Abstract. In heavy mineral concentrates of the Elbe, gold and platinum-group minerals (PGMs) are observed. Two fractions (> 63 and < 63 µm) of the concentrate are analyzed by reflected-light microscopy, scanning electron microscopy with automated mineralogy software and electron microprobe analysis (EPMA). Other heavy minerals are cassiterite, ferberite, monazite, uraninite, columbite–tantalite, magnetite, zircon and cinnabar. Scanning electron microscopy determined the modal abundance of PGMs, gold and the other heavy minerals. The PGMs are mainly Os–Ir–Ru–(Pt) alloys, Pt–Fe alloys, sperrylite and rustenburgite. Compositional variation of PGMs and gold was analyzed by EPMA. This showed that Pt–Fe alloys are (1) native platinum (> 80 atom %), (2) ferroan Pt (20 atom % to 50 atom % Fe), (3) isoferroplatinum (2.64 to 3.04 apfu of sum PGE, platinum-group element), (4) tetraferroplatinum group with Ni + Cu + Fe ≈ 50 atom %, and (5) γ(Pt,Fe) with sum PGE > 3.04 apfu. The Os–Ir–Ru–(Pt) alloys show large compositional variations. Platinum and Fe enrichment is typically observed for Ir-rich Os–Ir–Ru alloys. Gold particles often show compositional zoning of Ag-rich cores and Ag-poor rims due to selective leaching of Ag. Similarly, Hg-rich rims of gold particles are analyzed. These are interpreted as the results of in situ amalgamation due to mobilization of Hg from the associated cinnabar particles. The size and shape of the gold particles generally argue for short transportation distances. Similarly, almost euhedral sperrylite and Pt–Fe alloys suggest a source region close to the sampling site. However, roundish Os–Ir–Ru–(Pt) alloys presumably have experienced longer transportation in the river. Gabbroic dikes of the Lusatia block contain sperrylite and gold particles, which can be the source for these particles found in the concentrate. The composition of the Os–Ir–Ru–(Pt) alloys is similar to previous studies on the Vestřev placer in Czech Republic. Both locations are within the drainage area of the Elbe and can therefore be the source of the PGM and gold particles in the concentrate.
{"title":"Mineralogy and mineral chemistry of detrital platinum-group minerals and gold particles from the Elbe, Germany","authors":"M. Junge, S. Goldmann, H. Wotruba","doi":"10.5194/ejm-35-439-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-439-2023","url":null,"abstract":"Abstract. In heavy mineral concentrates of the Elbe, gold and\u0000platinum-group minerals (PGMs) are observed. Two fractions (> 63\u0000and < 63 µm) of the concentrate are analyzed by\u0000reflected-light microscopy, scanning electron microscopy with automated\u0000mineralogy software and electron microprobe analysis (EPMA). Other heavy\u0000minerals are cassiterite, ferberite, monazite, uraninite,\u0000columbite–tantalite, magnetite, zircon and cinnabar. Scanning electron\u0000microscopy determined the modal abundance of PGMs, gold and the other heavy\u0000minerals. The PGMs are mainly Os–Ir–Ru–(Pt) alloys, Pt–Fe alloys, sperrylite\u0000and rustenburgite. Compositional variation of PGMs and gold was analyzed by\u0000EPMA. This showed that Pt–Fe alloys are (1) native platinum (> 80 atom %), (2) ferroan Pt (20 atom % to 50 atom % Fe), (3) isoferroplatinum (2.64 to 3.04 apfu of sum PGE, platinum-group\u0000element), (4) tetraferroplatinum group with Ni + Cu + Fe ≈ 50 atom %, and (5)\u0000γ(Pt,Fe) with sum PGE > 3.04 apfu. The Os–Ir–Ru–(Pt)\u0000alloys show large compositional variations. Platinum and Fe enrichment is\u0000typically observed for Ir-rich Os–Ir–Ru alloys. Gold particles often show\u0000compositional zoning of Ag-rich cores and Ag-poor rims due to selective\u0000leaching of Ag. Similarly, Hg-rich rims of gold particles are analyzed.\u0000These are interpreted as the results of in situ amalgamation due to mobilization of\u0000Hg from the associated cinnabar particles. The size and shape of the gold\u0000particles generally argue for short transportation distances. Similarly,\u0000almost euhedral sperrylite and Pt–Fe alloys suggest a source region close to\u0000the sampling site. However, roundish Os–Ir–Ru–(Pt) alloys presumably have\u0000experienced longer transportation in the river. Gabbroic dikes of the\u0000Lusatia block contain sperrylite and gold particles, which can be the source\u0000for these particles found in the concentrate. The composition of the\u0000Os–Ir–Ru–(Pt) alloys is similar to previous studies on the Vestřev\u0000placer in Czech Republic. Both locations are within the drainage area of the\u0000Elbe and can therefore be the source of the PGM and gold particles in\u0000the concentrate.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48121856","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. In this paper we present a Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA-CNMNC)-accepted scheme for the classification and nomenclature of the triphylite group of minerals. The general formula of those minerals is M1M2TO4, where M1 and M2 refer to cations in an octahedral coordination: M1 = □, Na, Li; M2 = Mn2+, Fe2+, Mg, Fe3+, Mn3+, and T to tetrahedrally coordinated P5+ cations. The group contains the Li-bearing phosphates triphylite [LiFe2+(PO4)] and lithiophilite [LiMn2+(PO4)] and their oxidation products heterosite [Fe3+(PO4)] and purpurite [Mn3+(PO4)], as well as the Na-bearing phosphates natrophilite [NaMn2+(PO4)] and karenwebberite [NaFe2+(PO4)]. The Li–Mg-bearing phosphate simferite has been redefined as LiMg(PO4). Ferrisicklerite and sicklerite correspond to intermediate phases in the triphylite–heterosite and lithiophilite–purpurite solid solutions; consequently, according to the CNMNC dominant-constituent rule, they are discredited. A new mineral oxidation sequence is defined, which considers the different oxidation capacity of iron and manganese, and therefore replaces the traditional Quensel–Mason sequence. The formula calculation procedure for Li-bearing species, based on electron microprobe analyses and single-crystal X-ray diffraction data, is also described.
