Near-surface hydrothermal activity in the eastern Otago schist (Note)

Craw, D.; McKeag, S. A.

doi:10.1080/00288306.1987.10427547

Cited by 9 publications

(3 citation statements)

References 10 publications

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“…Similar widespread heating occurred in North Victoria Land (200 km to the north) in the Cretaceous, due to rifting between Antarctica and Australia (Delisle & Fromm 1984. Hydrothermal activity associated with extensional tectonics during the breakup of Gondwana has also been recognised in New Zealand (Craw & McKeag 1987;Craw & Norris 1991).…”

Section: Shallower Vein Systemsmentioning

confidence: 99%

Fluid inclusion evidence for widespread shallow hydrothermal activity in South Victoria Land, Antarctica

Craw¹,

Morrison²,

Walcott³

1992

New Zealand Journal of Geology and Geophysics

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Sparse but widespread veins cut Paleozoic basement, overlying Devonian-Triassic Beacon sediments and Jurassic Ferrar Dolerite in South Victoria Land. The hydrothermal activity was mainly fracture controlled, and resulted in formation of well-defined steeply dipping veins. The fluids that produced these veins were variable in composition, ranging from very low salinity water, through low-moderate salinity CO 2 -bearing water, to CaCl 2 -NaClbearing brine. Mineral deposition occurred during fluid immiscibility or boiling in several veins. Temperatures of deposition range from 390°C down to 120°C. Fluid pressure was estimated for four samples, and these range between 0.4 and 40 MPa, corresponding to depths of between 40 and 4000 m. Several veins were deposited during decreasing temperature and possibly decreasing depth. At least some of the hydrothermal activity was related to high heat flow accompanying intrusion of the Jurassic Ferrar Dolerite. Other activity occurred progressively during uplift of the Royal Society Range during mid-late Cenozoic rifting in the Ross Sea region.

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Section: Shallower Vein Systemsmentioning

confidence: 99%

Fluid inclusion evidence for widespread shallow hydrothermal activity in South Victoria Land, Antarctica

Craw¹,

Morrison²,

Walcott³

1992

New Zealand Journal of Geology and Geophysics

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“…Gold-bearing quartz occurred with major ore minerals scheelite (CaW04), stibnite (Sb2S3), and arsenopyrite (FeAsS), along with minor sulphide like pyrite (FeS2), sphalerite (ZnFeS), and galena (PbS). The catchment lithology of the Nenthorn area is mostly quartzofeldspathic schist and minor metabasites with cover sediments or volcanic (Craw et al 2009;Craw & McKeag 1987;Martin et al 2016).…”

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confidence: 99%

Geochemical characterisation of surface waters and precipitates in Nenthorn historic gold mine, East Otago, New Zealand

David

2023

Proceedings of the International Conference on Mine Closure

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Nenthorn is one of the historically mined gold districts in East Otago, Southern New Zealand. After mining ceased in the early 1900s, the mine battery and adits have exposed fresh schists and mineralised goldbearing quartz vein that has undergone continuous chemical weathering and alteration reactions mainly involving, arsenopyrite(AsFeS) and calcite (CaCO3); producing alkaline waters (pH range of 7.5 to 8) with elevated trace elements. Oxidation and dissolution of sulphide (ore) minerals usually results in elevated sulphate and other heavy metal concentration in mine waterways, hence creating a potential environmental concern. However, with semi-arid climates like East Otago, the occurrence of ochreous precipitates and efflorescence are common. Water samples and precipitates were collected from the mine workings and the adjacent creek to determine the major and trace element content in a one-time sampling program. The analytical data shows elevated concentration of trace elements in precipitates than the water samples, however, the study site was identified as not extremely concentrated or contaminated with heavy metals. The ochreous precipitates samples used for this study most likely formed from the precipitation of supergene alteration minerals like iron hydroxysulphates and iron oxyhydroxides, and primary minerals like arsenopyrite due to the elevated concentration of Iron, Arsenic, and Manganese. The sorption of metals like Copper, Lead, and Zinc to oxyhydroxides of Iron and Manganese sulphates could explain the absence of these metals in the water samples. The circumneutral pH of the water is caused by calcite dissolution, leading to very high Calcium (Ca) concentration in all the samples analysed, however highly undersaturated concerning halite, gypsum, and calcite. Conclusively, it was observed that in the Nenthorn area, arsenic concentration is above the maximum acceptable values for inorganic determinants of health significance in New Zealand. Contamination of surface waters quality in the abandoned Nenthorn mines is small enough that it does not affect the Deighton Creek just downstream. However the study does reflect the potential for even small mineral deposits to actively engage with the surrounding geochemical environment.

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“…1) was cbosen for this study because the goldbearing fault zones are steeply dipping and well-defined (Craw and McKeag, 1987). Much of the gold in unweathered rocks is found as 1O-100J.lIIl particles in grains of arsenopyrite.…”

Section: Introductionmentioning

confidence: 99%

Arsenic concentrations inHieracium pilosellaas a prospecting tool for gold-bearing quartz veins, Otago, New Zealand

Lee

Johnstone

Craw

1992

Journal of the Royal Society of New Zealand

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Gold mineralisation at Nenthom, central Otago, is located in scattered quartz reefs. The gold content of the reefs (typically less than 10 ppm) becomes diluted in soils or plants and hence is too low to be routinely detected by conventional methods. However the gold is associated with arsenopyrite (FeAsS) which is detectable as enriched concentrations of arsenic (typically over 50ppm) in the derived soils. In this study, arsenic concentrations in soil and plant shoot material were determined using X-ray fluorescence spectrometry on samples taken from along a transect across a known goldbearing quartz reef, in order to assess the relative accumulation of arsenic in local plants and their possible usefulness in biogeochemical prospecting for gold.On soils in which arsenic concentrations reached 156ppm, concentrations of arsenic in foliage from the indigenous tussock grasses Chionochloa rigida ssp. rig ida and Festuca novae-zelandiae remained consistently less than 2ppm, but in shoot material of the adventive hawkweed Hieracium pilosella, they reached 18ppm and showed a significant linear correlation with the levels of arsenic in the soil. Isolated samples of a range of other species growing on the reef indicated that only lichens and mosses attained arsenic concentrations greater than 4ppm in above-ground vegetative material.

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Near-surface hydrothermal activity in the eastern Otago schist (Note)

Cited by 9 publications

References 10 publications

Fluid inclusion evidence for widespread shallow hydrothermal activity in South Victoria Land, Antarctica

Fluid inclusion evidence for widespread shallow hydrothermal activity in South Victoria Land, Antarctica

Geochemical characterisation of surface waters and precipitates in Nenthorn historic gold mine, East Otago, New Zealand

Arsenic concentrations inHieracium pilosellaas a prospecting tool for gold-bearing quartz veins, Otago, New Zealand

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