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Mine Water and the Environment

, Volume 34, Issue 4, pp 404–416 | Cite as

Experimental Metalloid Mobilisation from a New Zealand Orogenic Gold Deposit

  • G. KerrEmail author
  • J. Pope
  • D. Trumm
  • D. Craw
Technical Article

Abstract

Elevated dissolved antimony (Sb) and arsenic (As) are common environmental issues around orogenic gold mines. The metalloids occur principally in stibnite (Sb2S3) and arsenopyrite (FeAsS), and are typically accompanied by pyrite (FeS2). Samples of arsenopyrite-rich (≈2.5 wt% As) and stibnite-rich (≈10 wt% Sb) ore were collected from the Globe-Progress mine in the Reefton goldfield, New Zealand. Crushed samples (<5 mm particles) were placed in kinetic leach columns and monitored for a year. Leachate was collected and analysed monthly. After 12 months, only a small portion (<1 %) of the total As and Sb had leached from the ore samples. Over the course of each month, the pH of all leachates decreased from ≈7 to ≈3 due to pyrite oxidation. Dissolution of Ca–Fe–Mg carbonates in the host rock was insufficient to neutralize the leachate. Dissolved As concentrations from the arsenopyrite-rich ore sample were initially 16 mg/L, but decreased to ≈2 mg/L over 12 months. Dissolved Sb concentrations from the stibnite-rich ore were >7 mg/L throughout the experimental period, with maxima of 12 mg/L. SEM analysis after 6 months showed secondary arsenolite (As2O3) and Ca–Al–Mg sulphates on arsenopyrite-rich ore surfaces, but an absence of secondary minerals, including Sb oxides, on stibnite-rich ore surfaces. These experiments document geochemical and mineralogical processes associated with short-term (days to weeks) water–rock interactions that yield relatively high concentrations of dissolved metalloids (>5 mg/L) where localised (1–10 m) acidification and limited oxidation occur in sulphide-rich rocks.

Keywords

Antimony Arsenic Kinetic test Acid Arsenopyrite Stibnite 

Experimentelle Mobilisierung von Halbmetallen aus einer orogenetisch gebildeten Goldlagerstätte in Neuseeland

Zusammenfassung

Erhöhte Antimon- und Arsengehalte im Umfeld von orogenetisch gebildeten Goldlagerstätten sind im Normalfall bekannt. Die Halbmetalle kommen prinzipiell als Stibnit (Sb2S3) und Arsenopyrit (FeAsS) vor und sind typischerweise vergesellschaftet mit Pyrit (FeS2). Für die Experimente wurden Arsenopyrit-reiche (≈2.5 Gew. % As) und Stibnit-reiche (≈10 Gew. % Sb) Erze aus dem Globe-Progress Bergwerk im Reefton Goldbezirk, Neuseeland, verwendet. Gemahlene Proben (Korngröße < 5 mm) wurden in kinetischen Säulenversuchen ein Jahr lang untersucht. Die Lösungsanalytik fand monatlich statt. Nach 12 Monaten war erst ein geringer Anteil (< 1 %) des totalen As- bzw. Sb-Gehalts aus den Erzproben gelöst worden. Bedingt durch die Pyritoxidation sank der pH-Wert der Lösungen im Beobachtungszeitraum von ≈7 auf ≈3. Die Freisetzung von Ca-Fe-Mg-Karbonaten aus dem Ausgangsgestein war nicht ausreichend, um die Lösungen zu neutralisieren. Die anfänglich gelöste As-Konzentration von 16 mg/L aus den pyritreichen Erzproben gingen nach 12 Monaten auf Werte von ≈2 mg/L zurück. Die gelöste Sb-Konzentration der Stibnit-reichen Erzproben betrug > 7 mg/L, mit Maximalkonzentrationen von 12 mg/L. SEM-Analysen nach sechs Monaten zeigt die Bildung von sekundärem Arsenolith (As2O3) und von Ca-Al-Mg-Sulfat auf den Arsenopyrit-reichen Erzoberflächen. Auf den Stibnit-reichen Erzoberflächen wurde kein Sekundärmineral (auch kein Sb-Oxid) gefunden. Die Experimente dokumentieren geochemische und mineralogische Prozesse, welche durch kurzfristig wirksame Wasser-Gesteins-Wechselwirkungen (Tage/Wochen) hohe Austräge von gelösten Halbmetallen (> 5 mg/L) aus lokalen Versauerungsbereichen (1 - 10 m) begrenzen und Oxidationsprozesse in sulfidreichen Gesteinen limitieren.