摘要在本文中，我们提出了国际矿物学协会(IMA-CNMNC)接受的新矿物、命名和分类委员会(Commission on New Minerals, naming and Classification)对三叶石矿物群的分类和命名方案。这些矿物的通式为M1M2TO4，其中M1和M2是指在八面体配位中的位置:M1 =□，Na, Li;M2 = Mn2+，Fe2+， Mg, Fe3+， Mn3+，和T到四面体配位p5 +阳离子。该基团含有含锂磷酸盐三叶石[LiFe2+(PO4)]、亲锂矿[LiMn2+(PO4)]及其氧化产物异质矿[Fe3+(PO4)]、紫砂矿[Mn3+(PO4)]，以及含钠磷酸盐亲钠矿[NaMn2+(PO4)]、卡伦钠矿[NaFe2+(PO4)]。含铁镁磷铁铁矿重新定义为LiMg(PO4)。铁绢石和镰绢石对应于三绿石-异质石和嗜石-紫石固溶体的中间相，因此，根据CNMNC优势成分规则，它们是不可信的。考虑到铁和锰的不同氧化能力，定义了一种新的矿物氧化序列，从而取代了传统的Quensel-Mason序列。本文还描述了基于电子探针分析和单晶x射线衍射数据的含锂物质的公式计算过程。
{"title":"Nomenclature of the triphylite group of minerals","authors":"L. Lyalina, E. Selivanova, F. Hatert","doi":"10.5194/ejm-35-427-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-427-2023","url":null,"abstract":"Abstract. In this paper we present a Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA-CNMNC)-accepted scheme for the\u0000classification and nomenclature of the triphylite group of minerals. The\u0000general formula of those minerals is M1M2TO4, where M1 and M2 refer to\u0000cations in an octahedral coordination: M1 = □, Na, Li; M2 = Mn2+,\u0000Fe2+, Mg, Fe3+, Mn3+, and T to tetrahedrally coordinated\u0000P5+ cations. The group contains the Li-bearing phosphates triphylite\u0000[LiFe2+(PO4)] and lithiophilite [LiMn2+(PO4)] and their\u0000oxidation products heterosite [Fe3+(PO4)] and purpurite\u0000[Mn3+(PO4)], as well as the Na-bearing phosphates natrophilite\u0000[NaMn2+(PO4)] and karenwebberite [NaFe2+(PO4)]. The\u0000Li–Mg-bearing phosphate simferite has been redefined as LiMg(PO4).\u0000Ferrisicklerite and sicklerite correspond to intermediate phases in the\u0000triphylite–heterosite and lithiophilite–purpurite solid solutions;\u0000consequently, according to the CNMNC dominant-constituent rule, they are\u0000discredited. A new mineral oxidation sequence is defined, which considers\u0000the different oxidation capacity of iron and manganese, and therefore\u0000replaces the traditional Quensel–Mason sequence. The formula calculation\u0000procedure for Li-bearing species, based on electron microprobe analyses and\u0000single-crystal X-ray diffraction data, is also described.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45699777","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Robin Hintzen, W. Werner, M. Hauck, R. Klemd, L. Fischer
Abstract. The Black Forest hosts a wide range of hydrothermal mineralization, including fluorite–barite vein deposits. In a detailed investigation of the Finstergrund and Tannenboden deposits in the Wieden mining district (southern Black Forest), the diversity, geochemical evolution and relative chronology of multistage fluorite precipitation is tracked on the basis of rare earth element (REE) geochemistry, geologic field relationships and crystal zoning. Geochemical discrimination and mathematical λ coefficients suggest a total of seven fluorite REE groups, at least three distinguishable post-Variscan fluid mobilization events and independent formation histories for the deposits despite their spatial proximity. Fluorite vein mineralization at the Finstergrund deposit evolved over three fluid generations, was derived from gneissic source aquifers and comprises five distinct fluorite REE groups: the first fluid generation is characterized by fluorite precipitation above 200 ∘C (“group III”), below 200 ∘C (“group I”) and after fractional crystallization (“group IV”); the second generation comprises remobilized fluorite (“group II”); and the third generation revealed fluorite precipitation by meteoric water mixing (“group V”). Fluorite vein formation at the Tannenboden deposit is associated with two distinct fluorite REE patterns derived from the same fluid generation: fluorite precipitation above 200 ∘C (“group VII”) and after cooling below 200 ∘C (“group VI”). Its fluid source aquifer lithology best matches migmatites contrary to previous models that suggest either gneissic or granitic aquifer rocks for fluorite vein precipitation in the Black Forest. The decoupled formation history between the deposits is tectonically controlled as suggested by a new genetic model for the Wieden mining district. The model argues for a change in the local fluid percolation network and the termination of hydrothermal activity at the Tannenboden deposit after the first fluid mobilization event. The geochemical evolution of multistage fluorite mineralization, as exemplified by the Tannenboden and Finstergrund deposits in combination with other fluorite mineralizations in the Black Forest, provides unique insights into the lithospheric origin and precipitation behaviour of fluorite by various fluid–rock interaction processes occurring in large hydrothermal systems. The local diversity of REE patterns emphasizes the need for detailed investigations of individual hydrothermal vein deposits.
