title: Mapping lithology and hydrothermal alteration in geothermal systems using portable X-ray fluorescence (pXRF): A case study from the Tauhara geothermal system, Taupo Volcanic Zone

authors: Mauriohooho, Kate

subjects: pXRF

abstract: Portable x-ray fluorescence (pXRF) analyzers are widely used in the environmental and mineral exploration fields. pXRF analyzers can rapidly and inexpensively provide chemical concentrations on a variety of elements, often with detection limits of ∼1–5 ppm. We compared portable XRF results from untreated geothermal drill cuttings with laboratory XRF results from pressed pellet and lithium borate fused beads prepared from powders crushed from the same samples. It is demonstrated that the portable XRF results are accurate for many elements, particularly for those with atomic numbers greater than 17. 304 cutting samples from three drillholes in the Tauhara geothermal field were subsequently analyzed by pXRF. Downhole elemental concentrations plotted against lithological units defined on geological well logs indicate that significant variations in elemental concentrations occur, some of which correlate with logged lithology boundaries. Other chemical variations appear to define previously unrecognized subunits, as well as areas of hydrothermal alteration. We suggest that pXRF should become a routine part of the characterization of geothermal cuttings during geothermal exploration and well drilling, as the chemical results are accurate, rapid and inexpensive, and the results can be used to define lithological boundaries and potentially correlate between drillholes, therefore improving geologic, stratigraphic and hydrothermal alteration models of the geothermal field.

text: Mapping lithology and hydrothermal alteration in geothermal systems using portable X-ray fluorescence (pXRF): A case study from the Tauhara geothermal system, Taupo Volcanic Zone Portable x-ray fluorescence (pXRF) analyzers are widely used in the environmental and mineral exploration fields. pXRF analyzers can rapidly and inexpensively provide chemical concentrations on a variety of elements, often with detection limits of ∼1–5 ppm. We compared portable XRF results from untreated geothermal drill cuttings with laboratory XRF results from pressed pellet and lithium borate fused beads prepared from powders crushed from the same samples. It is demonstrated that the portable XRF results are accurate for many elements, particularly for those with atomic numbers greater than 17. 304 cutting samples from three drillholes in the Tauhara geothermal field were subsequently analyzed by pXRF. Downhole elemental concentrations plotted against lithological units defined on geological well logs indicate that significant variations in elemental concentrations occur, some of which correlate with logged lithology boundaries. Other chemical variations appear to define previously unrecognized subunits, as well as areas of hydrothermal alteration. We suggest that pXRF should become a routine part of the characterization of geothermal cuttings during geothermal exploration and well drilling, as the chemical results are accurate, rapid and inexpensive, and the results can be used to define lithological boundaries and potentially correlate between drillholes, therefore improving geologic, stratigraphic and hydrothermal alteration models of the geothermal field.

year: 2016

title: Review: The denaturation and degradation of stable enzymes at high temperatures

authors: Daniel, Roy M.

subjects: enzyme

abstract: Now that enzymes are available that are stable above 100 °C it is possible to investigate conformational stability at this temperature, and also the effect of high-temperature degradative reactions in functioning enzymes and the inter-relationship between degradation and denaturation. The conformational stability of proteins depends upon stabilizing forces arising from a large number of weak interactions, which are opposed by an almost equally large destabilizing force due mostly to conformational entropy. The difference between these, the net free energy of stabilization, is relatively small, equivalent to a few interactions. The enhanced stability of very stable proteins can be achieved by an additional stabilizing force which is again equivalent to only a few stabilizing interactions. There is currently no strong evidence that any particular interaction (e.g. hydrogen bonds, hydrophobic interactions) plays a more important role in proteins that are stable at 100 °C than in those stable at 50 °C, or that the structures of very stable proteins are systematically different from those of less stable proteins. The major degradative mechanisms are deamidation of asparagine and glutamine, and succinamide formation at aspartate and glutamate leading to peptide bond hydrolysis. In addition to being temperature-dependent, these reactions are strongly dependent upon the conformational freedom of the susceptible amino acid residues. Evidence is accumulating which suggests that even at 100 °C deamidation and succinamide formation proceed slowly or not at all in conformationally intact (native) enzymes. Whether this is the case at higher temperatures is not yet clear, so it is not known whether denaturation or degradation will set the upper limit of stability for enzymes.

text: Review: The denaturation and degradation of stable enzymes at high temperatures Now that enzymes are available that are stable above 100 °C it is possible to investigate conformational stability at this temperature, and also the effect of high-temperature degradative reactions in functioning enzymes and the inter-relationship between degradation and denaturation. The conformational stability of proteins depends upon stabilizing forces arising from a large number of weak interactions, which are opposed by an almost equally large destabilizing force due mostly to conformational entropy. The difference between these, the net free energy of stabilization, is relatively small, equivalent to a few interactions. The enhanced stability of very stable proteins can be achieved by an additional stabilizing force which is again equivalent to only a few stabilizing interactions. There is currently no strong evidence that any particular interaction (e.g. hydrogen bonds, hydrophobic interactions) plays a more important role in proteins that are stable at 100 °C than in those stable at 50 °C, or that the structures of very stable proteins are systematically different from those of less stable proteins. The major degradative mechanisms are deamidation of asparagine and glutamine, and succinamide formation at aspartate and glutamate leading to peptide bond hydrolysis. In addition to being temperature-dependent, these reactions are strongly dependent upon the conformational freedom of the susceptible amino acid residues. Evidence is accumulating which suggests that even at 100 °C deamidation and succinamide formation proceed slowly or not at all in conformationally intact (native) enzymes. Whether this is the case at higher temperatures is not yet clear, so it is not known whether denaturation or degradation will set the upper limit of stability for enzymes.

year: 1996

title: The Critical Juncture in Aotearoa New Zealand and The Collective Future: Policy Issues in Settler/Invader Colonial Zombiism Found in “Biculturalism”

authors: Simon, Hemopereki

abstract: This theoretical Kaupapa Māori writing inquiry study seeks to explore the settler colonial nature of Aotearoa New Zealand. The research finds that biculturalism, as a neo-liberal and settler-colonial construct does not provide for either tino rangatiratanga or mana motuhake. Indeed, biculturalism fails to provide for indigenous inclusion and actively suppresses the recognition of mana motuhake. Biculturalism is found to fit Beck’s definition of Zombie Concepts. These are social concepts that are dead and yet kept alive in their use by scholars and society to describe the growing fiction of traditional social institutions and in being kept alive maintain, in this case, settler colonial and colonial power structures. The main argument is that Biculturalism is neoliberal and settler colonial public discourse, that needs to be unpacked and then discarded because it does not provide for tino rangatiranga or mana motuhake.

text: The Critical Juncture in Aotearoa New Zealand and The Collective Future: Policy Issues in Settler/Invader Colonial Zombiism Found in “Biculturalism” This theoretical Kaupapa Māori writing inquiry study seeks to explore the settler colonial nature of Aotearoa New Zealand. The research finds that biculturalism, as a neo-liberal and settler-colonial construct does not provide for either tino rangatiratanga or mana motuhake. Indeed, biculturalism fails to provide for indigenous inclusion and actively suppresses the recognition of mana motuhake. Biculturalism is found to fit Beck’s definition of Zombie Concepts. These are social concepts that are dead and yet kept alive in their use by scholars and society to describe the growing fiction of traditional social institutions and in being kept alive maintain, in this case, settler colonial and colonial power structures. The main argument is that Biculturalism is neoliberal and settler colonial public discourse, that needs to be unpacked and then discarded because it does not provide for tino rangatiranga or mana motuhake.

year: 2022