Elsevier

Ore Geology Reviews

Volume 67, June 2015, Pages 208-233
Ore Geology Reviews

Review
The “Calamines” and the “Others”: The great family of supergene nonsulfide zinc ores

https://doi.org/10.1016/j.oregeorev.2014.10.025Get rights and content

Abstract

“Nonsulfides” is a term, which comprises a series of oxidized Zn(Pb)-ore minerals. It has also been used to define a special deposit type, mainly considered as derived from the weathering of Zn(Pb) sulfide concentrations. However, nonsulfide zinc deposits have been distinguished between supergene and hypogene, according to their mineralogy, geological characteristics and genetic setting. The supergene deposits formed by weathering and oxidation at ambient temperatures, whereas the hypogene ones are considered hydrothermal, or associated with metamorphic processes on primary sulfide ores.

In this review paper, a comparison between a number of several nonsulfide deposits has been carried out: typical “Calamines”, peculiar “Calamines” and “Others”. The whole group comprises deposits of typical supergene origin, mixed supergene–hypogene mineralizations, and oxidized concentrations characterized by different metals only locally associated with zinc. The Zn–Pb nonsulfide concentrations hosted in carbonate rocks, which are mainly attributed to “wall-rock replacement” and “direct-replacement” supergene processes, are the typical “Calamines” (Liège district, Belgium; Iglesias district, Italy; Silesia–Cracow district, Poland). Peculiar “Calamine” deposits are those mineralizations that have been generally considered as supergene, but which are instead genetically related, at least partly, to hypogene processes (e.g. Angouran, Iran; Jabali, Yemen), though mineralogically and texturally similar to supergene nonsulfide deposits. The “Others” are prevailingly supergene nonsulfide zinc deposits not hosted in carbonate rocks (Skorpion, Namibia; Yanque, Peru), or characterized by other metals as main commodities, like lead (Magellan, Australia), silver (Sierra Mojada, Mexico; Wonawinta, Australia) or vanadium (Otavi Mountainland, Namibia).

Minerals of current economic importance in most “Calamine” deposits are smithsonite, hydrozincite, and cerussite. This mineralogical association is generally simple but, when the “Calamines” are dolomite-hosted, one of the consequences of the “wall-rock replacement” process is the generation of a series of economically useless Zn- and Mg-bearing mixed carbonate phases. Secondary deposits hosted in silicatic (sedimentary or volcanic) rocks mainly contain hemimorphite and/or sauconite. Lead-, Ag- and V-rich nonsulfide ores are characterized by a more complex mineralogical association: mixed Pb-carbonates, Pb-sulfates, Pb-phosphates, Pb-arsenates, various Ag-sulfosalts, and Zn–Pb–Cu-vanadates.

Carbon and oxygen stable isotope studies allow distinguishing between supergene and hypogene nonsulfide deposits, evaluating the effects of oxidative heating and even gaining indirect paleoclimatic information. The oxygen-isotope variation of the individual carbonate minerals within a deposit is relatively small, indicating constant formation temperatures and a single, meteoric fluid source. Carbon-isotope values are highly variable, thus suggesting several isotopically distinct carbon sources.

Periods of paleoclimatic switch-overs from seasonally humid/arid to hyperarid have been considered as the most favorable conditions for the formation and preservation of supergene nonsulfide deposits. However, while several recent nonsulfide deposits throughout the world are positioned between 15° and 45° N latitude, thus pointing to a warm and humid weathering climate, others have been deposited in sub-Arctic regions.

The economic value of the nonsulfide Zn(Pb–Ag–V) ores is highly variable, because more than in the case of metallic sulfide deposits, it resides not only on the geological setting, but also on their mineralogy that can directly influence processing and metallurgy.

Introduction

Despite the widespread occurrence of surficial zinc (lead) oxides (in gossans and soils), economic deposits of these metals in oxidized form, the so-called “nonsulfides”, are far less common than sulfide deposits. “Nonsulfides” is a term, which comprises a series of oxidized Zn(Pb)-ore minerals, but can also characterize a special deposit type, mainly considered as related to weathering of Zn(Pb) sulfide concentrations. Nonsulfide deposits have experienced a significant revival over the recent years, as a consequence of new developments in hydrometallurgical acid leaching, solvent extraction, and electrowinning techniques. The economic focus is generally on zinc nonsulfides, even though most deposits also contain variable amounts of lead. Silver can occasionally occur in selected ore districts (Sierra Mojada, Jabali, etc.).

The economic value of zinc nonsulfide ores is strictly dependent not only on the geologic setting of each deposit, but also on the nature of the ore and gangue minerals. Host-rock composition may have significantly influenced the mineralogy (and therefore metallurgy) of this kind of ores. Since the differences in dissolution rates of the zinc minerals may have strong implications for the production strategies and metallurgical requirements, a detailed mineralogical and petrographic study, already in the early phases of an exploration process, is a must for this kind of ores, even more than in the case of sulfide deposits.

