Roberto Borriello, F. Xiong, Chi Ma, Sofia Lorenzon, Enrico Mugnaioli, Jingsui Yang, Xiangzhen Xu, E. Grew
The new mineral jianmuite, ZrTi4+Ti3+5Al3O16 (IMA No. 2023-057) was found (1) as an inclusion in a corundum grain from the Cr-11 orebody near Kangjinla (29°11’N, 92°18’E), Tibet, China with wenjiite, Ti10(Si,P,☐)7, Al-rich spinel, osbornite, TiN, a Ca-amphibole particularly enriched in Ti, a Sr-rich dmisteinbergite, CaAl2Si2O8, and amorphous phases (probably residual melt) (holotype and first co-type) and (2) as several grains with corundum, mullite, Al6Si2O13, tistarite, Ti2O3, and kaitianite, Ti3+2Ti4+O5, in the matrix of the CV3 carbonaceous chondrite Allende (second co-type). Eight energy-dispersive spectroscopic analyses of the holotype normalized to 100% gave SiO2 1.83, ZrO2 23.17, Al2O3 18.41, Ti2O3 54.32, Sc2O3 1.25, MgO 1.03, Total 100.00 wt%. The empirical formula calculated on the basis of 10 cations and 16 oxygen atoms is VIIIZr VII(Ti3+3.034Ti4+0.602Zr0.364)Σ4.000VI(Ti3+1.845Al1.838Mg0.186Sc0.131)Σ4.000IV(Al0.780Si0.220)Σ1.000 O16. The simplified formula is Zr(Ti3+,Ti4+,Zr)4(Ti3+,Al)4(Al,Si)O16 and the ideal chemical formula is ZrTi4+Ti3+5Al3O16, which requires ZrO2 17.23 calculated wt%, TiO2 11.16 calculated wt%, Ti2O3 50.23 calculated wt% and Al2O3 21.38 calculated wt%, Total 100 wt.%. Six energy-dispersive spectroscopic analyses of the first co-type normalized to 100% gave SiO2 2.86, ZrO2 23.06, Al2O3 18.10, Ti2O3 53.78, Sc2O3 1.17, MgO 1.04, Total 100.00 wt%. Three-dimensional electron diffraction of the holotype determined jianmuite as I-centered tetragonal, space group: (I-4) (# 82), with a = 10.3675 (10) Å, b = 10.3675 (10) Å, c = 9.8125 (10) Å, V = 1054.70 (18) Å3 and Z = 4. Wavelength-dispersive spectroscopic electron probe microanalyses of Allende jianmuite (second co-type) gave for the two grains (5 analyses each) SiO2 2.32, 3.02, ZrO2 13.95, 10.79, Al2O3 26.82, 21.83, Ti2O3 44.68, 49.47, TiO2 12.62, 14.75, Sc2O3 0.12, 0.04, MgO 0.19, 0.80, FeO, 0.52, 0.55, CaO 0.17, 0.08, Total 101.40, 101.34 wt%.Weight% TiO2 and weight% Ti2O3 were calculated from formula units Ti+4 and Ti+3, which were determined assuming a stoichiometry of 10 cations and 16 oxygen atoms. Electron backscatter diffraction (EBSD) patterns on the Allende jianmuite (second co-type) can be indexed by the tetragonal I-4 structure obtained on the holotype, with a mean angular deviation of ~0.7°, thereby confirming identification of the Allende mineral as jianmuite. The structure of jianmuite consists of cations packed in distorted I-centered cubes. There are 8 independent cation sites, two inside distorted cubes with tetragonal ridged faces (CN = 8), two inside capped trigonal prisms (CN = 7), two inside distorted octahedra (CN = 6) and two inside tetrahedra (CN = 4). All coordination polyhedra are connected by edges, except for the tetrahedra, which are connected by vertexes with other polyhedra. Despite the similarity in composition with carmeltazite, ZrTi3+4Al2O11, the structures of the two minerals bear little resemblance to one another, most notably the
在中国西藏康金拉（北纬 29°11，东经 92°18）附近的 Cr-11 矿体中，发现了新矿物尖晶石 ZrTi4+Ti3+5Al3O16（IMA No.2023-057）是在中国西藏康金拉（北纬 29°11'，东经 92°18'）附近 Cr-11 矿体的一个刚玉晶粒中发现的（1），该晶粒中含有温氏尖晶石、Ti10(Si,P,☐)7、富铝尖晶石、乌蛇纹石、TiN、一种钙闪石（尤其富含 Ti）、一种富 Sr 的闪长岩（dmisteinbergite）、CaAl2Si2O8 和无定形相（可能是残余熔体）（主型和第一共型）；（2）在 CV3 碳质软玉阿连德（第二共型）的基质中，表现为几粒刚玉、莫来石、Al6Si2O13、榍石、Ti2O3 和开天石（Ti3+2Ti4+O5）。对主型进行的八次能量色散光谱分析归一化为 100%，得出 SiO2 1.83、ZrO2 23.17、Al2O3 18.41、Ti2O3 54.32、Sc2O3 1.25、MgO 1.03、总计 100.00 wt%。根据 10 个阳离子和 16 个氧原子计算得出的经验公式为 VIIIZr VII(Ti3+3.034Ti4+0.602Zr0.364)Σ4.000VI(Ti3+1.845Al1.838Mg0.186Sc0.131)Σ4.000IV(Al0.780Si0.220)Σ1.000 O16。简化式为 Zr(Ti3+,Ti4+,Zr)4(Ti3+,Al)4(Al,Si)O16，理想化学式为 ZrTi4+Ti3+5Al3O16，其中需要 ZrO2 17.23 计算重量百分比、TiO2 11.16 计算重量百分比、Ti2O3 50.23 计算重量百分比和 Al2O3 21.38 计算重量百分比，总计 100 重量百分比。对归一化为 100%的第一种共型进行六次能量色散光谱分析，结果为 SiO2 2.86、ZrO2 23.06、Al2O3 18.10、Ti2O3 53.78、Sc2O3 1.17、MgO 1.04，总计 100.00 wt%。通过对主型晶体的三维电子衍射，确定黝帘石为 I 心四方晶，空间群：(I-4) (# 82)，a = 10.3675 (10) Å，b = 10.3675 (10) Å，c = 9.8125 (10) Å，V = 1054.70 (18) Å3 和 Z = 4。对阿连德绳纹石（第二共型）的波长色散光谱电子探针显微分析表明，两个晶粒（各分析 5 次）的 SiO2 2.32、3.02，ZrO2 13.95、10.79，Al2O3 26.82、21.83，Ti2O3 44.68、49.47，TiO2 12.62、14.75，Sc2O3 0.12, 0.04, MgO 0.19, 0.80, FeO, 0.52, 0.55, CaO 0.17, 0.08, Total 101.40, 101.34 wt%.Weight% TiO2 and weight% Ti2O3 were calculated from formula units Ti+4 and Ti+3, which were determined assuming a stoichiometry of 10 cations and 16 oxygen atoms.阿连德绳纹石（第二共型）上的电子反向散射衍射（EBSD）图样可通过在主型上获得的四方 I-4 结构进行索引，其平均角度偏差约为 0.7°，从而确认阿连德矿物为绳纹石。黝帘石的结构由排列在扭曲的 I 型中心立方体中的阳离子组成。共有 8 个独立的阳离子位点，其中两个位于具有四方脊面的扭曲立方体内部（CN = 8），两个位于带帽三棱柱内部（CN = 7），两个位于扭曲八面体内部（CN = 6），两个位于四面体内部（CN = 4）。除了四面体通过顶点与其他多面体连接外，所有配位多面体都通过边连接。尽管与菱锰矿（ZrTi3+4Al2O11）的成分相似，但这两种矿物的结构几乎没有相似之处，最明显的是阳氧多面体的数量和类型。相反，菱锰矿的结构与辉绿超群矿物的结构有几个共同点，包括单胞参数相似，辉绿岩和菱锰矿分别为立方 a ≈ 10 Å 和四方 a ≈ c ≈ 10 Å，阳离子堆积在这两种结构中都是立方 I 型中心。
