The Experts below are selected from a list of 15942 Experts worldwide ranked by ideXlab platform
R. S. James - One of the best experts on this subject based on the ideXlab platform.
-
chlorine and alkali geochemical halos in the Footwall breccia and sublayer norite at the margin of the strathcona embayment sudbury structure ontario
Economic Geology, 2002Co-Authors: Kelli A. Mccormick, Andrew M. Mcdonald, C M Lesher, J S Fedorowich, R. S. JamesAbstract:The Ni-Cu-platinum-group element ores in the sublayer and Footwall breccia of the Sudbury structure have distinctive geochemical halos. In the Fraser mine, F/Cl ratios of the sublayer rocks appear to decrease, Na2O/K2O ratios of the Footwall breccia samples decrease, and Cl in both units increases with proximity to mineralization. These halos are interpreted to result from interaction of residual magmatic fluids with host rocks, which altered the host-rock mineralogy and precipitated Cl-bearing minerals. The results of this study, together with the results of previous studies, suggest that most ores at Sudbury, including sublayer- and Footwall breccia-hosted contact ores and Sudbury breccia-hosted Footwall ores, are surrounded by Cl and possibly alkali halos and that these geochemical signatures may be used to identify rocks that are proximal to mineralization.
-
A Textural, Mineralogical, and Statistical Study of the Footwall Breccia within the Strathcona Embayment of the Sudbury Structure
Economic Geology, 2002Co-Authors: Kelli A. Mccormick, John S. Fedorowich, Andrew M. Mcdonald, R. S. JamesAbstract:The Footwall breccia is one of the main Ni-Cu-(PGE) ore-hosting units of the Sudbury camp. This polymict, matrix-supported, contact-metamorphosed breccia occurs between the Sudbury Igneous Complex and the Footwall rocks along the west, north, and east margins of the Sudbury structure. In areas where there are depressions or embayments in the Footwall, the Footwall breccia and basal units of the Sudbury Igneous Complex are thickened, and the Footwall breccia is variably mineralized. Mineralogical and textural variations of Footwall breccia samples from the Strathcona embayment in proximity to the Fraser mine suggest that the mineralogy and texture of this unit vary as a function of proximity to the Sudbury Igneous Complex, proximity to ore, and location within the embayment. The most mafic Footwall breccia mineralogy is present proximal to the base of the Sudbury Igneous Complex within a transition zone. The presence of relatively mafic, hydrous, and Cl-rich silicate minerals (e.g., biotite and amphibole) characterize the Footwall breccia matrix around ore zones and form an alteration halo of up to 5 m thick. Textural variations include a coarsening of quartz and feldspar grains with increasing proximity to the Sudbury Igneous Complex contact. Textural coarsening also occurs from the margins of the Strathcona embayment to the center. Together, these mineralogical and textural variations influence the color of the Footwall breccia matrix and can explain some of the gray colors that are typical of mineralized Footwall breccia. These variations also constrain the timing of formation of this unit and suggest that at least three phases of Footwall breccia exist.
Matthias Bernet - One of the best experts on this subject based on the ideXlab platform.
-
extensional deformation along the Footwall fault below the hyde macraes shear zone otago schist new zealand
New Zealand Journal of Geology and Geophysics, 2018Co-Authors: Uwe Ring, N Mortimer, Christoph Butz, Matthias BernetAbstract:ABSTRACTWe describe ductile-to-brittle structures across the Footwall Fault directly below the Hyde-Macraes Shear Zone in the Otago Schist. These indicate that pervasive deformation along the Footwall Fault was due to northeast–southwest crustal extension. Structures below the Footwall Fault are ductile top-to-the-northeast extensional shear bands that formed in a penetrative lower greenschist facies foliation. With progressive deformation, shear bands formed at higher angles to the foliation, culminating in the shear bands being cut by low- and high-angle normal faults. In the hanging wall, extensional structures are much less pervasive and comprise a few high-angle normal faults. This sharp contrast in structural evolution of Footwall and hanging wall resembles the tectonic evolution of major extensional shear zones worldwide. We propose that mid Cretaceous normal movement on the low-angle Footwall Fault accompanied the formation of the steeper Waihemo Fault further north. On a regional scale, much of t...
