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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Exploration Methods and Applications".

Deadline for manuscript submissions: closed (31 July 2016) | Viewed by 64712

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Prof. Dr. Maria Economou-Eliopoulos

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Faculty of Geology and Geoenvironment, University of Athens, Panepistimiopolis, 15784 Athens, Greece
Interests: geochemistry of ore deposits and ore-forming processes; mineralization of platinum-group elements (PGE); bio-mineralization; contamination of soil and water by heavy metals and metalloids; contamination of groundwater by Cr(VI)
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Dear Colleagues,

We are pleased to announce a Special Issue, "Mineral Deposit Genesis and Exploration", which focuses on the origin and exploration of mineral deposits, such as the chromite deposits hosted in opholite complexes and porphyry-Cu-Mo-Au±Pd±Pt systems, both deposit types related to mantle dynamics and tectonics, partial melting of the metasomatized mantle wedge, subduction, collision, and mantle-lithospheric slab interactions, suggesting the recycling of crustal materials.

The discovery of new platinum-group element (PGE) sources is a topic of research interest for many authors. Estimated Pd, Pt and Au potential for porphyry deposits is consistent with model calculations, demonstrating the capacity of aqueous vapor and brine to scavenge sufficient quantities of Pt and Pd, and could contribute to the global PGE production. The geotectonic environment may be a significant factor of the precious/base metal endowment in the parent magma, and the oxidized nature of parent magmas may facilitate the capacity for transporting sufficient Au and PGE, but critical requirements, controlling the potential of porphyry deposits, are still uncertain. Apart from the well-established origin of small size PGM, in nature and experimentally, the stability of PGE-minerals, during subsequent stages of their crystallization is unclear and may be of genetic and environmental significance. A significant enrichment in platinum-group elements is a salient feature of exclusively small chromite occurrences in numerous of ophiolite complexes, but further research on that type of PGE-mineralization is required.

Prof. Dr. Maria Economou-Eliopoulos
Guest Editor

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Keywords

Chromite
porphyry deposits
platinum-group elements (PGE)
PGE-minerals
geochemistry

Published Papers (8 papers)

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6867 KiB

Open AccessArticle

Fibrous Platinum-Group Minerals in “Floating Chromitites” from the Loma Larga Ni-Laterite Deposit, Dominican Republic

by Thomas Aiglsperger, Joaquín A. Proenza, Francisco Longo, Mercè Font-Bardia, Salvador Galí, Josep Roqué and Sandra Baurier-Aymat

Minerals 2016, 6(4), 126; https://doi.org/10.3390/min6040126 - 30 Nov 2016

Cited by 6 | Viewed by 4993

Abstract

This contribution reports on the observation of enigmatic fibrous platinum-group minerals (PGM) found within a chromitite body included in limonite (“floating chromitite”) from Ni-laterites in the Dominican Republic. Fibrous PGM have a Ru-Os-Ir-Fe dominated composition and are characterized by fibrous textures explained by grain-forming fibers which are significantly longer (1–5 µm) than they are wide (~100 nm). Back-scattered electron (BSE) images suggest that these nanofibers are platinum-group elements (PGE)-bearing and form <5 µm thick layers of bundles which are oriented orthogonal to grains’ surfaces. Trace amounts of Si are most likely associated with PGE-bearing nanofibers. One characteristic fibrous PGM was studied in detail: XRD analyses point to ruthenian hexaferrum. However, the unpolished fibrous PGM shows numerous complex textures on its surface which are suggestive for neoformation processes: (i) features suggesting growth of PGE-bearing nanofibers; (ii) occurrence of PGM nanoparticles within film material (biofilm?) associated with PGE-bearing nanofibers; (iii) a Si-rich and crater-like texture hosting PGM nanoparticles and an Ir-rich accumulation of irregular shape; (iv) complex PGM nanoparticles with ragged morphologies, resembling sponge spicules and (v) oval forms (<1 µm in diameter) with included PGM nanoparticles, similar to those observed in experiments with PGE-reducing bacteria. Fibrous PGM found in the limonite may have formed due to supergene (bio-)weathering of fibrous Mg-silicates which were incorporated into desulphurized laurite during stages of serpentinization. Full article

(This article belongs to the Special Issue Mineral Deposit Genesis and Exploration)

