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Mine Water and the Environment

, Volume 34, Issue 4, pp 388–403 | Cite as

A Geoenvironmental Model for Orogenic Gold Deposits to Predict Potential Environmental Effects

  • Dave CrawEmail author
  • Jo Cavanagh
  • Joanna Druzbicka
  • Jon S. Harding
  • Gemma Kerr
  • James Pope
  • Dave Trumm
Technical Article

Abstract

Orogenic deposits are an important source of gold around the world, with associated environmental impacts. New Zealand has a broad spectrum of these orogenic deposits, providing an ideal setting to develop a general conceptual model that can be used to predict potential environmental issues associated with their exploration and mining. This model provides a practical and quantitative framework for permitting and managing mine operations, with a focus on downstream water quality. The model has been quantified using data collected from natural mineralised occurrences, two active mines, and numerous historic mine sites. Mine waters in and around orogenic deposits almost invariably have a pH of 7–8. Minor localised acidification occurs in excavations and waste rock, but it is readily neutralised by the abundant calcite in the host rock. The ore can have strongly elevated levels of As and Sb; the proportions of these metalloids are controlled by geological factors, especially the crustal level of emplacement and the structure of the mineralised rocks. Agitation of sulfide mineral slurries during processing and pressure oxidation in the processing system can lead to dissolved metalloid concentrations of tens to hundreds of mg/L in mine tailings waters. The gold also commonly contains Hg, up to 40 wt%, and discharge of this Hg to the atmosphere during processing is possible, but Hg is not significantly mobilised from other mine rocks. High metalloid concentrations are the most significant environmental issue, but are decreased by adsorption to iron oxyhydroxide as the water percolates through mine rocks and tailings. Even so, additional treatment may be needed to lower metalloid concentrations for discharge to rivers and lakes.

Keywords

Arsenic Antimony Mercury Adsorption Treatment Stream invertebrates Suspended solids 

Umweltgeologisches Modell zur Vorhersage potentieller Umweltauswirkungen orogener Goldlagerstätten

Zusammenfassung

Orogene Goldlagerstätten sind weltweit wichtiger Goldlieferant und mit entsprechenden Umweltbeeinflussungen verbunden. Neuseeland verfügt über ein breites Spektrum solcher orogener Lagerstätten und bietet so ideale Bedingungen für die Ableitung eines allgemeingültigen konzeptionellen Modells zur Prognose potentieller Umweltauswirkungen, die infolge Exploration und Abbau derartiger Lagerstätten entstehen können. Das vorgestellte Modell ist ein praxistaugliches und quantitatives Werkzeug für Genehmigung und Betrieb von Bergbauaktivitäten, und zwar mit Blick auf Fragen der Wasserbeschaffenheit von bergbaubeeinflussten Wässern. Die Modellvalidierung beruht auf Daten von natürlichen Mineralvorkommen, von zwei aktiven Minen sowie von einer Vielzahl historischer Bergbaustandorte. Bergbauwässer innerhalb sowie im Umfeld von orogenen Lagerstätten weisen nahezu ausschließlich pH-Werte zwischen 7 und 8 auf. Versauerung tritt nur untergeordnet und lokal in bergmännischen Hohlräumen und an Halden auf, die rasche Neutralisation beruht auf dem reichlich vorhandenen Kalzit der Nebengesteine. Das Erz kann stark erhöhte Konzentrationen von As und Sb aufweisen; das Verhältnis dieser Metalloide zueinander wird bestimmt durch geologische Faktoren, speziell die Teufe der Platznahme und die Struktur der mineralisierten Gesteine. Der Aufschluss sulfidhaltiger Schlämme während Aufbereitung und Druckoxidation kann Gelöst-Metalloid-Konzentrationen von mehreren zehn bis hundert mg/l in den Aufbereitungswässern nach sich ziehen. Gold enthält üblicherweise auch Hg und zwar bis zu 40 Ma.- %, so dass eine Hg-Freisetzung in die Atmosphäre während der Aufbereitung möglich ist; aus anderen Gesteinen wird Hg nicht nennenswert mobilisiert. Hohe Metalloid-Konzentrationen sind das bedeutendste Umweltproblem, sie werden jedoch während der Perkolation durch Grubengestein und Tailings infolge Adsorption an Eisenoxidhydraten gesenkt. Ungeachtet dessen, kann sich eine zusätzliche Wasserbehandlung zur Abtrennung von Metalloiden vor Ableitung der Bergbauwässer in die Vorflut als notwendig erweisen.

