title: Volcanic history of the Mount Misery rhyolite domes, Tauranga Volcanic Centre

authors: Kinley, Taya

abstract: The Mount Misery rhyolites are a group of three complex lava domes, which are part of the Minden Rhyolites within the Tauranga Volcanic Centre. The lava domes are a previously unstudied volcanic area and have in recent years been partially exposed by a series of quarries, creating an opportunity to understand the volcanic history. A pyroclastic succession flanking the side of the Pukunui dome was studied to compare it to the Otawera ignimbrite and potentially correlate it to the Pukunui succession. This study aims to determine the volcanic emplacement and post-emplacement processes of the Mount Misery series domes and pyroclastics, achieved through field work, thin section microscopy, X-ray diffraction, scanning electron microscopy, and X-ray fluorescence.

Key findings from this study show similar phenocryst assemblages but the groundmass textures are complex. The rhyolite groundmasses analysed varied between glassy, crystalline and devitrified, while key phenocrysts found were plagioclase and quartz, and within Maungatūtū/Mount Misery and Greenpark domes also minor clino- and orthopyroxenes. Quartz polymorphs such as cristobalite were common in the groundmass as needle-like structures, while at Pukunui, pure quartz composed the thin bands. The thin bands found at Pukunui and Greenpark formed as a strain feature that caused segregation of quartz along preferential axial planes. Sanidine was found at all three locations as devitrification of glass within the groundmasses. Maungatūtū/Mount Misery had sanidine present as radiating spherulites, while Greenpark had a new find of sub-circular crystalline inclusions which appeared to be some variation of a spherulite.

The domes have similar geochemical and mineralogical compositions, proving they are linked to the same source magma, but would have erupted at different points in time, likely with Maungatūtū/Mount Misery as the oldest and Pukunui as the youngest. The flow banding and flow folding present at Pukunui and Greenpark, and the lack of shearing features, have been used to identify the domes as endogenous. The Pukunui pyroclastic succession included multiple flow units that were correlated to the Otawera ignimbrite elsewhere, which was likely emplaced as a proximal ignimbrite from a dome collapse event at Pukunui. This was one of the final volcanic events in the Mount Misery series area.

text: Volcanic history of the Mount Misery rhyolite domes, Tauranga Volcanic Centre The Mount Misery rhyolites are a group of three complex lava domes, which are part of the Minden Rhyolites within the Tauranga Volcanic Centre. The lava domes are a previously unstudied volcanic area and have in recent years been partially exposed by a series of quarries, creating an opportunity to understand the volcanic history. A pyroclastic succession flanking the side of the Pukunui dome was studied to compare it to the Otawera ignimbrite and potentially correlate it to the Pukunui succession. This study aims to determine the volcanic emplacement and post-emplacement processes of the Mount Misery series domes and pyroclastics, achieved through field work, thin section microscopy, X-ray diffraction, scanning electron microscopy, and X-ray fluorescence.

Key findings from this study show similar phenocryst assemblages but the groundmass textures are complex. The rhyolite groundmasses analysed varied between glassy, crystalline and devitrified, while key phenocrysts found were plagioclase and quartz, and within Maungatūtū/Mount Misery and Greenpark domes also minor clino- and orthopyroxenes. Quartz polymorphs such as cristobalite were common in the groundmass as needle-like structures, while at Pukunui, pure quartz composed the thin bands. The thin bands found at Pukunui and Greenpark formed as a strain feature that caused segregation of quartz along preferential axial planes. Sanidine was found at all three locations as devitrification of glass within the groundmasses. Maungatūtū/Mount Misery had sanidine present as radiating spherulites, while Greenpark had a new find of sub-circular crystalline inclusions which appeared to be some variation of a spherulite.