-
Extensional deformation along the Footwall Fault below the Hyde-Macraes Shear Zone, Otago Schist, New Zealand
New Zealand Journal of Geology and Geophysics, 2018Co-Authors: Uwe Ring, N Mortimer, Christoph Butz, Matthias BernetAbstract:We describe ductile-to-brittle structures across the Footwall Fault directly below the Hyde-Macraes Shear Zone in the Otago Schist. These indicate that pervasive deformation along the Footwall Faul...
Kelli A. Mccormick - One of the best experts on this subject based on the ideXlab platform.
-
chlorine and alkali geochemical halos in the Footwall breccia and sublayer norite at the margin of the strathcona embayment sudbury structure ontario
Economic Geology, 2002Co-Authors: Kelli A. Mccormick, Andrew M. Mcdonald, C M Lesher, J S Fedorowich, R. S. JamesAbstract:The Ni-Cu-platinum-group element ores in the sublayer and Footwall breccia of the Sudbury structure have distinctive geochemical halos. In the Fraser mine, F/Cl ratios of the sublayer rocks appear to decrease, Na2O/K2O ratios of the Footwall breccia samples decrease, and Cl in both units increases with proximity to mineralization. These halos are interpreted to result from interaction of residual magmatic fluids with host rocks, which altered the host-rock mineralogy and precipitated Cl-bearing minerals. The results of this study, together with the results of previous studies, suggest that most ores at Sudbury, including sublayer- and Footwall breccia-hosted contact ores and Sudbury breccia-hosted Footwall ores, are surrounded by Cl and possibly alkali halos and that these geochemical signatures may be used to identify rocks that are proximal to mineralization.
-
A Textural, Mineralogical, and Statistical Study of the Footwall Breccia within the Strathcona Embayment of the Sudbury Structure
Economic Geology, 2002Co-Authors: Kelli A. Mccormick, John S. Fedorowich, Andrew M. Mcdonald, R. S. JamesAbstract:The Footwall breccia is one of the main Ni-Cu-(PGE) ore-hosting units of the Sudbury camp. This polymict, matrix-supported, contact-metamorphosed breccia occurs between the Sudbury Igneous Complex and the Footwall rocks along the west, north, and east margins of the Sudbury structure. In areas where there are depressions or embayments in the Footwall, the Footwall breccia and basal units of the Sudbury Igneous Complex are thickened, and the Footwall breccia is variably mineralized. Mineralogical and textural variations of Footwall breccia samples from the Strathcona embayment in proximity to the Fraser mine suggest that the mineralogy and texture of this unit vary as a function of proximity to the Sudbury Igneous Complex, proximity to ore, and location within the embayment. The most mafic Footwall breccia mineralogy is present proximal to the base of the Sudbury Igneous Complex within a transition zone. The presence of relatively mafic, hydrous, and Cl-rich silicate minerals (e.g., biotite and amphibole) characterize the Footwall breccia matrix around ore zones and form an alteration halo of up to 5 m thick. Textural variations include a coarsening of quartz and feldspar grains with increasing proximity to the Sudbury Igneous Complex contact. Textural coarsening also occurs from the margins of the Strathcona embayment to the center. Together, these mineralogical and textural variations influence the color of the Footwall breccia matrix and can explain some of the gray colors that are typical of mineralized Footwall breccia. These variations also constrain the timing of formation of this unit and suggest that at least three phases of Footwall breccia exist.
Uwe Ring - One of the best experts on this subject based on the ideXlab platform.
