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Minerals, Volume 9, Issue 3 (March 2019)

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Cover Story (view full-size image) Sample from the Queylus breccia, Chibougamau pluton: hand sample photography, microphotography [...] Read more.
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Open AccessArticle The Mineral Chemistry of Chlorites and Its Relationship with Uranium Mineralization from Huangsha Uranium Mining Area in the Middle Nanling Range, SE China
Minerals 2019, 9(3), 199; https://doi.org/10.3390/min9030199
Received: 22 February 2019 / Revised: 20 March 2019 / Accepted: 22 March 2019 / Published: 26 March 2019
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Abstract
The Huangsha uranium mining area is located in the Qingzhangshan uranium-bearing complex granite of the Middle Nanling Range, Southeast China. This uranium mining area contains three uranium deposits (Liangsanzhai, Egongtang, and Shangjiao) and multiple uranium occurrences, showing favorable mineralization conditions and prospecting potential [...] Read more.
The Huangsha uranium mining area is located in the Qingzhangshan uranium-bearing complex granite of the Middle Nanling Range, Southeast China. This uranium mining area contains three uranium deposits (Liangsanzhai, Egongtang, and Shangjiao) and multiple uranium occurrences, showing favorable mineralization conditions and prospecting potential for uranium mineral resources. Chloritization is one of the most important alteration types and prospecting indicators in this mining area. This study aims to unravel the formation environment of chlorites and the relationship between chloritization and uranium mineralization, based on detailed field work and petrographic studies of the wallrock and ore samples from the Huangsha uranium mining area. An electron probe microanalyzer (EPMA) was used in this study to analyze the paragenetic association, morphology, and chemical compositions of chlorite, to classify chemical types and to calculate formation temperatures and n(Al)/n(Al + Mg + Fe) values of chlorite. The formation mechanism and the relationship with uranium mineralization of the uranium mining area are presented. Some conclusions from this study are: (1) There are five types of chlorites, including the chlorite formed by the alteration of biotite (type-I), by the metasomatism of feldspar with Fe–Mg hydrothermal fluids (type-II), chlorite vein/veinlet filling in fissures (type-III), chlorite closely associated with uranium minerals (type-IV), and chlorite transformed from clay minerals by adsorbing Mg- and Fe-components (type-V). (2) The chlorite in the Huangsha uranium mining area belongs to iron-rich chlorite and is mainly composed of chamosite, partly clinochlore, which are the products of multiple stages of hydrothermal action. The original rocks are derived from argillite, and their formation temperatures vary from 195.7 °C to 283.0 °C, with an average of 233.2 °C, suggesting they formed under a medium to low temperature conditions. (3) The chlorites were formed under reducing conditions with low oxygen fugacity and relatively high sulfur fugacity through two formation mechanisms: dissolution–precipitation and dissolution–migration–precipitation; (4) The chloritization provided the required environment for uranium mineralization, and promoted the activation, migration, and deposition of uranium. Full article
(This article belongs to the Special Issue Geology and Mineralogy of Uranium Deposits)
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Open AccessArticle Pore Connectivity Characterization of Lacustrine Shales in Changling Fault Depression, Songliao Basin, China: Insights into the Effects of Mineral Compositions on Connected Pores
Minerals 2019, 9(3), 198; https://doi.org/10.3390/min9030198
Received: 22 February 2019 / Revised: 14 March 2019 / Accepted: 22 March 2019 / Published: 26 March 2019
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Abstract
Pore connectivity of lacustrine shales was inadequately documented in previous papers. In this work, lacustrine shales from the lower Cretaceous Shahezi Formation in the Changling Fault Depression (CFD) were investigated using field emission scanning electron microscopy (FE-SEM), mercury intrusion capillary pressure (MICP), low [...] Read more.
Pore connectivity of lacustrine shales was inadequately documented in previous papers. In this work, lacustrine shales from the lower Cretaceous Shahezi Formation in the Changling Fault Depression (CFD) were investigated using field emission scanning electron microscopy (FE-SEM), mercury intrusion capillary pressure (MICP), low pressure gas (CO2 and N2) sorption (LPGA) and spontaneous fluid imbibition (SFI) experiments. The results show that pores observed from FE-SEM images are primarily interparticle (interP) pores in clay minerals and organic matter (OM) pores. The dominant pore width obtained from LPGA and MICP data is in the range of 0.3–0.7 nm and 3–20 nm. The slopes of n-decane and deionized (DI) water SFI are in the range of 0.34–0.55 and 0.22–0.38, respectively, suggesting a mixed wetting nature and better-connected hydrophobic pores than hydrophilic pores in the Shahezi shales. Low pore connectivity is identified by the dominant nano-size pore widths (0.3–20 nm), low DI water SFI slopes (around 0.25), high geometric tortuosity (4.75–8.89) and effective tortuosity (1212–6122). Pore connectivity follows the order of calcareous shale > argillaceous shale > siliceous shale. The connected pores of Shahezi shales is mainly affected by the high abundance and coexistence of OM pores and clay, carbonate minerals host pores. Full article
(This article belongs to the Special Issue Nanomineralogy)
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Open AccessArticle Transformation of Vanadium-Bearing Titanomagnetite Concentrate in Additive-Free Roasting and Alkaline-Pressure Leaching for Extracting Vanadium (V)
Minerals 2019, 9(3), 197; https://doi.org/10.3390/min9030197
Received: 24 February 2019 / Revised: 19 March 2019 / Accepted: 21 March 2019 / Published: 26 March 2019
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Abstract
With a view to satisfying the requirements of environmental protest and efficient usage of resources, a novel process for efficiently extracting vanadium (V), titanium (Ti), and iron (Fe) from vanadium-bearing titanomagnetite concentrate was developed. In the new process, vanadium is pre-extracted by additive-free [...] Read more.
With a view to satisfying the requirements of environmental protest and efficient usage of resources, a novel process for efficiently extracting vanadium (V), titanium (Ti), and iron (Fe) from vanadium-bearing titanomagnetite concentrate was developed. In the new process, vanadium is pre-extracted by additive-free roasting under the air atmosphere and alkaline leaching technologies. In this paper, transformation of vanadium-bearing titanomagnetite concentrate in the roasting is investigated based on thermodynamic analyses and experimental discussion. Thermodynamic analyses show that oxidation of V(III) into V(V) would happen in the roasting experiment over the range of 327–1327 °C and vanadium-iron spinel phase (FeV2O4) can be oxidized more easily than magnetite (Fe3O4) when the temperature is higher than 861 °C. Experimental results show that some compounds (V2O5, Fe2Al4Si5O18, and Fe2SiO4) with low melting temperature were obtained by solid reactions at low temperature and melted as a binding phase at elevated temperature. Liquids were generated due to some chemical reactions or phase transformation reaction (Fe2V2O4(s) → Fe2O3(s) + liquid) at elevated temperature. Main phases of Fe2O3 and Fe2TiO5 are connected and sintered with the binding phases of the compounds with low melting temperature or the mixtures with low liquidus temperature. In addition, higher roasting temperature leads to higher vanadium leaching efficiency over the range of 800–1200 °C. However, over-burning would happen at 1250 °C, some of vanadium oxide was wrapped by silicate network, and the conversion of V(III) into V(V) was prevented from occurring. Therefore, the vanadium leaching efficiency decreased from 59.1% (Troa. = 1200 °C) to 57% (Troa. = 1250 °C). Full article
(This article belongs to the Section Mineral Processing and Metallurgy)
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Open AccessArticle The Effect of Sodium Alginate on Chlorite and Serpentine in Chalcopyrite Flotation
Minerals 2019, 9(3), 196; https://doi.org/10.3390/min9030196
Received: 23 February 2019 / Revised: 21 March 2019 / Accepted: 22 March 2019 / Published: 26 March 2019
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Abstract
Chlorite and serpentine are common magnesium-containing gangue minerals in copper sulfide flotation. In this study, sodium alginate, a natural hydrophilic polysaccharide, was introduced as a selective depressant for these gangue minerals. Micro-flotation tests were conducted on both single minerals and synthetic mixtures. The [...] Read more.
