Extreme chemical conditions of crystallisation of Umbrian Melilitolites and wealth of rare, late stage/hydrothermal minerals

Abstract

Melilitolites of the Umbria Latium Ultra-alkaline District display a complete crystallisation sequence of peculiar, late-stage mineral phases and hydrothermal/cement minerals, analogous to fractionated mineral associations from the Kola Peninsula. This paper summarises 20 years of research which has resulted in the identification of a large number of mineral species, some very rare or completely new and some not yet classified. The progressive increasing alkalinity of the residual liquid allowed the formation of Zr-Ti phases and further delhayelitemacdonaldite mineral crystallisation in the groundmass. The presence of leucite and kalsilite in the igneous assemblage is unusual and gives a kamafugitic nature to the rocks. Passage to non-igneous temperatures (T<600 • C) is marked by the metastable reaction and formation of a rare and complex zeolite association (T<300 • C). Circulation of low-temperature (T<100 • C) K-Ca-Ba-CO 2 -SO 2 -fluids led to the precipitation of sulphates and hydrated and/or hydroxylated silicate-sulphate-carbonates. As a whole, this mineral assemblage can be considered typical of ultra-alkaline carbonatitic rocks.

Mafic-ultramafic rocks and alkaline-carbonatitic magmatism and associated hydrothermal mineralization: A special issue (Part-I) dedicated to Piero Comin-Chiaramonti

“…Hydrous fluids from less alkaline mafic-ultramafic complexes seem different and are more specific for tellurium and PGE concentration as suggested by the papers of Dora et al [5], who studied the mineralisation of Gondpipri, Central India, and the paper by Devaraju et al [6], which describes the Channagiri complex, India. Even small volcanic or subvolcanic outcrops may have undergone the intense action of magmatic fluids as observed in the small melilitolitic sub-volcanics in Central Italy described by Stoppa and Schiazza [7], or the regional swarm of ultramafic dykes described by Comin-Chiaramoti et al [8] from Planalto da Serra, Brazil, which show several generations of latestage minerals. These two localities have a kamafugitic affinity and are related by the authors to a metasomatised mantle source enriched in K and radiogenic Sr.…”

Late-stage magmatic to deuteric/metasomatic accessory minerals from the Cerro Boggiani agpaitic complex (Alto Paraguay Alkaline Province)

“…Main accessory phases are apatite, eudialyte, låvenite, pyrophanite, rosenbuschite, titanite and uraninite; carbonates can be also present as patches and/or veins (Comin-Chiaramonti et al, 2005). Deuteric and metasomatic conditions of crystallization (Stoppa and Schiazza, 2014) are emphasized by the presence of cancrinite and zeolites.…”

Hydrothermal Aluminum-Phosphate-Sulfates in Ash from the 2014 Hydrothermal Eruption at Ontake Volcano, Central Honshu, Japan

“…In these cases, euhedral, commonly bladed, hydrothermal alunite often shows a core of APS with crandallite-woodhouseite-svanbergite (Table 1) compositions [15][16][17][18][19][20][21][22][23]. APS is detected also along the contact between alkaline-igneous rocks and arigillitic country-rocks, coexisting with cement phased minerals (Calcium Silicate Hydrate (CSH), Calcium Alumium Silicate Hydrate (CASH) [24,25]). Fluid inclusion microthermometry and stable isotopic geothermometry indicate formation temperatures between 200 • C and 350 • C [16,17,23].…”