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Se-Bearing Minerals: Structure, Composition, and Origin

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A special issue of Minerals (ISSN 2075-163X).

Deadline for manuscript submissions: closed (31 March 2018) | Viewed by 45554

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Dr. Hans-Jürgen Förster

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Helmholtz Centre Potsdam German, Research Centre for Geosciences, GFZ DE-14473 Potsdam, Germany
Interests: granitoid rocks and associated leucocratic mineral deposits; primary and secondary accessory minerals; micas; Se-bearing minerals; fluid−mineral−rock interactions; lithosphere thermal studies; petrophysical and thermal rock properties
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Dear Colleagues,

Selenium, discovered in 1817 by Berzelius, is a nonmetal with properties intermediate between sulfur and tellurium. It usually occurs as trace and minor element in sulfide ores. In nature, Se occurs in several inorganic forms, including selenide, selenate, and selenite, but these minerals are rare. In the past few years, a few new Se species were discovered, reflecting that Se-bearing ores are still in the focus of scientific research. Although telethermal Se deposits predominate, other types of Se mineralization also exist. The thermodynamic properties and the phase relations of the diverse Se species are yet imperfectly known, as are the p−T−X conditions that prevailed during their precipitation. The formation conditions of Se ores are known in general, but the sources of the Se and the accompanying elements are often a matter of speculation. A great deal of analytical effort has been spent on elucidating the composition of Se-bearing minerals, but the crystal structures of many species are not yet fully examined. Papers dealing with all these and other aspects of the formation of Se-bearing species are welcome in this Special issue.

Dr. habil. Hans-Jürgen Förster
Guest Editor

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Keywords

Se-bearing minerals
Crystal structure
Chemical composition
Thermodynamic properties
Phase relations
Elemental sources
P-T-X conditions of formation
Origin of Se deposits

Published Papers (7 papers)

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Research

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22 pages, 10263 KiB

Open AccessArticle

The Sierra de Cacheuta Vein-Type Se Mineralization, Mendoza Province, Argentina

by Günter Grundmann and Hans-Jürgen Förster

Minerals 2018, 8(4), 127; https://doi.org/10.3390/min8040127 - 22 Mar 2018

Cited by 5 | Viewed by 4077

Abstract

The Sierra de Cacheuta vein-type Se mineralization in the Mendoza Province predominantly consists of clausthalite, klockmannite, eskebornite, eucairite, and naumannite. These primary selenides formed in a fault zone, cutting through fine-grained trachytic host rock. Cross-sections perpendicular to the veinlets, polarized light microscopy, and scanning-electron microscopy, combined with electron-microprobe analysis, provide a record of the relationship between different crystallization and deformation events. Mineralization encompasses four episodes of fault formation (d1–d4): early zonal selenide crystallization (stage (I)); ductile deformation of the selenides (stage (II)); fault re-opening, fluid-mediated metal mobilization, metalliferous-fluid infiltration, and mineral precipitation (stage (III)); and subsequent alteration (stage (IV)). The Se vein originated from multiple injections of highly oxidized, metal-rich fluids. These low-T solutions (estimated max. temperature 100 °C, max. pressure 1 bar) possessed high to exceptionally high Se fugacities (log f_Se2 between −14.5 and −11.2) that prevailed for most of the evolution of the deposit. The source of the Se and the accompanying metals (Cu, Ag, Pb, and Fe) is probably the neighboring bituminous shale. The deposition of Se minerals occurred when the oxidized metal-bearing solutions came in contact with a reductant, which caused the reduction of mobile selenate to immobile selenide or elemental Se. We identified several features that permit us to safely distinguish samples from Cacheuta from Argentinian Se deposits in the Province of La Rioja: (I) trachytic host rock fragments containing bitumen and TiO₂ pseudomorphs after titanomagnetite; (II) early Co-rich and Ni-poor krut’aite (Co < 6.7 wt %, Ni < 1.2 wt %) partly replaced by clausthalite, umangite, klockmannite, eskebornite, Ni-poor tyrrellite (Ni < 2.7 wt %), Ni-poor trogtalite (Ni < 1.2 wt %), and end-member krut’aite and petříčekite; (III) lack of calcite gangue; and (VI) Se-bearing alteration minerals comprising chalcomenite, molybdomenite, cobaltomenite, an unnamed Cu selenide (for which the ideal formula may be either Cu₂Se₃ or Cu₅Se₈), and possibly mandarinoite, mereheadite, orlandiite, and scotlandite as new species for this occurrence. Full article