{"title":"Multistage fluorite mineralization in the southern Black Forest, Germany: evidence from rare earth element (REE) geochemistry","authors":"Robin Hintzen, W. Werner, M. Hauck, R. Klemd, L. Fischer","doi":"10.5194/ejm-35-403-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-403-2023","url":null,"abstract":"Abstract. The Black Forest hosts a wide range of hydrothermal\u0000mineralization, including fluorite–barite vein deposits. In a detailed\u0000investigation of the Finstergrund and Tannenboden deposits in the Wieden\u0000mining district (southern Black Forest), the diversity, geochemical evolution\u0000and relative chronology of multistage fluorite precipitation is tracked on\u0000the basis of rare earth element (REE) geochemistry, geologic field relationships and crystal\u0000zoning. Geochemical discrimination and mathematical λ coefficients\u0000suggest a total of seven fluorite REE groups, at least three distinguishable\u0000post-Variscan fluid mobilization events and independent formation histories\u0000for the deposits despite their spatial proximity. Fluorite vein\u0000mineralization at the Finstergrund deposit evolved over three fluid\u0000generations, was derived from gneissic source aquifers and comprises five\u0000distinct fluorite REE groups: the first fluid generation is characterized by\u0000fluorite precipitation above 200 ∘C (“group III”), below 200 ∘C (“group I”) and after fractional crystallization (“group IV”);\u0000the second generation comprises remobilized fluorite (“group II”); and the\u0000third generation revealed fluorite precipitation by meteoric water mixing\u0000(“group V”). Fluorite vein formation at the Tannenboden deposit is\u0000associated with two distinct fluorite REE patterns derived from the same\u0000fluid generation: fluorite precipitation above 200 ∘C (“group\u0000VII”) and after cooling below 200 ∘C (“group VI”). Its fluid\u0000source aquifer lithology best matches migmatites contrary to previous models\u0000that suggest either gneissic or granitic aquifer rocks for fluorite vein\u0000precipitation in the Black Forest. The decoupled formation history between\u0000the deposits is tectonically controlled as suggested by a new genetic model\u0000for the Wieden mining district. The model argues for a change in the local\u0000fluid percolation network and the termination of hydrothermal activity at\u0000the Tannenboden deposit after the first fluid mobilization event. The geochemical evolution of multistage fluorite mineralization, as\u0000exemplified by the Tannenboden and Finstergrund deposits in combination with\u0000other fluorite mineralizations in the Black Forest, provides unique insights\u0000into the lithospheric origin and precipitation behaviour of fluorite by\u0000various fluid–rock interaction processes occurring in large hydrothermal\u0000systems. The local diversity of REE patterns emphasizes the need for\u0000detailed investigations of individual hydrothermal vein deposits.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41426744","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ferdinando Bosi, Frédéric Hatert, Marco Pasero, Stuart J. Mills
{"title":"IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) – Newsletter 73","authors":"Ferdinando Bosi, Frédéric Hatert, Marco Pasero, Stuart J. Mills","doi":"10.5194/ejm-35-397-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-397-2023","url":null,"abstract":"","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135335911","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Marques, T. Allard, C. Gautheron, B. Baptiste, R. Pinna‐Jamme, G. Morin, L. Delbes, P. Vidal‐Torrado
Abstract. Interpreting the ages of supergene mineralogical phases in laterite is complex because they consist of polycrystalline mixtures of different phases at the microscopic scale that could be crystalized at different epochs. Among the geochronometers, the (U-Th)/He method on hematite and goethite is more often used, but ages can be difficult to interpret due to phases mixing. To resolve this issue, this study proposes a methodology for performing detailed mineralogical analysis of hematite and goethite single grains prior to their dating using the (U-Th)/He method. Strictly non-destructive mineralogy of single grains is not achievable by classical tools, such as conventional powder XRD (X-ray diffraction; requiring at least some milligrams of powder) or SEM (scanning electron microscopy; that can contaminate the grain by coating or fixing). Therefore, we performed X-ray diffraction patterns of single grains using high-flux X-ray beams from both a rotating anode (XRD_rotat) laboratory diffractometer and a synchrotron beamline (XRD_synch) and compared the results in order to design a method based on XRD_rotat only. For this purpose, two samples from the pisolitic facies of a Brazilian ferruginous duricrust (Alto Paranaíba region, Minas Gerais State, Brazil) were chosen because they presented a usual heterogeneity. Rietveld refinements of the XRD patterns obtained from both XRD_rotat and XRD_synch yielded similar results for the weight percentage ratio of the main phases and mean coherent domain sizes and less similar results for Al substitution