Abstract
Gorceixite from the Upper Cambrian Rocks of the podwiśniówka Mine Pit, Holy Cross Mountains (South-Central Poland)This report presents the results of a petrographical, mineralogical (SEM/EDS, XRD) and geochemical (XRF, CV-AAS, ICP-MS) study of gorceixite (barium aluminophosphate) from the abandoned Podwiśniówka mine pit. This site is highlighted by the presence of highly acidic pit pond whose chemistry is strongly affected by the exposed pyrite-bearing zone. The gorceixite occurs in the Upper Cambrian carbonaceous clayey shales, quartzites and tuffs in form of minute accumulations varying from about 0.5 to 100 μm in diameter. These accumulations infill voids, cavities, cracks and partly fissures in the rocks examined. The other minerals of the crandallite series, i.e. florencite and goyazite, can be found only in trace amounts. The gorceixite-bearing rocks, especially carbonaceous clayey shales, are characterized by the highest concentrations of REE reaching 455.09 mg·kg-1. In addition, these rocks are distinctly enriched in light rare earth elements (LREE), with the La/Yb ratio ranging from 24.44 through 36.30. Some of the examined gorceixite accumulations are paragenetically linked to the veined pyrite and nacrite. The latter mineral is indicative of crystallization temperatures of about 200 to 300°C. The coexistence of gorceixite with the veined nacrite or pyrite mineralization and the volcaniclastic rocks, as well as the microtextural features and high concentrations of REE in the gorceixite-bearing parent rocks suggest that this mineral formed as a result of both hydrothermal and volcanic activity in a shallow-marine basin during the late Cambrian.
Highlights
Like other secondary aluminophosphate and phosphate minerals, i.e. florencite (REE)Al3(PO4)2(OH)6 (Pouliot, Hofmann 1981), crandallite CaHAl3[(PO4)2(OH)6] (Scott 1987), goyazite SrHAl3[(PO4)2(OH)6] (Kato, Radoslovich 1968), apatite (Ca,...)5(PO4,...)3(F,Cl,OH), xenotime Y[PO4], gorceixite is isostructural with alunite
Rakowiecka 4, 00-975 Warszawa, Poland; e-mail: ewastarn@yahoo.com (Ca,...)5(PO4,...)3(F,Cl,OH), xenotime Y[PO4], gorceixite is isostructural with alunite. It belongs to the crandallite series of aluminum-phosphate-sulphate (APS) minerals, and its chemical formula is differently reported by various authors: BaAl3(PO4)2(OH)5×H2O (Dill et al 1995; Ward et al 1996; Rasmussen et al 1998), BaAl3H[(OH)6(PO4)2] (Kato, Radoslovich 1968; Dill 2001; Manecki 2004) or BaAl3(PO4)(PO3OH)(OH)6 (Dill et al 2006)
For the purpose of this study the selected quartzite, clayey shale, tuff and pyrite-quartz bulk samples were analysed for 23 major and trace elements, i.e. Al (50), As (3), Ba (10), Ca (50), Cd (3), Co (3), Cr (3), Cu (5), Fe (100), K (50), Mg (100), Mn (10), Mo (2), Na (100), Ni (5), P (50), Pb (3), Sr (2), Ti (10), V (5) and Zn (2), using X-ray fluorescence spectrometry (XRF; spectrometer Philips PW 2400)
Summary
Like other secondary aluminophosphate and phosphate minerals, i.e. florencite (REE)Al3(PO4)2(OH) (Pouliot, Hofmann 1981), crandallite CaHAl3[(PO4)2(OH)6] (Scott 1987), goyazite SrHAl3[(PO4)2(OH)6] (Kato, Radoslovich 1968), apatite (Ca,...)5(PO4,...)3(F,Cl,OH), xenotime Y[PO4], gorceixite is isostructural (hexagonal) with alunite. It belongs to the crandallite series of aluminum-phosphate-sulphate (APS) minerals, and its chemical formula is differently reported by various authors: BaAl3(PO4)2(OH)5×H2O (Dill et al 1995; Ward et al 1996; Rasmussen et al 1998), BaAl3H[(OH)6(PO4)2] (Kato, Radoslovich 1968; Dill 2001; Manecki 2004) or BaAl3(PO4)(PO3OH)(OH) (Dill et al 2006). Gorceixite is resistant to weathering and dissolves only in strong acids at ambient pressure and temperature of above 400°C This mineral is hard (6 in hardness scale), brown, glassy and dull. The calculations predict that gorceixite is most stable from pH 4.0 to 6.8 (Jerden, Sinha 2006)
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