(This article belongs to the Special Issue Se-Bearing Minerals: Structure, Composition, and Origin)

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28 pages, 27782 KiB

Open AccessArticle

Nanoscale Study of Clausthalite-Bearing Symplectites in Cu-Au-(U) Ores: Implications for Ore Genesis

by Nicholas D. Owen, Cristiana L. Ciobanu, Nigel J. Cook, Ashley Slattery and Animesh Basak

Minerals 2018, 8(2), 67; https://doi.org/10.3390/min8020067 - 13 Feb 2018

Cited by 21 | Viewed by 5468

Abstract

Symplectites comprising clausthalite (PbSe) and host Cu-(Fe)-sulphides (chalcocite, bornite, and chalcopyrite) are instructive for constraining the genesis of Cu-Au-(U) ores if adequately addressed at the nanoscale. The present study is carried out on samples representative of all three Cu-(Fe)-sulphides displaying clausthalite inclusions that vary in size, from a few µm down to the nm-scale (<5 nm), as well as in morphology and inclusion density. A Transmission Electron Microscopy (TEM) study was undertaken on foils prepared by Focussed Ion Beam and included atom-scale High-Angle Annular Dark-Field Scanning TEM (HAADF-STEM) imaging. Emphasis is placed on phase relationships and their changes in speciation during cooling, as well as on boundaries between inclusions and host sulphide. Three species from the chalcocite group (Cu_2–xS) are identified as 6a digenite superstructure, monoclinic chalcocite, and djurleite. Bornite is represented by superstructures, of which 2a and 4a are discussed here, placing constraints for ore formation at T > 265 °C. A minimum temperature of 165 °C is considered for clausthalite-bearing symplectites from the relationships with antiphase boundaries in 6a digenite. The results show that alongside rods, blebs, and needle-like grains of clausthalite within the chalcocite that likely formed via exsolution, a second, overprinting set of replacement textures, extending down to the nanoscale, occurs and affects the primary symplectites. In addition, other reactions between pre-existing Se, present in solid solution within the Cu-(Fe)-sulphides, and Pb, transported within a fluid phase, account for the formation of composite, commonly pore-attached PbSe and Bi-bearing nanoparticles within the chalcopyrite. The inferred reorganisation of PbSe nanoparticles into larger tetragonal superlattices represents a link between the solid solution and the symplectite formation and represents the first such example in natural materials. Epitaxial growth between clausthalite and monazite is further evidence for the interaction between pre-existing Cu ores and fluids carrying REE, P, and most likely Pb. In U-bearing ores, such Pb can form via decay of uranium within the ore, implying hydrothermal activity after the initial ore deposition. The U-Pb ages obtained for such ores therefore need to be carefully assessed as to whether they represent primary ore deposition or, more likely, an overprinting event. A latest phase of fluid infiltration is the recognised formation of Cu-selenide bellidoite (Cu₂Se), as well as Fe oxides. Full article

(This article belongs to the Special Issue Se-Bearing Minerals: Structure, Composition, and Origin)

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16147 KiB

Open AccessArticle

Selenium and Other Trace Element Mobility in Waste Products and Weathered Sediments at Parys Mountain Copper Mine, Anglesey, UK

by Liam A. Bullock, John Parnell, Magali Perez, Joerg Feldmann and Joseph G. Armstrong

Minerals 2017, 7(11), 229; https://doi.org/10.3390/min7110229 - 22 Nov 2017

Cited by 17 | Viewed by 8285

Abstract

The Parys Mountain copper mining district (Anglesey, North Wales) hosts exposed pyritic bedrock, solid mine waste spoil heaps, and acid drainage (ochre sediment) deposits. Both natural and waste deposits show elevated trace element concentrations, including selenium (Se), at abundances of both economic and environmental consideration. Elevated concentrations of semi-metals such as Se in waste smelts highlight the potential for economic reserves in this and similar base metal mining sites. Selenium is sourced from the pyritic bedrock and concentrations are retained in red weathering smelt soils, but lost in bedrock-weathered soils and clays. Selenium correlates with Te, Au, Bi, Cd, Hg, Pb, S, and Sb across bedrock and weathered deposits. Man-made mine waste deposits show enrichment of As, Bi, Cu, Sb, and Te, with Fe oxide-rich smelt materials containing high Pb, up to 1.5 wt %, and Au contents, up to 1.2 ppm. The trace elements As, Co, Cu, and Pb are retained from bedrock to all sediments, including high Cu content in Fe oxide-rich ochre sediments. The high abundance and mobility of trace elements in sediments and waters should be considered as potential pollutants to the area, and also as a source for economic reserves of previously extracted and new strategic commodities. Full article