Un modelo geoambiental para depósitos orogénicos de oro para predecir potenciales efectos ambientales

Resumen

Los depósitos orogénicos son una importante fuente de oro en el mundo que tiene impactos ambientales asociados. Nueva Zelanda tiene un amplio espectro de estos depósitos proveyendo una zona ideal para desarrollar un modelo conceptual general que pueda ser usado para predecir posibles impactos ambientales asociados con su exploración y explotación. Este modelo proporciona un marco práctico y cuantitativo para la habilitación y el manejo de las operaciones de la mina, focalizadas en la calidad del agua producida en el proceso. El modelo ha sido cuantificado usando datos colectados desde zonas naturales, dos minas activas y de numerosos sitios de explotación minera. Las aguas de minas tanto en la zona de los depósitos orogénicos como en sus alrededores casi siempre tienen un pH de 7-8. Acidificaciones menores se encontraron en excavaciones y residuos de roca pero es neutralizada por la abundante calcita presente en la roca. El mineral puede tener altos niveles de As y Sb; las proporciones de estos metaloides son controlados por factores geológicos, especialmente el nivel cortical del emplazamiento y la estructura de las rocas mineralizadas. La agitación del mineral sulfurado durante el procesamiento y la oxidación a presión pueden provocar la disolución de metaloides hasta concentraciones desde decenas a centenas de mg/L en las aguas de las colas de mina. El oro también contiene usualmente Hg, hasta 40 % p/p, y la descarga de este Hg a la atmósfera durante el procesamiento es posible aunque Hg no es significativamente movilizado desde otras rocas de la mina. Las altas concentraciones de metaloides son el más significativo problema ambiental pero decrecen por la adsorción sobre los oxihidroxos de hierro a medida que el agua percola a través de las rocas de la mina y de las colas. Aún así, puede ser necesario un tratamiento adicional para bajar las concentraciones de metaloides para descargar a ríos y lagos.

造山带型金矿地质环境模型的潜在环境影响预测

抽象

造山带型矿床是金矿最重要的矿藏类型之一,造山带型金矿开采对环境产生了系列影响。新西兰拥有系列造山带型金床,为建立一种普适性地质环境概念模型提供了理想条件,这个模型能够预测金矿勘探与开采的潜在环境影响。以下游水质保护为焦点,模型为金矿批准和运行管理提供了实用的、定量评价框架。利用矿区天然矿化本底特征值及2个生产矿井和多个历史遗留矿井数据量化了概念模型。造山带型金矿内及周围矿井水的pH值都稳定于7 ~ 8。虽然坑道及废石堆可能会发生局部轻微酸化,但很容易被主岩中大量的方解石中和。矿石可能含有大量As和Sb;它们的含量主要由地质条件尤其岩浆的地壳侵位水平及岩石成矿结构控制。在矿物加工和加压氧化过程中,硫化矿浆的搅动使尾矿水中可溶解类金属浓度达几十~几百mg/L。金中也常含有Hg,重量百分比可高达40 %;Hg可能在矿物加工过程中排放到大气当中;但其它矿石中Hg并未被活化。因此,高浓度类金属污染是造山带型金矿开采及加工最主要的环境问题;但是当矿水穿过矿石及尾矿时,类金属为铁氢氧化物吸附而含量降低。即使如此,也有必要增加降低类金属浓度的矿水处理过程,矿井水才能被排放入河流及湖泊。

Notes

Acknowledgments

This research resulted from a multidisciplinary programme funded by New Zealand Ministry for Business, Innovation and Employment to CRL Energy Ltd. Discussions, data sets, and logistical support were provided over many years by OceanaGold Ltd personnel, especially John Bywater, Simone Creedy, and Quenton Johnston. The photograph of the mayfly in Fig. 9 was taken by Paddy Ryan.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • Dave Craw
    • 1
    Email author
  • Jo Cavanagh
    • 2
  • Joanna Druzbicka
    • 1
  • Jon S. Harding
    • 3
  • Gemma Kerr
    • 1
  • James Pope
    • 4
  • Dave Trumm
    • 4
  1. 1.Geology DepartmentUniversity of OtagoDunedinNew Zealand
  2. 2.Landcare ResearchLincolnNew Zealand
  3. 3.School of Biological SciencesUniversity of CanterburyChristchurchNew Zealand
  4. 4.CRL EnergyChristchurchNew Zealand

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