rates, thus validating the XRD_rotat approach. No beam damage was observed when increasing X-ray exposure time, neither on XRD patterns nor on (U-Th)/He ages. Hence, sub-millimeter, undisturbed grains can be used to analyze the mineralogy of ferruginous duricrusts by XRD_rotat with a short exposure, and the same grains can subsequently be dated by (U-Th)/He geochronology analysis. The (U-Th)/He dating of pisolitic core and cortex grains also provided meaningful ages: they revealed two evolution phases of the ferruginous duricrust, which occurred at or before the Oligocene for the pisolitic core and middle Miocene for the pisolitic cortex, agreeing with the previous model for the development of pisolites. The mineralogy of single grains selected for dating is helpful for discussing the crystallization ages, and the high-flux XRD approach may be applied to other supergene mineral parageneses used for absolute dating.
{"title":"Supergene phases from ferruginous duricrusts: non-destructive microsampling and mineralogy prior to (U–Th) ∕ He geochronological analysis","authors":"K. Marques, T. Allard, C. Gautheron, B. Baptiste, R. Pinna‐Jamme, G. Morin, L. Delbes, P. Vidal‐Torrado","doi":"10.5194/ejm-35-383-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-383-2023","url":null,"abstract":"Abstract. Interpreting the ages of supergene mineralogical phases in\u0000laterite is complex because they consist of polycrystalline mixtures of\u0000different phases at the microscopic scale that could be crystalized at\u0000different epochs. Among the geochronometers, the (U-Th)/He method on\u0000hematite and goethite is more often used, but ages can be difficult to interpret\u0000due to phases mixing. To resolve this issue, this study proposes a\u0000methodology for performing detailed mineralogical analysis of hematite and\u0000goethite single grains prior to their dating using the (U-Th)/He method.\u0000Strictly non-destructive mineralogy of single grains is not achievable by\u0000classical tools, such as conventional powder XRD (X-ray diffraction; requiring at least some milligrams\u0000of powder) or SEM (scanning electron microscopy; that can contaminate the grain by coating or fixing).\u0000Therefore, we performed X-ray diffraction patterns of single grains using\u0000high-flux X-ray beams from both a rotating anode (XRD_rotat)\u0000laboratory diffractometer and a synchrotron beamline (XRD_synch) and compared the results in order to design a method based on\u0000XRD_rotat only. For this purpose, two samples from the\u0000pisolitic facies of a Brazilian ferruginous duricrust (Alto Paranaíba\u0000region, Minas Gerais State, Brazil) were chosen because they presented a\u0000usual heterogeneity. Rietveld refinements of the XRD patterns obtained from\u0000both XRD_rotat and XRD_synch yielded similar\u0000results for the weight percentage ratio of the main phases and mean coherent domain\u0000sizes and less similar results for Al substitution rates, thus validating the\u0000XRD_rotat approach. No beam damage was observed when\u0000increasing X-ray exposure time, neither on XRD patterns nor on (U-Th)/He ages. Hence, sub-millimeter, undisturbed grains can be used to analyze the\u0000mineralogy of ferruginous duricrusts by XRD_rotat with a\u0000short exposure, and the same grains can subsequently be dated by (U-Th)/He geochronology analysis. The (U-Th)/He dating of pisolitic core and cortex\u0000grains also provided meaningful ages: they revealed two evolution phases of\u0000the ferruginous duricrust, which occurred at or before the Oligocene for\u0000the pisolitic core and middle Miocene for the pisolitic cortex, agreeing with the\u0000previous model for the development of pisolites. The mineralogy of single\u0000grains selected for dating is helpful for discussing the crystallization\u0000ages, and the high-flux XRD approach may be applied to other supergene\u0000mineral parageneses used for absolute dating.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43306824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. A natural sample of Fe-bearing paramontroseite (V0.84Fe0.19Al0.03O2; a = 4.8960(14), b = 9.395(3), c = 2.9163(5) Å, V = 134.14(6) Å3; space group Pbnm) from Prachovice mine (Czech Republic) was investigated to shed light on cation partitioning and behavior upon heating. XRD experiments showed that V and Fe are not vicariant of one another, as V occupies the octahedral site at (0.09, 0.14, 0.25), whereas Fe enters a tetrahedral site at (0.41, 0.06, 0.25), the latter expected to be empty in the ideal structure. Thermal expansion is anisotropic, leading to the following β coefficients: -2.0×10-5, 3.0×10-5, 0.8×10-5 and 1.8×10-5 ∘C−1 for a, b, c and V, respectively. At T higher than 350 ∘C, V undergoes oxidation, from [4+] to [5+], and paramontroseite decomposes into Fe-tetrapolyvanadate (Fe2V4O13) and V-pentoxide (V2O5). µ-Raman spectroscopy analyses confirmed that paramontroseite is sensitive to heating: the crystal surface invested by the laser beam degrades very quickly, leading to the phases revealed by diffraction measurements. There is no evidence for the formation at high T of a rutile-type phase, as we observed for iso-structural ramsdellite MnO2.