Chlorite and serpentine are common magnesium-containing gangue minerals in copper sulfide flotation. In this study, sodium alginate, a natural hydrophilic polysaccharide, was introduced as a selective depressant for these gangue minerals. Micro-flotation tests were conducted on both single minerals and synthetic mixtures. The flotation results showed that sodium alginate could simultaneously depress the flotation of chlorite and serpentine effectively, but seldom influenced the floatability of chalcopyrite at pH 9. In the ternary mixture flotation, a concentrate with a Cu grade of 31% could be achieved at Cu recovery of 90%. The selective depression of chlorite and serpentine was also validated by the real ore flotation experiments. The selective depression mechanism was investigated through adsorption tests, zeta potential measurements, and FTIR analyses. The adsorption density results implied that sodium alginate selectively adsorbed on the surface of phyllosilicates, but no adsorption on the chalcopyrite surface was observed. The zeta potential results showed that the sodium alginate could selectively decrease the surface charge of chlorite and serpentine. The FTIR results revealed the chemical adsorption of sodium alginate on the chlorite and serpentine surface and no form of adsorption on chalcopyrite, agreeing well with the adsorption density results. On the basis of these results, a selective adsorption model of sodium alginate on the mineral surface was proposed. Full article
(This article belongs to the Special Issue Hydrometallurgical Processing of Base Metal Sulphides)
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Open AccessArticle Magma Mixing Genesis of the Mafic Enclaves in the Qingshanbao Complex of Longshou Mountain, China: Evidence from Petrology, Geochemistry, and Zircon Chronology
Minerals 2019, 9(3), 195; https://doi.org/10.3390/min9030195
Received: 10 January 2019 / Revised: 7 March 2019 / Accepted: 18 March 2019 / Published: 25 March 2019
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Abstract
The Qingshanbao complex, part of the uranium metallogenic belt of the Longshou-Qilian mountains, is located in the center of the Longshou Mountain next to the Jiling complex that hosts a number of U deposits. However, little research has been conducted in this area. [...] Read more.
The Qingshanbao complex, part of the uranium metallogenic belt of the Longshou-Qilian mountains, is located in the center of the Longshou Mountain next to the Jiling complex that hosts a number of U deposits. However, little research has been conducted in this area. In order to investigate the origin and formation of mafic enclaves observed in the Qingshanbao body and the implications for magmatic-tectonic dynamics, we systematically studied the mineralogy, petrography, and geochemistry of these enclaves. Our results showed that the enclaves contain plagioclase enwrapped by early dark minerals. These enclaves also showed round quartz crystals and acicular apatite in association with the plagioclase. Electron probe analyses showed that the plagioclase in the host rocks (such as K-feldspar granite, adamellite, granodiorite, etc.) show normal zoning, while the plagioclase in the mafic enclaves has a discontinuous rim composition and shows instances of reverse zoning. Major elemental geochemistry revealed that the mafic enclaves belong to the calc-alkaline rocks that are rich in titanium, iron, aluminum, and depleted in silica, while the host rocks are calc-alkaline to alkaline rocks with enrichment in silica. On Harker diagrams, SiO2 contents are negatively correlated with all major oxides but K2O. Both the mafic enclaves and host rock are rich in large ion lithophile elements such as Rb and K, as well as elements such as La, Nd, and Sm, and relatively poor in high field strength elements such as Nb, Ta, P, Ti, and U. Element ratios of Nb/La, Rb/Sr, and Nb/Ta indicate that the mafic enclaves were formed by the mixing of mafic and felsic magma. In terms of rare earth elements, both the mafic enclaves and the host rock show right-inclined trends with similar weak to medium degrees of negative Eu anomaly and with no obvious Ce anomaly. Zircon LA-ICP-MS (Laser ablation inductively coupled plasma mass spectrometry) U-Pb concordant ages of the mafic enclaves and host rock were determined to be 431.8 ± 5.2 Ma (MSWD (mean standard weighted deviation) = 1.5, n = 14) and 432.8 ± 4.2 Ma (MSWD = 1.7, n = 16), respectively, consistent with that for the zircon U-Pb ages of the granite and medium-coarse grained K-feldspar granites of the Qingshanbao complex. The estimated ages coincide with the timing of the late Caledonian collision of the Alashan Block. This comprehensive analysis allowed us to conclude that the mafic enclaves in the Qingshanbao complex were formed by the mixing of crust-mantle magma with mantle-derived magma due to underplating, which caused partial melting of the ancient basement crust during the collisional orogenesis between the Alashan Block and Qilian rock mass in the early Silurian Period. Full article
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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Open AccessArticle Spiridonovite, (Cu1-xAgx)2Te (x ≈ 0.4), a New Telluride from the Good Hope Mine, Vulcan, Colorado (U.S.A.)
Minerals 2019, 9(3), 194; https://doi.org/10.3390/min9030194
Received: 7 March 2019 / Revised: 19 March 2019 / Accepted: 22 March 2019 / Published: 24 March 2019
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Abstract
Here we describe a new mineral in the Cu-Ag-Te system, spiridonovite. The specimen was discovered in a fragment from the cameronite [ideally, Cu5-x(Cu,Ag)3+xTe10] holotype material from the Good Hope mine, Vulcan, Colorado (U.S.A.). It occurs as black [...] Read more.
Here we describe a new mineral in the Cu-Ag-Te system, spiridonovite. The specimen was discovered in a fragment from the cameronite [ideally, Cu5-x(Cu,Ag)3+xTe10] holotype material from the Good Hope mine, Vulcan, Colorado (U.S.A.). It occurs as black grains of subhedral to anhedral morphology, with a maximum size up to 65 μm, and shows black streaks. No cleavage is observed and the Vickers hardness (VHN100) is 158 kg·mm−2. Reflectance percentages in air for Rmin and Rmax are 38.1, 38.9 (471.1 nm), 36.5, 37.3 (548.3 nm), 35.8, 36.5 (586.6 nm), 34.7, 35.4 (652.3 nm). Spiridonovite has formula (Cu1.24Ag0.75)Σ1.99Te1.01, ideally (Cu1-xAgx)2Te (x ≈ 0.4). The mineral is trigonal and belongs to the space group P-3c1, with the following unit-cell parameters: a = 4.630(2) Å, c = 22.551(9) Å, V = 418.7(4) Å 3, and Z = 6. The crystal structure has been solved and refined to R1 = 0.0256. It can be described as a rhombohedrally-compressed antifluorite structure, with a rough ccp arrangement of Te atoms. It consists of two Te sites and three M (metal) sites, occupied by Cu and Ag, and is characterized by the presence of edge-sharing tetrahedra, where the four-fold coordinated M atoms lie. The mineral and its name have been approved by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association (No. 2018-136). Full article
(This article belongs to the collection New Minerals)
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Open AccessFeature PaperArticle Exploratory Analysis of Provenance Data Using R and the Provenance Package
Minerals 2019, 9(3), 193; https://doi.org/10.3390/min9030193
Received: 17 January 2019 / Revised: 9 March 2019 / Accepted: 15 March 2019 / Published: 22 March 2019
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Abstract
The provenance of siliclastic sediment may be traced using a wide variety of chemical, mineralogical and isotopic proxies. These define three distinct data types: (1) compositional data such as chemical concentrations; (2) point-counting data such as heavy mineral compositions; and (3) distributional data [...] Read more.
