Guest Editor
Prof. Dr. Michael Meyer
Institute of Mineralogy and Economic Geology, RWTH Aachen University, Wüllnerstrasse 2, 52056 Aachen, Germany
Website: http://www.emr.rwth-aachen.de/aw/EMR/Energy_Mineral_Resources/Zielgruppen/iml/Mitarbeiter/mitglieder/Mitarbeiter/~wby/michael_meyer/?lang=en
E-Mail: m.meyer@rwth-aachen.de
Phone: +49 241 80 95774
Fax: +49 241 80 92153
Interests: economic geology; geometallurgy of high-tech metals; mineralogy and geochemistry of hydrothermal systems; ore petrology

Dear Colleagues,

Recent concern about available resources for rare and scarce commodities has led to the concept of criticality of ore minerals and associated metals. The two central dimensions of criticality are importance in use and availability. Critical minerals and metals (e.g., Sb, In, Be, Nb, PGM, Ga, REE, Ge, Ta, etc) are thus defined by the risks for supply shortage and their impacts on emerging technologies. Availability reflects firstly considerations on distribution and abundance of critical minerals and secondly knowledge of efficient extraction and processing methods. The purpose of this special issue “Advances in Economic Minerals” is to publish recent research that focuses on sulphide and oxide ore mineralogy and mineral chemistry as well as mineral technology. The special issue will highlight recent advances in both fundamental and applied studies across a wide range of areas involved in the formation of ore-grade concentrations of critical minerals, as well as the application of mineralogical and geochemical methods to exploration, ore dressing, and waste management.

Prof. Dr. Michael Meyer
Guest Editor

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• ore mineralogy
• mineral chemistry
• high-tech metals
• geometallurgy
• ore deposits

Title: High and Low Temperature Gold Mineralizations in the Fe-Cu-Zn Sulphide Deposits of Corchia Ophiolite, Northern Italian Apennine
Authors: Federica Zaccarini and Giorgio Garuti
Affiliation: Department of Applied Geosciences and Geophysics, University of Leoben, Peter Tunner-Str. 5, A-8700 Leoben, Austria; E-Mail: Federica.Zaccarini@unileoben.ac.at
Abstract: In this work we report on two different styles of gold mineralizations recently discovered in the volcanogenic massive sulphides (VMS) of the Corchia ophiolite located in the northern Italian Apennine. The Corchia ophiolite consists of an allochtonous block of about 1.5 X 3.5 km in size. It belongs to the so called External Ligurides units, that are remnant of the oceanic lithosphere of the Jurassic Ligurian Tethys. The Corchia ophiolite is composed of serpentinite and pillow lava embedded in a sedimentary mélange of Calpionella limestone and Palombini shale. Small body of granitic rocks are in tectonic contact with the Corchia ophiolitic rocks. The investigated gold mineralizations occur in different mines, that have been exploited in the past: Donnini, Cantiere Speranza and Pozzo. The ore bodies in Donnini and Cantiere Speranza form irregular lens of massive sulphides, composed of pyrite, chalcopyrite with minor sphalerite. They show a detrital texture in which fragments of sulphides occur in a matrix composed of quartz, calcite, chlorite and clay minerals. These sulphide mineralizations formed in the ancient sea floor, and it represents the equivalent fossil of the present-day black smokers. Shells of microfossils replaced by sulfide have been observed. Their sulphur isotope composition (ä¹⁴S°/_°°), obtained on separated sulphides varies in the following: pyrite = 0.9–4.4 (av. 2.9), chalcopyrite = −2.4–5.8 (av. 0.3), sphalerite = 0–5.3 (av. 3.4).  In these mines, gold occurs as rare and tiny grains (less than 10 µm) in the gangue of the massive sulphides. According to its composition (Au > 80 at%) it can be classified as pure gold. The Pozzo mine is located few km far from the Donnini and Cantiere Speranza mine. In this area, the mineralization consists of a lens of massive sulphides with a thikness up to 1.5 m and with a lateral extension of several ten meters. It is hosted in a block of strongly serpentinized peridotite, in contact with a mélange of sedimentary rocks. The main ore minerals are pyrite, chalcopyrite and magnetite, accompanied by minor siegenite, sphalerite and molibdenite. The matrix is composed of serpentine, talc, chlorite and minor Ca-Mg carbonates, whereas quartz is absent. The values of ä¹⁴S°/_°° ranges from 0.4–1.4 (av. 0.7) and 0.5–0.9 (av. 0.7) in pyrite and chalcopyrite, respectively. At Pozzo the gold minerals are very abundant (up to more than 50 grains in one single sections of about 2 square cm). They have a size comprised between 1 and 50 µm and occur, in most cases, included in chalcopyrite or pyrite. Gold forms single phase or polyphasic grains, associated with magnetite, sphalerite and chlorite. The Pozzo gold minerals contain appreciable concentration of Ag, and they can be classified as electrum. On the basis of geological, mineralogical and geochemical observations, Gold in the Donnini and Cantiere Speranza mines formed at low temperature in a sea-floor environment by loss of Ag during submarine weathering, in a way similar to that described for weathered gold nuggets in terrestrial placers and laterite hosted gold deposits. As a consequence, the weathering process was one of the major factor controlling the concentration of gold in this mine. The Pozzo mine represents the metamorphic product of an enigmatic magmatic sulfide mineralization, formed at high temperature in the mantle. Therefore, the crystallization of gold in this mine started at high temperature, possibly during the formation of an immiscible sulfide liquid. The effects on the gold minerals produced by the metamorphic overprint are still not understood and need further investigation.

