Controlled-source, azimuthal, time-domain, electromagnetic (TDEM) surveys were conducted over a schist formation with uniformly striking, nearly vertical foliation. Direct current electrical resistivity and seismic refraction surveys provided additional independent assessment of the field site. Quantitative interpretation of the TDEM survey used a theoretical electromagnetic model of a vertical transverse anisotropic conducting half-space. The combination of forward modeling and azimuthal acquisition geometry provides an innovative geophysical technique useful for mapping poorly exposed metamorphic terrains, and possibly determining fracture system orientations and assessing anisotropic hydraulic conductivity. Metamorphic rocks may exhibit transverse electrical anisotropy detectable by time-domain electromagnetics due to the characteristics of foliated rocks. For this reason, the field site was chosen within the Packsaddle Schist exposed in Mason County, Texas. Foliation of the Packsaddle Schist at the survey site strikes 146? and dips 82? NE. Polar plots of early-time, TDEM voltages, measured at large transmitter-receiver separations (> 40m) exhibit a symmetric two-lobed curve that agrees with theoretical model responses calculated for a vertical transverse anisotropic half space. The long axis of the symmetric two lobe response function is oriented 137?, which is nearly parallel to schist foliation of 146?. A best-fit forward model to the data indicates the electrical conductivity parallel and perpendicular to foliation are 0.015 S/m and 0.0012 S/m, respectively. Small transmitter-receiver separations (< 40m) exhibit azimuthal responses typical of an isotropic half space, which indicates the presence of a layer overlying the schist probably produced by weathering. An additional independent azimuthal Wenner resistivity survey exhibits apparent resistivity in the form of an ellipse with the major axis (direction of maximum conductivity) oriented 149?, which is nearly parallel to schist foliation of 146?. Analysis of data indicates the apparent electrical conductivity parallel and perpendicular to foliation are 0.0163 S/m and 0.0094 S/m, respectively. Results of TDEM and direct current resistivity closely match in both orientation and electrical conductivity values. Preliminary seismic refraction data were compatible with the TDEM data and also indicated anisotropy, but were not as conclusive.

Thesis (M.Sc.) -- University of Adelaide, Dept. of Geology, 1976.

Quartz and pyrite samples from Pliocene-recent, sub-economic orogenic gold mineralisation in the Southern Alps and Mesozoic economic deposits in the Otago Schist Belt have been analysed for noble gases and halogens. Palaeo-hydrothermal fluids preserved in fluid inclusions were released by crushing and analysed by mass spectrometry. Helium isotope measurements confirm the absence of a mantle-derived fluid component in gold-bearing veins from the Southern Alps and at the large gold deposit at Macraes in Otago. A possible minor mantle helium component is observed in veins within 10km of the Alpine Fault that do not contain gold. Halogen ratios support the absence of mantle-derived fluid and support the presence of a crustal fluid derived from sediments, indicated by high I/Cl ratios. Mixing trends between 40Ar/36Ar and Cl/36Ar indicate mixing between a meteoric-derived fluid or air and crust-derived fluid in all sample types. A correlation between 40Ar/36Ar and 132Xe/36Ar shows that xenon is also sourced from the crustal fluid. Despite a strong crustal-radiogenic Ar signal in some samples, measured neon isotope ratios are atmosphere like. Noble gas elemental ratios show strongly fractionated 20Ne/36Ar away from air-saturated water and air values in deeper formed veins, suggesting air contamination is not dominant. Evidence for the presence of a significant trapped vapour phase is provided by calculated noble gas concentrations in water. Formation of this vapour phase using a two-stage model of de-gassing of meteoric water, and subsequent partial re-dissolution by a Rayleigh fractionation process could account for fractionated 20Ne/36Ar and atmospheric neon isotope ratios. In the Southern Alps, three main types of mineralisation can be identified by noble gas and halogen properties. Deep forming veins contain the most gold and are characterised by 20Ne/36Ar greater than air, 132Xe/36Ar ratios up to 75 times the air value, indicating metamorphic and meteoric fluid components. Some deep ankeritic type veins that display evidence of a CO2-rich component fluid show the highest 20Ne/36Ar ratios. Shallow, late veins have 20Ne/36Ar between air-saturated water and air values, and lower xenon and iodine contents. These veins formed from a boiling rock-exchanged meteoric fluid with a minor metamorphic fluid component and contain less gold. The characteristics of the Nenthorn deposit in Otago are similar to those of the shallow Alpine veins. The economically significant Macraes deposit possibly formed from a meteoric component and a strong metamorphic fluid component derived from the original sediments. This is indicated by the highest levels of excess xenon (relative to air) determined in this study. There is some potential for xenon to be used to fingerprint gold bearing fluids sourced from similar metasedimentary piles in orogenic belts.