{"title":"9362R: Jianmuite, ZrTi4+Ti3+5Al3O16, a new mineral from the Allende meteorite and from chromitite near Kangjinla, Tibet, China","authors":"Roberto Borriello, F. Xiong, Chi Ma, Sofia Lorenzon, Enrico Mugnaioli, Jingsui Yang, Xiangzhen Xu, E. Grew","doi":"10.2138/am-2024-9362","DOIUrl":"https://doi.org/10.2138/am-2024-9362","url":null,"abstract":"\u0000 The new mineral jianmuite, ZrTi4+Ti3+5Al3O16 (IMA No. 2023-057) was found (1) as an inclusion in a corundum grain from the Cr-11 orebody near Kangjinla (29°11’N, 92°18’E), Tibet, China with wenjiite, Ti10(Si,P,☐)7, Al-rich spinel, osbornite, TiN, a Ca-amphibole particularly enriched in Ti, a Sr-rich dmisteinbergite, CaAl2Si2O8, and amorphous phases (probably residual melt) (holotype and first co-type) and (2) as several grains with corundum, mullite, Al6Si2O13, tistarite, Ti2O3, and kaitianite, Ti3+2Ti4+O5, in the matrix of the CV3 carbonaceous chondrite Allende (second co-type). Eight energy-dispersive spectroscopic analyses of the holotype normalized to 100% gave SiO2 1.83, ZrO2 23.17, Al2O3 18.41, Ti2O3 54.32, Sc2O3 1.25, MgO 1.03, Total 100.00 wt%. The empirical formula calculated on the basis of 10 cations and 16 oxygen atoms is VIIIZr VII(Ti3+3.034Ti4+0.602Zr0.364)Σ4.000VI(Ti3+1.845Al1.838Mg0.186Sc0.131)Σ4.000IV(Al0.780Si0.220)Σ1.000 O16. The simplified formula is Zr(Ti3+,Ti4+,Zr)4(Ti3+,Al)4(Al,Si)O16 and the ideal chemical formula is ZrTi4+Ti3+5Al3O16, which requires ZrO2 17.23 calculated wt%, TiO2 11.16 calculated wt%, Ti2O3 50.23 calculated wt% and Al2O3 21.38 calculated wt%, Total 100 wt.%. Six energy-dispersive spectroscopic analyses of the first co-type normalized to 100% gave SiO2 2.86, ZrO2 23.06, Al2O3 18.10, Ti2O3 53.78, Sc2O3 1.17, MgO 1.04, Total 100.00 wt%. Three-dimensional electron diffraction of the holotype determined jianmuite as I-centered tetragonal, space group: (I-4) (# 82), with a = 10.3675 (10) Å, b = 10.3675 (10) Å, c = 9.8125 (10) Å, V = 1054.70 (18) Å3 and Z = 4. Wavelength-dispersive spectroscopic electron probe microanalyses of Allende jianmuite (second co-type) gave for the two grains (5 analyses each) SiO2 2.32, 3.02, ZrO2 13.95, 10.79, Al2O3 26.82, 21.83, Ti2O3 44.68, 49.47, TiO2 12.62, 14.75, Sc2O3 0.12, 0.04, MgO 0.19, 0.80, FeO, 0.52, 0.55, CaO 0.17, 0.08, Total 101.40, 101.34 wt%.Weight% TiO2 and weight% Ti2O3 were calculated from formula units Ti+4 and Ti+3, which were determined assuming a stoichiometry of 10 cations and 16 oxygen atoms. Electron backscatter diffraction (EBSD) patterns on the Allende jianmuite (second co-type) can be indexed by the tetragonal I-4 structure obtained on the holotype, with a mean angular deviation of ~0.7°, thereby confirming identification of the Allende mineral as jianmuite. The structure of jianmuite consists of cations packed in distorted I-centered cubes. There are 8 independent cation sites, two inside distorted cubes with tetragonal ridged faces (CN = 8), two inside capped trigonal prisms (CN = 7), two inside distorted octahedra (CN = 6) and two inside tetrahedra (CN = 4). All coordination polyhedra are connected by edges, except for the tetrahedra, which are connected by vertexes with other polyhedra. Despite the similarity in composition with carmeltazite, ZrTi3+4Al2O11, the structures of the two minerals bear little resemblance to one another, most notably the ","PeriodicalId":7768,"journal":{"name":"American Mineralogist","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141924495","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}
Evgeny Galuskin, I. Galuskina, Y. Vapnik, Joachim Kusz, Beata Marciniak-Maliszewska, Grzegorz Zieliński
In anorthite-diopside-tridymite paralava of the Hatrurim Complex, Daba-Siwaqa, Jordan, phosphides from two facies environments were found. Large xenomorphic phosphide aggregates, presented by minerals of the barringerite-transjordanite series, murashkoite and zuktamrurite, were noted at the intimate contact of the paralava with the host rocks. Moreover, the contact facies of the paralava, composed of large diopside crystals up to 1 cm in size and cemented by hydrosilicates, zeolites and calcite, are enriched in phosphides. In the contact facies, it was possible to observe pseudomorphs of barringerite and murashkoite after fish bones and inclusions of minute needle-like barringerite crystals in diopside with morphological manifestations of the simultaneous crystallization of these minerals. In the central part of the weakly altered paralava with abundant amygdules, two nodules containing ore minerals were detected. In the first nodule, barringerite and schreibersite were found; the second