Physical controls on the formation of halophytic saline substrates near Alexandra, Central Otago, New Zealand

Craw, Dave; Rufaut, Cathy; Pillai, Dhana; Read, Stephen

doi:10.1080/00288306.2021.1936575

Cited by 7 publications

(8 citation statements)

References 18 publications

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“…Far-field deformation associated with the Alpine Fault and rise of the Southern Alps during the Pliocene and Pleistocene has caused regional-scale folding, uplift, and partial erosion of the Miocene unconformity zone (Fig. 2b; Craw et al 2022a). Gold has been recycled into Pleistocene sediments during this uplift, and one mine site discussed in this study was developed at the unconformity between Pleistocene gravels and underlying Miocene lacustrine mudstone (Fig.…”

Section: General Settingmentioning

confidence: 85%

“…This paper includes a synthesis of general observations and data from a wide range of natural and anthropogenic sites within New Zealand's rain shadow, with details recorded by Craw et al (2022aCraw et al ( , b, 2023. Climate information was obtained from NIWA (2021) and ORC (2021).…”

Section: Methodsmentioning

confidence: 99%

“…1b, c, e; NIWA 2021; Craw et al 2022aCraw et al , b, 2023Weightman et al 2020). Many of these evaporative encrustations and associated ephemeral surface waters are derived from marine aerosols in rain and have compositions reflective of seawater, dominated by NaCl (Craw et al 2022a(Craw et al , b, 2023. Evaporative encrustations are most prominent on relatively impermeable soil-free surfaces that include clay-rich outcrops and redeposited clay-rich depositional pans.…”

Section: General Settingmentioning

confidence: 99%

“…Consequently, the goldfield has a cool semiarid climate in which precipitation (300-600 mm/year) is less than evapotranspiration (> 700 mm/year) and surface waters are readily evaporated to leave precipitated mineral encrustations (Fig. 1b, c, e; NIWA 2021; Craw et al 2022aCraw et al , b, 2023Weightman et al 2020). Many of these evaporative encrustations and associated ephemeral surface waters are derived from marine aerosols in rain and have compositions reflective of seawater, dominated by NaCl (Craw et al 2022a(Craw et al , b, 2023.…”

Section: General Settingmentioning

confidence: 99%

“…In our previous work on this topic, we outlined the general principles of this approach to biodiversity-enhanced rehabilitation for acid and circumneutral mine drainage (Craw and Rufaut 2021;Rufaut et al 2018). We also developed a regional scale understanding of the geochemical processes that lead to formation of alkaline saline substrates above a wide range of rock types (Craw et al 2022a(Craw et al , b, 2023). This regional scale work evolved from initial studies of two placer mine sites (Druzbicka et al 2015) that had limited geochemical variability.…”

Section: Introductionmentioning

confidence: 99%

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Evolution of Alkaline Mine Drainage and Unique Biodiversity on Soil-Free Mine Substrates, Southern New Zealand

2023

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Relatively impermeable soil-free substrates (clay-rich outcrops and sediments) exposed at eight abandoned placer gold mines generate alkaline mine drainage through evaporation and minor interaction between water and rock in a semi-arid rain shadow climate. Original mine sluicing a century ago created drainage channels over the land surface that still control the flow of ephemeral surface waters, with localised construction of erosional outwash pans. Ephemeral surface waters and associated evaporitic salts are dominated by halite derived from marine aerosols in rain, yielding circumneutral pH and electrical conductivity (EC) values locally exceeding 50 mS/cm. Weakly altered schist basement rocks and Miocene mudstone exposed at the surface contain abundant calcite, and surface waters are supersaturated with respect to Ca-carbonate minerals with a pH of ≈ 8 and an EC of ≈ 1 mS/cm. Water interaction with albite increases the dissolved Na/Cl molar ratio to > 1, and evaporative formation of Na-carbonate precipitates can raise the pH to > 10. Pyrite oxidation does not offset the alkaline pH in any of these processes, although dissolved sulfate can rise to high levels (> 2000 mg/L; EC ≈ 5 mS/cm), forming evaporative sulfate minerals. Ephemeral waters drain down outcrops and the relatively impermeable erosional pans, leaving salt encrustations with variable mineralogy and associated waters with pH and EC values that are partially controlled by rates of dissolution and reprecipitation of the minerals in the salts. The saline alkaline chemistry of the pans excludes most vegetation and has allowed development of salt-tolerant ecosystems with rare endemic halophytic plants. Maintenance of soil-free halophytic surfaces has potential applications in dryland mine sites around the world, especially as climate change enhances and extends aridity.

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Section: General Settingmentioning

confidence: 85%

Section: Methodsmentioning

confidence: 99%