摘要含铁副斜长辉石(v0.84 fe0.19 al0.030 o2;= 4.8960 (14), b = 9.395 (3), c = 2.9163 (5), V = 134.14 (6) A3;研究了来自捷克共和国prachovice矿的空间群Pbnm)，以揭示其在加热时的阳离子分配和行为。XRD实验表明，在理想结构中，V和Fe不是相互替换的，V在(0.09,0.14,0.25)处占据八面体位置，而Fe在(0.41,0.06,0.25)处进入四面体位置，四面体位置为空。热膨胀是各向异性的，导致β系数如下:-2.0×10-5, 3.0×10-5, 0.8×10-5 and1.8×10-5对a, b, C和V分别是C−1。在T大于350°C时，V发生从[4+]到[5+]的氧化，副斜锰矿分解成四多钒酸铁(Fe2V4O13)和五氧化钒(V2O5)。微拉曼光谱分析证实，顺滑石对加热很敏感:激光束注入的晶体表面降解得非常快，导致衍射测量显示的相。没有证据表明在高温度下形成金红石型相，而我们在等结构的ramsdellite MnO2中观察到这一点。
{"title":"Fe-bearing vanadium dioxide–paramontroseite: structural details and high-temperature transformation","authors":"N. Curetti, A. Pavese","doi":"10.5194/ejm-35-373-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-373-2023","url":null,"abstract":"Abstract. A natural sample of Fe-bearing paramontroseite\u0000(V0.84Fe0.19Al0.03O2; a = 4.8960(14), b = 9.395(3),\u0000c = 2.9163(5) Å, V = 134.14(6) Å3; space group Pbnm) from\u0000Prachovice mine (Czech Republic) was investigated to shed light on cation\u0000partitioning and behavior upon heating. XRD experiments showed that V and Fe\u0000are not vicariant of one another, as V occupies the octahedral site at (0.09, 0.14, 0.25), whereas Fe enters a tetrahedral site at (0.41, 0.06, 0.25), the\u0000latter expected to be empty in the ideal structure. Thermal expansion is\u0000anisotropic, leading to the following β coefficients: -2.0×10-5, 3.0×10-5, 0.8×10-5 and\u00001.8×10-5 ∘C−1 for a, b, c and V,\u0000respectively. At T higher than 350 ∘C, V undergoes oxidation, from\u0000[4+] to [5+], and paramontroseite decomposes into Fe-tetrapolyvanadate\u0000(Fe2V4O13) and V-pentoxide (V2O5). µ-Raman\u0000spectroscopy analyses confirmed that paramontroseite is sensitive to heating:\u0000the crystal surface invested by the laser beam degrades very quickly,\u0000leading to the phases revealed by diffraction measurements. There is no\u0000evidence for the formation at high T of a rutile-type phase, as we observed\u0000for iso-structural ramsdellite MnO2.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71223816","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yanjuan Wang, F. Nestola, Huai-kun Li, Z. Hou, M. Pamato, D. Novella, Alessandra Lorenzetti, Pia Antonietta Antignani, P. Cornale, J. Nava, G. Dong, Kai Qu
Abstract. We have investigated a suite of natural diamonds from the kimberlite pipe of the Changma Kimberlite Belt, Mengyin County, Shandong Province, China, with the aim of constraining pressures and temperatures of formation. Here we report the non-destructive investigation of an olivine inclusion still entrapped within a lithospheric diamond by single-crystal X-ray diffraction. We were able to refine anisotropically its crystal structure to R1= 1.42 % using ionized scattering curves; this allows estimation of the composition of the olivine as Mg1.82Fe0.18SiO4. This composition corresponds to a calculated unit-cell volume equal to V= 292.70 Å3 at room temperature and pressure. We have validated the above-calculated composition and unit-cell volume by releasing the inclusion from the diamond host, resulting in a consistent composition calculated using non-destructive methods of Mg1.84Fe0.16SiO4 and V= 292.80 ± 0.07 Å3. Considering that the unit-cell volume of the olivine still inside its diamond host is V= 289.7 ± 0.2 Å3, we calculated a residual pressure Pinc= 1.4 ± 0.1 GPa with respect to the released crystal and Pinc= 1.3 ± 0.2 GPa with respect to the volume calculated from the “composition” indirectly retrieved by the structure refinement under ambient conditions. The two values of Pinc overlap within experimental uncertainty. We performed Fourier transform infrared (FTIR) analysis on the diamond host in order to calculate its mantle residence temperature, Tres, which resulted in a value of 1189 ∘C (for an assumed diamond age of 3 Ga) and 1218 ∘C (for an age of 1 Ga), with an average Tres equal to 1204 ± 15 ∘C. Using the most up-to-date pressure–volume–temperature equations of state for olivine and diamond, the residual pressure Pinc= 1.4 ± 0.1 GPa and average residence temperature of the diamond host Tres= 1204 ∘C, we retrieved a pressure of entrapment Ptrap= 6.3 ± 0.4 GPa. Using the non-destructive approach and relative Pinc = 1.3 GPa, we obtained a perfectly overlapping Ptrap= 6.2 GPa, within experimental uncertainty. This entrapment pressure corresponds to depths of about 190 ± 12 km. These results demonstrate that for high-quality crystal structure data measured on inclusions still trapped within diamond hosts, even a non-destructive approach can be used to calculate the depth of formation of diamond–olivine pairs. In terms of geological implications, the results from this work show that Changma diamonds formed under a conductive geotherm lying between 35 and 40 mW m−2, at a depth of about 190 km. This value lies within the recently reported upper limit of the average depth of formation of worldwide lithospheric diamonds, which is 175 ± 15 km and is in agreement with P–T data obtained in the literature from kimberlite xenoliths.
