Italian carbonatite system: From mantle to ore-deposit

Francesco Stoppa, Mariangela Schiazza, Gianluigi Rosatelli, Francesca Castorina, Victor V. Sharygin, Francesco Antonio Ambrosio, Noemi Vicentini

Research output: Contribution to journalReview articlepeer-review

13 Citations (Scopus)

Abstract

A new discovery of carbonatites at Pianciano, Ficoreto and Forcinelle in the Roman Region demonstrates that Italian carbonatites are not just isolated, mantle xenoliths-bearing, primitive diatremic rocks but also evolved subtype fluor-calciocarbonatite (F ~ 10 wt%) associated with fluor ore (F ~ 30 wt%). New data constrain a multi-stage petrogenetic process, 1-orthomagmatic, 2-carbothermal, 3-hydrothermal. Petrography and geochemistry are conducive to processes of immiscibility and decarbonation, rather than assimilation and crystal fractionation. A CO2-rich, ultra-alkaline magma is inferred to produce immiscible melilite leucitite and carbonatite melts, at lithospheric mantle depths. At the crustal level and in the presence of massive CO2 exsolution, decarbonation reactions may be the dominant processes. Decarbonation consumes dolomite and produces calcite and periclase, which, in turn, react with silica to produce forsterite and Ca silicates (monticellite, melilite, andradite). Under carbothermal conditions, carbonate breakdown releases Sr, Ba and LREE; F and S become concentrated in residual fluids, allowing precipitation of fluorite and barite, as well as celestine and anhydrite. Fluor-calciocarbonatite is the best candidate to exsolve fluids able to deposit fluor ore, which has a smaller volume. At the hydrothermal stage, REE concentration and temperature dropping allow the formation of LREEF2+ and LREECO3+ ligands, which control the precipitation of interstitial LREE fluorcarbonate and silicates: (bastnäsite-(Ce), Ce(CO3)F and britholite-(Ce), (Ce,Ca)5(SiO4,PO4)3(OH,F). Vanadates such as wakefieldite-(Ce), CeVO4, vanadinite, Pb5(VO4)3Cl and coronadite Pb(Mn4+ 6 Mn3+ 2)O16 characterise the matrix. At temperatures of ≤100 °C analcime, halloysite, quartz, barren calcite, and zeolites (K-Ca) precipitate in expansion fractures, veins and dyke aureoles.

Original languageEnglish
Article number103041
Number of pages17
JournalOre Geology Reviews
Volume114
DOIs
Publication statusPublished - 1 Nov 2019

Keywords

  • Carbonatite petrogenetic model
  • Fluor-calciocarbonatite
  • Immiscibility
  • Italian carbonatites
  • Melt decarbonation
  • REE
  • LIQUID IMMISCIBILITY
  • COMPLEX
  • REE DEPOSITS
  • PIAN-DI-CELLE
  • SICHUAN PROVINCE
  • IMMISCIBLE CARBONATITE
  • STABLE-ISOTOPE
  • MELT INCLUSIONS
  • MINERAL CHEMISTRY
  • VULTURE VOLCANO

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