contained nickelphosphide. In this paper we discuss the hypothesis that phosphides at the contact facies of the paralava formed as a result of reducing carbothermal reactions with the participation of thermally altered and graphitized fish-bone remains as a source of carbon and phosphorus and oxidised pyrite framboids as an iron source: Fe2O3 + 3C = 2Fe(lq) + 3CO(g), 2Ca5(PO4)3F + 14C = 3P2(g) + 14CO(g) + 10CaO + F2(g) and nFe(lq) +1/2P2(g) = FenP, where n = ½, 1, 2, 3. The process of phosphide formation during hot paralava injection, the temperature of which exceeded 1400°C, into previously altered host rocks with contamination of material containing bone remains, took place in a small volume in a kinetic mode, which led to the preservation of the primary form of bone remains when they were replaced by phosphides. The formation of phosphides in the central part of the paralava occurred with the participation of gases that transported phosphorus reduced as a result of carbothermal reactions. The phosphorous was absorbed by drops of metal or sulphide melt, which led to the formation of phosphides.
{"title":"Two modes of terrestrial phosphide formation","authors":"Evgeny Galuskin, I. Galuskina, Y. Vapnik, Joachim Kusz, Beata Marciniak-Maliszewska, Grzegorz Zieliński","doi":"10.2138/am-2024-9315","DOIUrl":"https://doi.org/10.2138/am-2024-9315","url":null,"abstract":"\u0000 In anorthite-diopside-tridymite paralava of the Hatrurim Complex, Daba-Siwaqa, Jordan, phosphides from two facies environments were found. Large xenomorphic phosphide aggregates, presented by minerals of the barringerite-transjordanite series, murashkoite and zuktamrurite, were noted at the intimate contact of the paralava with the host rocks. Moreover, the contact facies of the paralava, composed of large diopside crystals up to 1 cm in size and cemented by hydrosilicates, zeolites and calcite, are enriched in phosphides. In the contact facies, it was possible to observe pseudomorphs of barringerite and murashkoite after fish bones and inclusions of minute needle-like barringerite crystals in diopside with morphological manifestations of the simultaneous crystallization of these minerals. In the central part of the weakly altered paralava with abundant amygdules, two nodules containing ore minerals were detected. In the first nodule, barringerite and schreibersite were found; the second contained nickelphosphide. In this paper we discuss the hypothesis that phosphides at the contact facies of the paralava formed as a result of reducing carbothermal reactions with the participation of thermally altered and graphitized fish-bone remains as a source of carbon and phosphorus and oxidised pyrite framboids as an iron source: Fe2O3 + 3C = 2Fe(lq) + 3CO(g), 2Ca5(PO4)3F + 14C = 3P2(g) + 14CO(g) + 10CaO + F2(g) and nFe(lq) +1/2P2(g) = FenP, where n = ½, 1, 2, 3. The process of phosphide formation during hot paralava injection, the temperature of which exceeded 1400°C, into previously altered host rocks with contamination of material containing bone remains, took place in a small volume in a kinetic mode, which led to the preservation of the primary form of bone remains when they were replaced by phosphides. The formation of phosphides in the central part of the paralava occurred with the participation of gases that transported phosphorus reduced as a result of carbothermal reactions. The phosphorous was absorbed by drops of metal or sulphide melt, which led to the formation of phosphides.","PeriodicalId":7768,"journal":{"name":"American Mineralogist","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141923362","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}
Y. Zhuang, Jin Liu, Chaojia Lv, Liangxu Xu, Wenli Bi, Qingyang Hu, Dongzhou Zhang, Gaston Garbarino, Shengcai Zhu, Youjun Zhang
The high-pressure behavior of iron nitrides has garnered significant attention due to the possibility of deep nitrogen reservoirs within the Earth’s interior. Here, we investigate the magnetic, structural, electrical, and thermal properties of Fe3N up to 62 GPa and 2100 K, using multiple probes coupled with the diamond-anvil cell technique (including synchrotron X-ray diffraction, synchrotron Mössbauer spectroscopy, and electrical measurements). Fe3N undergoes a magnetic phase transformation from the ferromagnetic to paramagnetic state at ~17-20 GPa, 300 K. The equation of state was determined as, V0/Z = 42.8(1) Å3, and K0 = 151.8(1) GPa, with K′ fixed at 4. Additionally, Fe3N exhibits unexpectedly low electrical and thermal conductivity under high-pressure and high-temperature conditions. This result suggests that deep nitrogen cycling may contribute to the thermal evolution of the deep interiors of Earth and other terrestrial bodies.