Type of Paper: Article
Title: Magmatic Origin and Low Temperature Evolution of Platinum Group Minerals (PGM) in Stratiform Chromitites of the Niquelandia Complex, Brazil
Authors: Garuti Giorgio ¹, Federica Zaccarini ¹, Oskar Thalhammer ¹, Joaquin Proenza ² and Nelson Angeli ³
Affiliations: ¹ Department of Applied Geological Sciences, University of Leoben, 8700 Leoben, Austria; E-Mail: giorgio.garuti@unileoben.ac.at
² Departament de Cristallografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, Martí i Franquès s/n, Barcelona 08028, Spain; E-Mail: japroenza@ub.edu
³ Department of Petrology and Metallogeny, University of São Paulo State(UNESP), 24-A Avenue, 1515, Rio Claro (SP) 13506-710, Brazil; E-Mail: nangeli@rc.unesp.br
Abstract: The Niquelandia layered intrusion was emplaced in the Middle Proterozoic (1560–1600 Ma) as a result of continental rifting, and underwent amphibolite to granulite facies metamorphism at about
770–795 Ma. Chromitite layering occurs at two stratigraphic levels located in the ultramafic zone, at about 1 and 2 km from the base respectively. Two distinct population of PGM have been recognized in the Niquelandia chromitites: (1) primary, i.e., formed at magmatic temperature and (2) secondary, i.e., altered and reworked at low temperature during the metamorphic post magmatic evolution of the Niquelandia complex. The origin and the significance of the primary and secondary PGM are discussed.

Type of Paper: Article
Title: Geology and Age Constraints on the Origin of the Intrusion-Related, Sheeted Vein-Type Gold Deposit at Åkerberg, Skellefte District, Sweden
Author: Kjell Billström, Benny Mattson, Ulf Söderlund, Hans Årebäck, Curt Broman and Ingmar Lundström
Affiliation: Laboratory for Isotope Geology, Swedish Museum of Natural History, Box 50007, Stockholm SE-104 05, Sweden; E-Mail: kjell.billstrom@nrm.se
Abstract: The Åkerberg gold ore, located in the Skellefte district in northern Sweden, represents an unusual mineralisation given the noted lack of alteration, a scarcity of sulphides and gold associated with thin (mm-cm scale) parallel quartz veins hosted in a 1.88 Ga gabbro. The ore constitutes a sheeted vein complex which developed in dilational zones, and the veins are due to mechanical rupturing when a granodioritic magma intruded the competent gabbro. Unmixing of the felsic magma also produced pegmatite bodies and a gel-like melt which invaded fractures in the gabbro and deposited silica. The Åkerberg ore is classified as an intrusion-related style of gold mineralisation.

Type of Paper: Article
Title: Indium-Carrier Minerals in Polymetallic Sulfide Ore Deposits: A Crystal Chemical Insight to Indium Binding State Supported by X-ray Absorption Spectroscopy Data
Authors: Maria-Ondina Figueiredo, Teresa Pereira da Silva, Daniel de Oliveira and Diogo Rosa
Affiliation: Laboratório Nacional de Energia e Geologia, Unidade de Investigação de Recursos Minerais e Geofísica, Apartado 7586, 2721-866 Alfragide, Portugal; E-Mails: ondina.figueiredo@lneg.pt (M.F.); teresa.pena@lneg.pt (T.P.S.); daniel.oliveira@lneg.pt (D.O.)
Abstract: Indium is a typical chalcophile element with a very low average content in the Earth's crust seldom forming specific minerals and occurring mainly dispersed in polymetallic sulphides. Being a strategic metal for usual technologic fields (e.g. low melting-temperature alloys and solders) and for many innovative nano-technologies, an increase in indium demand is still expected within next years, focusing a special interest in promising polymetallic sulphide ore deposits like the Iberian Pyrite Belt (IPB). Indium recovery stands mostly on zinc extraction from sphalerite, the prototype of so-called tetrahedral sulphides where metal ions fill half of the available tetrahedral sites within the cubic closest packing of sulphur anions, leaving interstices accessible for further in-filling. Ascertaining the tendency towards the establishment of In-In interactions through X-ray absorption spectroscopy efficiently contributes to understand the behaviour of indium in the carrier mineral. The successful results of applying such absorption study (XANES) at the In L₃-edge to ore samples from the Lagoa Salgada IPB deposit are described and the crystal chemistry of indium is re-evaluated, disclosing a challenging clue for the metal binding state in polymetallic sulphides.

