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The Canadian Mineralogist

Research Article| September 01, 2018 Ghosts of Apatite Past: Using Hyperspectral Cathodoluminescence and Micro-Geochemical Data To Reveal Multi-Generational Apatite in the Gifford Creek Carbonatite Complex, Australia Paul Slezak; Paul Slezak § Department of Geoscience, James Cook University, Townsville, Queensland 4811 Australia § Corresponding author e-mail address: paul.slezak@my.jcu.edu.au Search for other works by this author on: GSW Google Scholar Carl Spandler; Carl Spandler Department of Geoscience, James Cook University, Townsville, Queensland 4811 Australia Search for other works by this author on: GSW Google Scholar Kevin Blake Kevin Blake Advanced Analytical Centre, James Cook University, Townsville, Queensland 4811 Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Paul Slezak § Department of Geoscience, James Cook University, Townsville, Queensland 4811 Australia Carl Spandler Department of Geoscience, James Cook University, Townsville, Queensland 4811 Australia Kevin Blake Advanced Analytical Centre, James Cook University, Townsville, Queensland 4811 Australia § Corresponding author e-mail address: paul.slezak@my.jcu.edu.au Publisher: Mineralogical Association of Canada First Online: 25 Oct 2018 Online Issn: 1499-1276 Print Issn: 0008-4476 © 2018 Mineralogical Association of Canada The Canadian Mineralogist (2018) 56 (5): 773–797. https://doi.org/10.3749/canmin.1800021 Article history First Online: 25 Oct 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paul Slezak, Carl Spandler, Kevin Blake; Ghosts of Apatite Past: Using Hyperspectral Cathodoluminescence and Micro-Geochemical Data To Reveal Multi-Generational Apatite in the Gifford Creek Carbonatite Complex, Australia. The Canadian Mineralogist 2018;; 56 (5): 773–797. doi: https://doi.org/10.3749/canmin.1800021 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyThe Canadian Mineralogist Search Advanced Search Abstract Apatite can host significant levels of trace elements, including REE, within its crystal lattice, making it particularly useful for deciphering geological events and processes. This study employs hyperspectral cathodoluminescence (CL) and in situ microchemical techniques to identify and characterize various generations of apatite occurring in the phoscorites, carbonatites, and fenites of the Gifford Creek Carbonatite Complex (GCCC), Western Australia. Hyperspectral CL revealed that apatite crystals in all samples have complex internal zoning, including multiple distinct generations, with zones of relatively bright CL generally having more complex spectra compared to darker CL zones. Most of the CL spectra have prominent sharp peaks at ∼1.4 eV and ∼2.l eV as well as a broad peak between 2.3 eV and 3.5 eV. We relate these different peaks to individual REE activators and groups of activators, in particular Nd3+, Eu3+, Sm3+, and Ce3+.Trace element analyses of apatite confirm the relative enrichment of REE in the CL brighter zones. Most apatite generations exhibit concave-down to sinusoidal REY patterns lacking Eu anomalies, but often feature distinct negative Y anomalies. The depletion in LREE is interpreted to be due to LREE sequestration into monazite, which is relatively abundant in most of the samples. Most apatite samples contain very low Si contents, but appreciable Na, so REE incorporation into apatite was primarily via a coupled substitution of REE + Na replacing 2Ca, which is consistent with the highly alkaline, low SiO2 environment under which the apatite formed. Based on the combined trace-element signatures and CL textures, we interpret the multiple generations of apatite to reflect magmatic growth from alkaline magmas followed by recrystallization during subsequent metamorphic/hydrothermal events. The notable exception is the apatite core domains from a fenite sample that contain relatively high Si and Mn contents, low Sr, and relatively HREE-enriched REY patterns with distinct negative Eu anomalies. This apatite is interpreted to be relict from the granitic precursor to fenitization.The apatite samples also show systematic compositional variations across the GCCC, with apatite from phoscorite samples from the southeast part of the complex containing higher Sr, lower Gd/Ce, and lower λ3 values (normalized REE pattern inflections) compared to apatite from the northwest part of the complex. Recognition of these spatial variations in apatite compositions from the intra-grain micro-scale through to the district scale demonstrates the utility of combining advanced petrographic methods, such as hyperspectral CL, with micro-chemical analysis to reveal complex geological records preserved in apatite. As apatite is a common accessory mineral, these techniques may be more broadly applicable to igneous source tracing, understanding metamorphic and/or metasomatic processes, provenance studies from detrital mineral records, and studies of the evolution of ore systems. 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Ghosts of Apatite Past: Using Hyperspectral Cathodoluminescence and Micro-Geochemical Data To Reveal Multi-Generational Apatite in the Gifford Creek Carbonatite Complex, Australia