由于地球内部可能存在深层氮库，氮化铁的高压行为引起了人们的极大关注。在此，我们使用多种探针并结合金刚石振荡池技术（包括同步辐射 X 射线衍射、同步辐射莫斯鲍尔光谱和电学测量），研究了高达 62 GPa 和 2100 K 的 Fe3N 的磁性、结构、电学和热学特性。确定的状态方程为：V0/Z = 42.8(1) Å3，K0 = 151.8(1) GPa，K′固定为 4。此外，在高压和高温条件下，Fe3N 表现出意想不到的低导电性和导热性。这一结果表明，深层氮循环可能有助于地球和其他陆地天体深层内部的热演化。
{"title":"Magnetic collapse and low conductivity of Fe3N in the deep interiors of Earth-like planets","authors":"Y. Zhuang, Jin Liu, Chaojia Lv, Liangxu Xu, Wenli Bi, Qingyang Hu, Dongzhou Zhang, Gaston Garbarino, Shengcai Zhu, Youjun Zhang","doi":"10.2138/am-2023-9251","DOIUrl":"https://doi.org/10.2138/am-2023-9251","url":null,"abstract":"\u0000 The high-pressure behavior of iron nitrides has garnered significant attention due to the possibility of deep nitrogen reservoirs within the Earth’s interior. Here, we investigate the magnetic, structural, electrical, and thermal properties of Fe3N up to 62 GPa and 2100 K, using multiple probes coupled with the diamond-anvil cell technique (including synchrotron X-ray diffraction, synchrotron Mössbauer spectroscopy, and electrical measurements). Fe3N undergoes a magnetic phase transformation from the ferromagnetic to paramagnetic state at ~17-20 GPa, 300 K. The equation of state was determined as, V0/Z = 42.8(1) Å3, and K0 = 151.8(1) GPa, with K′ fixed at 4. Additionally, Fe3N exhibits unexpectedly low electrical and thermal conductivity under high-pressure and high-temperature conditions. This result suggests that deep nitrogen cycling may contribute to the thermal evolution of the deep interiors of Earth and other terrestrial bodies.","PeriodicalId":7768,"journal":{"name":"American Mineralogist","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141924099","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}
Joël Brugger, S. Cuchet, Ate van der Burgt, Mischa Crumbach, B. Etschmann, Yanlu Xing, Rahul Ram, Paul Michaut, Oliver Nebel, Massimo Raveggi, Roland Maas, Mark A. Pearce, Daryl L. Howard
The High Field Strength Elements (HFSE) Ti, Nb and rare earth elements (REE) are commonly regarded as immobile during hydrothermal activity and metamorphism, making them important tracers of geological processes. Here, we report a Ti-REE-Nb-As mineralisation recently discovered in quartz, feldspar, muscovite ± biotite, fluorapatite, hematite, epidote and dravite-schorl veins hosted in quartz ± feldspar ± muscovite ± biotite gneisses from the Monte Leone nappe (Switzerland/Italy). The veins formed during prograde metamorphism and were boudinaged and/or folded during peak metamorphism under lower amphibolite facies. The mineralisation consists of megacrysts (≫ 2 cm) of allanite-(Ce) and Nb-REE-rich titanite-(I). Titanite-(I) displays prominent primary oscillatory- and sector-zonings in Y+REE and Nb. Allanite-(Ce) and titanite are also present as metamorphic minerals disseminated in the host-rock. The vein-hosted megacrysts and their host rocks have identical Nd isotope systematics, indicating that the HFSE mineralisation results from small-scale remobilisation of host-rock components. Localised, fluid-assisted dissolution of vein-hosted allanite-(Ce), epidote, and dravite-schorl during retrograde alpine deuteric alteration resulted in cavities lined with chlorite, muscovite, hematite, and diverse REE minerals. The same fluids caused titanite-(I) to break down into a porous assemblage of acicular niobian rutile with lamellae of crichtonite-group minerals and/or hematite and a suite of REE-Nb-Ti micro-minerals. A few titanite (titanite-II) crystals preserve an intermediate stage of the dissolution-reprecipitation process. Unlike titanite-(I), they display a patchwork-like micro-texture (100 μm-sized subgrains with inhomogeneous Nb concentrations); they host lamellae of crichtonite-group minerals within cleavage planes of the parent titanite, as well as secondary Y+Nb+REE oxides and calcite along subgrain boundaries. Calcite indicates that CO2-enriched fluids promoted the destabilisation of titanite-(I). Highly localised fluid flow accounts for the common occurrence of fresh and altered allanite-(Ce) and titanite in close proximity. The HFSE-enriched veins reveal a complex history of mobility of minor elements (Ti, Nb, REE, As ± B, Be) together with major components (Si, Al, K, Na, Fe) from the host rock, resulting in their early (prograde) concentration within the veins, and their remobilisation upon the action of oxidised CO2-bearing fluids during retrograde metamorphism. In general, crystallisation of enriched phases during prograde metamorphism may be an important step in determining the fertility of a source rock for hydrothermal HFSE deposits.
{"title":"Titanite and allanite as a record of multistage co-mobility of Ti-REE-Nb-As during metamorphism in the Central Alps","authors":"Joël Brugger, S. Cuchet, Ate van der Burgt, Mischa Crumbach, B. Etschmann, Yanlu Xing, Rahul Ram, Paul Michaut, Oliver Nebel, Massimo Raveggi, Roland Maas, Mark A. Pearce, Daryl L. Howard","doi":"10.2138/am-2024-9378","DOIUrl":"https://doi.org/10.2138/am-2024-9378","url":null,"abstract":"\u0000 The High Field Strength Elements (HFSE) Ti, Nb and rare earth elements (REE) are commonly regarded as immobile during hydrothermal activity and metamorphism, making them important tracers of geological processes. Here, we report a Ti-REE-Nb-As mineralisation recently discovered in quartz, feldspar, muscovite ± biotite, fluorapatite, hematite, epidote and dravite-schorl veins hosted in quartz ± feldspar ± muscovite ± biotite gneisses from the Monte Leone nappe (Switzerland/Italy). The veins formed during prograde metamorphism and were boudinaged and/or folded during peak metamorphism under lower amphibolite facies. The mineralisation consists of megacrysts (≫ 2 cm) of allanite-(Ce) and Nb-REE-rich titanite-(I). Titanite-(I) displays prominent primary oscillatory- and sector-zonings in Y+REE and Nb. Allanite-(Ce) and titanite are also present as metamorphic minerals disseminated in the host-rock. The vein-hosted megacrysts and their host rocks have identical Nd isotope systematics, indicating that the HFSE mineralisation results from small-scale remobilisation of host-rock components.\u0000 Localised, fluid-assisted dissolution of vein-hosted allanite-(Ce), epidote, and dravite-schorl during retrograde alpine deuteric alteration resulted in cavities lined with chlorite, muscovite, hematite, and diverse REE minerals. The same fluids caused titanite-(I) to break down into a porous assemblage of acicular niobian rutile with lamellae of crichtonite-group minerals and/or hematite and a suite of REE-Nb-Ti micro-minerals. A few titanite (titanite-II) crystals preserve an intermediate stage of the dissolution-reprecipitation process. Unlike titanite-(I), they display a patchwork-like micro-texture (100 μm-sized subgrains with inhomogeneous Nb concentrations); they host lamellae of crichtonite-group minerals within cleavage planes of the parent titanite, as well as secondary Y+Nb+REE oxides and calcite along subgrain boundaries. Calcite indicates that CO2-enriched fluids promoted the destabilisation of titanite-(I). Highly localised fluid flow accounts for the common occurrence of fresh and altered allanite-(Ce) and titanite in close proximity.\u0000 The HFSE-enriched veins reveal a complex history of mobility of minor elements (Ti, Nb, REE, As ± B, Be) together with major components (Si, Al, K, Na, Fe) from the host rock, resulting in their early (prograde) concentration within the veins, and their remobilisation upon the action of oxidised CO2-bearing fluids during retrograde metamorphism. In general, crystallisation of enriched phases during prograde metamorphism may be an important step in determining the fertility of a source rock for hydrothermal HFSE deposits.","PeriodicalId":7768,"journal":{"name":"American Mineralogist","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141805294","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}