Movilización de metaloides desde un depósito de oro orogénico, Nueva Zelanda

Resumen

Elevadas disoluciones de antimonio (Sb) y arsénico (As) son problemas ambientales comunes asociados a las minas de oro orogénicas. Los metaloides se encuentran principalmente como estibnita (Sb2S3) y arsenopirita (FeAsS) y están usualmente acompañadas por pirita (FeS2). Muestras de minerales ricas en arsenopirita (≈2,5 % p/p As) y en estibnita (≈10 % p/p Sb) fueron colectadas en la mina Globe-Progress en la región minera Reefton, Nueva Zelanda. Muestras molidas (partículas <5 mm) se colocaron en columnas de lixiviación y fueron monitoreadas por un año. Los lixiviados fueron colectados y analizados mensualmente. Después de 12 meses, sólo una pequeña porción (<1%) del total de As y Sb había sido lixiviado desde las muestras. En el curso de cada mes, el pH de todos los lixiviados decreció desde ≈7 a ≈3 debido a la oxidación de pirita. La disolución de carbonatos de Ca-Fe-Mg fue insuficiente para neutralizar el lixiviado. La concentración de As disuelto desde la muestra rica en arsenopirita fue inicialmente 16 mg/L, pero decreció hasta ≈2 mg/L a los 12 meses. La concentración de Sb disuelto desde la muestra rica en estibnita fue >7 mg/L a lo largo del experimento con un valor máximo de 12 mg/L. El análisis SEM después de seis meses mostró arsenolita (As2O3) y sulfatos de Ca-Al-Mg sobre las superficies ricas en arsenopirita pero una ausencia de minerales secundarios, incluyendo óxidos de Sb, sobre las muestras ricas en estibnita. Estos experimentos documentan los procesos geoquímicos y mineralógicos asociados con las interacciones de corto plazo (días a semanas) entre roca y agua que dan relativamente altas concentraciones de metaloides disueltos (>5 mg/L) donde localizada (1-10 m) acidificación y limitada oxidación ocurren en rocas ricas en sulfuros.

新西兰造山带型金矿准金属活性试验研究

摘要

溶解态锑(Sb)和砷(As)浓度的升高是造山带型金矿附近最常见的水环境问题。准金属主要赋存于辉锑矿(Sb2S3)和砷黄铁矿(FeAsS)中,并为黄铁矿(FeS2)所伴生。富含砷黄铁矿(As的质量分数为2.5%)和辉锑矿(Sb的质量分数为10%)矿石样品取自新西兰雷夫顿金矿带(Reefton goldfield)的Globe-Progres矿。矿石被粉碎后(颗径<5mm)放置于淋滤柱中进行为期一年的动态淋滤实验。每月集取并分析淋滤液一次。在试验12个月之后,仅有一小部分(<1%)的砷(As)和锑(Sb)被淋滤出来。在淋滤过程中,黄铁矿的氧化作用使淋滤液的pH值由7左右降到了3左右。淋滤试验母岩中Ca-Fe-Mg碳酸盐溶液不足以中和淋滤液的酸性。富砷黄铁矿样品淋滤液中砷(As)浓度最初为16mg/L,在12个月后降到约2mg/L。富辉锑矿样品淋滤液的锑(Sb)浓度在实验期间均大于7mg/L,最大浓度曾达12mg/L。淋滤试验六个月之后的电子显微镜扫描(SEM)显示,富砷黄铁矿矿石表面有次生砷华(As2O3)和Ca-Al-Mg硫酸盐生成,但富辉锑矿矿石表面却未见锑(Sb)氧化物等次生矿物。实验记录了矿石样品水-岩之间的短期(数日至数周)地球化学和矿物学过程,证明由于富含硫化物岩石表面的局部(1-10m)酸化及氧化作用产生了高浓度的溶解态类金属(>5 mg/L)。

Notes

Acknowledgments

This research was supported by the Ministry of Science and Innovation, and additional funding was provided by the University of Otago. Kat Lilly expertly produced the SEM images. We are grateful to Oceana Gold Ltd, especially John Bywater, for ongoing support of this research, and access to monitoring data and the mine site for collection of the experimental materials. Joanna Druzbicka provided data and helpful discussions. Able and efficient technical assistance with the leaching experiments was provided by Helen Rogers and Meng Shi at CRL Energy in Christchurch. Constructive comments by two anonymous referees substantially improved the paper.

Supplementary material

10230_2015_332_MOESM1_ESM.pdf (39 kb)
Supplementary material 1 (PDF 38 kb)

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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  1. 1.Geology DepartmentUniversity of OtagoDunedinNew Zealand
  2. 2.CRL EnergyChristchurchNew Zealand

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