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Open AccessArticle

Genesis and Multi-Episodic Alteration of Zircon-Bearing Chromitites from the Ayios Stefanos Mine, Othris Massif, Greece: Assessment of an Unconventional Hypothesis on the Origin of Zircon in Ophiolitic Chromitites

by Argyrios Kapsiotis, Annie Ewing Rassios, Aspasia Antonelou and Evangelos Tzamos

Minerals 2016, 6(4), 124; https://doi.org/10.3390/min6040124 - 21 Nov 2016

Cited by 12 | Viewed by 6731

Abstract

Several small chromium (Cr) ore bodies are hosted within a unit of tectonically thinned dunite in the retired Ayios Stefanos mine of the western Othris ophiolite complex in Greece. Chromium ores consist of tectonically imprinted bodies of semi-massive to massive, podiform and lenticular chromitites composed of chromian spinel [Cr-spinel] with high Cr# [Cr/(Cr + Al) = 0.51–0.66] and Mg# [Mg/(Mg + Fe²⁺) = 0.58–0.76], low Fe³⁺# [Fe³⁺/(Fe³⁺ + Fe²⁺) ≤ 0.43] and low TiO₂ (≤0.21 wt %) content. This composition is characteristic of Cr-spinels in equilibrium with melts of intermediate affinity between island-arc tholeiites (IATs) and mid-ocean ridge basalts (MORBs). Several Cr-spinel crystals in these ores exhibit imperfect zones made up of spinel hosting oriented lamellae of Mg-silicates (mostly chlorite) locally overgrown by porous domains along grain boundaries and fractures. From the Cr-spinel core to the lamellae-rich rim Cr#, Mg# and Fe³⁺# generally increase (0.68–0.87, 0.78–0.88 and 0.55–0.80, respectively), whereas from the core or the spinel zones with oriented lamellae to the porous domains Mg# and Fe³⁺# generally decrease (0.45–0.74 and ≤0.51, correspondingly). The lamellae-rich rims formed at oxidizing conditions, whereas the porous rims resulted from a later reducing event. Several tiny (≤30 μm), subhedral to anhedral and elongated Zr-bearing silicate mineral grains were discovered mainly along open and healed fractures cutting Cr-spinel. Most of the Zr-bearing silicate minerals (30 out of 35 grains) were found in a chromitite boulder vastly intruded by a complex network of gabbroic dykes. The dominant Zr-bearing silicate phase is by far zircon displaying a homogeneous internal texture in cathodoluminescence (CL) images. Raman spectroscopy data indicate that zircons have experienced structural damage due to self-irradiation. Their trace-element contents suggest derivation from a plagioclase-bearing, low-SiO₂ intermediate to mafic source. Combined micro-textural and minerochemical data repeat the possibility of zircon derivation from limited volumes of high-T fluids emanating from the gabbroic intrusions. Once zircon is precipitated in cracks, it may be altered to Ca-rich Zr-bearing silicate phases (i.e., armstrongite, calciocatapleiite). Almost all zircons in these samples show evidence of gains in solvent compounds (CaO, Al₂O₃ and FeO) possibly due to re-equilibration with late deuteric fluids. Full article

(This article belongs to the Special Issue Mineral Deposit Genesis and Exploration)

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8774 KiB

Open AccessArticle

Mineralogy, Geochemistry and Fluid Inclusion Data from the Tumanpınarı Volcanic Rock-Hosted Fe-Mn-Ba Deposit, Balıkesir-Dursunbey, Turkey

