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Hydrothermal nickel deposits: Secular variation and diversity
Ore Geology Reviews 52 (2013) 1–3
Contents lists available at SciVerse ScienceDirect
Ore Geology Reviews journal homepage: www.elsevier.com/locate/oregeorev
Editorial
Hydrothermal nickel deposits: Secular variation and diversity I. González-Álvarez a, b,⁎, F. Pirajno b, d, R. Kerrich c a
CSIRO, Earth Science and Resource Engineering, Minerals Down Under Flagship, Discovery Theme, Kensington, Western Australia 6151, Australia Centre for Exploration Targeting, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia c Department of Geological Sciences, University of Saskatchewan, 112 Science Place, SK, Canada S7N 5E2 d Geological Survey of Western Australia, 100 Plain Street, East Perth, WA 6004, Australia b
a r t i c l e
i n f o
Article history: Received 18 November 2012 Received in revised form 27 November 2012 Accepted 27 November 2012 Available online 5 December 2012 Keywords: Trace element mobility Mineral systems Mineral exploration Hydrothermal systems Hydrothermal Ni
a b s t r a c t Hydrothermal nickel systems are one of the most puzzling mineral systems that involve trace element mobility in the Earth’s crust. Nickel is an abundant element in the crust. However, the processes that are involved in its mobility and accumulation at ore scale are challenging. A new empirical-stochastic model is required to gain a deeper insight into these systems. This Special Issue presents several studies on hydrothermal nickel accumulations world wide aiming to stimulate the debate on this intriguing deposit type. © 2012 Elsevier B.V. All rights reserved.
Hydrothermal systems, activated by tectonic and/or magmatic events, result in extensive mobilization and fractionation of trace element in the Earth's crust. However, within this framework, hydrothermal Ni systems are deeply puzzling and poorly understood. Nickel is an abundant element in the crust at 47 ppm (2000 ppm in ultramafic rocks), and evidences of its mobility in fluids are observed in many settings and mineral deposits, notably in unconformityrelated U deposits. However, the Ni mobility in hydrothermal fluids is poorly understood, in part due to the limited number of occurrences and/or deposits reported. Moreover, other types of mineral deposits are largely confined to very specific geological settings and time clusters, hydrothermal Ni systems are generally independent of geological time and tectonic setting. It is challenging to identify hydrothermal Ni systems, largely because they are characterized by ambiguous features that could mimic other ore forming processes, such as ore mineral paragenesis and alteration mineral assemblages. Since the milestone discovery in 1997 of the Avebury deposit in Tasmania, with 0.26 Mt Ni metal, more attention has been focused on this deposit type, contributing to additional Ni resources being identified as hydrothermal type, notably Enterprise, Zambia, and Doriri Creek, PNG. Some of the most perplexing questions related to hydrothermal Ni mineral systems relate to controls on the solubility of Ni in different ⁎ Corresponding author at: CSIRO, Earth Science and Resource Engineering, Minerals Down Under Flagship, Discovery Theme, Kensington 6151, Western Australia, Australia. Tel.: +61 8 6436 8687; fax: +61 8 6488 1178. E-mail address: [email protected] (I. González-Álvarez). 0169-1368/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.oregeorev.2012.11.006
environments at low temperature, and the diversity of potential ligands, which are different from its chemical neighbors (e.g., Cu, Co). Recent studies underline these solubility-ligands queries. Liu et al. (2012) in their study of Ni solubility in hydrothermal systems reported a lower solubility of nickel sulfides (NiS) compared to equivalent Co sulfide minerals. These experimental results partially explain the rarity of hydrothermal Ni deposits in comparison with Co counterparts exemplified by sandstone-hosted Cu–Co deposits. As a corollary, because Ni can be mobilized in a large variety of environments by diverse ligands, and or particularly at low temperatures (b250 °C), there remains the potential for discovery of new classes of hydrothermal Ni deposits. The general idea that hydrothermal NiS deposits are rare because they are residual owing to their resistance to mobilization, does not satisfactorily explain some of the conditions of the hydrothermal Ni systems in sedimentary sequences such as the Nick horizon, Canada, or Enterprise, Zambia, where the Ni accumulation are not easy to explain as the result of residual leaching. Organic ligands (Greenwood et al., 2012) and basinal brine chemistry could have the appropriate combination of chemical features as well as ligands to promote Ni mobility at low temperatures, fractionating it from Co and Cu. This leads to another intriguing question on hydrothermal Ni systems: how far are the fluids able to carry Ni in solution from the Ni source/s? Because of the lack of proper understanding of Ni mobilization, the conceptual-model-driven exploration for magmatic NiS deposits may have had a reductionist, deterministic effect, thereby hindering the discovery of hydrothermal Ni deposits. At the same time, reassessment of some NiS deposits post-mining poses new questions, often leading to
2
Table 1 Hydrothermal Ni deposits presented in this Special Issue. Craton/ terrane
Age
Deposit/prospect
Ore
Alteration assemblage
Metal budget
Ultramafic schist
Epoch
Pyrite, millerite, bravoite, and minor chalcopyrite and pentlandite.
