Arsenic residues from historic gold extraction, Snowy River, Westland, New Zealand

ABSTRACT

The Snowy River processing site was used to extract gold for the large historic Blackwater mine, Westland, between 1906 and 1938, and then abandoned. The site is now one of the best-preserved historic gold-processing localities, and access has been enhanced for visitors. The site has some high arsenic (As) concentrations on the surface, with some spots exceeding 40 wt% As. A variety of As-bearing minerals occurs along the former processing stream, from primary sulphides (arsenopyrite, pyrite) at the upstream end to arsenolite (As₂O₃) and scorodite (FeAsO₄.2H₂O) formed by the roasting of ore materials at the downstream end. Weathering over the past century of sulphide residues and some of the arsenolite has yielded more scorodite and some Ca arsenates. Minor authigenic As sulphide precipitates have formed on rotting wood. Arsenolite is principally distributed near to the roaster site, and this is the most soluble and potentially toxic mineral on site. Despite the locally abundant arsenolite, only minor As is mobilised into nearby waters.

KEYWORDS:

• Arsenolite
• scorodite
• industrial archaeology
• sulphide
• gold
• processing

Acknowledgements

The Department of Conservation (DOC) provided logistical assistance and we are particularly grateful for the enthusiastic support of Jim Staton throughout this project. The authors gratefully acknowledge the enthusiasm of Simon Nathan and the late Les Wright for documentation of the mining history of Waiuta in general and Snowy River in particular. Christine McLachlan and Kirstine Malloch provided expert knowledge from the Prohibition site and Alexander sites, respectively. Brent Pooley conducted expert sample preparation of difficult material. SEM work for the study was carried out at the Otago Micro and Nano Scale Imaging centre (OMNI), University of Otago. Constructive reviews from two journal referees improved the presentation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.

Additional information

Funding

This research was funded by Verum Group (formerly CRL Energy), Centre for Mine Environment Research (CMER), and University of Otago through contracts from the NZ Ministry of Business, Innovation and Employment.