Mineralised shear zones in Otago are often truncated by regional low-angle faults, which juxtapose schist of different metamorphic grade. The Footwall Fault and the Hyde-Macraes Shear Zone are one example for this kind of tectonic setting, and are the subject to this study. Although, the mechanisms for the development of the mineralised thrust-origin shear zones are well studied, the relationship to the truncating faults is still poorly understood. Currently, the truncating low-angle faults are assumed to be related to crustal extension, starting in the early Cretaceous after the schist passed the ductile-brittle transition. This study presents new kinematic data for the Footwall Fault, suggesting development of normal sense movement under ductile conditions due to an abundant shear band cleavage in the footwall, which dynamically recrystallises quartz grains. However, brittle high-angle normal faults truncating these shear bands indicate either reactivation of normal sense movement after passing the ductile-brittle transition or continuous normal sense movement during the transition. Furthermore, this study presents a model, which suggests a regional scale rolling hinge development, consisting of an array of individual low-angle normal faults along the boundary of the textural zone change from TZ IV to TZIII, and strike-parallel high-angle faults at the NE margin of the Otago schist.

In light of the recent increase of mineral exploration in the northern Cordillera, private, educational, and governmental agencies have been compelled to revisit and research areas of the Cordillera whose geologic evolution still remains enigmatic. The current study is concerned with better understanding how a region of the boundary zone separating the peri-Laurentian realm from the exotic, Insular realm evolved following deposition of the meta-sedimentary Kluane schist in the Late Cretaceous. The schist is a northwest striking 30 km wide and 160 km long belt of highly deformed greenschist to amphibolite facies meta-sedimentary rocks located east of Kluane Lake, southwestern Yukon Territory. These deformed sediments as well as numerous other deformed Jurassic-Cretaceous meta-sedimentary units present along the same boundary zone (north and south of the schist) represent important rocks that can help constrain how this part of the Cordillera has evolved since the mid-Mesozoic. To better understand how the Kluane schist evolved, detailed field mapping, petrography, and U-Pb geochronological studies were undertaken in the area encompassing the schist. This data is integrated with pre-existing and recently collected geologic databases from the region to propose a model for the tectonic and structural evolution of the Kluane schist. Conclusions drawn from this study indicate the Kluane sediments were likely deposited into a closing Late Cretaceous seaway from sources derived from Yukon-Tanana terrane (YTT) to the east. The basin into which the sediments were deposited represents a remnant ocean basin that was present between Insular terrane and YTT prior their amalgamation in the Jurassic. Thrusting of YTT over the Kluane schist basin resulted in burial, metamorphism, and ductile deformation of the schist. Contemporaneously, the early stages of the Ruby Range batholith (RRB) were intruding the schist as well as the schist/YTT contact. This batholith intruded syn- to post-tectonically from approximately ca. 77 Ma to 65 Ma and it is responsible for imparting a kilometer scale inverted contact metamophic aureole onto the Kluane schist wherein metamorphic grade decreases to the southwest. Subsequently, a gneissic sub-unit of the Kluane ‘schist’ was formed by partial melting of the RRB/Kluane schist contact. During this composite deformation event, the schist was transported to mid-crustal depths by an oblique sinistral shear zone. Shortly thereafter, the schist was exhumed and deformed by consistent northeast-over-southwest shearing. Regional scale, broad open folding of the schist ensued and likely occurred by flexural slip along foliation planes with low cohesion. Two syn- to post- tectonic igneous phases associated with Hayden Lake intrusive suite have been dated to ca. 55 Ma. This timing likely correlates with broad, open folding and a ‘late’ syn- to post-kinematic thermal overprint of the schist. The combined results of this study indicate that deformation and metamorphism of the Kluane schist was a long-lived event, extending from ca. 82 Ma to ca. 55 Ma.

The Amethyst hydro project was proposed on the West Coast of New Zealand as an answer to the increasing demand for power in the area. A previous hydro project in the area was deemed unviable to reopen so the current project was proposed. The scheme involves diverting water from the Amethyst Ravine down through penstocks in a 1040m tunnel and out to a powerhouse on the floodplain of the Wanganui River. The tunnel section of the scheme is the focus of this thesis. It has been excavated using drill and blast methods and is horseshoe shaped, with 3.5x3.5m dimensions. The tunnel was excavated into Haast Schist through its whole alignment, although the portal section was driven into debris flow material. The tunnel alignment and outflow portal is approximately 2km Southeast of the Alpine Fault, the right lateral thrusting surface expression of a tectonically complex and major plate boundary. The Amethyst Ravine at the intake portal is fault controlled, and this continuing regional tectonic regime has had an impact on the engineering strength of the rockmass through the orientation of defects. The rock is highly metamorphosed (gneissic in places) and is cut through with a number of large shears. Scanline mapping of the tunnel was completed along with re-logging of some core and data collection of all records kept during tunneling. Structural analysis was undertaken, along with looking at groundwater flow data over the length of the tunnel, in order to break the tunnel up into domains of similar rock characteristics and investigate the rockmass strength of the tunnel from first principles. A structural model, hydrological model and rockmass model were assembled, each showing the change in characteristics over the length of the tunnel. The data was then modeled using the 3DEC numerical modelling software. It was found that the shear zones form major structural controls on the rockmass, and schistosity changes drastically to either side of these zones. Schistosity in general steepens in dip up the tunnel and dip direction becomes increasingly parallel to the tunnel alignment. Water is linked to shear position, and a few major incursions of water (up to 205 l/s) can be linked to large (1.6m thick) shear zones. Modeling illustrated that the tunnel is most likely to deform through the invert, with movement also capable of occurring in the right rib above the springline and to a lesser extent in the left rib below the springline. This is due to the angle of schistosity and the interaction of joints, which act as cut off planes. The original support classes for tunnel construction were based on Barton’s Q-system, but due to complicated interactions between shears, foliations and joint sets, the designed support classes have been inadequate in places, leading to increased cost due to the use of supplementary support. Modeling has shown that the halos of bolts are insufficient due to the >1m spacing, which fails to support blocks which can be smaller than this in places due to the close spacing of the schistosity. It is recommended that a more broad support type be used in place of discreet solutions such as rock bolts, in order to most efficiently optimize the support classes and most effectively support the rock mass.