Peridotite and dunite cumulate suites
Avebury
Pentlandite with minor pyrrhotite.
talc-carbonate rocks that also contain dolomite, chlorite and magnesite Talc–serpentinite and clinopyroxene– amphibole skarn units
Doriri Creek
Amphibole and Chlorite and serpentine group chlorite–serpentine minerals in addition to Fe oxides, with a minor amount in group minerals pentlandite
Peridotites/ pyroxenites within a high MgO, noritic gabbro envelope North Karelia Paleoproterozoic Black schist schist belt, Finland
South China, Yangtze Platform
Early Cambrian
East European Devonian platform suture with the Uralides, Russia
Ni Mt
Status
Comments
Ni ⋙Cu 5.61 at 0.67%
Mined
No cumulate textures; no PGE; dominant oxide mineral is magnetite
Ni ⋙Cu 29.3 at 0.9%
Ceased production, in maintenance
Ni ⋙Cu ??? at 2.43% maximum
Exploration assessment
Quartz, micas, Ni > Cu 1550 at 0.22% graphite and sulfides, with rutile, apatite, zircon, feldspar, tourmaline garnet, uraninite, thucholite and Ni ⋙Cu ??? at Ni + Mo Black shales Maluhe deposit, Sancha, MoSC, pyrite, vaesite, bravoite, Organic matter, reaching up to fine-grained illite, Wangjiazhai, Ganziping, millerite, gersdorffite, and 14 wt.% sericite, quartz, calChuanyanping, Houping, jordisite, with minor cite, barite, and loLangxi, Daping, Xiaoping arsenopyrite, chalcopyrite, covellite, sphalerite, tennantite, cally abundant and the Cili deposits tiemannite, violarite, and native apatite and among others collophane Au Ishkinino, Ivanovka, Chalcopyrite–pyrite–pyrrhotite Talc–carbonate and Ni b Cu 2 Mt Dergamysh Mafic– Dergamysh and Co–Ni–sulfarsenide–sulfide chlorite deposit; 1.11 Mt ultramafic Ishkinino deposit; (dunitic and harzburgitic and 24 Mt for the lithologies) Ivanovka deposit at 0.1–0.49 wt.% Talvivaara
Pentlandite as inclusions in pyrrhotite, pyrite, pyrrhotite, sphalerite and chalcopyrite
References
Pirajno (1971), Baglow (1986) and Pirajno and Gonzalez-Alvarez (2013–this issue) Keays et al. (2009) Negative or absent correlations between Pt, Ir, Ru and Keays and Jowitt (2013–this issue) and Rh with Ni
Pd and Pt concentration together with apatite; enrichments of U, K and W
Fractured talc-carbonate rocks Producing and resource delineate the eastern border of the deposit; Minor occurevaluation rences of peridotite, serpentinite and talccarbonate rocks occur in the area Many deposits in production
Ni–Mo–PGE–Au sulfide ore layer enriched in organic and phosphatic materials; enriched in Se, Re, Os, As, Hg, and Sb (>104 times average continental crust)
Exploration and/or resource estimation
Associated to ophiolite complex; Pervasive serpentinization of peridotites and localized hydrous and carbonate alteration of mafic rocks under up to greenschist facies
Davies (1969), Lindley and Kirakar (2007) and González-Álvarez et al. (2013–this issue)
Ervamaa and Heino (1980), Loukola-Ruskeeniemi and Heino (1996) and Loukola-Ruskeeniemi and Lahtinen (2013–this issue) Coveney and Nansheng (1991), Lehmann et al. (2007), Xu et al. (2011) and Xu et al. (2013–this issue) Buchkovskiy (1970), Melekestseva (2005) and Melekestseva et al. (2013–this issue)
Ore Geology Reviews 52 (2013) 1–3
Neoproterozoic Zimbabwe, Filabusi Greenstone belt Late Devonian Tasmania, eastern margin of the Dundas Trough Cainozoic (?) Papuan Ultramafic Belt, PNG
Host lithology
Ore Geology Reviews 52 (2013) 1–3