Although it is improbable that production of Zn metal (and by analogy of Pb metal) from nonsulfide sources will ever completely replace production from conventional sulfide ores, nevertheless it is suggested that nonsulfide Zn (and Pb) deposits are growing in economic importance. One of their more conspicuous advantages is the paucity of sulfur in this kind of ores. Medium- to large-sized deposits currently in development or advanced exploitation stage include Skorpion (Namibia), Lan Ping (China), Angouran and Mehdiabad (Iran), Shaimerden (Kazakhstan), Jabali (Yemen), Hakkari (Turkey), Vazante (Brazil), Accha, Yanque and Bongarà (Peru), Torlon Hill (Guatemala) and Sierra Mojada (Mexico). In addition, there are a number of other localities hosting relatively small tonnages of nonsulfide Zn ores in Vietnam, Thailand, Turkey, British Columbia, Morocco, Algeria, and Egypt (Hitzman et al., 2003) (Fig. 1).

Nonsulfide zinc deposits have been distinguished between supergene and hypogene, according to their mineralogy, geological characteristics and genetic setting (Hitzman et al., 2003, Large, 2001). The supergene deposits formed by weathering and oxidation at ambient temperatures, whereas the hypogene ones are considered hydrothermal, or associated with metamorphic processes on primary sulfide ores. The hypogene deposits consist dominantly of anhydrous zinc silicates and oxides, such as willemite, zincite, franklinite, and other minerals, locally coexisting with variable amounts of sulfides. The most economically important concentrations of this type are the Vazante deposit (Brazil) in Proterozoic carbonates (Monteiro et al., 2006, Slezak et al., 2014) and the cluster of mineralizations in the Franklin (New Jersey, USA) ore belt, which are also associated with strong metamorphic processes (Dunn, 1995). Other occurrences are the Beltana-type deposits in Southern Australia (Groves and Carman, 2003) and of part of the oxidized ores contained in the Neoproterozoic belts of Namibia–Zambia (Boni et al., 2011b, Schneider et al., 2008).

The mineralogy and size of supergene deposits and their location relative to the precursor sulfide bodies reflect the composition of the primary sulfide assemblage and host rock, as well as the hydrologic regimes and climate throughout time. Hitzman et al. (2003) distinguished between “Direct Replacement” (of sulfides) and “Wallrock Replacement” (of host rock) nonsulfide ores. A third, much less common kind is the “Residual and karst-fill” deposit type (Hitzman et al., 2003). According to the extent of replacement of sulfides, the resulting ore is called mixed (a combination of sulfide and nonsulfide ores) or pure nonsulfide (also referred to as “oxide”) ore. Direct replacement deposits, also known as “red ores” because of their high content in Fe-(hydr)oxides, typically contain > 20% Zn, > 7% Fe and variable amounts of Pb or Ag (Reichert and Borg, 2008). Wallrock replacement deposits, also known as “white ores”, consist of smithsonite, hydrozincite and minor Fe-(hydr)oxides. They contain < 40% Zn, < 7% Fe and very low concentrations of Pb (Reichert and Borg, 2008). Nonsulfide ores can be located in proximity to the sulfide protore or up to several hundred meters away (Heyl and Bozion, 1962, Hitzman et al., 2003). Among the above-quoted deposit types, those hosted in limestone and dolomite (the “Calamines”) have a simple mineralogy, good extraction recovery, and higher grades.

A number of review papers on the subject of nonsulfide Zn(Pb,Ag) ores have been published over the last 15 years (Boni, 2005, Boni and Large, 2003, Borg, 2009, Hitzman et al., 2003, Large, 2001, Megaw, 2009, Reichert and Borg, 2008). The focus of this paper will be mainly on Zn nonsulfides, but also a few Pb–Ag-oxidized deposits and a peculiar case of vanadium supergene ores will be briefly considered (Table 1).

In order to show the high variety of this kind of ores, we will first discuss the typical “Calamine” mineralizations that comprehend the old European deposits and those of the Mediterranean realm, followed by a number of carbonate rock-hosted Zn occurrences in the world, some of which are far from being of supergene origin (e.g. Angouran, Iran). We will then consider a few examples of not carbonate rock-hosted deposits, starting with the case of the world class Skorpion deposit (Namibia).

Section snippets

History

In the past zinc was considered only for its importance in making brass (alloy of zinc and copper). Copper–zinc alloys were produced as early as the 5th millenium BC in China, and were widely in use in eastern and central Asia by the 2nd and 3rd century BC. It is likely that the alloys were smelted from zinc-rich copper ores, producing crude brass-like metals (Kharakwal and Gurjar, 2006).