(This article belongs to the Special Issue Se-Bearing Minerals: Structure, Composition, and Origin)

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55216 KiB

Open AccessArticle

Selenide Mineralization in the Příbram Uranium and Base-Metal District (Czech Republic)

by Pavel Škácha, Jiří Sejkora and Jakub Plášil

Minerals 2017, 7(6), 91; https://doi.org/10.3390/min7060091 - 4 Jun 2017

Cited by 31 | Viewed by 8505

Abstract

Selenium mineralization in the Příbram uranium and base-metal district (Central Bohemia, Czech Republic) bound to uraninite occurrences in calcite hydrothermal veins is extremely diverse. The selenides antimonselite, athabascaite, bellidoite, berzelianite, brodtkorbite, bukovite, bytízite, cadmoselite, chaméanite, clausthalite, crookesite, dzharkenite, eskebornite, eucairite, ferroselite, giraudite, hakite, klockmannite, naumannite, permingeatite, příbramite, sabatierite, tiemannite, and umangite were found here, including two new mineral phases: Hg-Cu-Sb and Cu-As selenides. Those selenides—and in some cases their sulphidic equivalents—are characterized using wavelength-dispersive spectroscopy, reflected light, powder X-ray diffraction, single crystal X-ray diffraction, Raman spectroscopy, and electron backscatter diffraction. The selenide mineralization in the Příbram uranium district is bound to the border of the carbonate-uraninite and subsequent carbonate-sulphidic stages. Selenides crystallized there at temperatures near 100 °C in the neutral-to-weakly-alkaline environment from solutions with high oxygen fugacity and a high Se₂/S₂ fugacity ratio. Full article

(This article belongs to the Special Issue Se-Bearing Minerals: Structure, Composition, and Origin)

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39284 KiB

Open AccessArticle

Origin of the El Dragón Selenium Mineralization, Quijarro Province, Potosí, Bolivia

by Günter Grundmann and Hans-Jürgen Förster

Minerals 2017, 7(5), 68; https://doi.org/10.3390/min7050068 - 29 Apr 2017

Cited by 15 | Viewed by 5987

Abstract

A re-examination of the El Dragón vein-type Se deposit using polarized light microscopy and scanning-electron microscopy combined with electron-microprobe analyses revealed the following results: the detection of (a) petříčekite, krut’aite and penroseite close to endmember composition; (b) a yet unknown mineral of the ideal composition CuNi2Se4; (c) intermediate members of the vaesite-pyrite solid-solution series; and (d) a mineral with a composition intermediate between athabascaite and its yet unknown S-equivalent, Cu4S5. Triggered by volcanic-hydrothermal activities around the Porco caldera, formation of the mineralization involved five episodes of fault formation and re-opening, fluid-mediated metal mobilization, metalliferous fluid infiltration, and mineral precipitation, re-deposition, and alteration that probably extended from 12 Ma until today. The origin of the Se-vein was accomplished by the multiple injection of highly oxidized, metal-rich fluids into a fault at the interface between black shale and siltstone. These low-T solutions (estimated max. temperature 100 °C, max. pressure 1 bar) possessed high to exceptionally Se fugacities (log fSe2 fluctuating between of −14.5 and −11.2) that prevailed for most of the evolution of the deposit, only interrupted once, during the episode of deposition of sulfides of Cu and Fe and resulting partial alteration of the pre-existing selenides. Formation of end-member krut’aite and native selenium implies a minimum log fSe2 of −11.2 at the final stage of vein formation. The likely source of Se and the accompanying metals (Cu, Ag, Ni, Co, Au, Pb, Hg, Cd, Fe and Bi) is the neighboring Kupferschiefer-type (possibly Devonian) black shale rich in framboidal pyrite, Cu-sulfide aggregates, and organic matter. Deposition of Se-minerals occurred where the oxidized metal-bearing solutions became in contact with a reductant, associated with the reduction of mobile selenate to immobile selenide or elemental Se. Full article

(This article belongs to the Special Issue Se-Bearing Minerals: Structure, Composition, and Origin)