The provenance of siliclastic sediment may be traced using a wide variety of chemical, mineralogical and isotopic proxies. These define three distinct data types: (1) compositional data such as chemical concentrations; (2) point-counting data such as heavy mineral compositions; and (3) distributional data such as zircon U-Pb age spectra. Each of these three data types requires separate statistical treatment. Central to any such treatment is the ability to quantify the ‘dissimilarity’ between two samples. For compositional data, this is best done using a logratio distance. Point-counting data may be compared using the chi-square distance, which deals better with missing components (zero values) than the logratio distance does. Finally, distributional data can be compared using the Kolmogorov–Smirnov and related statistics. For small datasets using a single provenance proxy, data interpretation can sometimes be done by visual inspection of ternary diagrams or age spectra. However, this no longer works for larger and more complex datasets. This paper reviews a number of multivariate ordination techniques to aid the interpretation of such studies. Multidimensional Scaling (MDS) is a generally applicable method that displays the salient dissimilarities and differences between multiple samples as a configuration of points in which similar samples plot close together and dissimilar samples plot far apart. For compositional data, classical MDS analysis of logratio data is shown to be equivalent to Principal Component Analysis (PCA). The resulting MDS configurations can be augmented with compositional information as biplots. For point-counting data, classical MDS analysis of chi-square distances is shown to be equivalent to Correspondence Analysis (CA). This technique also produces biplots. Thus, MDS provides a common platform to visualise and interpret all types of provenance data. Generalising the method to three-way dissimilarity tables provides an opportunity to combine several datasets together and thereby facilitate the interpretation of ‘Big Data’. This paper presents a set of tutorials using the statistical programming language R. It illustrates the theoretical underpinnings of compositional data analysis, PCA, MDS and other concepts using toy examples, before applying these methods to real datasets with the provenance package. Full article
(This article belongs to the Special Issue Heavy Minerals)
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Open AccessEditorial Editorial for Special Issue “Arctic Mineral Resources: Science and Technology”
Minerals 2019, 9(3), 192; https://doi.org/10.3390/min9030192
Received: 6 March 2019 / Accepted: 14 March 2019 / Published: 22 March 2019
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Abstract
The Arctic zone of the Earth is a major source of mineral and other natural resources for the future development of science and technology [...] Full article
Open AccessArticle Geological, Geochronological, and Geochemical Insights into the Formation of the Giant Pulang Porphyry Cu (–Mo–Au) Deposit in Northwestern Yunnan Province, SW China
Minerals 2019, 9(3), 191; https://doi.org/10.3390/min9030191
Received: 7 March 2019 / Revised: 19 March 2019 / Accepted: 19 March 2019 / Published: 21 March 2019
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Abstract
The giant Pulang porphyry Cu (–Mo–Au) deposit in Northwestern Yunnan Province, China, is located in the southern part of the Triassic Yidun Arc. The Cu orebodies are mainly hosted in quartz monzonite porphyry (QMP) intruding quartz diorite porphyry (QDP) and cut by granodiorite [...] Read more.
The giant Pulang porphyry Cu (–Mo–Au) deposit in Northwestern Yunnan Province, China, is located in the southern part of the Triassic Yidun Arc. The Cu orebodies are mainly hosted in quartz monzonite porphyry (QMP) intruding quartz diorite porphyry (QDP) and cut by granodiorite porphyry (GP). New LA-ICP-MS zircon U–Pb ages indicate that QDP (227 ± 2 Ma), QMP (218 ± 1 Ma, 219 ± 1 Ma), and GP (209 ± 1 Ma) are significantly different in age; however, the molybdenite Re–Os isochron age (218 ± 2 Ma) indicates a close temporal and genetic relationship between Cu mineralization and QMP. Pulang porphyry intrusions are enriched in light rare-earth elements (LREEs) and large ion lithophile elements (LILEs), and depleted in heavy rare-earth elements (HREEs) and high field-strength elements (HFSEs), with moderately negative Eu anomalies. They are high in SiO2, Al2O3, Sr, Na2O/K2O, Mg#, and Sr/Y, but low in Y, and Yb, suggesting a geochemical affinity to high-silica (HSA) adakitic rocks. These features are used to infer that the Pulang HSA porphyry intrusions were derived from the partial melting of a basaltic oceanic-slab. These magmas reacted with peridotite during their ascent through the mantle wedge. This is interpreted to indicate that the Pulang Cu deposit and associated magmatism can be linked to the synchronous westward subduction of the Ganzi–Litang oceanic lithosphere, which has been established as Late Triassic. Full article
(This article belongs to the Special Issue Polymetallic Metallogenic System)
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Open AccessArticle Ore-Fluid Evolution of the Sizhuang Orogenic Gold Deposit, Jiaodong Peninsula, China
Minerals 2019, 9(3), 190; https://doi.org/10.3390/min9030190
Received: 14 January 2019 / Revised: 15 March 2019 / Accepted: 16 March 2019 / Published: 21 March 2019
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Abstract
The Sizhuang gold deposit with a proven gold resource of >120 t, located in northwest Jiaodong Peninsula in China, lies in the southern part of the Jiaojia gold belt. Gold mineralization can be divided into altered rock type, auriferous quartz vein type, and [...] Read more.
The Sizhuang gold deposit with a proven gold resource of >120 t, located in northwest Jiaodong Peninsula in China, lies in the southern part of the Jiaojia gold belt. Gold mineralization can be divided into altered rock type, auriferous quartz vein type, and sulfide-quartz veinlet in K-feldspar altered granite. According to mineral paragenesis and mineral crosscutting relationships, three stages of metal mineralization can be identified: early stage, main stage, and late stage. Gold mainly occurs in the main stage. The petrography and microthermometry of fluid inclusion shows three types of inclusions (type 1 H2O–CO2 inclusions, type 2 aqueous inclusions, and type 3 CO2 inclusions). Early stage quartz-hosted inclusions have a trapped temperatures range 303–390 °C. The gold-rich main stage contains a fluid-inclusion cluster with both type 1 and 2 inclusions (trapped between 279 and 298 °C), and a wide range of homogenization temperatures of CO2 occurs to the vapor phase (17.6 to 30.5 °C). The late stage calcite only contains type 1 inclusions with homogenization temperatures between 195 and 289 °C. With evidences from the H–O isotope data and the study of water–rock interaction, the metamorphic water of the Jiaodong Group is considered to be the dominating source for the ore-forming fluid. The ore-fluid belonged to a CO2–H2O–NaCl system with medium-low temperature (160–360 °C), medium-low salinity (3.00–11.83 wt% NaCl eq.), and low density (1.51–1.02 g/cm3). Fluid immiscibility caused by pressure fluctuation is the key mechanism in inducing gold mineralization in the Sizhuang gold deposit. Full article
(This article belongs to the Special Issue Polymetallic Metallogenic System)
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Open AccessArticle Origin and Evolution of Ore-Forming Fluid and Gold-Deposition Processes at the Sanshandao Gold Deposit, Jiaodong Peninsula, Eastern China
Minerals 2019, 9(3), 189; https://doi.org/10.3390/min9030189
Received: 14 January 2019 / Revised: 3 March 2019 / Accepted: 7 March 2019 / Published: 19 March 2019
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Abstract
The Early Cretaceous Sanshandao gold deposit, the largest deposit in the Sanshandao-Cangshang goldfield, is located in the northwestern part of the Jiaodong peninsula. It is host to Mesozoic granitoids and is controlled by the north by northeast (NNE) to northeast (NE)-trending Sanshandao-Cangshang fault. [...] Read more.