Alice Taddei, P. Bonazzi, Hans-Jürgen Förster, Patrick Casey, D. Holtstam, Andreas Karlsson, Luca Bindi
A study of a skarn sample from the Malmkärra iron mines, Norberg, Västmanland (Sweden) revealed the occurrence of a peculiar epidote-supergroup mineral. It was examined using electron microprobe, single-crystal X-ray diffraction, Mössbauer and Fourier-transform infrared spectroscopy techniques. Structure refinements combined with electron-microprobe data indicate the following cation populations: A1 = Ca0.96REE3+0.03Mn0.01; A2 = REE3+0.99Ca0.01; M1 = Mg0.40Al0.32Fe3+0.26Fe2+0.02; M2 = Al0.98Fe3+0.02; M3 = Mg0.72Fe2+0.17Fe3+0.11; T1,2,3 = Si2.93Al0.07, accounting for a total positive charge of 24.64. The presence of Fe2+ is confirmed by Mössbauer data. The remarkable amount of divalent cations at both M1 and M3 (> 1 pfu, per formula unit) demands more than one monovalent anion pfu in the structure. As the mineral lacks fluorine, charge neutrality must be achieved through additional H+ (about 0.4 apfu). Only one independent hydrogen atom is located within the structure, with O10 as donor and O4 as acceptor, as in other epidote-supergroup minerals. Nonetheless, another O–O distance is suitable for a hydrogen bond, namely O10–O2. Although the existence of the additional OH group was not directly proved by vibrational spectroscopy, FT-IR data provided information related to this potential O10–O2 bridge. In the IR-spectrum acquired, several bands are observed in the OH-stretching region, and a secondary peak at 2140 cm–1 could be assigned to the bending mode of the O10–H…O2 group. To shed light onto this puzzling observation, one single crystal was subjected to annealing experiments at temperatures from 500 to 700°C, in 50°C steps, while a second one has undergone a heat treatment at 700°C. After the heat treatment, the IR-spectrum showed a decrease in intensity of all observed bands, in agreement with a dehydrogenation occurring at high temperatures. Although the structural position of the second hydrogen is still uncertain, it is reasonable to describe the composition of the epidote-supergroup mineral from Malmkärra as a solid solution between dissakisite-(Ce) (32%), ferriallanite-(Ce) (28%) and a yet undescribed end-member (40%), the (OH)-analogue of dollaseite-(Ce) – ideally CaREE3+Mg2AlSi3O11(OH)2.
{"title":"Multi-analytical characterization of an unusual epidote-supergroup mineral from Malmkärra, Sweden: Toward the new (OH)-analogue of dollaseite-(Ce)","authors":"Alice Taddei, P. Bonazzi, Hans-Jürgen Förster, Patrick Casey, D. Holtstam, Andreas Karlsson, Luca Bindi","doi":"10.2138/am-2024-9438","DOIUrl":"https://doi.org/10.2138/am-2024-9438","url":null,"abstract":"\u0000 A study of a skarn sample from the Malmkärra iron mines, Norberg, Västmanland (Sweden) revealed the occurrence of a peculiar epidote-supergroup mineral. It was examined using electron microprobe, single-crystal X-ray diffraction, Mössbauer and Fourier-transform infrared spectroscopy techniques. Structure refinements combined with electron-microprobe data indicate the following cation populations: A1 = Ca0.96REE3+0.03Mn0.01; A2 = REE3+0.99Ca0.01; M1 = Mg0.40Al0.32Fe3+0.26Fe2+0.02; M2 = Al0.98Fe3+0.02; M3 = Mg0.72Fe2+0.17Fe3+0.11; T1,2,3 = Si2.93Al0.07, accounting for a total positive charge of 24.64. The presence of Fe2+ is confirmed by Mössbauer data. The remarkable amount of divalent cations at both M1 and M3 (> 1 pfu, per formula unit) demands more than one monovalent anion pfu in the structure. As the mineral lacks fluorine, charge neutrality must be achieved through additional H+ (about 0.4 apfu). Only one independent hydrogen atom is located within the structure, with O10 as donor and O4 as acceptor, as in other epidote-supergroup minerals. Nonetheless, another O–O distance is suitable for a hydrogen bond, namely O10–O2. Although the existence of the additional OH group was not directly proved by vibrational spectroscopy, FT-IR data provided information related to this potential O10–O2 bridge. In the IR-spectrum acquired, several bands are observed in the OH-stretching region, and a secondary peak at 2140 cm–1 could be assigned to the bending mode of the O10–H…O2 group. To shed light onto this puzzling observation, one single crystal was subjected to annealing experiments at temperatures from 500 to 700°C, in 50°C steps, while a second one has undergone a heat treatment at 700°C. After the heat treatment, the IR-spectrum showed a decrease in intensity of all observed bands, in agreement with a dehydrogenation occurring at high temperatures. Although the structural position of the second hydrogen is still uncertain, it is reasonable to describe the composition of the epidote-supergroup mineral from Malmkärra as a solid solution between dissakisite-(Ce) (32%), ferriallanite-(Ce) (28%) and a yet undescribed end-member (40%), the (OH)-analogue of dollaseite-(Ce) – ideally CaREE3+Mg2AlSi3O11(OH)2.","PeriodicalId":7768,"journal":{"name":"American Mineralogist","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141822101","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}
Planetary surface missions have greatly benefitted from intelligent systems capable of semi-autonomous navigation and surveying. However, instruments onboard these missions are not similarly equipped with automated science analysis classifiers onboard rovers, which can further improve scientific yield and autonomy. Here, we present both single- and multi-mineral autonomous classifiers integrated using the results from a co-registered dual-band Raman spectrometer. This instrument consecutively irradiates the same spot size on the same sample using two excitation lasers of different wavelengths (532 nm and 785 nm). We identify the presence of mineral groups: pyroxene, olivine, potassium feldspar, quartz, mica, gypsum, and plagioclase, in 191 rocks. These minerals are among the major rock forming mineral groups and so their presence or absence within a sample is key for understanding rock composition and the environment in which it formed. We present machine learning methods used to train classifiers and leverage the multiple modalities of the dual-band Raman spectrometer. When testing on a novel sample set for single-mineral classification, we show accuracy scores up to 100% (varying by mineral), with a total classification rate (over all minerals) of 91%. When testing on a novel set of samples for multi-mineral classification, we show accuracy scores up to 96%, with a total classification rate of 73%. We end with several hypothesis tests, that demonstrate that dual-band Raman spectroscopy is more robust and improves the scientific yield for mineral classification over single-band spectroscopy, especially when combined with our multimodal neural network.