difficult challenges to the review of the original ideas on the nature of the deposit mined. In the above context, this Special Issue aims to contribute to developing a better understanding of hydrothermal Ni mineral systems by compiling and discussing some key examples of this deposit type (Table 1). The first part of this Special Issue deals with case study deposits associated with mafic–ultramafic suites: (1) Keys and Jowitt present novel geochemical data and exploration history of the Cambrian ultramafic peridotite hosted Avebury deposit in Tasmania, Australia; (2) Melekestseva et al. document the characteristics of several Ni– Co-bearing hydrothermal massive sulfide deposits associated with ultramafic–mafic rock suites in the Urals, Russia; and (3) GonzálezÁlvarez et al. report an intriguing case of hydrothermal Ni accumulation in the Cenozoic(?) Papuan Ultramafic Belt, which poses critical questions for the exploration approach for this deposit type. Following these case studies, (4) Pirajno and González-Álvarez re-appraise the Epoch Ni deposit, Zimbabwe, for the possibility of re-classifying what was previously considered a magmatic NiS deposit as being the result of mainly hydrothermal activity. The second part of this issue examines hydrothermal Ni accumulations, not associated with mafic–ultramafic rock suites, but within sedimentary sequences: (5) Xu et al. discuss Cambrian black shales of South China which host polymetallic Ni–Mo–PGE–Au mineralization thought to have formed by seawater scavenging; and (6) LoukolaRuskeeniemi et al. document geochemical evidence, based on new drillcore data, to explain hydrothermal sulfur in the Paleoproterozoic black-shales of the Talvivaara Ni–Cu–Zn–Mn deposit, Finland. The final paper of this special issue applies our current understanding of hydrothermal Ni mobilization and concentration to practical Ni targeting on a regional scale: (7) Lisitsin et al. apply a fuzzylogic-based mathematical model to mineral prospectivity modeling to map the potential of hydrothermal-remobilized Ni in western Victoria, Australia, in a geographical information system environment. These stochastic methodologies are based on integrating the probability of occurrence of individual components of a targeted mineral system based on empirical and/or conceptual models to derive the overall probability of occurrence of mineral deposits (e.g., GonzálezÁlvarez et al., 2010; Porwal et al., 2010). Developing a good understanding of geological processes involved in mineralization, at different scales of space and time, is critical for efficient mineral exploration, and also for understanding metal mobility in the Earth's crust (Kerrich et al., 2005; Hronsky and Groves, 2008; Pirajno, 2009; McCuaig et al., 2010). Key objective of this special issue is to draw the attention of the geological community to the intriguing but poorly understood, hydrothermal Ni systems. A new empiricalstochastic model is required to gain a deeper insight into these systems, which is necessarily not only from an economic point of view, but also for understanding the metal mobilization in general. Acknowledgments The Guest Editors of this special issue would like to express their gratitude to Nigel Cook for his insights and support as Chief Editor, as well as to Alok Porwal and Rob Hough for their critical reviews of this introduction, and to the following reviewers, which have generously given their time and contributed with their scientific expertise to ensure the high quality of the papers in this issue. In alphabetical order the reviewers are: Doreen Ames, Steve Barnes, John Carranza, Raymond Coveney, Paul Duuring, Isabel Fanlo, Marco Fiorentini, Ahmed Hassan Ahmed, Murray W. Hitzman, Dean Hoatson, Jon Hronsky, Simon Jowitt, John Lydon, Euan Nisbet, John Slack, Svetlana Tessalina
