Mineralne, petrološke in geokemične značilnosti berilovih pegmatitnih žil J-JV Pohorja

Ravnjak, Mihael (avtor), Zupančič, Nina (mentor), Miler, Miloš (komentor)

Na območju Pohorja se v granodioritu, kremenovem monzogabbru in metamorfnih kamninah pojavlja veliko pegmatitnih žil. Na J–JV delu masiva smo določili makroskopske, mikroskopske in geokemične značilnosti berilovih pegmatitov. Namen naloge je ugotoviti povečane vsebnosti slednih prvin, minerale, ki so njihovi nosilci in preveriti, ali so berilovi pegmatiti ekonomsko zanimivi, zlasti z vidika vsebnosti redkih zemelj. Pegmatiti imajo srednje do debelozrnato, celo zelo debelozrnato, neenakomerno holokristalno strukturo. Masivno kamnino sestavljajo plagioklazi, mikroklin (mikroklin pertit) in kremen, značilni granat, beril, turmalin in muskovit, akcesorni biotit, cirkon, rutil, apatit, titanit in neprozorni minerali. Sekundarni so minerali kloritove skupine (klorit). S SEM/EDS smo določil uraninit, fluorapatit, rutil, monazit–(Ce), ksenotim–(Y), tantalit–kolumbit, Fe–oksid/hidroksid, pirit, bizmit oziroma bizmutit in kasiterit. Glede na stopnjo diferenciacije na diagramu Sr–Ba–Rb ločimo tri skupine pegmatitov. V prvi skupini so trije najmanj diferencirani vzorci iz Cezlaka, kjer je Ba relativno več kot Rb. V drugo, bolj diferencirano skupino sodita oba pegmatita Polskave, trije iz Cezlaka in en iz Bistriškega vintgarja. Tretjo skupino zastopajo pegmatiti Bistriškega vintgarja, kjer je v glinencih bistveno več Rb kot Ba in Sr. Statistično značilno se pegmatiti iz treh lokacij razlikujejo po vsebnosti As, Ni, Sr, U in W. Glede na mineralne in geokemične lastnosti berilovi pegmatiti iz J–JV Pohorja ustrezajo skupini z litijem, cezijem in tantalom (LCT). Uvrščam jih v razred muskovitnih pegmatitov z REE (MSREL), podrazred MSREL–REE, oziroma podrazred REL–Li, tip beril, podtip beril–kolumbit. Vsebnost slednih prvin in poldragih kamnov v njih ekonomsko ni zanimiva.

• Jezik: Slovenski jezik
• Ključne besede: granat, turmalin, tantalit, kolumbit, REE, kemična sestava
• Vrsta gradiva: Diplomsko delo/naloga
• Organizacija: NTF - Naravoslovnotehniška fakulteta
• Leto izida: 2018
• PID: 20.500.12556/RUL-100787
• COBISS.SI-ID: 1400158
• Datum objave v RUL: 15.04.2018

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Mineralogical, petrological and geochemical characteristics of beryl pegmatite veins on S-SE Pohorje

Izvleček

In the broader area of Pohorje Mts. (Eastern Alps), there are a number of pegmatite veins hosted by granodiorite, quartz monzogabbro, and metamorphic rocks. The research was aimed towards macroscopic and microscopic classification and geochemical characterization of beryl–bearing pegmatites from S–SE Pohorje. Our primary interest was focused on pegmatites trace element enrichment and to determine associated minerals. Furthermore, we evaluated Pohorje beryl–bearing pegmatites economic potential as a source of critical and rare–earth elements. Pegmatites have mid– to coarse grained, in places very coarse grained uneven holocrystalline texture. Characteristic minerals of the pegmatites are plagioclase, microcline (microcline perthite) and quartz, accompanied by garnet, beryl, tourmaline and muscovite, accessory biotite, zircon, rutile, apatite, titanite and opaque minerals. Secondary are chlorite group minerals. By SEM/EDS analysis, uraninite, fluorapatite, monazite–(Ce), xenotime–(Y), tantalite–columbite, Fe–oxide/hydroxide, pyrite, bismite or busmutite and cassiterite were identified. Depending on the degree of differentiation in the Sr-Ba-Rb diagram, three groups of pegmatites are distinguished. The first group is represented by three least differentiated samples from Cezlak, where the Ba is relatively more than Rb. In second, the more differentiated group are both pegmatites from Polskava, three from Cezlak and single from Bistrica Gorge. The third group contains Bistrica Gorge pegmatites, where feldspar contains significantly higher Rb concentration than Ba and Sr. Statistically significant pegmatites from three sites differ in the content of As, Ni, Sr, U and W content. Beryl–bearing pegmatites from S–SE Pohorje Mts. are, based on their mineral assemblage and geochemical composition, corresponding with the group containing lithium, cesium, and tantalum (LCT). Pegmatites can be attributed to the class of muscovite pegmatites with REE (MSREL), MSREL–REE or REL–Li subclass, beryl–type and beryl–columbite sub–type. The content of the trace elements and gemstones in them are not economically interesting.

• Ključne besede: garnet, tourmaline, tantalite, columbite, REE, chemical composition