Type of Paper: Review
Title: Albitite-Type Uranium Deposits: A Review
Author: Andy Wilde
Affiliation: School of Geosciences, Monash University, PO Box 28E, Melbourne, VIC 3800, Australia; E-Mail: andy.wilde@paladinenergy.com.au
Abstract: The albitite-type (aka metasomatite-type) uranium deposit group collectively contains as much uranium as the unconformity-type group, although grade is lower. Production is currently limited to deposits in the Kirovograd-Krivoi Rog district of the Ukraine and the Lagoa Real deposits in Brazil. The deposits are located in Proterozoic, rocks often adjacent to deep-penetrating faults and large-scale synclinal axes. Host terranes range from those dominated by high grade metamorphic rocks, such as gneiss and migmatite to those dominated by greenschist- to amphibolites facies
meta-volcanic and sedimentary rocks. Uranium occurs in a wide range of albitized rocks and shows no preference for specific host-rocks. Thus chemical interaction of the ore-forming fluids and host-rock appears not to have been a critical factor in ore formation. The varying responses of the host rock package to deformation at, or close to the brittle/ductile transition are thought to be more significant. Uranium minerals include coffinite, uraninite and various U-Ti and U-Zr phases. Gangue minerals include fluorapatite, Ca- and Mg-rich carbonate minerals, riebeckite, aegirine, calcic garnet, magnetite, hematite and hydrothermal zircon. Uranium abundance correlates with a suite of high field strength elements including REE, Nb, Hf and Ta. Genesis involving F-rich gases derived from an alkaline suite of subjacent intrusions is suggested by the mineralogy of the deposits and numerous experimental studies. A genetic link between IOCG and albitite-type uranium has been previously mooted, but remains unconfirmed. More research is required to clarify many aspects of this enigmatic group of deposits.

Type of Paper: Article
Title: Composition and Distribution of Eudialyte-Group Minerals from the Norra Kärr Alkaline Complex, Southern Sweden
Authors: Axel S.L. Sjöqvist ^1,*, David H. Cornell ¹, Tom Andersen ², Muriel Erambert ², Mattias Ek ¹ and Magnus Leijd ³
Affiliations: ¹ Department of Earth Sciences, University of Gothenburg, PO Box 460, SE-405 30 Göteborg, Sweden; E-Mails: axel@student.gu.se (A.S.); cornell@gvc.gu.se (D.C.); mattias.ek@student.gu.se (M.E.)
² Department of Geosciences, University of Oslo, PO Box 1047 Blindern, N-0316 Oslo, Norway; E-Mails: tom.andersen@geo.uio.no (T.A.); m.m.l.erambert@geo.uio.no (M.Er.)
³ Tasman Metals Ltd., Skiftesvägen 14, SE-563 31 Gränna, Sweden; E-Mail: magnus.leijd@tasmanmetals.se (M.L.)
*Author to whom correspondence should be addressed; E-Mail: axel@student.gu.se
Abstract: The agpaitic nepheline syenites in the Norra Kärr Alkaline Complex, southern Sweden, host high concentrations of inter alia zirconium and rare earth elements (REE), which are mainly accommodated in eudialyte-group minerals (EGM). Here we compare SEM-EDS, WDS-EMPA, and LA-ICP-MS analyses of eudialyte-group minerals and trace-element whole-rock analyses from different units of the Norra Kärr Alkaline Complex. The whole-rock rare-earth signatures gradually change from the center of the intrusion and outwards from being light-rare-earth enriched to relatively richer in heavy-rare-earth elements, however the absolute concentrations decrease. This change in rare-earth signature is the result of a change in composition of the eudialyte-group minerals.