3
and Martin Wells. We thank Minerals Down Under Flagship and in particular the Discovery Theme within CSIRO for its support in the making of this Special Issue. References Baglow, N., 1986. The Epoch nickel deposit, Zimbabwe. In: Anhaeusser, C.R., Maske, S. (Eds.), Mineral Deposits of South Africa. Geological Society of South Africa, pp. 255–262. Buchkovskiy, E.S., 1970. Sulfide mineralization associated with ultramafic intrusions of the western limb of the Magnitogorskiy megasinclinorium, South Urals. Geol., Min. and Geochem. of Sulfide Deposits in the South Urals: Proceedings of the Ins. Geol. Bashkirian, AS USSR, pp. 114–125 (in Russian). Coveney Jr., R.M., Nansheng, C., 1991. Ni–Mo–PGE–Au-rich ores in Chinese black shales and speculations on possible analogues in the United States. Miner. Deposita 26 (2), 83–88. Davies, H.L., 1969. Notes on Papuan ultramafic belt mineral prospects, territory of Papua New Guinea. Bureau of Mineral Resources, Geology and Geophysics 1969/67. (13 pp.). Ervamaa, P., Heino, T., 1980. A progress report on ore prospecting in the Kainuu-North Savo black shale — serpentinite units in 1977–1979. Geological Survey of Finland. Unpublished report M19/3344/-80/1/10, 73 p. (in Finish). González-Álvarez, I., Porwal, A., Beresford, S.W., McCuaig, T.C., Maier, W.D., 2010. Hydrothermal Ni prospectivity analysis of Tasmania, Australia. Ore Geol. Rev. 38, 168–183. González-Álvarez, I., Sweetapple, M., Lindley, D., Kirakar, J., 2013. Hydrothermal Ni: Doriri Creek, Papua New Guinea. Ore Geology Reviews 52, 37–57 (this issue). Greenwood, P.F., Brocks, J.J., Grice, K., Schwark, L., Jaraula, C.M.B., Dick, J.M., Evans, K.A., 2012. Organic geochemistry and mineralogy: I. Characterisation of organic matter associated with metal deposits. Ore Geology Reviews. http://dx.doi.org/10.1016/ j.oregeorev.2012.10.004. Hronsky, J.M.A., Groves, D.I., 2008. Science of targeting: definition, strategies, targeting and performance measurement. Aust. J. Earth Sci. 55, 3–12. Keays, R.R., Jowitt, S.M., 2013. The Avebury Ni deposit, Tasmania; a case study of an unconventional Nickel deposit. Ore Geology Reviews 52, 4–17 (this issue). Keays, R.R., Jowitt, S.M., Callaghan, T., 2009. The Avebury Ni deposit, Tasmania: a case study of anunconventional Nickel deposit. In: Williams, P.J. (Ed.), Smart Science for Exploration and Mining: Proceedings of the Tenth Biennial SGA Meeting. Economic Geology Research Unit, Townsville, pp. 173–175. Kerrich, R., Goldfard, R.J., Richards, J.P., 2005. Metallogenic provinces in an evolving geodynamic framework. Society of Economic Geologists, Inc. Economic Geology 100th Anniversary Volume 1097–1136. Lehmann, B., Nägler, T.F., Holland, H.D., Wille, M., Mao, J.W., Pan, J.Y., Ma, D.S., Dulski, P., 2007. Highly metalliferous carbonaceous shale and Early Cambrian seawater. Geology 35, 403–406. Lindley, I.D., Kirakar, J.K., 2007. Hydrothermal alteration patterns in the Doriri Creek Pd–Pt–Ni Prospect, EL 1424 Mt Suckling, Northern Province. Papuan Precious Metals Internal Report (24 pp.). Liu, W., Migdisov, A., Williams-Jones, A., 2012. The stability of aqueous nickel(II) chloride complexes in hydrothermal solutions: results of UV–visible spectroscopic experiments. Geochim. Cosmochim. Acta 94, 276–290. Loukola-Ruskeeniemi, K., Heino, T., 1996. Geochemistry and genesis of the black shalehosted Ni–Cu–Zn deposit at Talvivaara, Finland. Econ. Geol. 