by Ali Haydar Gultekin and Nurgul Balci

Minerals 2016, 6(4), 120; https://doi.org/10.3390/min6040120 - 04 Nov 2016

Cited by 4 | Viewed by 6439

Abstract

The Tumanpınarı mineralization is a volcanic rock-hosted epithermal Fe-Mn-Ba deposit located in the southwestern part of Dursunbey, Balıkesir, Turkey. The deposit constitutes one of the most important deposits of the Havran-Dursunbey metallogenic sub-province in which numerous Early Miocene Fe-Mn-Ba deposits are distributed. The ore occurs as open-space fillings in faults, fractures, and breccias in the andesite. Early hydrothermal activity was responsible for four types of hypogene alteration in decreasing intensity: silicification, sericitization, hematization and argillic alteration. The mineral assemblage includes pyrolusite, psilomelane, hematite, and barite as well as minor magnetite, manganite, poliannite, limonite, braunite, bixbyite, galena, pyrite, and goethite. Mineralogically, three ore types are recognized as pyrolusite + psilomelane + hematite + barite ore, pyrolusite + psilomelane + poliannite ore and barite + pyrolusite + psilomelane + hematite ore (barite-dominant ore). In addition to Fe, Mn and Ba, the ore contains substantial quantities of Pb, Zn, As. Chemically, the transition from fresh to altered rocks has little effect on the elemental levels for Si, Al, Fe, Ca, Mg, K, Rb, Sr and H₂O. The homogenization temperature of fluid inclusions hosted in the main stage quartz and barite ranged from 113 to 410 °C with salinities ranging from 0.4 to 14.9 eq. wt % NaCl, respectively. Overall, the available data suggest that the deposits formed as the result of the interaction of two aqueous fluids: a higher-salinity fluid (probably magmatic) and a dilute meteoric fluid. Full article

(This article belongs to the Special Issue Mineral Deposit Genesis and Exploration)

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6280 KiB

Open AccessArticle

Platinum-Group Minerals and Other Accessory Phases in Chromite Deposits of the Alapaevsk Ophiolite, Central Urals, Russia

by Federica Zaccarini, Evgeny Pushkarev, Giorgio Garuti and Igor Kazakov

Minerals 2016, 6(4), 108; https://doi.org/10.3390/min6040108 - 19 Oct 2016

Cited by 20 | Viewed by 6719

Abstract

An electron microprobe study has been carried out on platinum-group minerals, accessory phases, and chromite in several chromite deposits of the Alapaevsk ophiolite (Central Urals, Russia) namely the Bakanov Kluch, Kurmanovskoe, Lesnoe, 3-d Podyony Rudnik, Bol’shaya Kruglyshka, and Krest deposits. These deposits occur in partially to totally serpentinized peridotites. The microprobe data shows that the chromite composition varies from Cr-rich to Al-rich. Tiny platinum-group minerals (PGM), 1–10 µm in size, have been found in the chromitites. The most abundant PGM is laurite, accompanied by minor cuproiridsite and alloys in the system Os–Ir–Ru. A small grain (about 20 μm) was found in the interstitial serpentine of the Bakanov Kluch chromitite, and its calculated stoichiometry corresponds to (Ni,Fe)₅P. Olivine, occurring in the silicate matrix or included in fresh chromite, has a mantle-compatible composition in terms of major and minor elements. Several inclusions of amphibole, Na-rich phlogopite, and clinopyroxene have been identified. The bimodal Cr–Al composition of chromite probably corresponds to a vertical distribution in the ophiolite sequence, implying formation of Cr-rich chromitites in the deep mantle, and Al-rich chromitites close to the Moho-transition zone, in a supra-subduction setting. The presence of abundant hydrous silicate inclusions, such as amphibole and phlogopite, suggests that the Alapaevsk chromitites crystallized as a result of the interaction between a melt enriched in fluids and peridotites. Laurite and cuproiridsite are considered to be magmatic in origin, i.e., entrapped as solid phases during the crystallization of chromite at high temperatures. The sulfur fugacity was relatively high to allow the precipitation of Ir-bearing sulfides, but below the Os–OsS₂ buffer. The alloys in the system Os–Ir–Ru are classified as secondary PGM, i.e., formed at low temperature during the serpentinization process. The (Ni,Fe)₅P phase is the first occurrence of a Ni-phosphide in terrestrial samples. Its composition indicates that it may be a new mineral. However, the small size has, so far, prevented a crystallographic study to support this conclusion. Full article

(This article belongs to the Special Issue Mineral Deposit Genesis and Exploration)

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10957 KiB

Open AccessArticle

Bismoclite (BiOCl) in the San Francisco de los Andes Bi–Cu–Au Deposit, Argentina. First Occurrence of a Bismuth Oxychloride in a Magmatic–Hydrothermal Breccia Pipe and Its Usefulness as an Indicator Phase in Mineral Exploration