The domes have similar geochemical and mineralogical compositions, proving they are linked to the same source magma, but would have erupted at different points in time, likely with Maungatūtū/Mount Misery as the oldest and Pukunui as the youngest. The flow banding and flow folding present at Pukunui and Greenpark, and the lack of shearing features, have been used to identify the domes as endogenous. The Pukunui pyroclastic succession included multiple flow units that were correlated to the Otawera ignimbrite elsewhere, which was likely emplaced as a proximal ignimbrite from a dome collapse event at Pukunui. This was one of the final volcanic events in the Mount Misery series area.

year: 2022

title: Emerging stable isotope techniques in hydrothermal research: new methods applied to carbonates and hydrous minerals in ore deposits and geothermal fields

authors: Mering, John

subjects: stable isotope

abstract: Over the last 70 years, stable isotopes have provided critical insight into the processes governing transfer of mass and energy through geologic systems. Significantly, isotopic signals in minerals reflect conditions of crystallisation, and subsequent alteration history. In hydrothermal systems, isotope tools have been applied to interpret fluid origin, temperature, and interaction with host rock. The research carried out here makes use of emerging techniques to measure hydrogen, oxygen, carbon, and clumped isotopes in carbonates and hydrous minerals. This work encompasses three themes: 

(i)	Development of new laser spectroscopy approaches for measuring δ2H and δ18O in hydrous minerals 
(ii)	Testing carbonate clumped isotope thermometry in geothermal fields and mineral deposits 
(iii)	Application of carbonate and hydrous mineral isotope tools in epithermal precious metal deposits 

A novel approach to measure δ2H and δ18O in hydrous minerals is presented in Chapters 3-4. Measurement was carried out on phyllosilicates, hydrous sulphates, and multimineralic whole rock assay pulps using a custom-built thermal dehydration-dehydroxylation Off-Axis Integrated Cavity Output Spectroscopy (TD-OA-ICOS) system. The δ2H methodology presented is equal to isotope ratio mass spectrometry in terms of speed and precision, but considerably lower in cost. This work represents the first hydrogen isotope measurements made by a laser spectroscopy system for serpentine, muscovite, sericite, talc, and biotite. 

The TD-OA-ICOS method was subsequently applied to measure δ18O in microvolumes of water, gypsum hydration water, and the hydroxyl component of phyllosilicate minerals (Chapter 4). Intramineral oxygen isotope fractionation values in kaolinite and muscovite, determined by comparison of δ18OOH measured by TD-OA-ICOS with δ18Osilicate measured by fluorination, are similar to existing constraints. Refinement of this approach should be carried out to test the relationship between formation temperature and intramineral oxygen isotope fractionation in clay minerals. 
TD-OA-ICOS was applied to reconstruct δ2H in well-constrained epithermal areas, exemplified by case studies at the Comstock Lode, USA (Chapter 4) and Miocene-aged adularia-sericite Au-Ag deposits at Waihi and Karangahake on the North Island (Chapter 6). Taking mineral-specific fractionation factors into account, whole rock hydrogen isotope measurements indicate relatively homogeneous fluids of meteoric origin were involved in alteration at each deposit. Accurate reconstruction of fluid δ2H requires constraints upon the balance of illite and chlorite in samples. Mineral δ2H is useful for fingerprinting paleo latitude or altitude of source fluids, as evidenced by results from Comstock, which were ~60 ‰ lower for δ2H, relative to Waihi and Karangahake. It is apparent that mineral δ2H has greater utility towards understanding mixing in systems where fluids are isotopically distinct. The low cost, safety, and simplicity of operation of TD-OA-ICOS should also make the method attractive for manufacturers and regulatory agencies wishing to use hydrogen and oxygen isotopes to determine the geographic origin of consumer products containing hydrous minerals.

Paleotemperature constraints around ore deposits are essential for characterising the relationship between advection, fluid circulation, and metal transport. In Chapter 5, carbonate clumped isotope thermometry (Δ47) is applied to identify temperature gradients in geothermal fields and hydrothermal ore deposits. This technique, based on quantification of thermodynamically sensitive 13C-18O bond abundance in carbonates, provides new capability to determine fluid δ18O, overcoming a problem which has undermined interpretation of carbonate isotope data in hydrothermal settings for more than 60 years. Geothermal fields (Wairakei, Ngatamariki, Broadlands-Ohaaki) in the Taupo Volcanic Zone, New Zealand served as natural laboratories to test the validity of clumped isotope calibrations in high temperature settings up to 300 °C. Taking local fluid δ18O into account, results indicate modern TVZ calcite precipitated in equilibrium with produced geothermal waters.