91, 80–110. Loukola-Ruskeeniemi, K., Lahtinen, H., 2013. Multiphase evolution in the black-shalehosted Ni–Cu–Zn–Co deposit at Talvivaara, Finland. Ore Geology Reviews 52, 85–99 (this issue). McCuaig, T.C., Beresford, S., Hronsky, J., 2010. Translating the mineral systems approach into an effective exploration targeting system. Ore Geol. Rev. 38, 128–138. Melekestseva, I.Yu., 2005. The first discovery of alloclasite at the Urals. Dokl. Earth Sci. 400, 239–242. Melekestseva, I.Yu., Zaykov, V.V., Nimis, P., Tret'yakov, G.A., Tessalina, S.G., 2013. Cu–(Ni–Co–Au)-bearing massive sulfide deposits associated with mafic–ultramafic rocks of the Main Urals Fault, South Urals: Geological structures, ore textural and mineralogical features, comparison with modern analogs. Ore Geology Reviews 52, 18–36 (this issue). Pirajno, F., González-Álvarez, I., 2013. A re-appraisal of the Epoch nickel sulphide deposit, Filabusi Greenstone Belt, Zimbabwe: A hydrothermal nickel mineral system? Ore Geology Reviews 52, 58–65 (this issue). Pirajno, F., 1971. Geology, petrology and mineralisation of the Epoch nickel claims, Rhodesia. Unpublished internal report, Prospecting Ventures Ltd. Pirajno, F., 2009. Hydrothermal Processes and Mineral Systems. Springer, Berlin, Germany. (1250 pp.). Porwal, A., González-Álvarez, I., Markwitz, V., McCuaig, T.C., Mamuse, A., 2010. Weights-of-evidence and logistic regression modeling of magmatic nickel sulfide prospectivity in the Yilgarn Craton, Western Australia. Ore Geol. Rev. 38, 184–196. Xu, L.G., Lehmanna, B., Mao, J.W., Qu, W.J., Du, A.D., 2011. Re–Os age of polymetallic Ni– Mo–PGE–Au mineralization in Early Cambrian black shales of South China — a reassessment. Econ. Geol. 106, 511–522. Xu, L.G., Lehmanna, B., Jingwen, M., 2013. Seawater contribution to polymetallic Ni– Mo–PGE–Au mineralization in Early 2 Cambrian black shales of South China: Evidence from Mo isotope, PGE, trace element, 3 and REE geochemistry. Ore Geology Reviews 52, 66–84 (this issue).
Contents lists available at SciVerse ScienceDirect
Ore Geology Reviews journal homepage: www.elsevier.com/locate/oregeorev
Editorial
Hydrothermal nickel deposits: Secular variation and diversity I. González-Álvarez a, b,⁎, F. Pirajno b, d, R. Kerrich c a
CSIRO, Earth Science and Resource Engineering, Minerals Down Under Flagship, Discovery Theme, Kensington, Western Australia 6151, Australia Centre for Exploration Targeting, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia c Department of Geological Sciences, University of Saskatchewan, 112 Science Place, SK, Canada S7N 5E2 d Geological Survey of Western Australia, 100 Plain Street, East Perth, WA 6004, Australia b
a r t i c l e
i n f o
Article history: Received 18 November 2012 Received in revised form 27 November 2012 Accepted 27 November 2012 Available online 5 December 2012 Keywords: Trace element mobility Mineral systems Mineral exploration Hydrothermal systems Hydrothermal Ni
a b s t r a c t Hydrothermal nickel systems are one of the most puzzling mineral systems that involve trace element mobility in the Earth’s crust. Nickel is an abundant element in the crust. However, the processes that are involved in its mobility and accumulation at ore scale are challenging. A new empirical-stochastic model is required to gain a deeper insight into these systems. This Special Issue presents several studies on hydrothermal nickel accumulations world wide aiming to stimulate the debate on this intriguing deposit type. © 2012 Elsevier B.V. All rights reserved.