The Early Cretaceous Sanshandao gold deposit, the largest deposit in the Sanshandao-Cangshang goldfield, is located in the northwestern part of the Jiaodong peninsula. It is host to Mesozoic granitoids and is controlled by the north by northeast (NNE) to northeast (NE)-trending Sanshandao-Cangshang fault. Two gold mineralizations were identified in the deposit’s disseminated and stockwork veinlets and quartz–sulfide veins, which are typically enveloped by broad alteration selvages. Based on the cross-cutting relationships and mineralogical and textural characteristics, four stages have been identified for both styles of mineralization: Pyrite–quartz (stage 1), quartz–pyrite (stage 2), quartz–pyrite–base metal–sulfide (stage 3), and quartz–carbonate (stage 4), with gold mainly occurring in stages 2 and 3. Three types of fluid inclusion have been distinguished on the basis of fluid-inclusion assemblages in quartz and calcite from the four stages: Pure CO2 gas (type I), CO2–H2O inclusions (type II), and aqueous inclusions (type III). Early-stage (stage 1) quartz primary inclusions are only type II inclusions, with trapping at 280–400 °C and salinity at 0.35 wt %–10.4 wt % NaCl equivalent. The main mineralizing stages (stages 2 and 3) typically contain primary fluid-inclusion assemblages of all three types, which show similar phase transition temperatures and are trapped between 210 and 320 °C. The late stage (stage 4) quartz and calcite contain only type III aqueous inclusions with trapping temperatures of 150–230 °C. The δ34S values of the hydrothermal sulfides from the main stage range from 7.7‰ to 12.6‰ with an average of 10.15‰. The δ18O values of hydrothermal quartz mainly occur between 9.7‰ and 15.1‰ (mainly 10.7‰–12.5‰, average 12.4‰); calculated fluid δ18O values are from 0.97‰ to 10.79‰ with a median value of 5.5‰. The δDwater values calculated from hydrothermal sericite range from −67‰ to −48‰. Considering the fluid-inclusion compositions, δ18O and δD compositions of ore-forming fluids, and regional geological events, the most likely ultimate potential fluid and metal would have originated from dehydration and desulfidation of the subducting paleo-Pacific slab and the subsequent devolatilization of the enriched mantle wedge. Fluid immiscibility occurred during the main ore-forming stage due to pressure decrease from the early stage (165–200 MPa) to the main stage (90–175 MPa). Followed by the changing physical and chemical conditions, the metallic elements (including Au) in the fluid could no longer exist in the form of complexes and precipitated from the fluid. Water–rock sulfidation and pressure fluctuations, with associated fluid unmixing and other chemical changes, were the two main mechanisms of gold deposition. Full article
(This article belongs to the Special Issue Polymetallic Metallogenic System)
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Open AccessArticle Migration Law of the Roof of a Composited Backfilling Longwall Face in a Steeply Dipping Coal Seam
Minerals 2019, 9(3), 188; https://doi.org/10.3390/min9030188
Received: 12 February 2019 / Revised: 13 March 2019 / Accepted: 14 March 2019 / Published: 18 March 2019
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Abstract
The artificial-caved rock composited backfilling approach can effectively restrain the dynamic phenomena in the coal seam and the associated roof and floor during mining operations, and can also improve the stability of the system of support and surrounding rock. In this study, based [...] Read more.
The artificial-caved rock composited backfilling approach can effectively restrain the dynamic phenomena in the coal seam and the associated roof and floor during mining operations, and can also improve the stability of the system of support and surrounding rock. In this study, based on the analysis of influencing factors affecting the surrounding rock movement and deformation of the composited backfilling longwall face in a steeply dipping coal seam, the roof mechanical model is developed, and the deflection differential equation is derived, to obtain the roof damage structure and the location of the roof fracture for the area without backfilling. The migration law of the roof under different inclination angles, mining depths, working face lengths, and backfilling ratios are analyzed. Finally, mine pressure is detected in the tested working face. Results show that the roof deflection, bending moment, and rotation drop with the increase of the inclination angle and backfilling ratio, whereas these parameters increase with greater mining depth and working face length. The roof failure location moves toward the upper area of the working face as the inclination angle and working face length increases, while it moves toward the center of the non-backfilling area with greater mining depth and backfilling ratio. Results from the proposed mechanical model agree well with the field test results, demonstrating the validity of the model, which can provide theoretical basis for a safe and efficient mining operation in steeply dipping coal seams. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessArticle Multiple Magma Conduits Model of the Jinchuan Ni-Cu-(PGE) Deposit, Northwestern China: Constraints from the Geochemistry of Platinum-Group Elements
Minerals 2019, 9(3), 187; https://doi.org/10.3390/min9030187
Received: 13 February 2019 / Revised: 12 March 2019 / Accepted: 14 March 2019 / Published: 18 March 2019
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Abstract
The giant Jinchuan nickel-copper-platinum-group element (PGE) deposit is hosted by two individual sub-vertical intrusions, referred to as the western and eastern intrusions (including segment II-W and segment II-E). Exactly how the Jinchuan deposit was formed by a system of sub-vertical magma conduits is [...] Read more.
The giant Jinchuan nickel-copper-platinum-group element (PGE) deposit is hosted by two individual sub-vertical intrusions, referred to as the western and eastern intrusions (including segment II-W and segment II-E). Exactly how the Jinchuan deposit was formed by a system of sub-vertical magma conduits is still not well understood. This paper reports new major elements, trace elements and PGEs data from the Jinchuan deposit to study the formation mechanism of sulfide ores with different textures and their relationship with the magma conduit system. Our study shows that the PGE tenors of disseminated and net-textured sulfide in segment II-E are significantly lower than segment II-W and the western intrusion, but the Cu/Pd ratios are opposite. In addition, net-textured sulfides in segment II-W show a negative correlation between IPGE (Ir, Ru and Rh) and PPGE (Pt and Pd) in contrast to the positive correlation in segment II-E and the western intrusion. These features indicate the parental magma sources of the western intrusion, segment II-W and segment II-E were originally three different surges of PGE-depleted magma. Modeling of parental magma in the western intrusion, segment II-W and segment II-E suggests that they were formed by the same initial picritic basalt (100 ppm Cu, 1 ppb Ir and 10 ppb Pd) with different prior sulfide segregations (0.0075%, 0.0085% and 0.011%). The three parts of Jinchuan sulfides show that the Pt/Pd and (Pt + Pd)/(Ir + Ru + Rh) ratios decrease from section III-5 toward both sides in the western intrusion and decrease from section II-14 toward all sides, whereas no regular spatial variations occur in segment II-E, showing the different fractionation processes of sulfide melt. The massive sulfides in the western intrusion and segment II-E experienced a ~20% to 40% and ~40% to 60% fractionation of sulfide melt, respectively. We propose that the Jinchuan deposit was generated in a metallogenic system of multiple magma conduits, where sulfides entrained in parental magma experienced different amounts of prior removal. Full article
(This article belongs to the Section Mineral Deposits)
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Open AccessArticle A Metastable Fo-III Wedge in Cold Slabs Subducted to the Lower Part of the Mantle Transition Zone: A Hypothesis Based on First-Principles Simulations
Minerals 2019, 9(3), 186; https://doi.org/10.3390/min9030186
Received: 3 February 2019 / Revised: 26 February 2019 / Accepted: 12 March 2019 / Published: 17 March 2019
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Abstract
The metastable olivine (Ol) wedge hypothesis assumes that Ol may exist as a metastable phase at the P conditions of the mantle transition zone (MTZ) and even deeper regions due to inhibition of the phase transitions from Ol to wadsleyite and ringwoodite caused [...] Read more.
