic sequences of tholeiitic basalt and associated komatiite are common to many Precambrian shields of the world. Recently discovered remnants of Archean greenstone belts in the northern Superior Province of Canada exhibit characteristics similar to larger belts of the southern Superior Province. Three of the best preserved belts are trapped in ca. 2.77--2.88 Ga tonalitic intrusives of the Faribault-Thury amphibolitic Complex (FTC), and provide direct evidence for the nature of the mantle prior to the major volcanic events of the late Archean (ca. 2.7 Ga). These belts consist of amphibolite facies rocks of volcanic and sedimentary origin, in one of which a wide variety of cumulates are preserved. The association of the lavas with meta-pelites, iron formations, marbles, and the lack of conglomerate and clearly crustally contaminated lavas suggest that the FTC lavas were erupted in an oceanic environment. The three belts are separated by over 100 km, but exhibit similar chemical characteristics and may represent the base of an extensive early mafic crust. (Abstract shortened by UMI.)

The Stikine Volcanic Belt is a lineament of Tertiary to Recent alkaline volcanic centres that cross disparate oceanic and continental terranes of the northern Canadian Cordillera, and extend onto the North America craton. This volcanic lineament thus offers an unique opportunity to probe the lithospheric mantle beneath these terranes and investigate the relative roles of lithospheric and asthenospheric mantle sources in the generation of alkaline lavas. / Alkaline lavas in twelve volcanic centres of the Stikine Volcanic Belt were sampled and studied for major and trace elements and Sr-Nd-Pb isotopic compositions. The primitive lavas of each volcanic centre define binary arrays between two compositional end-members, olivine nephelinite (NEPH) and hypersthene-normative olivine basalt (Hy-NORM). The NEPH end-member is characterized by large enrichments in incompatible trace elements with respect to primitive mantle, but is depleted in term of its isotopic composition. The presence of amphibole in its source suggests that this end-member is derived from the lithospheric mantle. The Hy-NORM end-member has lower incompatible trace element contents, but is still relatively enriched in incompatible elements compared to primitive mantle. Although this end-member has always more radiogenic Sr and Pb, and less radiogenic Nd isotopic ratios than the NEPH end-member, its isotopic signature varies with the tectonic belt in which it erupted, indicating a significant role for the lithospheric mantle in the derivation of the Hy-NORM basalts. / The Canadian Cordilleran, and other continental Hy-NORM basalts, have low Ca and high Na contents compared to their equivalents at oceanic hot spots such as Hawaii or associated with mid-ocean ridges. A comparison with experimental melts of mantle peridotite indicates that these characteristics reflect smaller degrees of partial melting (<10%) in continental regime. The range of observed lava compositions is explained by the melting of two distinct lithospheric components, a NEPH end-member representing the melting of amphibole-rich veins, and a Hy-NORM end-member resulting from small degrees of partial melting of their host garnet lherzolite. The high heat flow values reported in the northern Canadian Cordillera are consistent with a model in which ongoing melting and thinning of the lithospheric mantle is responsible for generating the mafic alkaline magmas.

The 80 x 20 km Migori segment of the Nyanza greenstone belt, Kenya, lies within the Archean Tanzanian Craton (2.8-2.5 Ga). Volcanic facies mapping has delineated eleven formations comprising the Macalder and Lolgorien Subgroups of the Migori Group. The subgroups represent adjacent volcanic centres with well-developed central and proximal facies, and interfingering distal facies. Rocks at the base of the group are submarine tholeiitic basalt and dolerite, and calc-alkaline dacite and rhyolite; overlying subaerial dacites and late granite intrusions define a high-K calc-alkaline suite. The tholeiitic volcanic rocks have 3.8 $<$ Zr/Y $<$ 6.5 and 1.0 $<$ La$ sb{ rm N}$/Yb$ sb{ rm N}$ $<$ 2.4, the calc-alkaline volcanic rocks 10 $<$ Zr/Y $<$ 21 and 19 $<$ La$ sb{ rm N}$/Yb$ sb{ rm N}$ $<$ 42, and the high-K calc-alkaline dacites 9 $<$ Zr/Y $<$ 16 and 21 $<$ La$ sb{ rm N}$/Yb$ sb{ rm N}$ $<$ 22. The calc-alkaline - high-K association in the segment points to a continental arc tectonic setting for the Migori segment. The central and proximal facies provide the greatest potential for volcanogenic sulphide deposits, whereas vein and stratabound gold mineralisation are present in all the facies.