-
extensional deformation along the Footwall fault below the hyde macraes shear zone otago schist new zealand
New Zealand Journal of Geology and Geophysics, 2018Co-Authors: Uwe Ring, N Mortimer, Christoph Butz, Matthias BernetAbstract:ABSTRACTWe describe ductile-to-brittle structures across the Footwall Fault directly below the Hyde-Macraes Shear Zone in the Otago Schist. These indicate that pervasive deformation along the Footwall Fault was due to northeast–southwest crustal extension. Structures below the Footwall Fault are ductile top-to-the-northeast extensional shear bands that formed in a penetrative lower greenschist facies foliation. With progressive deformation, shear bands formed at higher angles to the foliation, culminating in the shear bands being cut by low- and high-angle normal faults. In the hanging wall, extensional structures are much less pervasive and comprise a few high-angle normal faults. This sharp contrast in structural evolution of Footwall and hanging wall resembles the tectonic evolution of major extensional shear zones worldwide. We propose that mid Cretaceous normal movement on the low-angle Footwall Fault accompanied the formation of the steeper Waihemo Fault further north. On a regional scale, much of t...
-
Extensional deformation along the Footwall Fault below the Hyde-Macraes Shear Zone, Otago Schist, New Zealand
New Zealand Journal of Geology and Geophysics, 2018Co-Authors: Uwe Ring, N Mortimer, Christoph Butz, Matthias BernetAbstract:We describe ductile-to-brittle structures across the Footwall Fault directly below the Hyde-Macraes Shear Zone in the Otago Schist. These indicate that pervasive deformation along the Footwall Faul...
Russell Fulton - One of the best experts on this subject based on the ideXlab platform.
-
Geology, Genesis, and Exploration Implications of the Footwall and Hanging-Wall Alteration Associated with the Hellyer Volcanic-Hosted Massive Sulfide Deposit,
2001Co-Authors: J. Bruce Gemmell, Russell FultonAbstract:Hellyer is a large (16.2 million metric tons), high-grade (13.9% Zn, 7.1% Pb, 0.4% Cu, 168 g/t Ag, 2.5 g/t Au), sea-floor, mound-style, polymetallic volcanic-hosted massive sulfide (VHMS) deposit located in the Mount Read Volcanics of western Tasmania. The deposit is hosted by the Que-Hellyer Volcanics, a sequence of late Middle Cambrian mafic to felsic coherent volcanics and polymict volcaniclastics. Hydrothermal alteration occurs in the regional Footwall, immediate Footwall, and hanging wall. Alteration in the regional Footwall is confined to patchy quartz, albite, and chlorite, with minor sericite, epidote, and hematite. Underlying Hellyer is a zoned alteration pipe with a central siliceous core (quartz-sericite), which passes into zones of chlorite, chlorite-carbonate, sericite-chlorite, and finally sericite~quartz (stringer envelope zone) on the margin. Overlying the central part of the deposit, within the hanging-wall basalt, is a distinctive and zoned alteration plume. Five alteration zones have been identified: fuchsite, chlorite, carbonate, quartzalbite, and sericite. Fuchsite-dominated alteration occupies the central portion of the hanging-wall alteration plume. Chlorite and carbonate alteration surrounds the fuchsite zone with carbonate zones forming near to the ore deposit and chlorite zones extending above and lateral to the carbonate. Outward is quartz-ablite alteration, which extends laterally into distal sericite alteration. Mass-change calculations for the Footwall and hanging wall indicate that, in general, the Footwall alteration
-
Geology, Genesis, and Exploration Implications of the Footwall and Hanging-Wall Alteration Associated with the Hellyer Volcanic-Hosted Massive Sulfide Deposit, Tasmania, Australia