The clumped isotope technique was subsequently applied in epithermal (Waihi, NZ), skarn (Antamina, Peru), and carbonate-hosted (Mount Isa, Australia) metal deposits. Results highlight the potential for clumped isotopes to delineate the heat footprint around mineral deposits that contain carbonates. Further refinement of the clumped isotope method offers new potential to evaluate characteristics of ore deposit genesis, with respect to temperature, fluid source, and depth. This will prove especially useful in enigmatic carbonate-hosted hydrothermal settings, where temperature and hydrology are unresolved. Paired oxygen isotope and carbonate clumped isotope measurements at Waihi demonstrate that δ18O of hydrothermal calcite is primarily influenced by rock temperature, with variation in fluid composition due to water-rock exchange exerting secondary control. While calcite precipitates both in and out of phase with precious metals in epithermal areas (e.g. Waihi), clumped isotope signals reflect the overall thermal structure, providing a new avenue to identify hotter upwelling zones, where boiling drives deposition of Au, Ag and other metals. Ultimately, the findings presented herein are useful to workers in hydrothermal settings, with interest in mineral exploration and geothermal resource development, and are broadly applicable across the geologic sciences in topics ranging from paleoenvironmental studies to interpretation of basin histories.

text: Emerging stable isotope techniques in hydrothermal research: new methods applied to carbonates and hydrous minerals in ore deposits and geothermal fields Over the last 70 years, stable isotopes have provided critical insight into the processes governing transfer of mass and energy through geologic systems. Significantly, isotopic signals in minerals reflect conditions of crystallisation, and subsequent alteration history. In hydrothermal systems, isotope tools have been applied to interpret fluid origin, temperature, and interaction with host rock. The research carried out here makes use of emerging techniques to measure hydrogen, oxygen, carbon, and clumped isotopes in carbonates and hydrous minerals. This work encompasses three themes: 

(i)	Development of new laser spectroscopy approaches for measuring δ2H and δ18O in hydrous minerals 
(ii)	Testing carbonate clumped isotope thermometry in geothermal fields and mineral deposits 
(iii)	Application of carbonate and hydrous mineral isotope tools in epithermal precious metal deposits 

A novel approach to measure δ2H and δ18O in hydrous minerals is presented in Chapters 3-4. Measurement was carried out on phyllosilicates, hydrous sulphates, and multimineralic whole rock assay pulps using a custom-built thermal dehydration-dehydroxylation Off-Axis Integrated Cavity Output Spectroscopy (TD-OA-ICOS) system. The δ2H methodology presented is equal to isotope ratio mass spectrometry in terms of speed and precision, but considerably lower in cost. This work represents the first hydrogen isotope measurements made by a laser spectroscopy system for serpentine, muscovite, sericite, talc, and biotite. 

The TD-OA-ICOS method was subsequently applied to measure δ18O in microvolumes of water, gypsum hydration water, and the hydroxyl component of phyllosilicate minerals (Chapter 4). Intramineral oxygen isotope fractionation values in kaolinite and muscovite, determined by comparison of δ18OOH measured by TD-OA-ICOS with δ18Osilicate measured by fluorination, are similar to existing constraints. Refinement of this approach should be carried out to test the relationship between formation temperature and intramineral oxygen isotope fractionation in clay minerals. 
TD-OA-ICOS was applied to reconstruct δ2H in well-constrained epithermal areas, exemplified by case studies at the Comstock Lode, USA (Chapter 4) and Miocene-aged adularia-sericite Au-Ag deposits at Waihi and Karangahake on the North Island (Chapter 6). Taking mineral-specific fractionation factors into account, whole rock hydrogen isotope measurements indicate relatively homogeneous fluids of meteoric origin were involved in alteration at each deposit. Accurate reconstruction of fluid δ2H requires constraints upon the balance of illite and chlorite in samples. Mineral δ2H is useful for fingerprinting paleo latitude or altitude of source fluids, as evidenced by results from Comstock, which were ~60 ‰ lower for δ2H, relative to Waihi and Karangahake. It is apparent that mineral δ2H has greater utility towards understanding mixing in systems where fluids are isotopically distinct. The low cost, safety, and simplicity of operation of TD-OA-ICOS should also make the method attractive for manufacturers and regulatory agencies wishing to use hydrogen and oxygen isotopes to determine the geographic origin of consumer products containing hydrous minerals.

