Environmental Baseline Geochemistry of Sediments and Percolating Waters in the Modrić Cave, Croatia

Povzetek

Izdelana je bila predhodna podrobna študija jame Modriča, še preden bi jo uredili za turistični obisk. Meljasta ilovica z guanom vsebuje mnogo kremena, ilita in taranakita ter manjše količine vivianita in visoke koncentracije bakra (2869 mg/kg), cinka (951 mg/kg) in kadmija (28 mg/kg). Sedimenti, pomešani z guanom, so obogateni z rahlim REE in s povišanimi koncentracijami U, Th in Hg. Sedimenti z delci kosti vsebujejo kremen, ilit, kalcit in hidroxylapatit, a manj carnalita in nizke vrednosti težkih mineralov. Vsi analizirani sedimenti kažejo razlićno stopnjo kontaminacije Cu in Zn zaradi razsutega guana. Većina Zn in Cu v jamskih sedimentih kot tudi hidroxylapatitna skorja so v zvezi z železovim in manganovim hidroksidom ter organskimi delci. Organski delci v vzorcih sedimentov so pomembni, ker kažejo neposredni vpliv guana in hidroxylapatitnih skorij, medtem ko je v vzorcih sedimentov z drobci kosti najpomembnejši hidroksid. V dveh primerih smo opazovali vpliv guana na prenikajočo vodo v levem rovu, kjer je večja koncentracija ortofosfatov glede na hidroxylapatit

A comprehensive study of Modrič cave was undertaken to evaluate the baseline conditions before its utilization for tourism. Silty loams with guano contain abundant quartz, illite and taranakite and minor vivianite and high concentrations of Cu (2869 mg/kg), Zn (951 mg/kg) and Cd (28 mg/kg). Also sediments mixed with guano are enriched with light REE as well as elevated concentrations of U, Th, Rb and Hg. Sediments with bone fragments contain abundant quartz, illite, calcite and hydroxylapatite and minor carndallite and lower contents of heavy metals. All sediments analysed showed various degrees of contamination by Cu and Zn from dispersed guano. Most of the Zn and Cu in cave sediments and the hydroxyl-apatite crusts are mainly controlled by the iron and manganese hydroxide and the organic fractions, the organic fraction plays an important role in sediment samples with direct influence of guano and in hydroxylapatite crusts while in samples with bone fragments the hydroxide control is dominant. Guano influence on the percolating waters was observed in two cases in the left channel where due to the higher content of orthophosphates saturation in respect to hydroxyl-apatite is present.