title: Texture and chemistry of pyrite from the Waihi epithermal system, Hauraki Goldfield, New Zealand

authors: Eames, Anna G.

subjects: pyrite

abstract: The Waihi epithermal system is a low sulfidation epithermal system that hosts one of the largest epithermal Au-Ag deposits in the Southern Hemisphere. Various sulfide minerals are present within the system, including pyrite (FeS2), one of the most abundant sulfide minerals on Earth. Pyrite is an archive for hydrothermal fluid chemistry due to its crystal structure enabling incorporation of other elements such as Co, Ni, Se, As, Te. The presence or absence of these elements reflects the changes in the hydrothermal fluid chemistry throughout the growth of the grain. The textural variations in the grains indicates changes in growth conditions for each grain at the time of formation. The chemistry of each different zone, coupled with stages of growth, indicates the chemical influences on the pyrite in the Waihi system at that time. 

The use of petrographic, EPMA and LA-ICPMS analyses demonstrates distinctive textural zones within pyrite grains, varying in chemistry and appearance. Some zones contain elevated concentrations of Au and Ag, and varying concentrations of Cu, Pb or Zn. The textural observations indicate pyrite growth was interrupted by periods of dissolution before the grain continued growing. Most grains begin growth with high trace element concentrations. The lowest concentrations of trace elements occur in the outer growth phase. Inclusions are rich in Pb, Ca, Se, Zn, Au and Ni, and cause the ‘dirty’ texture observed in grains. The distinctive textural features are attributed to the varying concentrations in Au, As, Cu, Zn, Ag and Te. 

This research showcases the dynamics of hydrothermal fluid flow at Waihi, revealing that the gold-forming hydrothermal system at Waihi are more complex than initially thought. There is both evidence for periods of low gold pyrite growth, and periods of high pyrite growth.

text: Texture and chemistry of pyrite from the Waihi epithermal system, Hauraki Goldfield, New Zealand The Waihi epithermal system is a low sulfidation epithermal system that hosts one of the largest epithermal Au-Ag deposits in the Southern Hemisphere. Various sulfide minerals are present within the system, including pyrite (FeS2), one of the most abundant sulfide minerals on Earth. Pyrite is an archive for hydrothermal fluid chemistry due to its crystal structure enabling incorporation of other elements such as Co, Ni, Se, As, Te. The presence or absence of these elements reflects the changes in the hydrothermal fluid chemistry throughout the growth of the grain. The textural variations in the grains indicates changes in growth conditions for each grain at the time of formation. The chemistry of each different zone, coupled with stages of growth, indicates the chemical influences on the pyrite in the Waihi system at that time. 

The use of petrographic, EPMA and LA-ICPMS analyses demonstrates distinctive textural zones within pyrite grains, varying in chemistry and appearance. Some zones contain elevated concentrations of Au and Ag, and varying concentrations of Cu, Pb or Zn. The textural observations indicate pyrite growth was interrupted by periods of dissolution before the grain continued growing. Most grains begin growth with high trace element concentrations. The lowest concentrations of trace elements occur in the outer growth phase. Inclusions are rich in Pb, Ca, Se, Zn, Au and Ni, and cause the ‘dirty’ texture observed in grains. The distinctive textural features are attributed to the varying concentrations in Au, As, Cu, Zn, Ag and Te. 

This research showcases the dynamics of hydrothermal fluid flow at Waihi, revealing that the gold-forming hydrothermal system at Waihi are more complex than initially thought. There is both evidence for periods of low gold pyrite growth, and periods of high pyrite growth.

year: 2017

title: Is wellbeing and public policy on the same flight path as positive psychology?

authors: Weijers, Dan M.

abstract: In this talk, I outline the progress in wellbeing and public policy in New Zealand and discuss the potential roles for subjective measures of wellbeing. I will argue that subjective measures should be incorporated, including at the highest levels of the wellbeing model.

text: Is wellbeing and public policy on the same flight path as positive psychology? In this talk, I outline the progress in wellbeing and public policy in New Zealand and discuss the potential roles for subjective measures of wellbeing. I will argue that subjective measures should be incorporated, including at the highest levels of the wellbeing model.

year: 2018

title: Two-step human−environmental impact history for northern New Zealand linked to late-Holocene climate change

authors: Newnham, Rewi M.

subjects: New Zealand

abstract: Following resolution of a long-standing debate over the timing of the initial settlement of New Zealand from Polynesia (late 13th century), a prevailing paradigm has developed that invokes rapid transformation of the landscape, principally by fire, within a few decades of the first arrivals. This model has been constructed from evidence mostly from southern and eastern regions of New Zealand, but a more complicated pattern may apply in the more humid western and northern regions where forests are more resilient to burning. We present a new pollen record from Lake Pupuke, Auckland, northern New Zealand, that charts the changing vegetation cover over the last 1000 years, before and after the arrival of people. Previous results from this site concurred with the rapid transformation model, although sampling resolution, chronology and sediment disturbance make that interpretation equivocal. Our new record is dated principally by tephrochronology together with radiocarbon dating, and includes a cryptotephra deposit identified as Kaharoa tephra, a key marker for first settlement in northern New Zealand. Its discovery and stratigraphic position below two Rangitoto-derived tephras enables a clearer picture of environmental change to be drawn. The new pollen record shows an early phase (step 1) of minor, localised forest clearance around the time of Kaharoa tephra (c. 1314 AD) followed by a later, more extensive deforestation phase (step 2) commencing at around the time of deposition of the Rangitoto tephras (c. 1400‒1450 AD). This pattern, which needs to be corroborated from other well-resolved records from northern New Zealand, concurs with an emerging hypothesis that the ‘Little Ice Age’ had a significant impact on pre-European Māori with the onset of harsher conditions causing a consolidation of populations and later environmental impact in northern New Zealand.

text: Two-step human−environmental impact history for northern New Zealand linked to late-Holocene climate change Following resolution of a long-standing debate over the timing of the initial settlement of New Zealand from Polynesia (late 13th century), a prevailing paradigm has developed that invokes rapid transformation of the landscape, principally by fire, within a few decades of the first arrivals. This model has been constructed from evidence mostly from southern and eastern regions of New Zealand, but a more complicated pattern may apply in the more humid western and northern regions where forests are more resilient to burning. We present a new pollen record from Lake Pupuke, Auckland, northern New Zealand, that charts the changing vegetation cover over the last 1000 years, before and after the arrival of people. Previous results from this site concurred with the rapid transformation model, although sampling resolution, chronology and sediment disturbance make that interpretation equivocal. Our new record is dated principally by tephrochronology together with radiocarbon dating, and includes a cryptotephra deposit identified as Kaharoa tephra, a key marker for first settlement in northern New Zealand. Its discovery and stratigraphic position below two Rangitoto-derived tephras enables a clearer picture of environmental change to be drawn. The new pollen record shows an early phase (step 1) of minor, localised forest clearance around the time of Kaharoa tephra (c. 1314 AD) followed by a later, more extensive deforestation phase (step 2) commencing at around the time of deposition of the Rangitoto tephras (c. 1400‒1450 AD). This pattern, which needs to be corroborated from other well-resolved records from northern New Zealand, concurs with an emerging hypothesis that the ‘Little Ice Age’ had a significant impact on pre-European Māori with the onset of harsher conditions causing a consolidation of populations and later environmental impact in northern New Zealand.

year: 2018