by Francisco J. Testa, David R. Cooke, Lejun Zhang and Graciela R. Mas

Minerals 2016, 6(3), 62; https://doi.org/10.3390/min6030062 - 28 Jun 2016

Cited by 7 | Viewed by 10559

Abstract

The rare bismuth oxychloride, bismoclite (BiOCl), has been identified in the weathered tourmaline–cemented, magmatic–hydrothermal breccia complex at the San Francisco de los Andes Bi–Cu–Au deposit, Argentina. A wide variety of supergene minerals were detected in the oxidized zone, but only preisingerite (Bi₃(AsO₄)₂O(OH)) is intimately associated with bismoclite. Bismuth arsenate is present either as minor accessory phases or as traces in bismoclite-rich samples. This is the first documented occurrence of bismoclite in a porphyry-related, and magmatic–hydrothermal breccia pipe deposit. Bismoclite is interpreted to have formed by weathering of hypogene bismuthinite (Bi₂S₃), which originally occurred with arsenopyrite to cement the breccias. These appear to have reacted with O₂- and HCl-bearing meteoric waters to produce pockets of supergene bismoclite–preisingerite assemblages. Bismoclite samples have been characterized by means of X-ray diffractometry (XRD), geochemistry, petrography, scanning electron microscopy (SEM), differential thermal analysis–thermogravimetry analysis (DTA–TGA) and infrared analysis (IR) providing useful insights and updated information regarding this rare bismuth oxychloride and associated arsenate mineral. The San Francisco de los Andes breccia complex shows similar geometry, morphology and internal organization as those found in traditional magmatic–hydrothermal breccias associated with Cu–Mo porphyry deposits. Bismoclite and preisingerite form due to the presence of hypogene Bi-bearing minerals followed by appropriate supergene conditions. These hypogene minerals commonly occur only as trace phases, or are entirely absent, in porphyry and related magmatic–hydrothermal breccia deposits. The scarcity of hypogene Bi–mineral phases in porphyry and related magmatic–hydrothermal breccia deposits is the main reason why bismoclite has not previously been reported in these types of deposits. The detection of bismoclite as a mineral phase in the oxidized zone of weathered deposits highlights hypogene Bi mineralization at depth, and associated metals. Bismoclite is an insoluble mineral of particular interest in those supergene profiles which have been completely leached out of distinctive, water-soluble phases, such as Cu sulfate minerals, which are diagnostic of Cu mineralization at depth. Consequently, bismoclite could potentially be the only indicator of hypogene and supergene mineralization in lower portions of a bismuth bearing ore deposit. Full article

(This article belongs to the Special Issue Mineral Deposit Genesis and Exploration)

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12154 KiB

Open AccessArticle

Geochemistry of Hydrothermal Alteration Associated with Cenozoic Intrusion-Hosted Cu-Pb-Zn Mineralization at Tavşanlı Area, Kütahya, NW Turkey

by Mustafa Kumral, Amr Abdelnasser and Murat Budakoglu

Minerals 2016, 6(1), 13; https://doi.org/10.3390/min6010013 - 17 Feb 2016

Cited by 10 | Viewed by 10827

Abstract

The Miocene magmatic intrusion in the Tavşanlı zone of the Kütahya-Bolkardağ Belt (KBB) in the northwestern region of Turkey is represented by the Eğrigöz granitoids. This paper studies the petrology and geochemistry of hydrothermal alterations associated with the vein-type Cu-Pb-Zn mineralization hosted by this pluton, focusing on the determination of the mass gains and losses of chemical components, which reflect the chemical exchanges between the host rocks and hydrothermal fluids. Vein-type Cu-Pb-Zn mineralization is closely associated with intense hydrothermal alterations within the brecciation, quartz stockwork veining, and brittle fracture zones that are controlled by NW-SE trending faults cutting through the Eğrigöz granitoids. Paragenetic relationships reveal three stages of mineralization: pre-ore, ore, and supergene. The ore mineralogy typically includes hypogene chalcopyrite, sphalerite, galena, and pyrite, with locally supergene covellite, malachite, and azurite. Wall-rock hypogene hydrothermal alterations include pervasive silicification, sulfidation, sericitization, and selective carbonatization and albitization. These are distributed in three main alteration zones (zone 1: silicified/iron carbonatized alterations ± albite, zone 2: argillic-silicic alterations, and zone 3: phyllic alterations). Based on the gains and losses of mass and volume (calculated by the GEOISO-Windows™ program), zone 1 has a higher mass and volume gain than zones 2 and 3. Non-systematic zonal distributions of alterations are observed in which the silicic-carbonate alterations +/− albitization appeared in zone 1 in the center and the phyllic-argillic alterations appeared in zones 2 and 3, with an increase in base metals (Cu-Pb-Zn) in the zone from Cu, Cu-Pb, to Cu-Pb-Zn moving outwards. Full article