Hydrothermal systems, activated by tectonic and/or magmatic events, result in extensive mobilization and fractionation of trace element in the Earth's crust. However, within this framework, hydrothermal Ni systems are deeply puzzling and poorly understood. Nickel is an abundant element in the crust at 47 ppm (2000 ppm in ultramafic rocks), and evidences of its mobility in fluids are observed in many settings and mineral deposits, notably in unconformityrelated U deposits. However, the Ni mobility in hydrothermal fluids is poorly understood, in part due to the limited number of occurrences and/or deposits reported. Moreover, other types of mineral deposits are largely confined to very specific geological settings and time clusters, hydrothermal Ni systems are generally independent of geological time and tectonic setting. It is challenging to identify hydrothermal Ni systems, largely because they are characterized by ambiguous features that could mimic other ore forming processes, such as ore mineral paragenesis and alteration mineral assemblages. Since the milestone discovery in 1997 of the Avebury deposit in Tasmania, with 0.26 Mt Ni metal, more attention has been focused on this deposit type, contributing to additional Ni resources being identified as hydrothermal type, notably Enterprise, Zambia, and Doriri Creek, PNG. Some of the most perplexing questions related to hydrothermal Ni mineral systems relate to controls on the solubility of Ni in different ⁎ Corresponding author at: CSIRO, Earth Science and Resource Engineering, Minerals Down Under Flagship, Discovery Theme, Kensington 6151, Western Australia, Australia. Tel.: +61 8 6436 8687; fax: +61 8 6488 1178. E-mail address: [email protected] (I. González-Álvarez). 0169-1368/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.oregeorev.2012.11.006
environments at low temperature, and the diversity of potential ligands, which are different from its chemical neighbors (e.g., Cu, Co). Recent studies underline these solubility-ligands queries. Liu et al. (2012) in their study of Ni solubility in hydrothermal systems reported a lower solubility of nickel sulfides (NiS) compared to equivalent Co sulfide minerals. These experimental results partially explain the rarity of hydrothermal Ni deposits in comparison with Co counterparts exemplified by sandstone-hosted Cu–Co deposits. As a corollary, because Ni can be mobilized in a large variety of environments by diverse ligands, and or particularly at low temperatures (b250 °C), there remains the potential for discovery of new classes of hydrothermal Ni deposits. The general idea that hydrothermal NiS deposits are rare because they are residual owing to their resistance to mobilization, does not satisfactorily explain some of the conditions of the hydrothermal Ni systems in sedimentary sequences such as the Nick horizon, Canada, or Enterprise, Zambia, where the Ni accumulation are not easy to explain as the result of residual leaching. Organic ligands (Greenwood et al., 2012) and basinal brine chemistry could have the appropriate combination of chemical features as well as ligands to promote Ni mobility at low temperatures, fractionating it from Co and Cu. This leads to another intriguing question on hydrothermal Ni systems: how far are the fluids able to carry Ni in solution from the Ni source/s? Because of the lack of proper understanding of Ni mobilization, the conceptual-model-driven exploration for magmatic NiS deposits may have had a reductionist, deterministic effect, thereby hindering the discovery of hydrothermal Ni deposits. At the same time, reassessment of some NiS deposits post-mining poses new questions, often leading to
2
Table 1 Hydrothermal Ni deposits presented in this Special Issue. Craton/ terrane
Age
Deposit/prospect
Ore
Alteration assemblage
Metal budget
Ultramafic schist
Epoch
Pyrite, millerite, bravoite, and minor chalcopyrite and pentlandite.