The metastable olivine (Ol) wedge hypothesis assumes that Ol may exist as a metastable phase at the P conditions of the mantle transition zone (MTZ) and even deeper regions due to inhibition of the phase transitions from Ol to wadsleyite and ringwoodite caused by low T in the cold subducting slabs. It is commonly invoked to account for the stagnation of the descending slabs, deep focus earthquakes and other geophysical observations. In the last few years, several new structures with the forsterite (Fo) composition, namely Fo-II, Fo-III and Fo-IV, were either experimentally observed or theoretically predicted at very low T conditions. They may have important impacts on the metastable Ol wedge hypothesis. By performing first-principles calculations, we have systematically examined their crystallographic characteristics, elastic properties and dynamic stabilities from 0 to 100 GPa, and identified the Fo-III phase as the most likely metastable phase to occur in the cold slabs subducted to the depths equivalent to the lower part of the MTZ (below the ~600 km depth) and even the lower mantle. As disclosed by our theoretical simulations, the Fo-III phase is a post-spinel phase (space group Cmc21), has all cations in sixfold coordination at P < ~60 GPa, and shows dynamic stability for the entire P range from 0 to 100 GPa. Further, our static enthalpy calculations have suggested that the Fo-III phase may directly form from the Fo material at ~22 GPa (0 K), and our high-T phase relation calculations have located the Fo/Fo-III phase boundary at ~23.75 GPa (room T) with an averaged Clapeyron slope of ~−1.1 MPa/K for the T interval from 300 to 1800 K. All these calculated phase transition pressures are likely overestimated by ~3 GPa because of the GGA method used in this study. The discrepancy between our predicted phase transition P and the experimental observation (~58 GPa at 300 K) can be explained by slow reaction rate and short experimental durations. Taking into account the P-T conditions in the cold downgoing slabs, we therefore propose that the Fo-III phase, rather than the Ol, highly possibly occurs as the metastable phase in the cold slabs subducted to the P conditions of the lower part of the MTZ (below the ~600 km depth) and even the lower mantle. In addition, our calculation has showed that the Fo-III phase has higher bulk seismic velocity, and thus may make important contributions to the high seismic speeds observed in the cold slabs stagnated near the upper mantle-lower mantle boundary. Future seismic studies may discriminate the effects of the Fo-III phase and the low T. Surprisingly, the Fo-III phase will speed up, rather than slow down, the subducting process of the cold slabs, if it metastably forms from the Ol. In general, the Fo-III phase has a higher density than the warm MTZ, but has a lower density than the lower mantle, as suggested by our calculations. Full article
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Open AccessEditorial Editorial for Special Issue “Mineral Surface Reactions at the Nanoscale”
Minerals 2019, 9(3), 185; https://doi.org/10.3390/min9030185
Received: 14 March 2019 / Accepted: 15 March 2019 / Published: 17 March 2019
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Abstract
Reactions at mineral surfaces are central to all geochemical processes. As minerals comprise the rocks of the Earth, the processes occurring at the mineral–aqueous fluid interface control the evolution of the rocks and, hence, the structure of the crust of the Earth during [...] Read more.
Reactions at mineral surfaces are central to all geochemical processes. As minerals comprise the rocks of the Earth, the processes occurring at the mineral–aqueous fluid interface control the evolution of the rocks and, hence, the structure of the crust of the Earth during such processes at metamorphism, metasomatism, and weathering. In recent years, focus has been concentrated on mineral surface reactions made possible through the development of advanced analytical techniques, such as atomic force microscopy (AFM), advanced electron microscopies (SEM and TEM), phase shift interferometry, confocal Raman spectroscopy, advanced synchrotron-based applications, complemented by molecular simulations, to confirm or predict the results of experimental studies. In particular, the development of analytical methods that allow direct observations of mineral–fluid reactions at the nanoscale have revealed new and significant aspects of the kinetics and mechanisms of reactions taking place in fundamental mineral–fluid systems. These experimental and computational studies have enabled new and exciting possibilities to elucidate the mechanisms that govern mineral–fluid reactions, as well as the kinetics of these processes, and, hence, to enhance our ability to predict potential mineral behavior. In this Special Issue “Mineral Surface Reactions at the Nanoscale”, we present 12 contributions that highlight the role and importance of mineral surfaces in varying fields of research. Full article
(This article belongs to the Special Issue Mineral Surface Reactions at the Nanoscale)
Open AccessArticle Geochemical and Mineralogical Characteristics of the Middle Jurassic Coals from the Tongjialiang Mine in the Northern Datong Coalfield, Shanxi Province, China
Minerals 2019, 9(3), 184; https://doi.org/10.3390/min9030184
Received: 24 January 2019 / Revised: 8 March 2019 / Accepted: 12 March 2019 / Published: 16 March 2019
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Abstract
There is limited information available on the minerals and elements present in the Jurassic coals from Datong Coalfield. This paper investigates the geochemical and mineralogical characteristics of the Middle Jurassic coals from the Tongjialiang Mine using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry [...] Read more.
There is limited information available on the minerals and elements present in the Jurassic coals from Datong Coalfield. This paper investigates the geochemical and mineralogical characteristics of the Middle Jurassic coals from the Tongjialiang Mine using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and scanning electron microscopy in combination with energy-dispersive X-ray spectrometry (SEM-EDS). No.12 coal is a low-medium volatile bituminous coal and is characterized by low ash yield content, low moisture content, and ultra-low sulfur content. Compared with Chinese coals, the Tongjialiang coals have slightly higher average percentages of MgO and P2O5, and lower average percentages of the other major oxides, including SiO2, TiO2, Al2O3, Fe2O3, CaO, MnO, Na2O, and K2O. Compared with the World hard coals, Be, Cr, Co, Ni, Ge, Sn, Ta, and W are slightly enriched in the Tongjialiang coals. The concentrations of Li, F, Sc, V, Cu, Ga, Se, Sr, Zr, Nb, Hf, Pb, Th, and U are close to the average values of the world’s hard coals. The minerals in No.12 coal mainly include quartz, kaolinite, siderite, and ankerite, along with smaller amounts of pyrite, illite, calcite, and rutile. The formation of syngenetic siderite in No.12 coal is related to the weathering of biotite in the gneiss of the Yinshan Upland. The modes of occurrence of ankerite indicate that the coals may be affected by the injection of low temperature hydrothermal fluids. It is noteworthy that a portion of epigenetic ankerite may be a product of metasomatism between syngenetic siderite and the epigenetic Fe-Mg-Ca rich hydrothermal fluids. The ratios of Al2O3/TiO2, REY (rare earth elements and yittrium) enrichment patterns, the modes of occurrence of siderite and ankerite, as well as the enriched lithophile and siderophile elements indicate that the No.12 coal may have originated from the Yinshan Upland and may also have been influenced by low temperature hydrothermal fluids that might have circulated in the coal basin. Full article
(This article belongs to the collection Minerals in Coal and Coal Combustion Products)
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Open AccessFeature PaperReview X-ray Microcomputed Tomography (µCT) for Mineral Characterization: A Review of Data Analysis Methods
Minerals 2019, 9(3), 183; https://doi.org/10.3390/min9030183
Received: 19 February 2019 / Revised: 9 March 2019 / Accepted: 12 March 2019 / Published: 15 March 2019
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Abstract
The main advantage of X-ray microcomputed tomography (µCT) as a non-destructive imaging tool lies in its ability to analyze the three-dimensional (3D) interior of a sample, therefore eliminating the stereological error exhibited in conventional two-dimensional (2D) image analysis. Coupled with the correct data [...] Read more.
The main advantage of X-ray microcomputed tomography (µCT) as a non-destructive imaging tool lies in its ability to analyze the three-dimensional (3D) interior of a sample, therefore eliminating the stereological error exhibited in conventional two-dimensional (2D) image analysis. Coupled with the correct data analysis methods, µCT allows extraction of textural and mineralogical information from ore samples. This study provides a comprehensive overview on the available and potentially useful data analysis methods for processing 3D datasets acquired with laboratory µCT systems. Our study indicates that there is a rapid development of new techniques and algorithms capable of processing µCT datasets, but application of such techniques is often sample-specific. Several methods that have been successfully implemented for other similar materials (soils, aggregates, rocks) were also found to have the potential to be applied in mineral characterization. The main challenge in establishing a µCT system as a mineral characterization tool lies in the computational expenses of processing the large 3D dataset. Additionally, since most of the µCT dataset is based on the attenuation of the minerals, the presence of minerals with similar attenuations limits the capability of µCT in mineral segmentation. Further development on the data processing workflow is needed to accelerate the breakthrough of µCT as an analytical tool in mineral characterization. Full article
(This article belongs to the Special Issue Mineral Liberation)
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Open AccessArticle Petrogenesis of Low Sr and High Yb A-Type Granitoids in the Xianghualing Sn Polymetallic Deposit, South China: Constrains from Geochronology and Sr–Nd–Pb–Hf Isotopes
Minerals 2019, 9(3), 182; https://doi.org/10.3390/min9030182
Received: 16 January 2019 / Revised: 9 March 2019 / Accepted: 11 March 2019 / Published: 15 March 2019
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Abstract
The nature and origin of the early Yanshanian granitoids, widespread in the South China Block, shed light on their geodynamic setting; however, understanding their magmatism processes remains a challenge. In this paper, we present both major and trace elements of bulk rock, Sr–Nd–Pb [...] Read more.