(This article belongs to the Special Issue Mineral Deposit Genesis and Exploration)

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8782 KiB

Open AccessArticle

Mineralogy, Geochemistry and Stable Isotope Studies of the Dopolan Bauxite Deposit, Zagros Mountain, Iran

by Somayeh Salamab Ellahi, Batoul Taghipour, Alireza Zarasvandi, Michael I. Bird and Alireza K. Somarin

Minerals 2016, 6(1), 11; https://doi.org/10.3390/min6010011 - 06 Feb 2016

Cited by 21 | Viewed by 11056

Abstract

A new heterotrophic strain, named Providencia sp. JAT-1, was isolated and used in bioleaching of low-grade complex copper ore. The strain uses sodium citrate as a carbon source and urea as a nitrogen source to produce ammonia. The optimal growth condition of the strain is 30 C, initial pH 8, sodium citrate 10 g/L and urea 20 g/L, under which the cell density and ammonia concentration in the medium reached a maximum of 4.83 × 108 cells/mL and 14 g/L, respectively. Ammonia produced by the strain is used as the main lixiviant in bioleaching. Bioleaching results revealed that higher strain growth led to a higher copper recovery, while higher pulp density will cause a greater inhibitory effect on strain growth and ammonia production. The copper extraction reached the highest value of 54.5% at the pulp density of 1%. Malachite, chrysocolla and chalcocite are easy to leach out in this bioleaching system while chalcopyrite is difficult. Results of comparative leaching experiments show that bioleaching using JAT-1 is superior to ammonia leaching at the same condition. The metabolites produced by the strain other than ammonia are also involved in bioleaching. Full article

(This article belongs to the Special Issue Mineral Deposit Genesis and Exploration)

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Review

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12111 KiB

Open AccessReview

Paleozoic–Mesozoic Porphyry Cu(Mo) and Mo(Cu) Deposits within the Southern Margin of the Siberian Craton: Geochemistry, Geochronology, and Petrogenesis (a Review)

by Anita N. Berzina, Adel P. Berzina and Victor O. Gimon

Minerals 2016, 6(4), 125; https://doi.org/10.3390/min6040125 - 29 Nov 2016

Cited by 15 | Viewed by 6383

Abstract

The southern margin of the Siberian craton hosts numerous Cu(Mo) and Mo(Cu) porphyry deposits. This review provides the first comprehensive set of geological characteristics, geochronological data, petrochemistry, and Sr–Nd isotopic data of representative porphyry Cu(Mo) and Mo(Cu) deposits within the southern margin of the Siberian craton and discusses the igneous processes that controlled the evolution of these magmatic systems related to mineralization. Geochronological data show that these porphyry deposits have an eastward-younging trend evolving from the Early Paleozoic to Middle Mesozoic. The western part of the area (Altay-Sayan segment) hosts porphyry Cu and Mo–Cu deposits that generally formed in the Early Paleozoic time, whereas porphyry Cu–Mo deposits in the central part (Northern Mongolia) formed in the Late Paleozoic–Early Mesozoic. The geodynamic setting of the region during these mineralizing events is consistent with Early Paleozoic subduction of Paleo-Asian Ocean plate with the continuous accretion of oceanic components to the Siberian continent and Late Paleozoic–Early Mesozoic subduction of the west gulf of the Mongol–Okhotsk Ocean under the Siberian continent. The eastern part of the study area (Eastern Transbaikalia) hosts molybdenum-dominated Mo and Mo–Cu porphyry deposits that formed in the Jurassic. The regional geodynamic setting during this mineralizing process is related to the collision of the Siberian and North China–Mongolia continents during the closure of the central part of the Mongol–Okhotsk Ocean in the Jurassic. Available isotopic data show that the magmas related to porphyritic Cu–Mo and Mo–Cu mineralization during the Early Paleozoic and Late Paleozoic–Early Mesozoic were mainly derived from mantle materials. The generation of fertile melts, related to porphyritic Mo and Mo–Cu mineralization during the Jurassic involved variable amounts of metasomatized mantle source component, the ancient Precambrian crust, and the juvenile crust, contributed by mantle-derived magmatic underplating. Full article

(This article belongs to the Special Issue Mineral Deposit Genesis and Exploration)

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