Peridotite and dunite cumulate suites
Avebury
Pentlandite with minor pyrrhotite.
talc-carbonate rocks that also contain dolomite, chlorite and magnesite Talc–serpentinite and clinopyroxene– amphibole skarn units
Doriri Creek
Amphibole and Chlorite and serpentine group chlorite–serpentine minerals in addition to Fe oxides, with a minor amount in group minerals pentlandite
Peridotites/ pyroxenites within a high MgO, noritic gabbro envelope North Karelia Paleoproterozoic Black schist schist belt, Finland
South China, Yangtze Platform
Early Cambrian
East European Devonian platform suture with the Uralides, Russia
Ni Mt
Status
Comments
Ni ⋙Cu 5.61 at 0.67%
Mined
No cumulate textures; no PGE; dominant oxide mineral is magnetite
Ni ⋙Cu 29.3 at 0.9%
Ceased production, in maintenance
Ni ⋙Cu ??? at 2.43% maximum
Exploration assessment
Quartz, micas, Ni > Cu 1550 at 0.22% graphite and sulfides, with rutile, apatite, zircon, feldspar, tourmaline garnet, uraninite, thucholite and Ni ⋙Cu ??? at Ni + Mo Black shales Maluhe deposit, Sancha, MoSC, pyrite, vaesite, bravoite, Organic matter, reaching up to fine-grained illite, Wangjiazhai, Ganziping, millerite, gersdorffite, and 14 wt.% sericite, quartz, calChuanyanping, Houping, jordisite, with minor cite, barite, and loLangxi, Daping, Xiaoping arsenopyrite, chalcopyrite, covellite, sphalerite, tennantite, cally abundant and the Cili deposits tiemannite, violarite, and native apatite and among others collophane Au Ishkinino, Ivanovka, Chalcopyrite–pyrite–pyrrhotite Talc–carbonate and Ni b Cu 2 Mt Dergamysh Mafic– Dergamysh and Co–Ni–sulfarsenide–sulfide chlorite deposit; 1.11 Mt ultramafic Ishkinino deposit; (dunitic and harzburgitic and 24 Mt for the lithologies) Ivanovka deposit at 0.1–0.49 wt.% Talvivaara
Pentlandite as inclusions in pyrrhotite, pyrite, pyrrhotite, sphalerite and chalcopyrite
References
Pirajno (1971), Baglow (1986) and Pirajno and Gonzalez-Alvarez (2013–this issue) Keays et al. (2009) Negative or absent correlations between Pt, Ir, Ru and Keays and Jowitt (2013–this issue) and Rh with Ni
Pd and Pt concentration together with apatite; enrichments of U, K and W
Fractured talc-carbonate rocks Producing and resource delineate the eastern border of the deposit; Minor occurevaluation rences of peridotite, serpentinite and talccarbonate rocks occur in the area Many deposits in production
Ni–Mo–PGE–Au sulfide ore layer enriched in organic and phosphatic materials; enriched in Se, Re, Os, As, Hg, and Sb (>104 times average continental crust)
Exploration and/or resource estimation
Associated to ophiolite complex; Pervasive serpentinization of peridotites and localized hydrous and carbonate alteration of mafic rocks under up to greenschist facies
Davies (1969), Lindley and Kirakar (2007) and González-Álvarez et al. (2013–this issue)
Ervamaa and Heino (1980), Loukola-Ruskeeniemi and Heino (1996) and Loukola-Ruskeeniemi and Lahtinen (2013–this issue) Coveney and Nansheng (1991), Lehmann et al. (2007), Xu et al. (2011) and Xu et al. (2013–this issue) Buchkovskiy (1970), Melekestseva (2005) and Melekestseva et al. (2013–this issue)
Ore Geology Reviews 52 (2013) 1–3
Neoproterozoic Zimbabwe, Filabusi Greenstone belt Late Devonian Tasmania, eastern margin of the Dundas Trough Cainozoic (?) Papuan Ultramafic Belt, PNG
Host lithology
Ore Geology Reviews 52 (2013) 1–3
difficult challenges to the review of the original ideas on the nature of the deposit mined. In the above context, this Special Issue aims to contribute to developing a better understanding of hydrothermal Ni mineral systems by compiling and discussing some key examples of this deposit type (Table 1). The first part of this Special Issue deals with case study deposits associated with mafic–ultramafic suites: (1) Keys and Jowitt present novel geochemical data and exploration history of the Cambrian ultramafic peridotite hosted Avebury deposit in Tasmania, Australia; (2) Melekestseva et al. document the characteristics of several Ni– Co-bearing hydrothermal massive sulfide deposits associated with ultramafic–mafic rock suites in the Urals, Russia; and (3) GonzálezÁlvarez et al. report