The Lac Raudot complex is an Fe rich layered troctolite-anorthosite intrusion located in the Grenville province of southern Quebec. Corona textures developed between plagioclase and olivine indicate the Lac Raudot complex must have equilibrated at pressures of at least 6 to 8 kbar corresponding to depths greater than 15 km. / The crystallization sequence of the layered series is olivine, followed by plagioclase and then ulvospinel. The mineralogy and chemistry of the layered series indicate differentiation by crystal fractionation along an Fe enrichment trend with olivine compositions varying from Fo 72 at the base of the layered series to Fo 57 at the top. Plagioclase appears as a liquidus phase at an olivine composition of Fo 68, and ulvospinel at an olivine composition of Fo 64. The CMB composition is unusually Fe-rich (19-20 wt% FeO) and contains clinopyroxene but no olivine. / Model calculations indicate that a parental magma of the CMB's composition is capable of producing the layered series of the Lac Raudot intrusion if an Fe+3/Fe total ratio of 0.15 is imposed. This suggests that the parental magma of the Lac Raudot intrusion was an extreme example of the Fe-rich magmas found in Proterozoic anorthosite terranes.

The Ixtahuacan Sb-W deposits are hosted by the upper Pennsylvanian to Permian Tactic formation of the central Cordillera of Guatemala. The deposits consist of disseminated gold-bearing arsenopyrite, and stibnite in stratabound lenses, in quartz-ankerite veins and breccias, and as disseminations in pyritiferous black shale and sandstone units. Scheelite is found as disseminated crystals and in veinlets in limestone. / An excellent correlation of As with S and a negative correlation of Na with Sb and As in shales and sandstones in the Los Lirios mine suggest sulphidation of the ore fluid and leaching of Na during the mineralizing event. / Microthermometric measurements performed on inclusions in quartz and scheelite point to a low temperature (160 to 190$ sp circ$C) and low to moderate salinity (0 to 10 Wt.% NaCl eq.) NaCl-dominated aqueous ore fluid. Abundant vapour-rich inclusions suggest boiling of the ore fluid. / The Ixtahuacan deposits are interpreted to have formed at a low temperature probably at a depth of a few hundred metres from a fluid with intermediate pH and under relatively low $f rm O sb2$. A model is proposed in which a deep meteoric fluid heated by a felsic intrusion at depth was focused along faults into the nose of an anticline. (Abstract shortened by UMI.)

Recent measurements of dissolved oxygen (DO) along the Laurentian Trough revealed the presence of hypoxic waters in the bottom 50 meters of the water column of the Lower St. Lawrence Estuary (LSLE). In addition to the change in the oceanic regime on the continental shelf at the mouth of the Gulf of St. Lawrence proposed by others, a large sediment oxygen demand along the LSLE though to contribute to this DO depletion. To verify the latter hypothesis, I developed a laterally integrated, two-dimensional model of the DO distribution for the bottom waters of the Laurentian Trough. The fluid transport is parameterized in a simple advection-diffusion finite-element grid where the sedimentation of organic matter feeds the mineralization processes that lead to O2 depletion in the deep waters. Using realistic parameters obtained from field data, the diagenetic model reproduces the measured sediment oxygen demands (SODs) along the Gulf of St. Lawrence portion of the trough but overestimates them in the lower estuary. Since our modeled estuary DO levels are comparable to the measured DO values when a large SOD is applied, we suggest that the oxygen fluxes, calculated from the DO gradients measured with micro-electrodes across the sediment-water interface of cores recovered in the LSLE, are underestimated.

The Kawerau hydrothermal system lies at the northern end of the Taupo Volcanic Zone, on the some 20 km south of the Bay of Plenty. The system, which is thought to have been active for at least 200,000 years, is situated over an area which has been volcanically active through time. Relatively recent local magmatism is found in the 800 m high, 3000-10,000 year old Mt. Edgecumbe dacite massif and the 200 m high Onepu Dome complex which lie adjacent to and within, respectively, the present day resistivity anomaly. Shallow reservoir fluids show evidence of steam heating as expressed by elevated bicarbonate and/or sulphate contents and mildly to strongly acidic pH, whereas the deep fluids are dominantly alkaline at their respective temperatures. The calculated base fluid composition is comprised of 2.5 wt% CO$/sb2$ and ca. 890 mg/kg Cl at 310$/sp/circ$C. Fluid inclusion studies show a largely stable, boiling point thermal regime through time, whereas oxygen stable isotope studies on hydrothermal carbonates prove the existence of one or more pulses of isotopically heavy fluids into the reservoir at some time(s) in the past. Hydrothermal alteration associated with these isotopic anomalies indicate strongly oxidising conditions relative to both alteration elsewhere in the reservoir and the present day reservoir redox conditions. Collectively, the data suggest a magmatic source for these transient, isotopically heavy fluids. The present day system is ore forming, as evident from both metal rich scales formed in the production silencers of the geothermal wells and open fracture reservoir mineralogy. Stockwork environments in the deep reservoir are host to both base and precious metals, and evidence indicates that boiling is the main depositional mechanism for these ore phases. / Subscription resource available via Digital Dissertations only.