{"title":"In situ single-crystal X-ray diffraction of olivine inclusion in diamond from Shandong, China: implications for the depth of diamond formation","authors":"Yanjuan Wang, F. Nestola, Huai-kun Li, Z. Hou, M. Pamato, D. Novella, Alessandra Lorenzetti, Pia Antonietta Antignani, P. Cornale, J. Nava, G. Dong, Kai Qu","doi":"10.5194/ejm-35-361-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-361-2023","url":null,"abstract":"Abstract. We have investigated a suite of natural diamonds from the\u0000kimberlite pipe of the Changma Kimberlite Belt, Mengyin County, Shandong\u0000Province, China, with the aim of constraining pressures and temperatures of\u0000formation. Here we report the non-destructive investigation of an olivine\u0000inclusion still entrapped within a lithospheric diamond by single-crystal\u0000X-ray diffraction. We were able to refine anisotropically its crystal\u0000structure to R1= 1.42 % using ionized scattering curves; this\u0000allows estimation of the composition of the olivine as\u0000Mg1.82Fe0.18SiO4. This composition corresponds to a\u0000calculated unit-cell volume equal to V= 292.70 Å3 at room\u0000temperature and pressure. We have validated the above-calculated composition\u0000and unit-cell volume by releasing the inclusion from the diamond host,\u0000resulting in a consistent composition calculated using non-destructive\u0000methods of Mg1.84Fe0.16SiO4 and V= 292.80 ± 0.07 Å3. Considering that the unit-cell volume of the olivine still\u0000inside its diamond host is V= 289.7 ± 0.2 Å3, we calculated\u0000a residual pressure Pinc= 1.4 ± 0.1 GPa with respect to the\u0000released crystal and Pinc= 1.3 ± 0.2 GPa with respect to the\u0000volume calculated from the “composition” indirectly retrieved by the\u0000structure refinement under ambient conditions. The two values of Pinc\u0000overlap within experimental uncertainty. We performed Fourier transform infrared (FTIR) analysis on the\u0000diamond host in order to calculate its mantle residence temperature,\u0000Tres, which resulted in a value of 1189 ∘C (for an assumed\u0000diamond age of 3 Ga) and 1218 ∘C (for an age of 1 Ga), with an\u0000average Tres equal to 1204 ± 15 ∘C. Using the most up-to-date pressure–volume–temperature equations of state for\u0000olivine and diamond, the residual pressure Pinc= 1.4 ± 0.1 GPa\u0000and average residence temperature of the diamond host Tres= 1204 ∘C, we retrieved a pressure of entrapment Ptrap= 6.3 ± 0.4 GPa. Using the non-destructive approach and relative Pinc = 1.3 GPa, we obtained a perfectly overlapping Ptrap= 6.2 GPa,\u0000within experimental uncertainty. This entrapment pressure corresponds to\u0000depths of about 190 ± 12 km. These results demonstrate that for\u0000high-quality crystal structure data measured on inclusions still trapped\u0000within diamond hosts, even a non-destructive approach can be used to\u0000calculate the depth of formation of diamond–olivine pairs. In terms of\u0000geological implications, the results from this work show that Changma\u0000diamonds formed under a conductive geotherm lying between 35 and 40 mW m−2, at a depth of about 190 km. This value lies within the recently\u0000reported upper limit of the average depth of formation of worldwide\u0000lithospheric diamonds, which is 175 ± 15 km and is in agreement with\u0000P–T data obtained in the literature from kimberlite xenoliths.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46705032","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Barale, G. Capitani, P. Castello, R. Compagnoni, R. Cossio, G. Fiore, L. Pastero, M. Mellini
Abstract. The ultramafic body of Monte Avic (Aosta Valley, Western Alps, Italy) consists of antigorite serpentinite and Ti-clinohumite metadunite. They host late metamorphic veins, up to a couple of centimeters thick, compact, and homogeneous, with a “porcelain” appearance. Vein colors range from yellowish to light greenish, light yellowish fading to white, or rare orange. The veins consist of 15-sector PS-15 polygonal serpentine, with chemical composition Mg2.85 Fe0.08 Si2.05 O7.05 [OH]3.95. Recognition of this unusual phase is supported by diagnostic satellite reflections in the X-ray powder diffraction pattern (e.g., at dobs of 2.502, 2.336, 2.151, and 1.966 Å) TEM images (showing 15-sector polygonal fibers, mostly 200 nm in diameter and a few µm in length, forming a randomly oriented felt) and a µ-Raman wavenumber, matching previous data. This different evidence affords the successful distinction of PS-15 and PS-30, alternatively using TEM images, X-ray powder diffraction, or the low- and high-wavenumber µ-Raman spectra. At Monte Avic, the vein emplacement was accompanied by significant fluid pressure, as suggested by deformation and dismembering of the host rock, with PS-15 grown within isotropic stress microenvironments characterized by fluid-filled voids. Random growth of the mass-fiber polygonal serpentine was favored by low-strain conditions. PS-15 veins formed at the end of the long polyphase Alpine orogenic evolution, with hydrous fluids possibly deriving from serpentinite dehydration in the depth.
