Metallogeny of Eocene Syncollisional Granites of Motajica and Prosara Mountains

The geological setting is dominated by Eocene (48.7 Ma) syncollisional granitoids in the form of a small pluton in the Motajica Mt. and in the form of numerous sills and dykes in the Prosara Mt. Microelement paragenesis of these magmatites, pegmatites, greisens and quartz veins are distinguished by U, Th, Ce, Y, P, Nb, Ta, B, Li, F, Be, Sn, Mo, W, Fe, Cu, Pb. These elements and 87Sr/86Sr and δ18O isotopic values indicate the mantle origin of magma contaminated by relatively sterile lithospheric rocks. The most probable hypothesis of such a hybrid magma formation is the “slab break-off model”. Deep erosion of Motajica granitoid pluton opened its acrobatholitic and epibatholitic level with numerous, but small pegmatite deposits (beryllites, tourmalinites, emeraldites and sylexites with piezoelectric quartz). Greisenization marked by strong silicification and muscovitization affected less than 1% of pluton. It is characterized by minor and accessory molybdenite, wolframite, huebnerite, scheelite, fluorite. Hydrothermal occurrences, galena and Fe minerals have only a mineralogical significance. Economically significant are numerous autochthonous kaolin deposits formed in Pliocene-Pleistocene time. Prosara apomagmatic granitoids, exclusively granite dykes are metallogenetically sterile. Ključne riječi: Planine Motajica i Prosara, sjeverna Bosna. Eocenski sinkolizioni granitoidi. pegmatiti, grajzeni, kvarcne žile, kaolin. Sažetak Eocenski (48.7 Ma) sinkolizioni granitoidi izgrađuju Motajicu u obliku malog plutona te kao brojni silovi i dajkovi Prosaru. Parageneze mikroelemenata tih magmatita, pegmatita, grajzena i kvarcnih žila: U, Th, Ce, Y, P, Nb, Ta, B, Li, F, Be, Sn, Mo, W, Fe, Cu, Pb kao i vrijednosti 87Sr/86Sr te δ18O indiciraju porijeklo magme iz omotača koja ja kontaminirana relativno metalogeno sterilnim stijenama litosfere. Najvjerojatnija hipoteza formiranja takove hibridne magme je “slab break-off model”. Duboka erozija granitoidnog plutona Motajice otvorila je njegov akroi epibatolitski nivo sa brojnim skromnim ležištima pegmatita (beriliti, turmaliniti, esmerladiti, sileksiti, s piezoelektričnim kvarcem). Grajzenizacijom je zahvaćeno manje od 1 % plutona i karakterizira je izrazita silifikacija i muskovitizacija granitoida sa sporednim ili akcesornim molibdenitom, volframitom, hibneritom, šelitom, fluoritom. Hidrotermalne pojave galenita i Fe minerala imaju samo mineraloški značaj. Značajna su u ekonomskom smislu autohtona ležišta kaolina formirana na granitoidima u pliocen-pleistocenu. Apomagmatske granitoidne, isključivo žilne stijene planine Prosare su metalogenetski sterilne.