TheREE-and HFSE-bearing phases in the Itatiaia alkaline complex (Brazil) and geochemical evolution of feldspar-rich felsic melts

Abstract

The Late Cretaceous Itatiaia complex is made up of nepheline syenite grading to peralkaline varieties, quartz syenite and granite, emplaced in the metamorphic rocks of the Serra do Mar, SE Brazil. The nepheline syenites are characterized by assemblages with alkali feldspar, nepheline, Fe-Ti oxides, clinopyroxene, amphibole, apatite and titanite, while the peralkaline nepheline syenites have F-disilicates (rinkite, wöhlerite, hiortdahlite, låvenite), britholite and pyrophanite as the accessory phases. The silica-oversaturated rocks have alkali feldspar, plagioclase, quartz, amphibole, clinopyroxene and Fe-Ti oxides; the chevkinite-group minerals are the featured accessory phases and are found with allanite, fluorapatite, fluorite, zircon, thorite, yttrialite, zirconolite, pyrochlore and yttrocolumbite. The major- A nd trace-element composition of the Itatiaia rocks have variations linked to the amount of accessory phases, have smooth, enriched chondritenormalized rare-earth element (REE) distribution patterns in the least-evolved nepheline syenites and convex patterns in the most-evolved nepheline syenites. The REE distribution patterns of the quartz syenites and granites show a typical pattern caused by fractional crystallization of feldspar and amphibole, in an environment characterized by relatively high oxygen fugacity (>NiNiO buffer) and high concentrations of H2O and F, supporting the crystallization of hydrous phases, fluorite and F-disilicates. The removal of small amounts of titanite in the transition from the least-evolved to the most-evolved nepheline syenites stems from petrogenetic models involving REE, and is shown to be a common feature of the magmatic evolution of many other syenitic/trachytic/phonolitic complexes of the Serra do Mar and elsewhere

Mineralogical and Chemical Characterization of Zr-REE-Nb Ores from Khalzan Buregtei (Mongolia)—Approaches to More Efficient Extraction of Rare Metals from Alkaline Granitoids

“…Alkaline rock hosted rare metal deposits yield potential as future resource for commodities like Zr, Nb, Hf, Y, and the REE. The economic interest in this deposit type is underlined by various international studies of the last decade [1,7,9,10,30]. The complexity of the ore with respect to texture, composition, and variable types of ore minerals is often caused by post-magmatic alteration of the ore-bearing rock suite.…”

“…Enrichment of HFSE to enhanced grades in alkaline intrusions is generally thought to be caused by magmatic fractionation, but mineralogical and petrologic evidence often points to post-magmatic pneumatolytic or hydrothermal processes. Post-magmatic mineralization events are commonly associated with intensive and highly variable alteration types of both intrusive and wall rocks, thereby superimposing primary petrographic features [1,2,6,[8][9][10].…”

“…Furthermore, formation in multistage and partially superimposing magmatic to hydrothermal processes frequently leads to narrow and complex intergrowths of fine grained and irregularly sized and shaped crystals. Thus, such rocks display a remarkable spatial variability and heterogeneity in terms of mineral composition, grain size, mineral association, and texture [1,9,10].…”

Automated SEM Mineral Liberation Analysis (MLA) with Generically Labelled EDX Spectra in the Mineral Processing of Rare Earth Element Ores

“…Rare earth element (REE) ore deposits occur in a wide variety of geological contexts and are hosted by a considerable diversity of host rocks [1]. Igneous host rocks appear mainly carbonatites and peralkaline plutonic rocks as nepheline syenites [2][3][4][5]. Although pegmatites may also contain significant amounts of REE-bearing minerals [6], they are usually too small in volume to be of economic significance.…”

Antecristais e xenocristais máficos em diques ultrabá¡sicos de tendência alcalina da Serra da Mantiqueira (SP)

“…Brechas magmáticas, estruturas anelares e minerais exóticos são característicos a tais litotipos félsicos (Alves et al, 1992;Brotzu et al, 1989Brotzu et al, , 1992Brotzu et al, , 1997Brotzu et al, , 2005Atencio et al, 1999;Enrich et al, 2005Enrich et al, , 2009Marins, 2012;Lopes, 2015;Melluso et al, 2017;Rosa, 2012Rosa, , 2017Rosa & Ruberti, 2018).…”