In light of the recent increase of mineral exploration in the northern Cordillera, private, educational, and governmental agencies have been compelled to revisit and research areas of the Cordillera whose geologic evolution still remains enigmatic. The current study is concerned with better understanding how a region of the boundary zone separating the peri-Laurentian realm from the exotic, Insular realm evolved following deposition of the meta-sedimentary Kluane schist in the Late Cretaceous. The schist is a northwest striking 30 km wide and 160 km long belt of highly deformed greenschist to amphibolite facies meta-sedimentary rocks located east of Kluane Lake, southwestern Yukon Territory. These deformed sediments as well as numerous other deformed Jurassic-Cretaceous meta-sedimentary units present along the same boundary zone (north and south of the schist) represent important rocks that can help constrain how this part of the Cordillera has evolved since the mid-Mesozoic. To better understand how the Kluane schist evolved, detailed field mapping, petrography, and U-Pb geochronological studies were undertaken in the area encompassing the schist. This data is integrated with pre-existing and recently collected geologic databases from the region to propose a model for the tectonic and structural evolution of the Kluane schist. Conclusions drawn from this study indicate the Kluane sediments were likely deposited into a closing Late Cretaceous seaway from sources derived from Yukon-Tanana terrane (YTT) to the east. The basin into which the sediments were deposited represents a remnant ocean basin that was present between Insular terrane and YTT prior their amalgamation in the Jurassic. Thrusting of YTT over the Kluane schist basin resulted in burial, metamorphism, and ductile deformation of the schist. Contemporaneously, the early stages of the Ruby Range batholith (RRB) were intruding the schist as well as the schist/YTT contact. This batholith intruded syn- to post-tectonically from approximately ca. 77 Ma to 65 Ma and it is responsible for imparting a kilometer scale inverted contact metamophic aureole onto the Kluane schist wherein metamorphic grade decreases to the southwest. Subsequently, a gneissic sub-unit of the Kluane ‘schist’ was formed by partial melting of the RRB/Kluane schist contact. During this composite deformation event, the schist was transported to mid-crustal depths by an oblique sinistral shear zone. Shortly thereafter, the schist was exhumed and deformed by consistent northeast-over-southwest shearing. Regional scale, broad open folding of the schist ensued and likely occurred by flexural slip along foliation planes with low cohesion. Two syn- to post- tectonic igneous phases associated with Hayden Lake intrusive suite have been dated to ca. 55 Ma. This timing likely correlates with broad, open folding and a ‘late’ syn- to post-kinematic thermal overprint of the schist. The combined results of this study indicate that deformation and metamorphism of the Kluane schist was a long-lived event, extending from ca. 82 Ma to ca. 55 Ma.

Mineralised shear zones in Otago are often truncated by regional low-angle faults, which juxtapose schist of different metamorphic grade. The Footwall Fault and the Hyde-Macraes Shear Zone are one example for this kind of tectonic setting, and are the subject to this study. Although, the mechanisms for the development of the mineralised thrust-origin shear zones are well studied, the relationship to the truncating faults is still poorly understood. Currently, the truncating low-angle faults are assumed to be related to crustal extension, starting in the early Cretaceous after the schist passed the ductile-brittle transition. This study presents new kinematic data for the Footwall Fault, suggesting development of normal sense movement under ductile conditions due to an abundant shear band cleavage in the footwall, which dynamically recrystallises quartz grains. However, brittle high-angle normal faults truncating these shear bands indicate either reactivation of normal sense movement after passing the ductile-brittle transition or continuous normal sense movement during the transition. Furthermore, this study presents a model, which suggests a regional scale rolling hinge development, consisting of an array of individual low-angle normal faults along the boundary of the textural zone change from TZ IV to TZIII, and strike-parallel high-angle faults at the NE margin of the Otago schist.

A scapolite-hornblende-biotite schist from the Grenville province of the Canadian Shield has been analysed for Tl by an atomic absorption technique with a high sensitivity. K, Rb and some major oxides were determined by wet chemistry. Tl, K/Rb, K/Tl and Tl/Rb were compared to several other rocks and for this report were found to be 432ppb, 429, 4.85x10³ and 88.4x10⁻³ respectively. These values are similar to those quoted for other rocks. / Thesis / Bachelor of Science (BSc)

No description available.