T257 Rare Earth Elements: The Behavior of Critical Minerals in Sedimentary, Magmatic, and Magmatic-Hydrothermal Systems

Friday, 30 October 2020
10:00 AM - 2:00 PM
Meeting Rooms

REE-PHASES IN FLUOR-CARBONATITE AND FLUOR-SYENITE FROM THE ROMAN REGION, CENTRAL ITALY

Paper number: T257-8
Program: Technical Sessions
Time: 11:05 AM – 11:10 AM

Authors

Abstract

Owing the exponential increase of REE demand of the high-tech market and monopolistic control, the REE-minerals became a primary requirement of the frontier research rather than mineralogical oddities. This implies a need to investigate new potential REE supply in the western country, whose resources are not sufficiently exploited or well assessed, so far. A promising candidate for new REE-ore is the Roman Region of Central Italy, where leucitites and fluorite-carbonatites are co-eruptive to abundant alkaline syenite ejecta.

SEM-EDS and EMPA analyses confirm the occurrence of a variety of REE-minerals. REE minerals precipitate as LREE fluor-carbonate and fluor-phosphate (bastnäsite-(Ce) and britholite-(Ce)) and vanadates, (wakefieldite-(Ce)), in carbonatites [1]. REE-F-silicates, vicanite-(Ce) (LREE3.8 Th3.3 U0.9 Y0.3 Ca5.3)13.6 As5+0.95 (As3+)1 (Fe3+0.5 Al3+0.7)1.2 Si5 B5 O40 F7, hellandite-(Ce)/mottanaite-(Ce) intergrowth (Ca3.9 Na0.01 Mg0.04)3.9 (Ca0.6 Th0.4 U0.1 La0.1 Ce0.4 Pr0.1 Nd0.2 Sm0.03 Y0.02)1.9 (Al3+0.4 Mn0.1 Fe3+0.5 Ti0.1) Si4.2 B3.8 O22, brockite (La0.1 Ce0.4 Th0.1 Nd0.1 Ca0.3)(P0.75 Si0.05 □0.2) O4* H2O, percleveite-(Ce) (Ce1.1 La0.6 Th0.2 Ca0.1)2 (Si1.9 Al3+0.1)2 O7 and an unknown REE silicate phase are found in syenites. Syenites consist of K-feldspar, albite, clinopyroxene, fluor-phlogopite, sphene, Ti-magnetite and abundant fluorite.

High silica activity and higher temperature favour the precipitation of REE silicate phosphate phases in syenites. Passing from an orthomagmatic stage to a carbothermal stage, LREEF2+ and LREECO3+ ligands formation is favoured, producing precipitation of fluor-carbonatites and fluor-ore. At the hydrothermal stage, the solubility of REE in F-rich fluids increases, brockite is dissolved and bastnäsite-(Ce), britholite-(Ce), wakefieldite-(Ce), with other different REE phases precipitate.

If confirmed, percleveite-(Ce) would be the first occurrence known hitherto in Italy and the sixth worldwide. The depicted processes is of paramount importance in defining a new promising exploration REE-field in Italy and Europe.

[1] Stoppa et al.,(2019). Ore Geology Reviews 114 (2019) 103041.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-351629

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