The nature and origin of the early Yanshanian granitoids, widespread in the South China Block, shed light on their geodynamic setting; however, understanding their magmatism processes remains a challenge. In this paper, we present both major and trace elements of bulk rock, Sr–Nd–Pb isotopic geochemistry, and zircon U–Pb–Hf isotopes of the low Sr and high Yb A2-type granites, which were investigated with the aim to further constrain their petrogenesis and tectonic implications. Zircon U–Pb dating indicates that these granites were emplaced at ca. 153 Ma. The granites are characterized by high SiO2 (>74 wt.%) and low Al2O3 content (11.0 wt.%–12.7 wt.%; <13.9 wt.%). They are enriched in large ion lithophile elements (LILEs) (e.g., Rb, Th, U, and K) and Yb, but depleted in high field-strength elements (HFSEs) (e.g., Nb, Ta, Zr and Hf), Sr, Ba P, Ti and Eu concentrations. They exhibit enriched rare earth elements (REEs) with pronounced negative Eu anomalies. They have εNd(t) values in a range from −6.5 to −9.3, and a corresponding TDM model age of 1.5 to 1.7 Ga. They have a (206Pb/204Pb)t value ranging from 18.523 to 18.654, a (207Pb/204Pb)t value varying from 15.762 to 15.797, and a (208Pb/204Pb)t value ranging from 39.101 to 39.272. The yield εHf(t) ranges from −6.1 to −2.1, with crustal model ages (TDMC) of 1.3 to 1.6 Ga. These features indicate that the low Sr and high Yb weakly peraluminous A2-type granites were generated by overlying partial melting caused by the upwelling of the asthenosphere in an extensional tectonic setting. The rollback of the Paleo-Pacific Plate is the most plausible combined mechanism for the petrogenesis of A2-type granites, which contributed to the Sn–W polymetallic mineralization along the Shi-Hang zone in South China. Full article
(This article belongs to the Special Issue Polymetallic Metallogenic System)
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Open AccessFeature PaperArticle Design of Flotation Circuits Using Tabu-Search Algorithms: Multispecies, Equipment Design, and Profitability Parameters
Minerals 2019, 9(3), 181; https://doi.org/10.3390/min9030181
Received: 31 January 2019 / Revised: 8 March 2019 / Accepted: 9 March 2019 / Published: 15 March 2019
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Abstract
The design of a flotation circuit based on optimization techniques requires a superstructure for representing a set of alternatives, a mathematical model for modeling the alternatives, and an optimization technique for solving the problem. The optimization techniques are classified into exact and approximate [...] Read more.
The design of a flotation circuit based on optimization techniques requires a superstructure for representing a set of alternatives, a mathematical model for modeling the alternatives, and an optimization technique for solving the problem. The optimization techniques are classified into exact and approximate methods. The first has been widely used. However, the probability of finding an optimal solution decreases when the problem size increases. Genetic algorithms have been the approximate method used for designing flotation circuits when the studied problems were small. The Tabu-search algorithm (TSA) is an approximate method used for solving combinatorial optimization problems. This algorithm is an adaptive procedure that has the ability to employ many other methods. The TSA uses short-term memory to prevent the algorithm from being trapped in cycles. The TSA has many practical advantages but has not been used for designing flotation circuits. We propose using the TSA for solving the flotation circuit design problem. The TSA implemented in this work applies diversification and intensification strategies: diversification is used for exploring new regions, and intensification for exploring regions close to a good solution. Four cases were analyzed to demonstrate the applicability of the algorithm: different objective function, different mathematical models, and a benchmarking between TSA and Baron solver. The results indicate that the developed algorithm presents the ability to converge to a solution optimal or near optimal for a complex combination of requirements and constraints, whereas other methods do not. TSA and the Baron solver provide similar designs, but TSA is faster. We conclude that the developed TSA could be useful in the design of full-scale concentration circuits. Full article
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Open AccessArticle Spatial Mapping of Acidity and Geochemical Properties of Oxidized Tailings within the Former Eagle/Telbel Mine Site
Minerals 2019, 9(3), 180; https://doi.org/10.3390/min9030180
Received: 14 January 2019 / Revised: 6 March 2019 / Accepted: 12 March 2019 / Published: 14 March 2019
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Abstract
At some orphaned and abandoned mine sites, acid mine drainage can represent a complex challenge due to the advanced tailings’ oxidation state as well as the combination of other factors. At the field scale, several parameters control sulfides’ oxidation rates and, therefore, the [...] Read more.
At some orphaned and abandoned mine sites, acid mine drainage can represent a complex challenge due to the advanced tailings’ oxidation state as well as the combination of other factors. At the field scale, several parameters control sulfides’ oxidation rates and, therefore, the acidity generation. The objective of this paper is to map the acidity and geochemical properties of oxidized tailings within a closed tailings storage facility. Based on systematic sampling, various geochemical parameters were measured within the oxidized Joutel tailings, including the: Neutralization potential, acid-generating potential, net neutralization potential, neutralization potential ratio, paste pH, thickness of oxidized, hardpan, and transition zones. The different parameters were integrated in geographical information system (GISs) databases to quantify the spatial variability of the acidity and geochemical properties of oxidized tailings. The oxidized tailings were characterized by low sulfide (mainly as pyrite) and carbonate (mainly as siderite/ankerite) contents compared to unweathered tailings. Acidic zones, identified based on paste pH, were located in the eastern portion of the southern zone and at the northern tip of the northern zone. Full article
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Open AccessArticle Lithospheric Architecture and Metallogenesis in Liaodong Peninsula, North China Craton: Insights from Zircon Hf-Nd Isotope Mapping
Minerals 2019, 9(3), 179; https://doi.org/10.3390/min9030179
Received: 17 January 2019 / Revised: 19 February 2019 / Accepted: 8 March 2019 / Published: 14 March 2019
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Abstract
The Liaodong Peninsula is an important mineral province in northern China. Elucidating its lithospheric architecture and structural evolution is important for gold metallogenic research and exploration in the region. In this study, Hf-Nd isotope maps from magmatic rocks are constructed and compared to [...] Read more.
The Liaodong Peninsula is an important mineral province in northern China. Elucidating its lithospheric architecture and structural evolution is important for gold metallogenic research and exploration in the region. In this study, Hf-Nd isotope maps from magmatic rocks are constructed and compared to geological maps to correlate isotopic signatures with geological features. It is found that gold deposits of different age periods in Liaodong are located in areas with specific εHf(t) and εNd ranges (Triassic: from −8 to −4 and from −12 to −8, Jurassic: from −22 to −8 and from −14 to −8, Cretaceous: from −12 to −10 and from −22 to −20), respectively. This may reflect that when the Paleo-Pacific plate was subducted beneath the North China Craton, the magma was derived from the juvenile lower crust and the ancient lower crust, and formed the low-to-moderate hydrothermal Au-(Ag) and Pb-Zn deposits in the Triassic. In the Jurassic, continued subduction may have led to lithospheric thickening. Subsequently, the magma from the ancient lower crust upwelled and formed low-to-moderate hydrothermal Au deposits and porphyry Mo deposits. In the Cretaceous, crustal delamination may have taken place. The magma from the ancient lower crust upwelled and formed various low-to-moderate hydrothermal Au deposits. Full article
(This article belongs to the Special Issue Polymetallic Metallogenic System)
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Open AccessFeature PaperArticle Precipitation of CaCO3 Polymorphs from Aqueous Solutions: The Role of pH and Sulphate Groups
Minerals 2019, 9(3), 178; https://doi.org/10.3390/min9030178
Received: 15 February 2019 / Revised: 6 March 2019 / Accepted: 10 March 2019 / Published: 13 March 2019
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Abstract
In this work, we aimed to experimentally study the nucleation and growth of CaCO3 phases precipitated from supersaturated aqueous solutions in the presence of varying concentrations of sulphate oxyanion. The experiments were conducted under pH conditions close to neutral (7.6) and by [...] Read more.
