Ivan Dragičević

Magmatic provenance and diagenesis of Miocene tuffs from the Dinaride Lake System (the Sinj Basin, Croatia)

This study presents new insights on the provenance, genesis, and post-depositional history of the Miocene pyroclastic tuffaceous layers (~18 and ~15 Ma) preserved in argillaceous sediments and interbedded within the lacustrine sedimentary succession of the Sinj Basin in central Dalmatia (Dinaride Lake System, Croatia). Analysed tuffs are classified as smectitic tuffs composed of three main lithotypes: (a) vitriclastic tuffs, (b) altered vitriclastic tuff, and (c) tuffaceous clays. The high field strength element (HFSE) contents of the tuffs, as well as the major- element chemistry of the vitric glass, suggests that parental magmas were high-K calc-alkaline trachyandesites. This is consistent with the distinctive heavy-mineral assemblages including clinopyroxene, zircon and apatite, identified in less evolved parental magmas, and biotite in more evolved ones. The regional geological data imply the placement of the parent volcano(es) outside the Dinaric Alps region, most probably in an area corresponding to the present-day southern margin of the Pannonian Basin where volcanic rock suites of analogous age and geochemistry are reported. Minor compaction and high permeability of coarse ash-sized pyroclastic material allowed for extensive in situ diagenetic clay mineral formation dominated by smectite. Following discrete smectite formation, the illite-smectite mixed-layering took place as a result of mica/illite alteration or surface illitization processes. On the basis of the very-low grade alteration of volcanic materials, it is suggested that diagenesis operated in an open hydrologic system of a lacustrine environment.

RESEARCH OF BAUXITE DEPOSITS FROM UNDERGROUND MINING WORKS

This paper presents a new approach to exploring bauxite deposits from underground mining works in the bauxitebearing mines of Bešpelj near Jajce in Bosnia and Herzegovina. In the area under consideration, bauxite deposits have been investigated and exploited for over 60 years. Despite the high degree of exploration in the geologically complicated structures of Bešpelj, there are numerous unexplored reserves. Up to now, they have been mainly investigated by drilling from the surface into the borehole network as dictated by legal geological regulations. Due to the increase in depths on which deposits are located and complex structural relationships, such research has become more expensive and less effective. From a geological point of view, the bauxite deposits have developed in the horizontal position. However, longlasting geological evolution from the Upper Cretaceous to the present, has brought deposits in very di erent structural positions. That is why we nd them in an inclined position, in subvertical and vertical, and often in an overturned position. For further research to become rational and e cient, a new approach of study from underground mining works was developed that will serve for study and then for the exploitation of bauxite deposits.