{"title":"Single and Multi-Mineral Classification using Dual-Band Raman Spectroscopy for Planetary Surface Missions","authors":"Timothy K. Johnsen, Virginia C. Gulick","doi":"10.2138/am-2023-9072","DOIUrl":"https://doi.org/10.2138/am-2023-9072","url":null,"abstract":"\u0000 Planetary surface missions have greatly benefitted from intelligent systems capable of semi-autonomous navigation and surveying. However, instruments onboard these missions are not similarly equipped with automated science analysis classifiers onboard rovers, which can further improve scientific yield and autonomy. Here, we present both single- and multi-mineral autonomous classifiers integrated using the results from a co-registered dual-band Raman spectrometer. This instrument consecutively irradiates the same spot size on the same sample using two excitation lasers of different wavelengths (532 nm and 785 nm). We identify the presence of mineral groups: pyroxene, olivine, potassium feldspar, quartz, mica, gypsum, and plagioclase, in 191 rocks. These minerals are among the major rock forming mineral groups and so their presence or absence within a sample is key for understanding rock composition and the environment in which it formed. We present machine learning methods used to train classifiers and leverage the multiple modalities of the dual-band Raman spectrometer. When testing on a novel sample set for single-mineral classification, we show accuracy scores up to 100% (varying by mineral), with a total classification rate (over all minerals) of 91%. When testing on a novel set of samples for multi-mineral classification, we show accuracy scores up to 96%, with a total classification rate of 73%. We end with several hypothesis tests, that demonstrate that dual-band Raman spectroscopy is more robust and improves the scientific yield for mineral classification over single-band spectroscopy, especially when combined with our multimodal neural network.","PeriodicalId":7768,"journal":{"name":"American Mineralogist","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141820524","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}
Néstor Cano, J. González-Jiménez, Antoni Camprubí, J. Proenza, E. González-Partida
Lead-bismuth (Pb-Bi) minerals of the galena (PbS)-matildite (AgBiS2) series and lillianite homologues (Pb3–2xAgxBi2+xS6) are intergrown with electrum (Au-Ag alloy) and chalcopyrite (CuFeS2) in specific bands within a colloform-banded vein at the Switchback epithermal deposit in southern Mexico. A macro-to-nano scale study revealed that these minerals fill small (<200 µm) cavities in the gangue minerals, showing curvilinear boundaries, bleb-like morphologies, and rounded nanoparticles (~100 nm). These observations are consistent with growth in a molten system from a precursor Pb-Bi melt containing Au, Ag, and Cu. Minerals in the galena-matildite series typically display Widmanstätten textures (i.e., octahedral-like or basket-weave matilditess lamellae in the galenass matrix), which have been traditionally linked to the decomposition of a high-temperature solid solution. However, galenass and matilditess show nano-scale sinuous reaction fronts and replacement relicts (“islands”) while maintaining the [011]Galena || [100]Matildite crystallographic orientation relationship. This suggests a topotaxial growth of matilditess mediated by coupled dissolution-reprecipitation reactions between galenass and the metallic melt upon cooling. A similar scenario is proposed for Pb-Bi sulfosalt intergrowths, which replace galena-matildite and electrum and grow topotaxially along (200)Galena. Collectively, these results suggest that Pb-Bi melts can exist in epithermal fluids, acting as precursors for the crystallization of ore minerals and able to sequester precious metals. This model explains abnormally high Au-Ag enrichments observed in some deposits that contain Pb-Bi ores.