Paleotemperature constraints around ore deposits are essential for characterising the relationship between advection, fluid circulation, and metal transport. In Chapter 5, carbonate clumped isotope thermometry (Δ47) is applied to identify temperature gradients in geothermal fields and hydrothermal ore deposits. This technique, based on quantification of thermodynamically sensitive 13C-18O bond abundance in carbonates, provides new capability to determine fluid δ18O, overcoming a problem which has undermined interpretation of carbonate isotope data in hydrothermal settings for more than 60 years. Geothermal fields (Wairakei, Ngatamariki, Broadlands-Ohaaki) in the Taupo Volcanic Zone, New Zealand served as natural laboratories to test the validity of clumped isotope calibrations in high temperature settings up to 300 °C. Taking local fluid δ18O into account, results indicate modern TVZ calcite precipitated in equilibrium with produced geothermal waters.

The clumped isotope technique was subsequently applied in epithermal (Waihi, NZ), skarn (Antamina, Peru), and carbonate-hosted (Mount Isa, Australia) metal deposits. Results highlight the potential for clumped isotopes to delineate the heat footprint around mineral deposits that contain carbonates. Further refinement of the clumped isotope method offers new potential to evaluate characteristics of ore deposit genesis, with respect to temperature, fluid source, and depth. This will prove especially useful in enigmatic carbonate-hosted hydrothermal settings, where temperature and hydrology are unresolved. Paired oxygen isotope and carbonate clumped isotope measurements at Waihi demonstrate that δ18O of hydrothermal calcite is primarily influenced by rock temperature, with variation in fluid composition due to water-rock exchange exerting secondary control. While calcite precipitates both in and out of phase with precious metals in epithermal areas (e.g. Waihi), clumped isotope signals reflect the overall thermal structure, providing a new avenue to identify hotter upwelling zones, where boiling drives deposition of Au, Ag and other metals. Ultimately, the findings presented herein are useful to workers in hydrothermal settings, with interest in mineral exploration and geothermal resource development, and are broadly applicable across the geologic sciences in topics ranging from paleoenvironmental studies to interpretation of basin histories.

year: 2019

title: Collectivism, cultural identity and employee mental health: A study of New Zealand Māori

authors: Brougham, David M.

subjects: Anxiety

abstract: Māori are a collectivistic people living within a largely individualistic country. The present study tested whether Māori who practice higher levels of workplace collectivism feel greater alignment with their overall cultural beliefs, and report better mental health results because of their lower levels of anxiety and depression. Three hundred and thirty-six Māori employees were surveyed, and a regression analysis showed significant direct effects, with collectivism accounting for a sizable 20 % of the variance in both anxiety and depression. Two moderators relating to cultural knowledge and cultural language were also tested. Significant two-way interactions were found: high collectivism and high cultural knowledge led to low depression, and high cultural knowledge and high cultural language skills led to low depression and anxiety. A three-way interaction was found between anxiety, collectivism and cultural knowledge and/or language: low anxiety was reported by respondents with high collectivism and either high cultural knowledge or cultural language. Overall, the study highlights the importance of collectivism and cultural identity for Māori employees' mental health

text: Collectivism, cultural identity and employee mental health: A study of New Zealand Māori Māori are a collectivistic people living within a largely individualistic country. The present study tested whether Māori who practice higher levels of workplace collectivism feel greater alignment with their overall cultural beliefs, and report better mental health results because of their lower levels of anxiety and depression. Three hundred and thirty-six Māori employees were surveyed, and a regression analysis showed significant direct effects, with collectivism accounting for a sizable 20 % of the variance in both anxiety and depression. Two moderators relating to cultural knowledge and cultural language were also tested. Significant two-way interactions were found: high collectivism and high cultural knowledge led to low depression, and high cultural knowledge and high cultural language skills led to low depression and anxiety. A three-way interaction was found between anxiety, collectivism and cultural knowledge and/or language: low anxiety was reported by respondents with high collectivism and either high cultural knowledge or cultural language. Overall, the study highlights the importance of collectivism and cultural identity for Māori employees' mental health

year: 2012