{"title":"Late metamorphic veins with dominant PS-15 polygonal serpentine in the Monte Avic ultramafite","authors":"L. Barale, G. Capitani, P. Castello, R. Compagnoni, R. Cossio, G. Fiore, L. Pastero, M. Mellini","doi":"10.5194/ejm-35-347-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-347-2023","url":null,"abstract":"Abstract. The ultramafic body of Monte Avic (Aosta Valley, Western Alps,\u0000Italy) consists of antigorite serpentinite and Ti-clinohumite metadunite.\u0000They host late metamorphic veins, up to a couple of centimeters thick,\u0000compact, and homogeneous, with a “porcelain” appearance. Vein colors range\u0000from yellowish to light greenish, light yellowish fading to white, or rare\u0000orange. The veins consist of 15-sector PS-15 polygonal serpentine,\u0000with chemical composition Mg2.85 Fe0.08 Si2.05 O7.05\u0000[OH]3.95. Recognition of this unusual phase is supported by diagnostic\u0000satellite reflections in the X-ray powder diffraction pattern (e.g., at\u0000dobs of 2.502, 2.336, 2.151, and 1.966 Å) TEM images (showing\u000015-sector polygonal fibers, mostly 200 nm in diameter and a few µm in\u0000length, forming a randomly oriented felt) and a µ-Raman wavenumber,\u0000matching previous data. This different evidence affords the successful\u0000distinction of PS-15 and PS-30, alternatively using TEM images, X-ray powder\u0000diffraction, or the low- and high-wavenumber µ-Raman spectra. At Monte\u0000Avic, the vein emplacement was accompanied by significant fluid pressure, as\u0000suggested by deformation and dismembering of the host rock, with PS-15 grown\u0000within isotropic stress microenvironments characterized by fluid-filled\u0000voids. Random growth of the mass-fiber polygonal serpentine was favored by\u0000low-strain conditions. PS-15 veins formed at the end of the long polyphase\u0000Alpine orogenic evolution, with hydrous fluids possibly deriving from\u0000serpentinite dehydration in the depth.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46794704","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. A new occurrence of pyrite crystals with rhombohedral habit, up to several centimeters in length, is described from the Madan Pb–Zn ore field (Rhodope Massif, south Bulgaria), where it constitutes a late pyrite generation. As observed in the past in other deposits, the ideal rhombohedron is derived from the pyritohedron by suppression of half of its faces (six “polar faces”) around a ternary axis. In studied crystals, together with six main “equatorial faces”, additional minor faces correspond to cube faces as well as polar faces. Such a dissymmetry indicates that the crystallographic point group of these crystals is 3‾, a subgroup of the eigensymmetry 3‾2/m of a rhombohedron taken as geometric face form. Twinning by metric merohedry confirms such a symmetry decrease and permits the definition of this type of pyrite as a dimorph of cubic pyrite, i.e., pseudo-cubic trigonal pyrite (pyrite-R). Twin operations belong to the set of symmetry operations absent in point group 3‾ relative to pyrite symmetry m3‾: reflection about the {100} plane or two-fold rotation about the <100> direction. Four twin types have been distinguished (name, chromatic point group): three contact twins (reflection, m′; rotation, 2′; trapezoidal, (m(2)m(2)2(2))(4)), as well as one penetration twin (crossed, 2′/m′). Composition planes always correspond to {100}, but there are two types of twin interfaces. More complex twinned samples may develop erratically during crystal growth. Other twin variations as well as genetic aspects of such a type of pyrite are discussed.