{"title":"Macro-to-nanoscale investigation unlocks gold and silver enrichment by lead-bismuth metallic melts in the Switchback epithermal deposit, southern Mexico","authors":"Néstor Cano, J. González-Jiménez, Antoni Camprubí, J. Proenza, E. González-Partida","doi":"10.2138/am-2024-9388","DOIUrl":"https://doi.org/10.2138/am-2024-9388","url":null,"abstract":"\u0000 Lead-bismuth (Pb-Bi) minerals of the galena (PbS)-matildite (AgBiS2) series and lillianite homologues (Pb3–2xAgxBi2+xS6) are intergrown with electrum (Au-Ag alloy) and chalcopyrite (CuFeS2) in specific bands within a colloform-banded vein at the Switchback epithermal deposit in southern Mexico. A macro-to-nano scale study revealed that these minerals fill small (<200 µm) cavities in the gangue minerals, showing curvilinear boundaries, bleb-like morphologies, and rounded nanoparticles (~100 nm). These observations are consistent with growth in a molten system from a precursor Pb-Bi melt containing Au, Ag, and Cu. Minerals in the galena-matildite series typically display Widmanstätten textures (i.e., octahedral-like or basket-weave matilditess lamellae in the galenass matrix), which have been traditionally linked to the decomposition of a high-temperature solid solution. However, galenass and matilditess show nano-scale sinuous reaction fronts and replacement relicts (“islands”) while maintaining the [011]Galena || [100]Matildite crystallographic orientation relationship. This suggests a topotaxial growth of matilditess mediated by coupled dissolution-reprecipitation reactions between galenass and the metallic melt upon cooling. A similar scenario is proposed for Pb-Bi sulfosalt intergrowths, which replace galena-matildite and electrum and grow topotaxially along (200)Galena. Collectively, these results suggest that Pb-Bi melts can exist in epithermal fluids, acting as precursors for the crystallization of ore minerals and able to sequester precious metals. This model explains abnormally high Au-Ag enrichments observed in some deposits that contain Pb-Bi ores.","PeriodicalId":7768,"journal":{"name":"American Mineralogist","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141823807","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}
Xi Zhang, Xiandong Liu, Yingchun Zhang, Xiancai Lu
Surface acid chemistry is central to interfacial properties of orthoclase. In this study, we report a first principles molecular dynamics (FPMD) study of interfacial structures and acid constants (pKa) of orthoclase (001) with the presence of Na+/K+ cation on the surface. Detailed structural analyses show that Na+ and K+ show similar coordination structures on the surface while the exchange of Na+ for K+ hardly changes hydration structures of surface groups. The surface groups (i.e., ≡SiOH, ≡AlOH, and ≡AlOH2) have pKas of 11.5, 18.5, and 7.8 with K+ on the surface and 5.5, 17.7, and 4.3 with Na+ on the surface, respectively. FPMD derived pKas indicate that with K+ on the surface ≡AlOH2 is the only active group in the common pH range while Na+ decreases surface pKas of surface groups, that makes ≡AlOH2 and ≡SiOH active. Based on the pKas, we derive a PZC (point of zero charge) of 9.7 and 4.9 for orthoclase (001) with surface K+ and Na+, respectively. This means that Na+ significantly enhances surface acid reactivity. The implication for understanding geochemical properties of orthoclase was discussed with the focus on surface complexation of metal cations.
{"title":"Interfacial structure and acidity of orthoclase (001) surface: understanding the effect of surface metal cation","authors":"Xi Zhang, Xiandong Liu, Yingchun Zhang, Xiancai Lu","doi":"10.2138/am-2023-9207","DOIUrl":"https://doi.org/10.2138/am-2023-9207","url":null,"abstract":"\u0000 Surface acid chemistry is central to interfacial properties of orthoclase. In this study, we report a first principles molecular dynamics (FPMD) study of interfacial structures and acid constants (pKa) of orthoclase (001) with the presence of Na+/K+ cation on the surface. Detailed structural analyses show that Na+ and K+ show similar coordination structures on the surface while the exchange of Na+ for K+ hardly changes hydration structures of surface groups. The surface groups (i.e., ≡SiOH, ≡AlOH, and ≡AlOH2) have pKas of 11.5, 18.5, and 7.8 with K+ on the surface and 5.5, 17.7, and 4.3 with Na+ on the surface, respectively. FPMD derived pKas indicate that with K+ on the surface ≡AlOH2 is the only active group in the common pH range while Na+ decreases surface pKas of surface groups, that makes ≡AlOH2 and ≡SiOH active. Based on the pKas, we derive a PZC (point of zero charge) of 9.7 and 4.9 for orthoclase (001) with surface K+ and Na+, respectively. This means that Na+ significantly enhances surface acid reactivity. The implication for understanding geochemical properties of orthoclase was discussed with the focus on surface complexation of metal cations.","PeriodicalId":7768,"journal":{"name":"American Mineralogist","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141821479","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}
Xuyang Meng, David R. Mole, A. Simon, Jingwen Mao, D. Kontak, P. Jugo, Jackie Kleinsasser
Sodic volcanoplutonic terranes in the Archean can be well preserved, but why oxidized S-rich sodic magmas and porphyry-type Cu-Au deposits are so rare remains poorly understood. Here we addressed this issue by measuring the S concentration and S6+/ΣS ratio of primary apatite grains in >2.7 Ga felsic volcanic rocks from the well-characterized Neoarchean Abitibi Greenstone Belt of the Superior Province, Canada. Whereas apatite grains in most samples contain low S concentrations (<0.01 wt%, n = 24), a few apatite samples are S-rich (0.14 ± 0.03 wt%, 1σ) and have low S6+/ΣS ratios (0.56 ± 0.17; 1σ, n = 4). Samples with S-poor apatite have variable whole-rock La/Yb ratios (generally <30) and zircon 10000*(Eu/Eu*)/Yb ratios of 11 ± 8 (1σ), which may be products of plume-driven or over-thickened crustal melting. In contrast, the samples with S-rich apatite have elevated La/Yb ratios of 49 ± 15 (1σ), zircon 10000*(Eu/EuN*)/Yb ratios of 26 ± 7 (1σ), and zircon δ18O values of 5.8 ± 0.1 ‰ (1σ), consistent with a deep, hydrous and homogeneous mantle-like source for the melts dominated by amphibole ± garnet fractionation that is reminiscent of subduction-like process. These are the first reported results documenting the predominant accommodation of relatively reduced S in S-rich apatite grains crystallized from terrestrial silicate melts, possibly reflecting slight oxidation associated with the hydration of Neoarchean mantle and crystal fractionation over the magma evolution. The more common S-poor apatite data suggest that suppressed oxidation of the parental sodic magmas led to weak S emission from Earth’s interior to its evolving surface, explaining the rarity of porphyry-type Cu deposits in > 2.7 Ga Archean sodic volcanoplutonic terranes.
阿寒带的钠质火山岩地层保存完好，但富含S的氧化钠质岩浆和斑岩型铜金矿床为何如此罕见，至今仍不甚明了。在这里，我们通过测量加拿大苏必利尔省特征良好的新奥陶纪阿比提比绿岩带中大于2.7 Ga的长英质火山岩中原生磷灰石晶粒的S浓度和S6+/ΣS比率来解决这个问题。而大多数样本中的磷灰石颗粒都含有较低的 S 浓度（2.7 Ga Archean sodic volcanoplutonic terranes.
