Spectroscopic study of barite from the Kremikovtsi Deposit (Bulgaria) with implication for its origin

Abstract

Different genetic types (endogene and supergene) of barite from the Kremikovtsi deposit (Bulgaria) were studied by Laser-induced time-resolved luminescence (LITRL), Infrared (IR) and Raman spectroscopy. The IR spectra of the endogene barites are quite similar to those reported in the literature and do not show appreciable differences among them. The IR spectra of the supergene barites are almost identical to those of the endogene ones in respect to the positions of the vibrational modes ?1, ?2 and ?4 of SO4 2 except for a shift of 3 cm-1 for the ? 3 band. They displayed a presence of additional bands, which are close to the ?3 and ?1 modes of CO3 2- in calcite. The Raman studies support the suggestion that the supergene barite contains traces of calcite. The modern LITRL technique allowed the detection of several luminescent centers in the endogene barite. Eu3+ luminescence was identified for the first time in barite. The different emission spectra at 266 and 532 nm excitations suggest there are at least 2 structural positions for Eu3+ in the barite crystal lattice. The luminescent spectra also revealed a rather unusual violet-blue Nd3+ emission, which usually occurs in the IR spectral range, as well as emissions of Ce3+, Eu2+, Tb3+, Ag+, Sn2+(?) and UO2 2+. The oxidation state of cations isomorphically present in the barite crystal lattice suggests the endogene barite in the Kremikovtsi deposit precipitated from reduced fluids supposedly subjected to cooling (conductive/convective) and oxidation (mixing with seawater).Razliciti genetski tipovi barita (endogeni i supergeni) iz kremikovackog lezista u Bugarskoj proucavani su spektroskopskim metodima LITRL, IR i Raman. Infracrveni spektri endogenih barita slicni su spektrima iz literature i ne pokazuju medjusobne razlike. IR spektri supergenih barita su skoro identicni spektrima endogenih barita u pogledu polozaja vibracionih pikova ?1, ?2 i ?4 SO4 2- osim za pomak od 3 cm-1 kod ?3. Spektri su prikazivali prisustvo dodatnih traka koje su bliske pikovima ?3 i ?1 CO3 2- u kalcitu. Ramanova spektroskopska proucavanja idu u prilog nagovestaja da supergeni barit sadrzi tragove kalcita. Savremena tehnika LITRL omogucava otkrivanje nekoliko luminescentnih centara u endogenim baritu. Po prvi put je u baritu utvrdjena luminescencija Eu3+. Razliciti emisioni spektri pri pobudjivanju od 266 i 532 nm ukazuju da postoje bar dva strukturna polozaja Eu3+ u kristalnoj resetki barita. Luminescentni spektri su takodje otkrili neobicnu ljubicasto-plavu emisiju Nd3+, koja se obicno javlja u infracrvenom opsegu spektra, kao i emisije Ce3+, Eu2+, Tb3+, Ag+, Sn2+(?) i UO2 2+. Stepen oksidacije katijona izomorfno prisutnih u kristalnoj resetki barita ukazuje da je endogeni barit u lezistu Kremikovci natalozen iz redukovanih fluida za koje se pretpostavlja da su bili izlozeni hladjenju (konduktivno odnosno konvektivno) ili oksidaciji (mesanjem sa morskom vodom).