A contribution to the mineralogy of Sicily, Italy – Kintoreite from the Tripi mine, Peloritani Mountains: occurrence and crystal structure

Abstract

A new occurrence of kintoreite, ideally PbFe3(PO4)(PO3OH)(OH)6, is described from the Tripi mine, Alì, Peloritani Mountains, northeastern Sicily, Italy. Kintoreite occurs as yellow equant crystals, up to 0.05 mm in size, on quartz, associated with another alunite-supergroup mineral currently under study. The studied grains of kintoreite are chemically zoned, showing the occurrence of two distinct domains. Electron microprobe analyses gave (in wt.%): SO3 5.47(27), P2O5 17.55(14), Al2O3 7.81(35), Fe2O3 23.81(44), PbO 35.11(41), H2Ocalc 9.93, total 99.68 (darker domains) and SO3 6.03(5), P2O5 16.66(23), Al2O3 4.22(2), Fe2O3 27.31(6), PbO 33.78(22), H2Ocalc 10.25, total 98.25 (brighter domains). On the basis of 14 O atoms per formula unit (apfu) and (P+S) = 2 apfu, the darker and brighter domains have chemical formula Pb1.00(Fe3+1.89Al0.97)Σ2.86[P1.57S0.43O7.43(OH)0.57][(OH)5.58(H2O)0.42]Σ6.00 and Pb0.98(Fe3+2.21Al0.53)Σ2.74[P1.51S0.49O7.49(OH)0.51][(OH)5.18(H2O)0.82]Σ6.00, respectively. Single-crystal X-ray diffraction was performed on a grain extracted from the same sample. Unit-cell parameters are a = 7.2191(10), c = 16.834(3) Å, V = 759.8(3) Å3 and Z = 3; space group R $\bar{3}$ m. The crystal structure was refined on the basis of 226 unique reflections with Fo > 4σ(Fo) and 31 least-square parameters to R1 = 0.0415. Kintoreite is isotypic with other alunite-supergroup minerals. Micro-Raman spectroscopy suggests the possible occurrence of H2O groups, supporting the possible protonation of (OH) groups as a charge-balance mechanism in this mineral. Kintoreite may play an environmental role in the Alì area, where previous authors detected high concentrations of potentially toxic elements in soils.

Occurrence and crystal chemistry of austinite, conichalcite and zincolivenite from the Peloritani Mountains, northeastern Sicily, Italy

“…The crystal chemical characterisation of austinite, conichalcite and zincolivenite is a further step in the knowledge of the supergene phases formed through the alteration of base-metal ore deposits of the Peloritani Mountains, after the study on the alunite-supergroup mineral kintoreite (Mauro et al , 2022). In particular, the identification of these three arsenates gives interesting insights for the speciation, transport and dispersion of As in this sector of Sicily, where, as discussed briefly in the Introduction, high contents of this toxic element (as well as other PTE) have been reported in stream sediments and soils since the beginning of the 1990s (e.g.…”

“…However, crystal chemical data for these arsenates are lacking and no further details on supergene assemblages was given. Recently, Mauro et al (2022) investigated a supergene mineral belonging to the alunite supergroup from the Tripi mine (Alì, Messina Province), identifying it as the lead-iron phosphate kintoreite. The Tripi mine (latitude 38°00′50″N; 15°24′27″E), located some hundred metres SSW of the small hamlet of Alì, exploited a stratabound fine-banded ore, mainly composed of sphalerite and Ag-bearing galena, with rare pyrite and trace amounts of chalcopyrite, arsenopyrite, pyrrhotite and covellite; quartz and fluorite are gangue minerals (Saccà et al , 2007).…”

Minerals, crystal structures and geochemistry

“…One more secondary phosphate, kintoreite [ideally PbFe 3 (PO 4 )(PO 3 OH)(OH) 6 ], from the Tripi mine, Alì, Peloritani Mountains, Sicily, Italy, is described by Daniela Mauro, Cristian Biagioni and Federica Zaccarini, in the article ‘A contribution to the mineralogy of Sicily, Italy – Kintoreite from the Tripi mine, Peloritani Mountains: occurrence and crystal structure'. This mineral with origins related to the weathering of primary ores, is suggested by the authors, “as a potential host for lead”, which together with other lead containing minerals, such as pyromorphite, could play a role in controlling the geochemical behaviour of this element (Mauro et al ., 2022).…”

Graulichite-(La), LaFe<sup>3+</sup><sub>3</sub>(AsO<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>, a new addition to the alunite supergroup from the Patte d'Oie mine, Bou Skour mining district, Morocco

“…Arsenic can also partially replace S in jarosite in acid mine drainage systems, with important implications on the As mobility (e.g., Gieré et al, 2003;Martín Romero et al, 2010;Burton et al, 2021). Moreover, the identification of alunite supergroup minerals may explain other geogenic PTE anomalies in some localities (e.g., Mauro et al, 2021).…”