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11955 KiB

Open AccessArticle

Quijarroite, Cu₆HgPb₂Bi₄Se₁₂, a New Selenide from the El Dragόn Mine, Bolivia

by Hans-Jürgen Förster, Luca Bindi, Günter Grundmann and Chris J. Stanley

Minerals 2016, 6(4), 123; https://doi.org/10.3390/min6040123 - 18 Nov 2016

Cited by 8 | Viewed by 5267

Abstract

Quijarroite, ideally Cu₆HgPb₂Bi₄Se₁₂, is a new selenide species from the El Dragόn mine, Department of Potosí, Bolivia. It most frequently occurs as lath-shaped thin plates (up to 150 µm in length and 20 µm in width) intimately (subparallel) intergrown with hansblockite, forming an angular network-like intersertal texture. Quijarroite is occasionally also present as sub- to anhedral grains up to 200 µm in length and 50 µm in width. It is non-fluorescent, black and opaque with a metallic luster and black streak. It is brittle, with an irregular fracture and no obvious cleavage and parting. In plane-polarized incident light, quijarroite is weakly pleochroic from cream to very slightly more brownish-cream, displaying no internal reflections. Between crossed polars, quijarroite is moderately anisotropic with pale orange-brown to blue rotation tints. Lamellar twinning on {110} is common; parquet twinning occurs rarely. The reflectance values in the air for the COM (Commission on Ore Mineralogy) standard wavelengths (R₁ and R₂) are: 46.7, 46.8 (470 nm), 47.4, 48.2 (546 nm), 47.1, 48.5 (589 nm), and 46.6, 48.7 (650 nm). Electron-microprobe analyses yielded a mean composition of Cu 13.34, Ag 1.02, Hg 7.67, Pb 16.87, Co 0.03, Ni 0.15, Bi 27.65, Se 33.52, total 100.24 wt %. The mean empirical formula, normalized to 25 apfu (atoms per formula unit), is (Cu_5.84Ag_0.26)_{Σ = 6.10}(Hg_1.06Ni_0.07Co_0.01)_{Σ = 1.14}Pb_2.27Bi_3.68Se_11.81 (n = 24). The simplified formula is Cu₆HgPb₂Bi₄Se₁₂. Quijarroite is orthorhombic, space group Pmn2₁, with a = 9.2413(8), b = 9.0206(7), c = 9.6219(8) Å, V = 802.1(1) Å³, Z = 1. The calculated density is 5.771 g·cm⁻³. The five strongest X-ray powder-diffraction lines (d in Å (I/I₀) (hkl)) are: 5.36 (55) (111), 3.785 (60) (211), 3.291 (90) (022), 3.125 (100) (212), and 2.312 (50) (400). The crystal structure of quijarroite can be considered a galena derivative and could be derived from that of bournonite. It is a primary mineral, deposited from an oxidizing low-T hydrothermal fluid at a

f_{{S e}_{2}}

f_{S_{2}}

ratio greater than unity. The new species has been approved by the IMA-CNMNC (2016-052) and is named for the Quijarro Province in Bolivia, in which the El Dragón mine is located. Full article

(This article belongs to the Special Issue Se-Bearing Minerals: Structure, Composition, and Origin)

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Review

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5708 KiB

Open AccessReview

The Thermodynamics of Selenium Minerals in Near-Surface Environments

by Vladimir Krivovichev, Marina Charykova and Andrey Vishnevsky

Minerals 2017, 7(10), 188; https://doi.org/10.3390/min7100188 - 6 Oct 2017

Cited by 23 | Viewed by 6707

Abstract

Selenium compounds are relatively rare as minerals; there are presently only 118 known mineral species. This work is intended to codify and systematize the data of mineral systems and the thermodynamics of selenium minerals, which are unstable (selenides) or formed in near-surface environments (selenites), where the behavior of selenium is controlled by variations of the redox potential and the acidity of solutions at low temperatures and pressures. These parameters determine the migration of selenium and its precipitation as various solid phases. All selenium minerals are divided into four groups—native selenium, oxide, selenides, and oxysalts—anhydrous selenites (I) and hydrous selenites and selenates (II). Within each of the groups, minerals are codified according to the minimum number of independent elements necessary to define the composition of the mineral system. Eh–pH diagrams were calculated and plotted using the Geochemist’s Workbench (GMB 9.0) software package. The Eh–pH diagrams of the Me–Se–H2O systems (where Me = Co, Ni, Fe, Cu, Pb, Zn, Cd, Hg, Ag, Bi, As, Sb, Al and Ca) were plotted for the average contents of these elements in acidic waters in the oxidation zones of sulfide deposits. The possibility of the formation of Zn, Cd, Ag and Hg selenites under natural oxidation conditions in near surface environments is discussed. Full article

(This article belongs to the Special Issue Se-Bearing Minerals: Structure, Composition, and Origin)

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