an intriguing case of hydrothermal Ni accumulation in the Cenozoic(?) Papuan Ultramafic Belt, which poses critical questions for the exploration approach for this deposit type. Following these case studies, (4) Pirajno and González-Álvarez re-appraise the Epoch Ni deposit, Zimbabwe, for the possibility of re-classifying what was previously considered a magmatic NiS deposit as being the result of mainly hydrothermal activity. The second part of this issue examines hydrothermal Ni accumulations, not associated with mafic–ultramafic rock suites, but within sedimentary sequences: (5) Xu et al. discuss Cambrian black shales of South China which host polymetallic Ni–Mo–PGE–Au mineralization thought to have formed by seawater scavenging; and (6) LoukolaRuskeeniemi et al. document geochemical evidence, based on new drillcore data, to explain hydrothermal sulfur in the Paleoproterozoic black-shales of the Talvivaara Ni–Cu–Zn–Mn deposit, Finland. The final paper of this special issue applies our current understanding of hydrothermal Ni mobilization and concentration to practical Ni targeting on a regional scale: (7) Lisitsin et al. apply a fuzzylogic-based mathematical model to mineral prospectivity modeling to map the potential of hydrothermal-remobilized Ni in western Victoria, Australia, in a geographical information system environment. These stochastic methodologies are based on integrating the probability of occurrence of individual components of a targeted mineral system based on empirical and/or conceptual models to derive the overall probability of occurrence of mineral deposits (e.g., GonzálezÁlvarez et al., 2010; Porwal et al., 2010). Developing a good understanding of geological processes involved in mineralization, at different scales of space and time, is critical for efficient mineral exploration, and also for understanding metal mobility in the Earth's crust (Kerrich et al., 2005; Hronsky and Groves, 2008; Pirajno, 2009; McCuaig et al., 2010). Key objective of this special issue is to draw the attention of the geological community to the intriguing but poorly understood, hydrothermal Ni systems. A new empiricalstochastic model is required to gain a deeper insight into these systems, which is necessarily not only from an economic point of view, but also for understanding the metal mobilization in general. Acknowledgments The Guest Editors of this special issue would like to express their gratitude to Nigel Cook for his insights and support as Chief Editor, as well as to Alok Porwal and Rob Hough for their critical reviews of this introduction, and to the following reviewers, which have generously given their time and contributed with their scientific expertise to ensure the high quality of the papers in this issue. In alphabetical order the reviewers are: Doreen Ames, Steve Barnes, John Carranza, Raymond Coveney, Paul Duuring, Isabel Fanlo, Marco Fiorentini, Ahmed Hassan Ahmed, Murray W. Hitzman, Dean Hoatson, Jon Hronsky, Simon Jowitt, John Lydon, Euan Nisbet, John Slack, Svetlana Tessalina
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and Martin Wells. We thank Minerals Down Under Flagship and in particular the Discovery Theme within CSIRO for its support in the making of this Special Issue. References Baglow, N., 1986. The Epoch nickel deposit, Zimbabwe. In: Anhaeusser, C.R., Maske, S. (Eds.), Mineral Deposits of South Africa. Geological Society of South Africa, pp. 255–262. Buchkovskiy, E.S., 1970. Sulfide mineralization associated with ultramafic intrusions of the western limb of the Magnitogorskiy megasinclinorium, South Urals. Geol., Min. and Geochem. of Sulfide Deposits in the South Urals: Proceedings of the Ins. Geol. Bashkirian, AS USSR, pp. 114–125 (in Russian). Coveney Jr., R.M., Nansheng, C., 1991. Ni–Mo–PGE–Au-rich ores in Chinese black shales and speculations on possible analogues in the United States. Miner. Deposita 26 (2), 83–88. Davies, H.L., 1969. Notes on Papuan ultramafic belt mineral prospects, territory of Papua New Guinea. Bureau of Mineral Resources, Geology and Geophysics 1969/67. (13 pp.). 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