{"title":"Unusual sulfide-rich magmatic apatite crystals from >2.7 Ga Abitibi Greenstone Belt, Canada","authors":"Xuyang Meng, David R. Mole, A. Simon, Jingwen Mao, D. Kontak, P. Jugo, Jackie Kleinsasser","doi":"10.2138/am-2024-9387","DOIUrl":"https://doi.org/10.2138/am-2024-9387","url":null,"abstract":"\u0000 Sodic volcanoplutonic terranes in the Archean can be well preserved, but why oxidized S-rich sodic magmas and porphyry-type Cu-Au deposits are so rare remains poorly understood. Here we addressed this issue by measuring the S concentration and S6+/ΣS ratio of primary apatite grains in >2.7 Ga felsic volcanic rocks from the well-characterized Neoarchean Abitibi Greenstone Belt of the Superior Province, Canada. Whereas apatite grains in most samples contain low S concentrations (<0.01 wt%, n = 24), a few apatite samples are S-rich (0.14 ± 0.03 wt%, 1σ) and have low S6+/ΣS ratios (0.56 ± 0.17; 1σ, n = 4). Samples with S-poor apatite have variable whole-rock La/Yb ratios (generally <30) and zircon 10000*(Eu/Eu*)/Yb ratios of 11 ± 8 (1σ), which may be products of plume-driven or over-thickened crustal melting. In contrast, the samples with S-rich apatite have elevated La/Yb ratios of 49 ± 15 (1σ), zircon 10000*(Eu/EuN*)/Yb ratios of 26 ± 7 (1σ), and zircon δ18O values of 5.8 ± 0.1 ‰ (1σ), consistent with a deep, hydrous and homogeneous mantle-like source for the melts dominated by amphibole ± garnet fractionation that is reminiscent of subduction-like process. These are the first reported results documenting the predominant accommodation of relatively reduced S in S-rich apatite grains crystallized from terrestrial silicate melts, possibly reflecting slight oxidation associated with the hydration of Neoarchean mantle and crystal fractionation over the magma evolution. The more common S-poor apatite data suggest that suppressed oxidation of the parental sodic magmas led to weak S emission from Earth’s interior to its evolving surface, explaining the rarity of porphyry-type Cu deposits in > 2.7 Ga Archean sodic volcanoplutonic terranes.","PeriodicalId":7768,"journal":{"name":"American Mineralogist","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141823598","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}
Carbonatites are carbonate-rich and silica-undersaturated igneous rocks. The presence of various silicates in carbonatites has sparked discussions about the source of silica. In this study, abundant fluorbritholite-(Ce) and humite group minerals are identified in the No. 1 carbonatite dike at the Bayan Obo REE-Nb-Fe deposit. These silicates are relatively rare and poorly understood in carbonatite systems. Mineral textures, in-situ EPMA and LA-ICP-MS analyses have been combined to constrain the mineral genesis in the carbonatite. Fluorbritholite-(Ce), member of the apatite super-group, occurs as euhedral to subhedral crystals in the dike. They are characterized by remarkably high concentrations of REE2O3 (56.0-63.7 wt.%), SiO2 (19.6-21.2 wt.%) and F (2.47-3.47 wt.%), along with relatively lower P2O5 (0.25-3.69 wt.%) and CaO (10.3-14.2 wt.%) contents compared to common fluorapatite species. Additionally, their high Y (961-3435 ppm) and low Sr/Y (0.59-2.70) values suggest a hydrothermal origin from a fluid rich in SiO2, REE and F. Humite group minerals, mainly chondrodite and humite, display irregular mineral textures. They also exhibit elevated SiO2 (32.5-34.7 wt.%), and F content (3.59-7.32 wt.%), with notably low TiO2 content (0.02-0.08 wt.%), indicating a hydrothermal origin induced by fenitization in the shallow crust. Our results favor a model of crustal silica contamination for the fenitization fluids, enriched in F, LREE and SiO2. More importantly, the fluid-assisted silica contamination from wall rocks within carbonatites is likely to be a critical trigger of REE deposition in the carbonatite ore-forming systems.
{"title":"Mineralogical fingerprints of crustal silica contamination in the Bayan Obo carbonatite","authors":"Yulun Xiao, Wubin Yang, Xiaoyong Yang, Yonghua Cao, Pengfei Tian, Zhuang Zhao","doi":"10.2138/am-2023-9297","DOIUrl":"https://doi.org/10.2138/am-2023-9297","url":null,"abstract":"\u0000 Carbonatites are carbonate-rich and silica-undersaturated igneous rocks. The presence of various silicates in carbonatites has sparked discussions about the source of silica. In this study, abundant fluorbritholite-(Ce) and humite group minerals are identified in the No. 1 carbonatite dike at the Bayan Obo REE-Nb-Fe deposit. These silicates are relatively rare and poorly understood in carbonatite systems. Mineral textures, in-situ EPMA and LA-ICP-MS analyses have been combined to constrain the mineral genesis in the carbonatite. Fluorbritholite-(Ce), member of the apatite super-group, occurs as euhedral to subhedral crystals in the dike. They are characterized by remarkably high concentrations of REE2O3 (56.0-63.7 wt.%), SiO2 (19.6-21.2 wt.%) and F (2.47-3.47 wt.%), along with relatively lower P2O5 (0.25-3.69 wt.%) and CaO (10.3-14.2 wt.%) contents compared to common fluorapatite species. Additionally, their high Y (961-3435 ppm) and low Sr/Y (0.59-2.70) values suggest a hydrothermal origin from a fluid rich in SiO2, REE and F. Humite group minerals, mainly chondrodite and humite, display irregular mineral textures. They also exhibit elevated SiO2 (32.5-34.7 wt.%), and F content (3.59-7.32 wt.%), with notably low TiO2 content (0.02-0.08 wt.%), indicating a hydrothermal origin induced by fenitization in the shallow crust. Our results favor a model of crustal silica contamination for the fenitization fluids, enriched in F, LREE and SiO2. More importantly, the fluid-assisted silica contamination from wall rocks within carbonatites is likely to be a critical trigger of REE deposition in the carbonatite ore-forming systems.","PeriodicalId":7768,"journal":{"name":"American Mineralogist","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141823874","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：