In this work, we aimed to experimentally study the nucleation and growth of CaCO3 phases precipitated from supersaturated aqueous solutions in the presence of varying concentrations of sulphate oxyanion. The experiments were conducted under pH conditions close to neutral (7.6) and by considering a wide range of initial (SO42−)/(CO32−) ratios (0 to approx. 68) in the aqueous solution. We paid special attention to the evolution of the precipitates during ageing within a time framework of 14 days. The mineralogy, morphology, and composition of the precipitates were studied by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and EDX microanalysis. The concentration of sulphate ions in the reacted aqueous solution was studied by ICPs. The experimental results showed that the mineral composition of the precipitate recovered in each run varied with the (SO42−)/(CO32−) ratio in the parental solution, which influenced the mineral evolution of the precipitates during ageing. We observed that high concentrations of sulphate in the aqueous solution stabilized the vaterite precipitates and inhibited calcite formation. Furthermore, aragonite never precipitated directly from the solution, and it was only formed via a dissolution-precipitation process in solutions with a high (SO42−)/(CO32−) ratio after long reaction times. Finally, gypsum only precipitated after long ageing in those aqueous solutions with the highest concentration of sulphate. The reaction pathways during ageing, the morphology of the calcite crystals, and the composition of vaterite and calcite were discussed considering both kinetic and thermodynamic factors. These results showed a considerably more complex behavior of the system than that observed in experiments conducted under higher pHs and supersaturation levels and lower (SO42−)/(CO32−) ratios in the aqueous phase. Full article
(This article belongs to the Special Issue Crystallization in Solid Solution-Aqueous Solution Systems)
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Open AccessArticle The Geochemistry and Bioturbation of Clay Sediments Associated with Amalgamated Crusts at the Gagua Ridge
Minerals 2019, 9(3), 177; https://doi.org/10.3390/min9030177
Received: 15 February 2019 / Revised: 3 March 2019 / Accepted: 8 March 2019 / Published: 13 March 2019
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Abstract
Based on the analysis of geochemical and mineralogical compositions, deep sea clay sediment characteristics and their material sources were examined in the eastern flank of the Gagua Ridge. The mineralogy mainly consists of detrital clay minerals, quartz, and authigenic phillipsite. There is scarce [...] Read more.
Based on the analysis of geochemical and mineralogical compositions, deep sea clay sediment characteristics and their material sources were examined in the eastern flank of the Gagua Ridge. The mineralogy mainly consists of detrital clay minerals, quartz, and authigenic phillipsite. There is scarce biogenic debris (siliceous or calcareous). The consolidated sediments are more enriched in Si, Al, K, Na, Li, Sc, Cr, Rb, and Cs than the associated crusts and nodules. The unmixed sediment samples were mainlycontributed by Asian eolian dust. The onset of the outer Fe-Mn crust growth nearly coincides with the Central Asia aridification event at ~3.5 Ma, which resulted in an abrupt increase in eolian flux of Asian dust. Intensified surface primary productivity is assumed to bring more metals to deep waters, and eventually facilitate the outer Fe-Mn crust formation. Authigenic phillipsite may come from the alteration of local basic volcanic glasses and cause excess Al, high Al/Ti, and low Si/Al ratios. However, phillipsites hardly affect the abundance of rare earth elements (REEs) and their patterns. In addition, the investigation of two kinds of burrows inside the consolidated sediments reveals that the inner nodules of the amalgamated crusts may remain on the oxic sediment surface, due to frequent benthic activities. Full article
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Open AccessCase Report Heavy Mineral Sands in Brazil: Deposits, Characteristics, and Extraction Potential of Selected Areas
Minerals 2019, 9(3), 176; https://doi.org/10.3390/min9030176
Received: 15 January 2019 / Revised: 21 February 2019 / Accepted: 6 March 2019 / Published: 13 March 2019
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Abstract
In Brazil, heavy mineral sand deposits are still barely exploited, despite some references to Brazilian reserves and ilmenite concentrate production. The goal of this project is to characterize and investigate the potential recovery of heavy minerals from selected Brazilian placer occurrences. Two areas [...] Read more.
In Brazil, heavy mineral sand deposits are still barely exploited, despite some references to Brazilian reserves and ilmenite concentrate production. The goal of this project is to characterize and investigate the potential recovery of heavy minerals from selected Brazilian placer occurrences. Two areas of the coastal region were chosen, in Piaui state and in Bahia Provinces. In all samples, the heavy minerals of interest (ilmenite, monazite, rutile, and zircon) were identified by scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques and also quantified by X-ray fluorescence spectrometry (XRF) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The total heavy minerals (THM) in the Piaui samples were 6.45% and 10.14% THM, while the figure for the Bahia sample was 3.4% THM. The recovery test of the Bahia sample, using only physical separation equipment such as a shaking table and magnetic separator, showed valuable metallurgical recoveries at around or greater than 70% for each stage, and the final concentrate of pure ilmenite was composed of up to 60.0% titanium dioxide after the differential magnetic separation. Another aim is to compile accessible information about Brazilian heavy mineral main deposits complemented with a short economic overview. Full article
(This article belongs to the Special Issue Physical Separation and Enrichment)
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Open AccessArticle Utilisation of Water-Washing Pre-Treated Phosphogypsum for Cemented Paste Backfill
Minerals 2019, 9(3), 175; https://doi.org/10.3390/min9030175
Received: 22 January 2019 / Revised: 7 March 2019 / Accepted: 9 March 2019 / Published: 12 March 2019
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Abstract
Recycling phosphogypsum (PG) for cemented paste backfill (CPB) has been widely used at phosphate mines in China. However, the impurities in PG prolong the setting time and reduce the uniaxial compressive strength (UCS), limiting the engineering application of PG. This paper aims to [...] Read more.
Recycling phosphogypsum (PG) for cemented paste backfill (CPB) has been widely used at phosphate mines in China. However, the impurities in PG prolong the setting time and reduce the uniaxial compressive strength (UCS), limiting the engineering application of PG. This paper aims to investigate the feasibility of treated PG (TPG) washed repeatedly using deionised water (DW) for CPB. A water-washing pre-experiment was first conducted to find the proportion with the least DW demand and the effects of water-washing on ordinary PG (OPG). Then, based on the PG:DW ratio obtained from the pre-experiment, the properties of the OPG-based CPB (OCPB) and TPG-based CPB (TCPB) were tested using slump tests, UCS tests, and microstructural analysis. The results show that (1) after 11 water-washings at the PG:DW ratio of 1:1.75, the pH of the supernatant (pH = 6.328) meets the requirements of Chinese standard GB 8978-1996. (2) Water-washing improves the particle gradation quality of PG and removes the soluble impurities adsorbed at the surface of PG crystals. (3) The initial slump values of TCPB are 0.19–1.15 cm higher than that of OCPB, furthermore, the diffusivity values of TCPB are better than the performance of OCPB, with 0.61–1.68 cm of superiority. (4) The UCS values of TCPB are up to 0.838 MPa, 1.953 MPa, and 2.531 MPa, after curing for 7, 14, and 28 days. These are 0.283 MPa, 0.823 MPa, and 0.881 MPa higher than that of OCPB, respectively. It can be concluded that water-washing pre-treatment greatly improves the workability and mechanical property of PG-based CPB. These results are of great value for creating a reliable and environmentally superior alternative for the recycling of PG and for safer mining production. Full article
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Open AccessFeature PaperArticle Petrogenetic Study of the Multiphase Chibougamau Pluton: Archaean Magmas Associated with Cu–Au Magmato-Hydrothermal Systems
Minerals 2019, 9(3), 174; https://doi.org/10.3390/min9030174
Received: 13 February 2019 / Revised: 28 February 2019 / Accepted: 8 March 2019 / Published: 12 March 2019
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Abstract
The Chibougamau pluton is a Neoarchean multiphase intrusion that is related to Cu–Au porphyry-style deposits. In Archean greenstone belts, porphyries are marginal and poorly documented mineralizations. Such deposits are, however, important in the Chibougamau area, where the main historical mining camp (Central Camp) [...] Read more.
