Feldspar mineralogy and rare-earth element (re)mobilization in iron-oxide copper gold systems from South Australia: a nanoscale study
作者： Alkis Kontonikas-Charos , Cristiana L. Ciobanu , Nigel J. Cook , Kathy Ehrig , Roniza Ismail
DOI: 10.1180/MINMAG.2017.081.040
关键词: Vein (geology) 、 Andesine 、 Perthite 、 Albite 、 Mineralogy 、 Orthoclase 、 Feldspar 、 Geology 、 Geochemistry 、 Hyalophane 、 Iron oxide copper gold ore deposits
摘要: Nanoscale characterization (TEM on FIB-SEM-prepared foils) was undertaken feldspars undergoing transformation from early post-magmatic (deuteric) to hydrothermal stages in granites hosting the Olympic Dam Cu-U-Au-Ag deposit, and Cu-Au skarn at Hillside within same iron-oxide copper-gold (IOCG) province, South Australia. These include complex perthitic textures, anomalously Ba-, Fe-, or REE-rich compositions, andREE-flourocarbonate + molybdenite assemblages which pseudomorph pre-existing feldspars. Epitaxial orientations between cryptoperthite (magmatic), patch perthite (dueteric) replacive albite (hydrothermal) vein support interface-mediated reactions alkali-feldspars and pervading fluid, irrespective of micro-scale crystal morphology. Such observations are consistent with a coupled dissolution-reprecipitation reaction mechanism, assists grain-scale element remobilization via the generation transient interconnected microporosity. Micro-scale aggregates hyalophane (Ba-rich K-feldspar), crystallizing previously albitized areas andesine, reveal a assemblage calc-silicate, As-bearing fluorapatite Fe oxides along boundaries enclosing albite-sericite typical deuteric alteration. inclusions good REE repositories their presence supports during Iron-metasomatism is recognized by nanoscale maghemite ‘red-stained’ orthoclase, as well hematite REE-fluorocarbonates, reflect broader-scale zonation patterns for IOCG systems. Potassium-feldspar contact alkali-granite characterized 100–1000 ppm REE, attributable pervasive calc-silicates, concentrated microfractures, pore-attached. Feldspar replacement REE-fluorcarbonates Dam calc-silicate feldspar both strong evidence role concentrating intense metasomatism. Differences mineralogical expression due availability associated elements. Lattice-scale intergrowths indicative Fe-metasomatism, REE-enrichment sulfide deposition spatial temporal relationship these processes.
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