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Crystals from the Powellite-Scheelite Series at the Nanoscale: A Case Study from the Zhibula Cu Skarn, Gangdese Belt, Tibet
Xu, Jing1,2; Ciobanu, Cristiana L.1; Cook, Nigel J.1; Slattery, Ashley3
2019-06-01
Source PublicationMINERALS
ISSN2075-163X
Volume9Issue:6Pages:23
AbstractScheelite (CaWO4) and powellite (CaMoO4) are isostructural minerals considered as a non-ideal solid solution series. Micron- to nanoscale investigation of a specimen of skarnoid from Zhibula, Gangdese Belt, Tibet, China, was carried out to assess the identity of the phases within a broad scheelite-powellite (Sch-Pow) compositional range, and to place additional constraints on redox changes during ore formation. An electron probe microanalysis shows that Mo-rich domains within complex oscillatory-zoned single crystals, and as thin sliver-like domains, have a compositional range from 20 mol.% to 80 mol.% Pow. These occur within a matrix of unzoned, close-to-end-member scheelite aggregates (87 mol.%-95 mol.% Sch). Laser-ablation inductively coupled plasma mass spectrometry spot analysis and element mapping reveal systematic partitioning behaviour of trace elements in skarn minerals (grossular(50), diopside(80), anorthite, and retrograde clinozoisite) and scheelite-powellite aggregates. The Mo-rich domains feature higher concentrations of As, Nb, and light rare earth elements LREE, whereas W-rich domains are comparatively enriched in Y and Sr. Transmission electron microscopy (TEM) was carried out on focused-ion-beam-prepared foils extracted in situ from domains with oscillatory zoning occurring as slivers of 20 mol.%-40 mol.% Pow and 48 mol.%-80 mol.% Pow composition within an unzoned low-Mo matrix (20 mol.% Pow). Electron diffractions, high-angular annular dark field (HAADF) scanning-TEM (STEM) imaging, and energy-dispersive spectroscopy STEM mapping show chemical oscillatory zoning with interfaces that have continuity in crystal orientation throughout each defined structure, zoned grain or sliver. Non-linear thermodynamics likely govern the patterning and presence of compositionally and texturally distinct domains, in agreement with a non-ideal solid solution. We show that the sharpest compositional contrasts are also recognisable by variation in growth direction. Atomic-scale resolution imaging and STEM simulation confirm the presence of scheelite-powellite within the analysed range (20 mol.%-80 mol.% Pow). Xenotime-(Y) inclusions occur as nm-wide needles with epitaxial orientation to the host scheelite-powellite matrix throughout both types of patterns, but no discrete Mo- or W-bearing inclusions are observed. The observed geochemical and petrographic features can be reconciled with a redox model involving prograde deposition of a scheelite+molybdenite assemblage (reduced), followed by interaction with low-T fluids, leading to molybdenite dissolution and reprecipitation of Mo as powellite-rich domains (retrograde stage, oxidised). The observation of nanoscale inclusions of xenotime-(Y) within scheelite carries implications for the meaningful interpretation of petrogenesis based on rare earth element (REE) concentrations and fractionation patterns. This research demonstrates that HAADF-STEM is a versatile technique to address issues of solid solution and compositional heterogeneity.
Keywordscheelite-powellite HAADF STEM solid solution Zhibula skarn
DOI10.3390/min9060340
Funding OrganizationNational Natural Science Foundation of China ; National Natural Science Foundation of China ; Key Laboratory of Mineral Resources ; Key Laboratory of Mineral Resources ; China Postdoctoral Science Foundation ; China Postdoctoral Science Foundation ; China Scholarship Council ; China Scholarship Council ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; Key Laboratory of Mineral Resources ; Key Laboratory of Mineral Resources ; China Postdoctoral Science Foundation ; China Postdoctoral Science Foundation ; China Scholarship Council ; China Scholarship Council ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; Key Laboratory of Mineral Resources ; Key Laboratory of Mineral Resources ; China Postdoctoral Science Foundation ; China Postdoctoral Science Foundation ; China Scholarship Council ; China Scholarship Council ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; Key Laboratory of Mineral Resources ; Key Laboratory of Mineral Resources ; China Postdoctoral Science Foundation ; China Postdoctoral Science Foundation ; China Scholarship Council ; China Scholarship Council
WOS KeywordTRACE-ELEMENTS ; MINERAL CHEMISTRY ; GOLD DEPOSITS ; REE ; PETROGENESIS ; CONSTRAINTS ; PROVINCE ; GARNETS ; SYSTEMS
Language英语
Funding ProjectNational Natural Science Foundation of China[41802098] ; Key Laboratory of Mineral Resources[KLMR2017-13] ; China Postdoctoral Science Foundation ; China Scholarship Council
Funding OrganizationNational Natural Science Foundation of China ; National Natural Science Foundation of China ; Key Laboratory of Mineral Resources ; Key Laboratory of Mineral Resources ; China Postdoctoral Science Foundation ; China Postdoctoral Science Foundation ; China Scholarship Council ; China Scholarship Council ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; Key Laboratory of Mineral Resources ; Key Laboratory of Mineral Resources ; China Postdoctoral Science Foundation ; China Postdoctoral Science Foundation ; China Scholarship Council ; China Scholarship Council ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; Key Laboratory of Mineral Resources ; Key Laboratory of Mineral Resources ; China Postdoctoral Science Foundation ; China Postdoctoral Science Foundation ; China Scholarship Council ; China Scholarship Council ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; Key Laboratory of Mineral Resources ; Key Laboratory of Mineral Resources ; China Postdoctoral Science Foundation ; China Postdoctoral Science Foundation ; China Scholarship Council ; China Scholarship Council
WOS Research AreaMineralogy ; Mining & Mineral Processing
WOS SubjectMineralogy ; Mining & Mineral Processing
WOS IDWOS:000473809300013
PublisherMDPI
Citation statistics
Cited Times:3[WOS]   [WOS Record]     [Related Records in WOS]
Document Type期刊论文
Identifierhttp://ir.iggcas.ac.cn/handle/132A11/92678
Collection矿产资源研究院重点实验室
Corresponding AuthorXu, Jing
Affiliation1.Univ Adelaide, Sch Chem Engn, Adelaide, SA 5005, Australia
2.Chinese Acad Sci, Inst Geol & Geophys, Key Lab Mineral Resources, Beijing 100029, Peoples R China
3.Univ Adelaide, Adelaide Microscopy, Adelaide, SA 5005, Australia
Recommended Citation
GB/T 7714
Xu, Jing,Ciobanu, Cristiana L.,Cook, Nigel J.,et al. Crystals from the Powellite-Scheelite Series at the Nanoscale: A Case Study from the Zhibula Cu Skarn, Gangdese Belt, Tibet[J]. MINERALS,2019,9(6):23.
APA Xu, Jing,Ciobanu, Cristiana L.,Cook, Nigel J.,&Slattery, Ashley.(2019).Crystals from the Powellite-Scheelite Series at the Nanoscale: A Case Study from the Zhibula Cu Skarn, Gangdese Belt, Tibet.MINERALS,9(6),23.
MLA Xu, Jing,et al."Crystals from the Powellite-Scheelite Series at the Nanoscale: A Case Study from the Zhibula Cu Skarn, Gangdese Belt, Tibet".MINERALS 9.6(2019):23.
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