Type of Paper: Review
Title: Vein-Type Graphite Deposits: Geological Settings, Origin and Economic Significance
Authors: F.J. Luque, E. Crespo, J.F. Barrenechea and L. Ortega
Affiliation: Dpto. de Cristalografía y Mineralogía. Facultad de Ciencias Geológicas. Universidad complutense. c/ José Antonio Nováis n° 2. 28040-Madrid, Spain; E-Mail: jluque@geo.ucm.es (J.J.L.)
Abstract: Graphite deposits result from the metamorphism of sedimentary levels rich in carbonaceous matter or from deposition by carbon-bearing fluids. The latter are structurally-controlled and usually occur as veins cross-cutting granulites or igneous rocks. The origin of carbon, the mechanisms of transport and the factors controlling graphite deposition in these mineralizations are discussed in relation to their geological settings. Graphite in this kind of deposit is characterized by its high purity and crystallinity, thus providing a suitable mineral for applications in advanced technologies. In addition, recent discovery of natural graphite precipitation at moderate temperatures might provide an alternative method for the manufacture of highly crystalline synthetic graphite.

Type of Paper: Review
Title: Three Times W: Why, When and Where. Aspects of the Economic Significance of Oceanic Mineral Resources
Author: Krzysztof Szamalek
Affiliation: Faculty of Geology, Warsaw University, Warsaw PL-00681, Poland; E-Mail: kszamale@uw.edu.pl
Abstract: Oceanic mineral raw materials are, with the exception of deposits located in the deep lithosphere, the last reserve base of mineral commodities for world economy. Seabed minerals constitute a possible new source for mineral commodities. Marine mineral resources occur in the bedrocks beneath the ocean floor, the ocean floor itself, in the sea water and in the shallow, coastal zones. The perspective of their extraction is shaped by the following factors: 1. Geological; 2. Legal; 3. Technical; 4. Technological; 5. Environmental; 6. Economical. It appears that in spite of years of on-going research, mineral resources of seas and oceans are still known insufficiently. This applies in particular to polymetallic massive sulphides ores, Co-crusts, metalliferous clays or methane gas hydrates. The deposits of crude oil and gas in seas and oceans are still poorly known in the deeper parts of the oceans. Mineral researches of oceans are conducted by several countries (e.g., Russia, USA, France, Japan, Germany, South Korea, China, Poland); their activity is regulated and controlled by the International Seabed Authority. The perspective of marine minerals extraction is more imminent in rich, technological advanced countries; having access to the sea in itself is a factor of lesser importance. Underwater geological surveys are costly and can be undertaken only by countries which are characterized by either a strong economy and/ or willingness to conduct an active concession policy and close cooperation in managing of measured mineral reserves. What is the current stage of knowledge concerning the distribution/location, resources and reserves of marine minerals? What kind of limitations block the commencement of large scale mineral extraction from the deep-sea? What is the significance and value of metals present in Fe-Mn nodules, Co-rich crust, polymetallic massive sulphides and metalliferous sediments? Taking into account many factors, this paper aims at answering the above questions and discusses when extraction of oceanic mineral resources will be both possible and feasible.

Type of Paper: Article
Title: Major- and Trace-Element Compositions of Indicator Minerals that Occur as Macro- and Megacrysts, and of Xenoliths, from Kimberlites on the Northeastern Angola
Authors: Sandra E. Robles-Cruz ¹, Joan C. Melgarejo ¹, Salvador Galí ¹ and Monica Escayola ²
Affiliations: ¹ Department de Cristal•lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona, Martí i Franquès s/n, Barcelona, Catalonia 08028, Spain; E-Mails: sandra_robles@ub.edu (S.E.R.); sandrarobc@gmail.com (S.E.R.)
² CONICET-IDEAN Instituto de Estudios Andinos, Laboratorio de Tectónica Andina., Universidad de Buenos Aires, Buenos Aires, Capital Federal C1033AAJ, Argentina
Abstract: This study compares the major- and trace-element compositions of olivine, garnet, and clinopyroxene that occur as macro- and megacrysts (119 grains), with those derived from xenoliths (51 xenoliths) from six kimberlites on the Lucapa area, northeastern Angola: Tchiuzo, Anomaly 116, Catoca, Alto Cuilo-4, Alto Cuilo-63, and Cucumbi-79. The samples were analyzed using electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results suggest different paragenetic associations for these kimberlites in the Lucapa area. Compositional overlap in some of the macrocryst and xenolith samples indicates their xenocrystic origin. The xenocrystic composition is indicative of possible diamond presence. Geothermobarometrical calculations were carried out using EPMA data from xenoliths by applying the program PTEXL.XLT. Additional well calibrated single-clinopyroxene thermobaromether of Nimis and Taylor (2000) was also applied. Results indicate that the kimberlites experienced different equilibration conditions. Subsequent metasomatic enrichment events also support a hypothesis of different sources for the kimberlites. These findings contribute to a better understanding of the petrogenetic evolution of the kimberlites in northeastern Angola and have important implications for diamond exploration.
Keywords: Kimberlite; Angola; olivine; garnet; clinopyroxene; composition