The Kawerau hydrothermal system lies at the northern end of the Taupo Volcanic Zone, on the some 20 km south of the Bay of Plenty. The system, which is thought to have been active for at least 200,000 years, is situated over an area which has been volcanically active through time. Relatively recent local magmatism is found in the 800 m high, 3000-10,000 year old Mt. Edgecumbe dacite massif and the 200 m high Onepu Dome complex which lie adjacent to and within, respectively, the present day resistivity anomaly. Shallow reservoir fluids show evidence of steam heating as expressed by elevated bicarbonate and/or sulphate contents and mildly to strongly acidic pH, whereas the deep fluids are dominantly alkaline at their respective temperatures. The calculated base fluid composition is comprised of 2.5 wt% CO$/sb2$ and ca. 890 mg/kg Cl at 310$/sp/circ$C. Fluid inclusion studies show a largely stable, boiling point thermal regime through time, whereas oxygen stable isotope studies on hydrothermal carbonates prove the existence of one or more pulses of isotopically heavy fluids into the reservoir at some time(s) in the past. Hydrothermal alteration associated with these isotopic anomalies indicate strongly oxidising conditions relative to both alteration elsewhere in the reservoir and the present day reservoir redox conditions. Collectively, the data suggest a magmatic source for these transient, isotopically heavy fluids. The present day system is ore forming, as evident from both metal rich scales formed in the production silencers of the geothermal wells and open fracture reservoir mineralogy. Stockwork environments in the deep reservoir are host to both base and precious metals, and evidence indicates that boiling is the main depositional mechanism for these ore phases. / Subscription resource available via Digital Dissertations only.

The Kawerau hydrothermal system lies at the northern end of the Taupo Volcanic Zone, on the some 20 km south of the Bay of Plenty. The system, which is thought to have been active for at least 200,000 years, is situated over an area which has been volcanically active through time. Relatively recent local magmatism is found in the 800 m high, 3000-10,000 year old Mt. Edgecumbe dacite massif and the 200 m high Onepu Dome complex which lie adjacent to and within, respectively, the present day resistivity anomaly. Shallow reservoir fluids show evidence of steam heating as expressed by elevated bicarbonate and/or sulphate contents and mildly to strongly acidic pH, whereas the deep fluids are dominantly alkaline at their respective temperatures. The calculated base fluid composition is comprised of 2.5 wt% CO$/sb2$ and ca. 890 mg/kg Cl at 310$/sp/circ$C. Fluid inclusion studies show a largely stable, boiling point thermal regime through time, whereas oxygen stable isotope studies on hydrothermal carbonates prove the existence of one or more pulses of isotopically heavy fluids into the reservoir at some time(s) in the past. Hydrothermal alteration associated with these isotopic anomalies indicate strongly oxidising conditions relative to both alteration elsewhere in the reservoir and the present day reservoir redox conditions. Collectively, the data suggest a magmatic source for these transient, isotopically heavy fluids. The present day system is ore forming, as evident from both metal rich scales formed in the production silencers of the geothermal wells and open fracture reservoir mineralogy. Stockwork environments in the deep reservoir are host to both base and precious metals, and evidence indicates that boiling is the main depositional mechanism for these ore phases. / Subscription resource available via Digital Dissertations only.

The Kawerau hydrothermal system lies at the northern end of the Taupo Volcanic Zone, on the some 20 km south of the Bay of Plenty. The system, which is thought to have been active for at least 200,000 years, is situated over an area which has been volcanically active through time. Relatively recent local magmatism is found in the 800 m high, 3000-10,000 year old Mt. Edgecumbe dacite massif and the 200 m high Onepu Dome complex which lie adjacent to and within, respectively, the present day resistivity anomaly. Shallow reservoir fluids show evidence of steam heating as expressed by elevated bicarbonate and/or sulphate contents and mildly to strongly acidic pH, whereas the deep fluids are dominantly alkaline at their respective temperatures. The calculated base fluid composition is comprised of 2.5 wt% CO$/sb2$ and ca. 890 mg/kg Cl at 310$/sp/circ$C. Fluid inclusion studies show a largely stable, boiling point thermal regime through time, whereas oxygen stable isotope studies on hydrothermal carbonates prove the existence of one or more pulses of isotopically heavy fluids into the reservoir at some time(s) in the past. Hydrothermal alteration associated with these isotopic anomalies indicate strongly oxidising conditions relative to both alteration elsewhere in the reservoir and the present day reservoir redox conditions. Collectively, the data suggest a magmatic source for these transient, isotopically heavy fluids. The present day system is ore forming, as evident from both metal rich scales formed in the production silencers of the geothermal wells and open fracture reservoir mineralogy. Stockwork environments in the deep reservoir are host to both base and precious metals, and evidence indicates that boiling is the main depositional mechanism for these ore phases. / Subscription resource available via Digital Dissertations only.