REE-bearing minerals in sediment-hosted stratiform pyrite mineralization zones of the Wiśniówka area (Holy Cross Mts., Poland)

Abstract

There are two arsenical pyrite (As-FeS 2 ) mineralization zones cropping out in the Podwiśniówka and Wiśniówka Duża quarries where quartzites and quartzitic sandstones have been extracted for over a century. A large amount of pyrite in the Wiśniówka siliciclastics is unusual in the hard rock mining throughout the world. The pyritiferous beds contain a variety of REE-bearing minerals, including a crandallite series of aluminum-phosphate-sulfate (APS) minerals, e.g., predominant goyazite SrHAl 3 [(PO 4 ) 2 (OH) 6 ] with subordinate gorceixite BaHAl 3 [(PO 4 ) 2 (OH) 6 ] and very occasional crandallite CaHAl 3 [(PO 4 ) 2 (OH) 6 ]. By contrast, the other REE-phosphate minerals, e.g., xenotime YPO 4 , bur particularly monazite CePO 4 occur in a lesser amount. Goyazite prevails somewhat in the Podwiśniówka beds whereas xenotime in the Wiśniówka Duża beds. Of the other REE-bearing minerals, bastnäsite REECO 3 (F,OH), florencite (REE)Al 3 (PO 4 ) 2 (OH) 6 and synchysite CaCe[CO 3 ] 2 F occur in trace amounts. Interestingly, the quite common phosphate minerals, i.e., wavellite (Al 3 [(OH,F) 3 |(PO 4 ) 2 ]×5H 2 O and variscite Al[PO 4 ]×2H 2 O) are depleted in REEs with only Ce attaining 0.09 wt.% as documented by an electron-probe microanalysis. In contrast to quartzites/quartzitic sandstones, carbonaceous clayey-silty shales and bentonites/tuffites are distinctly enriched in REE-bearing minerals. This diversity is also mirrored in the mean total REE concentrations varying from 204 to 314 mg/kg, in clayey-silty shales and bentonites, attaining 457 mg/kg in some Podwiśniówka shale beds. Results of this and the previous petrographic, mineralogical and geochemical studies have indicated that REE-bearing minerals formed generally along with As-rich pyrite, nacrite/dickite and probably TiO 2 polymorphs as a result of multiphase hydrothermal vent activity that took place in the Wiśniówka Late Cambrian sedimentary basin. This evidence is also backed up by the values of LREE NASC /HREE NASC (1.44–1.75) and Eu/Eu NASC (1.24–1.30) coefficients in the clayey-silty shales. This positive Eu anomaly (³1.20) points to the formation of REE-bearing minerals in a reducing environment.