The Chibougamau pluton is a Neoarchean multiphase intrusion that is related to Cu–Au porphyry-style deposits. In Archean greenstone belts, porphyries are marginal and poorly documented mineralizations. Such deposits are, however, important in the Chibougamau area, where the main historical mining camp (Central Camp) is a magmato-hydrothermal system. Understanding such systems requires documenting the related magmatic rocks. This contribution focuses on the petrogenesis of the Chibougamau pluton to elucidate how the intrusion participated in Cu and Au mineralized systems. Using field descriptions, whole-rock analyses, and petrographic observations, we describe the source, emplacement mechanism, and chemical evolution of the Chibougamau pluton. The Chibougamau pluton is a TTD (tonalite-trondhjemite-diorite) suite that contains more K than most plutons of similar age. This suite was produced from a heterogeneous source; i.e., a hydrated basalt and possibly a metasomatized mantle. These are rare (and thus prospective) characteristics for an Archean intrusion. In addition, differentiation may have been sufficiently prolonged in the diorite phase to concentrate metals and fluids in the evolved magma. These magmatic constraints must now be tested against a renewed understanding of the Cu-dominated mineralized systems of the Chibougamau area. Full article
(This article belongs to the Section Mineral Deposits)
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Open AccessArticle Measuring Copper, Lead and Zinc Concentrations and Oral Bioaccessibility as Part of the Soils in Scottish Schools Project
Minerals 2019, 9(3), 173; https://doi.org/10.3390/min9030173
Received: 6 February 2019 / Revised: 5 March 2019 / Accepted: 7 March 2019 / Published: 11 March 2019
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Abstract
Determination of potentially toxic elements in soils with which children have regular contact can provide valuable information to support health risk assessment. It is also important to engage schoolchildren with soil science so that they become well-informed citizens. The Soils in Scottish Schools [...] Read more.
Determination of potentially toxic elements in soils with which children have regular contact can provide valuable information to support health risk assessment. It is also important to engage schoolchildren with soil science so that they become well-informed citizens. The Soils in Scottish Schools project involved pupils across Scotland in the collection of soil from school grounds for determination of copper, lead and zinc. Samples were subjected to microwave-assisted aqua-regia digestion to determine pseudototal analyte concentrations. The simplified bioaccessibility extraction test was applied to estimate bioaccessibility. Analysis was performed by inductively coupled plasma mass spectrometry. Pseudototal analyte concentrations varied widely: Cu 15.6–220 mg∙kg−1; Pb 24.6–479 mg∙kg−1 and Zn 52.5–860 mg∙kg−1. Higher concentrations were measured in urban areas, which were historically home to heavy manufacturing industries, with lower concentrations in soils from more rural schools. Bioaccessible analyte concentrations also varied widely (Cu 3.94–126 mg∙kg−1; Pb 6.29–216 mg∙kg−1 and Zn 4.38–549 mg∙kg−1) and followed similar trends to pseudototal concentrations. None of the elements studied posed a significant health risk to children through accidental soil ingestion whilst at play during breaks in the school day, although the relatively high bioaccessible levels of lead at some locations are worthy of further investigation. Full article
(This article belongs to the Special Issue Medical Geology)
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Open AccessArticle Mine Backfilling in the Permafrost, Part II: Effect of Declining Curing Temperature on the Short-Term Unconfined Compressive Strength of Cemented Paste Backfills
Minerals 2019, 9(3), 172; https://doi.org/10.3390/min9030172
Received: 30 January 2019 / Revised: 5 March 2019 / Accepted: 7 March 2019 / Published: 11 March 2019
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Abstract
When cemented paste backfill (CPB) is used to fill underground stopes opened in permafrost, depending on the distance from the permafrost wall, the curing temperature within the CPB matrix decreases progressively over time until equilibrium with the permafrost is reached (after several years). [...] Read more.
When cemented paste backfill (CPB) is used to fill underground stopes opened in permafrost, depending on the distance from the permafrost wall, the curing temperature within the CPB matrix decreases progressively over time until equilibrium with the permafrost is reached (after several years). In this study, the influence of declining curing temperature (above freezing temperature) on the evolution of the unconfined compressive strength (UCS) of CPB over 28 days’ curing is investigated. CPB mixtures were prepared with a high early (HE) cement and a blend of 80% slag and 20% General Use cement (S-GU) at 5% and 3% contents and cured at room temperature in a humidity chamber and under decreasing temperatures in a temperature-controlled chamber. Results indicate that UCS is higher for CPB cured at room temperature than under declining temperatures. UCS increases progressively from the stope wall toward the inside of the CPB mass. Under declines in curing temperature, HE cement provides better short-term compressive strength than does S-GU binder. In addition, the gradual decline in temperature does not appear to affect the fact that the higher the binder proportion, the greater the strength development. Therefore, UCS is higher for samples prepared with 5% than 3% HE cement. Findings are discussed in terms of practical applications. Full article
(This article belongs to the Special Issue Backfilling Materials for Underground Mining)
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Open AccessEditorial Editorial for Special Issue “Structural Control of Mineral Deposits: Theory and Reality”
Minerals 2019, 9(3), 171; https://doi.org/10.3390/min9030171
Received: 7 March 2019 / Accepted: 8 March 2019 / Published: 11 March 2019
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Abstract
“Structural Control” remains a crucial point that is frequently absent in scientific and/or economic analyses of ore deposits, whatever their type and class, although a selection of references illustrates its importance [...] Full article
Open AccessArticle The Overmaraat-Gol Alkaline Pluton in Northern Mongolia: U–Pb Age and Preliminary Implications for Magma Sources and Tectonic Setting
Minerals 2019, 9(3), 170; https://doi.org/10.3390/min9030170
Received: 11 January 2019 / Revised: 6 March 2019 / Accepted: 6 March 2019 / Published: 10 March 2019
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Abstract
A new Wenlockian zircon U–Pb age (~426 Ma) of the Overmaraat-Gol nepheline syenite (foyaite, juvite) pluton in the SW Lake Hovsgol area (Northern Mongolia) prompts a long history of alkaline magmatism in the western Central Asian Orogenic Belt, exceeding the duration of the [...] Read more.
A new Wenlockian zircon U–Pb age (~426 Ma) of the Overmaraat-Gol nepheline syenite (foyaite, juvite) pluton in the SW Lake Hovsgol area (Northern Mongolia) prompts a long history of alkaline magmatism in the western Central Asian Orogenic Belt, exceeding the duration of the Devonian and Permian–Triassic events. The LILE and HFSE patterns of pluton samples analyzed by X-ray fluorescence (XRF) and inductively coupled plasma (ICP-MS) methods indicate intrusion in a complex tectonic setting during interaction of a mantle plume with accretionary-collisional complexes that previously formed on the active continental margin. As a result, the parent magma had a heterogeneous source with mixed mantle (PREMA and EM) and crustal components. This source composition is consistent with Nd–Sr isotope ratios of the Overmaraat-Gol alkaline rocks, from −0.1 to −1.2 εNd(t) and from ~0.706 to 0.707 87Sr/86Sr(t). Full article
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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