Greek and Roman documents suggest that the intentional production of alloys similar to modern brass, using

Mineralogy of supergene nonsulfides and classification

The supergene nonsulfide deposits are far more widespread, and considered so far to be more economically important than the hypogene ones. The main minerals associated in nonsulfide Pb and Zn deposits and their physical and chemical properties useful in field identification are quoted in Hitzman et al. (2003) and McConachy et al. (2007). In Table 2 we have listed the most common minerals occurring in the nonsulfide deposits quoted in text, with their chemical formulas and the related amounts of

Methods of analysis

Mineralogy and petrography of nonsulfide Zn–Pb deposits are generally investigated using several laboratory methods (optical microscopy, chemical analyses, X-ray diffraction, scanning electron microscopy, microprobe, QEMSCAN®). Recently, spectral reflectance has been measured on several minerals occurring in nonsulfide deposits, with the aim to use the results as an exploration tool (McConachy et al., 2007). Because the reader is certainly familiar with most of the methods used in the

Examples of “Calamines”

Most nonsulfide Zn(Pb) deposits belong to the category of “Calamine”, that is: “concentrations of Zn(Pb) oxidized minerals derived from deep weathering of carbonate-hosted primary sulfide ores”. “Calamine” is a historic name for oxidized zinc ore, derived from the Belgian town of Kelmis (“La Calamine” in French), which was home to an important zinc mine and processing plant.

The mineralized protore can be either a Mississippi Valley-type deposit, or a SEDEX, or a polymetallic CRD. Calamine-type

Skorpion (Namibia) — everybody's dream

The Skorpion nonsulfide zinc deposit is located approximately 40 km north of the Orange River in the southernmost Namib Desert, Namibia (Fig. 13). It comprises a significant nonsulfide ore body (at the beginning of exploitation it consisted of 24.6 Mt @ 10.6% Zn, Borg et al., 2003) and subordinate amounts of primary hypogene base metal sulfide concentrations, which underlie the nonsulfide ores at depth. The mining commenced in October 2001 with the stripping of the overburden and exposure of the

The lead version: Magellan (Australia)

The Magellan Pb deposit is located in an outlier of the Palaeoproterozoic Earaheedy Group overlying the southeast Yerrida Basin (Pirajno et al., 2010) (Fig. 16), and likely represents a new category within the nonsulfide class of ore deposits. Its measured and indicated ore resources consist of 21.4 Mt grading 5.8% Pb; inferred resources are of 7.2 Mt grading 4.6% Pb (SEG Newsletter, April 2006, No. 65, p. 27). The deposit is currently exploited, due to its low cost metal production. The lead

Supergene vs. not-supergene

For a long time, nonsulfide Zn–Pb deposits seemed to belong to a fairly easy-to-describe type of ores, consisting of variable amounts of oxidized minerals considered as derived from the weathering of sulfides and resembling deeper gossans. As stated in the Introduction, the first blow to these over-simplified genetic concepts on the nonsulfide ores was given by the discovery that not all of them were weathering products, but those characterized by willemite as prevailing mineral were instead

Conclusive remarks

In conclusion, from the geological, mineralogical and geochemical point of view there is an entire world comprised in the concept of “nonsulfide Zn(Pb–Ag–V) ores”. Their economic value is highly variable: more than in the case of metallic sulfide deposits, it resides on the mineralogy of the contained metals. Some technical problems encountered during processing can be thus mitigated by a better identification of the mineralogical association of the metallic and nonmetallic minerals. This

Acknowledgments

First of all, one of us (M.B.) would like to thank Duncan Large, for having introduced her to the fascinating world of nonsulfides, which, until 2001, she rather regarded as rubbish and not as real ore. Our research benefitted from the discussion with G. Balassone, C. Allen, V. Arseneau, G. Borg, A. Clegg, V. Coppola, L. DeJonghe, H.A. Gilg, B. Grist, R. Herrington, M. Hitzman, C. Laukamp, M. Joachimski, G. Olivo, S. Paradis, F. Pirajno, G. Rollinson, L. Santoro, P. Schmidt, G. Stanley, B.

References (86)

  • J. Reichert et al.

    Numerical simulation and a geochemical model of supergene carbonate-hosted nonsulphide zinc deposits

    Ore Geol. Rev.

    (2008)
  • L. Santoro et al.

    The Hakkari nonsulfide Zn–Pb deposit in the context of other nonsulfide Zn–Pb deposits in the Tethyan Metallogenetic Belt of Turkey

    Ore Geol. Rev.

    (2013)
  • J. Schneider et al.