Economic Geology, 2001Co-Authors: J. Bruce Gemmell, Russell FultonAbstract:Hellyer is a large (16.2 million metric tons), high-grade (13.9% Zn, 7.1% Pb, 0.4% Cu, 168 g/t Ag, 2.5 g/t Au), sea-floor, mound-style, polymetallic volcanic-hosted massive sulfide (VHMS) deposit located in the Mount Read Volcanics of western Tasmania. The deposit is hosted by the Que-Hellyer Volcanics, a sequence of late Middle Cambrian mafic to felsic coherent volcanics and polymict volcaniclastics. Hydrothermal alteration occurs in the regional Footwall, immediate Footwall, and hanging wall. Alteration in the regional Footwall is confined to patchy quartz, albite, and chlorite, with minor sericite, epidote, and hematite. Underlying Hellyer is a zoned alteration pipe with a central siliceous core (quartz-sericite), which passes into zones of chlorite, chlorite-carbonate, sericite-chlorite, and finally sericite-quartz (stringer envelope zone) on the margin. Overlying the central part of the deposit, within the hanging-wall basalt, is a distinctive and zoned alteration plume. Five alteration zones have been identified: fuchsite, chlorite, carbonate, quartzalbite, and sericite. Fuchsite-dominated alteration occupies the central portion of the hanging-wall alteration plume. Chlorite and carbonate alteration surrounds the fuchsite zone with carbonate zones forming near to the ore deposit and chlorite zones extending above and lateral to the carbonate. Outward is quartz-ablite alteration, which extends laterally into distal sericite alteration. Mass-change calculations for the Footwall and hanging wall indicate that, in general, the Footwall alteration zones are depleted in CaO, Na2O, La, Sr, Ni, Cr, and V but have enrichments of Fe2O3, MnO, MgO, K2O, S, and most metals. Compared to the host basalt, the hanging-wall alteration has gained CaO, K2O, Na2O, CO2, S, in Rb, Ba, Ag, As, Mo, Sb, Cs, and Tl, while Fe2O3, MnO, MgO, P2O5, La, Sr, Pb, Zn, Th, U, Cd, and Nd are depleted. CaO, Na2O, Cr, V, and Ni are depleted in the Footwall andesite but enriched in the hanging-wall alteration plume. This relationship suggests that these elements were sourced from the breakdown of feldspars, pyroxenes, and andesitic groundmass of the Footwall lithologies and transported in the hydrothermal fluid into the overlying basalt and precipitated as albite, calcite, and white micas in the hanging-wall alteration. The development of alteration associated with the Hellyer VHMS deposit occurred in three stages. Stage 1 regional Footwall alteration was formed by unfocused hydrothermal convection of seawater down into the recently deposited volcanic pile at temperatures between approximately 250 degrees celsius and 200 degrees celsius and at low to moderate water/rock ratios. Stage 2 alteration formed by structurally controlled fluid flow from a deep intensifying hydrothermal convection system and created the Footwall alteration pipe. Decreasing water/rock ratios and temperatures, over a range of 350 degrees celsius to less than 200 degrees celsius, led to the development of the concentric alteration pipe mineral zones. Based on modeling of whole-rock d18Ofr values, geochemical modeling, and mineral assemblages, the siliceous core is interpreted to have formed at temperatures near 350 degrees celsius, the chlorite-rich alteration zone at 300 degrees celsius to 250 degrees celsius, and the outer sericite-rich alteration at temperatures of 250 degrees celsius to 150 degrees celsius. The final, synmineralization fluid-flow event, stage 3, created the hanging-wall alteration plume. After rapid burial of the deposit by basalt, continuation of upward hydrothermal fluid flow created the zoned hanging-wall alteration. Distribution of hanging-wall alteration assemblages suggests a temperature gradient from approximately 250 degrees celsius for the fuchsite zone to lower temperatures (150 degrees celsius) for the distal quartz-albite and sericite alteration zones. Alteration mineralogy, mineral chemistry, lithogeochemistry, and stable isotope characteristics of the Footwall and hanging-wall alteration have been combined into a comprehensive set of vectors, which can be used in exploration for VHMS deposits in similar geologic settings.