{"title":"Pseudo-cubic trigonal pyrite from the Madan Pb–Zn ore field (Rhodope Massif, Bulgaria): morphology and twinning","authors":"Y. Moëlo","doi":"10.5194/ejm-35-333-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-333-2023","url":null,"abstract":"Abstract. A new occurrence of pyrite crystals with rhombohedral\u0000habit, up to several centimeters in length, is described from the Madan Pb–Zn\u0000ore field (Rhodope Massif, south Bulgaria), where it constitutes a late\u0000pyrite generation. As observed in the past in other deposits, the ideal\u0000rhombohedron is derived from the pyritohedron by suppression of half of its\u0000faces (six “polar faces”) around a ternary axis. In studied crystals,\u0000together with six main “equatorial faces”, additional minor faces\u0000correspond to cube faces as well as polar faces. Such a dissymmetry\u0000indicates that the crystallographic point group of these crystals is\u00003‾, a subgroup of the eigensymmetry 3‾2/m of a rhombohedron\u0000taken as geometric face form. Twinning by metric merohedry confirms such a\u0000symmetry decrease and permits the definition of this type of pyrite as a dimorph of\u0000cubic pyrite, i.e., pseudo-cubic trigonal pyrite (pyrite-R). Twin operations\u0000belong to the set of symmetry operations absent in point group 3‾\u0000relative to pyrite symmetry m3‾: reflection about the {100} plane or two-fold rotation about the <100> direction. Four twin types have been distinguished (name,\u0000chromatic point group): three contact twins (reflection, m′; rotation, 2′;\u0000trapezoidal, (m(2)m(2)2(2))(4)), as well as one penetration twin\u0000(crossed, 2′/m′). Composition planes always correspond to {100}, but there are two types of twin interfaces. More\u0000complex twinned samples may develop erratically during crystal growth. Other\u0000twin variations as well as genetic aspects of such a type of pyrite are\u0000discussed.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46213374","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shashank Prabha-Mohan, K. Koga, A. Mathieu, Franck Pointud, D. Narvaez
Abstract. In this paper, we present a new design for a 1 atm gas-mixing furnace using the gas mixture CO–CO2–SO2. This furnace can simulate disequilibrium processes such as magmatic and volcanic degassing. Here, we present the technical aspects of the design. The furnace can sustain temperatures of up to 1650 ∘C and has a hot zone that spans 200 mm vertically, where the hotspot is determined to be ∼ 32 mm below the midpoint of the furnace enclosure. The four mass flow controllers are individually calibrated and accurate to within 0.8 % of the specified value. The fO2 is accurately reproduced in the furnace within ±0.002 log units, as calibrated by the Fe–FeO reaction across the iron–wüstite (IW) buffer at 1300 ∘C. The furnace can reliably simulate dynamic conditions, where the fO2 can be modulated at a maximum rate of 2.0 log units min−1 by varying the gas mixture. A delay of 40 s is observed to attain the fO2 calculated from the gas mixture, at the hotspot. A series of safety measures to protect the user from exposure to the toxic gases are detailed. In our experiments, the furnace is used to determine sulfur isotope fractionation factors among melt, sulfide, and the gas phase, within a magmatic context, using either crystals of olivine or silica glass tubes. The furnace has the potential to investigate various other dynamic high-temperature reactions occurring on Earth.
{"title":"One-atmosphere high-temperature CO–CO2–SO2 gas-mixing furnace: design, operation, and applications","authors":"Shashank Prabha-Mohan, K. Koga, A. Mathieu, Franck Pointud, D. Narvaez","doi":"10.5194/ejm-35-321-2023","DOIUrl":"https://doi.org/10.5194/ejm-35-321-2023","url":null,"abstract":"Abstract. In this paper, we present a new design for a 1 atm gas-mixing furnace using the gas mixture CO–CO2–SO2. This furnace can simulate disequilibrium processes such as magmatic and volcanic degassing. Here, we present the technical aspects of the design. The furnace can sustain temperatures of up to 1650 ∘C and has a hot zone that spans 200 mm vertically, where the hotspot is determined to be ∼ 32 mm below the midpoint of the furnace enclosure. The four mass flow controllers are individually calibrated and accurate to within 0.8 % of the specified value. The fO2 is accurately reproduced in the furnace within ±0.002 log units, as calibrated by the Fe–FeO reaction across the iron–wüstite (IW) buffer at 1300 ∘C. The furnace can reliably simulate dynamic conditions, where the fO2 can be modulated at a maximum rate of 2.0 log units min−1 by varying the gas mixture. A delay of 40 s is observed to attain the fO2 calculated from the gas mixture, at the hotspot. A series of safety measures to protect the user from exposure to the toxic gases are detailed. In our experiments, the furnace is used to determine sulfur isotope fractionation factors among melt, sulfide, and the gas phase, within a magmatic context, using either crystals of olivine or silica glass tubes. The furnace has the potential to investigate various other dynamic high-temperature reactions occurring on Earth.\u0000","PeriodicalId":11971,"journal":{"name":"European Journal of Mineralogy","volume":null,"pages":null},"PeriodicalIF":2.1,"publicationDate":"2023-05-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47479064","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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