    Willemite (Zn2SiO4) as a possible Rb–Sr geochronometer for dating nonsulfide Zn–Pb mineralization: examples from the Otavi Mountainland (Namibia)

    Ore Geol. Rev.

    (2008)
  • P.R. Slezak et al.

    Geology, mineralogy, and geochemistry of the Vazante Northern Extension zinc silicate deposit, Minas Gerais, Brazil

    Ore Geol. Rev.

    (2014)
  • G. Agricola

    De Re Metallica. The 1950 Edition, translated by Hoover H.C. and Hoover L.H.

    (1556)
  • I. Al Ganad et al.

    Jabali, a Zn–Pb–(Ag) carbonate-hosted deposit associated with Late Jurassic rifting in Yemen

    Miner. Depos.

    (1994)
  • Al-Ameri A., 2011. Regional Stable Isotope and Hydrochemistry Investigation in Yemen and in the Representative Area...
  • Geoscience Australia, 2004. Australian Mines and Mineral Deposits Map, Scale 1:10,000,000. Geoscience Australia, Dept....
  • A. Blot et al.

    La chloritisation supergene zincifère des phlogopites de Canoas (PR, Brésil)

    CR Acad. Sci. Paris

    (1995)
  • M. Boni

    The geology and mineralogy of nonsulfide zinc ore deposits

    Proceedings LEAD and ZINC '05, Kyoto 17–19 October 2005

    (2005)
  • M. Boni

    Discovery and mining history of the “Calamine”in SW Sardinia (Italy)

  • M. Boni et al.

    Nonsulfide mineralization in Europe: an overview

    Econ. Geol.

    (2003)
  • M. Boni et al.

    Base metal ores in the lower Palaeozoic of South Western Sardinia

  • M. Boni et al.

    The “Calamine” of SW Sardinia (Italy): geology, mineralogy and stable isotope geochemistry of a supergene Zn-mineralization

    Econ. Geol.

    (2003)
  • M. Boni et al.

    Hypogene Zn carbonate ores in the Angouran deposit, NW Iran

    Miner. Depos.

    (2007)
  • M. Boni et al.

    Genesis of vanadium ores in the Otavi Mountainland (Namibia)

    Econ. Geol.

    (2007)
  • M. Boni et al.

    The nonsulfide zinc deposit at Accha (Southern Peru): geological and mineralogical characterization

    Econ. Geol.

    (2009)
  • M. Boni et al.

    Zincian dolomite: a peculiar dedolomitization case?

    Geology

    (2011)
  • M. Boni et al.

    The carbonate-hosted willemite prospects of the Zambezi Metamorphic Belt (Zambia)

    Miner. Depos.

    (2011)
  • M. Boni et al.

    Zincian dolomite related to supergene alteration in the Iglesias mining district (SW Sardinia)

    Int. J. Earth Sci. (Geol. Rundsch.)

    (2013)
  • G. Borg

    The role of fault structures and deep oxidation in supergene base metal deposits

  • G. Borg et al.

    Geology of the Skorpion non-sulphide deposit, southern Namibia

    Econ. Geol.

    (2003)
  • J. Brugger et al.

    Formation of willemite in hydrothermal environments

    Econ. Geol.

    (2003)
  • Ceyhan N., 2003. Lead Isotope Geochemistry of Pb–Zn Deposits From Eastern Taurides, Turkey. Unpub. MSc Dissertation....
  • F. Choulet et al.

    Non-sulfide zinc deposits of the Moroccan High Atlas: multi-scale characterization and origin

    Ore Geol. Rev.

    (2013)
  • V. Coppola et al.

    Nonsulfide Zinc deposits in the Silesia–Cracow district, Southern Poland

    Miner. Depos.

    (2009)
  • L. Dejonghe et al.

    Atlas des gisements plombo-zincifères du Synclinorim de Verviers (Est de la Belgique)

    (1993)
  • P.J. Dunn

    Franklin and Sterling Hill, New Jersey: The World's Most Magnificent Mineral Deposits

    (1995)
  • A. Emberger

    Carte des minéralisations plombo-zincifères du Maroc map: gîtes et indices renfermant du plomb ou du zinc en element majeur ou mineur [map]

    (1969)
  • A. Emberger

    Méthodologie de la recherché métallogénique: la classification morpho-lithologique des minéralisations plombo-zincifère du Maroc

    Notes et Mém. Serv. Géol. Maroc.

    (1970)
  • J. Emsely

    Nature's Building Blocks: An A–Z Guide to the Elements

    (2001)
  • D. Fleitmann et al.

    The speleothem record of climate change in Saudi Arabia

  • J. Gnoinski

    Skorpion Zinc: optimization and innovation

    J. S. Afr. Inst. Min. Metall.

    (2007)
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