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The Late Cretaceous explosive volcanism and facies distribution in Bolnisi district: insights into the lithological control on ore deposits, Lesser Caucasus, Georgia

Nino Popkhadze1 , Robert Moritz2, Şafak Utku Sönmez2, Malkhaz Natsvlishvili3, Joni Shubitidze3

  • Affiliations:  1A. Janelidze Institute of Geology of I.Javakhishvili Tbilisi State University, Department of Volcanology and Minerals Geology, A.Politkovskaya31, 0186, Tbilisi, Georgia & RMG Rich Metals Group; 2Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, 1205 Geneva, Switzerland; 3RMG Rich Metals Group Company, M.Aleksidze 1, 0160, Tbilisi, Georgia 

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 24

  • Programme No: 4.1.15

  • Theme 4 > Session 1

Abstract

The Bolnisi district of the northern Lesser Caucasus continues west into the Eastern Pontides, Turkey. It represents one of the major mining districts within the Tethyan metallogenic belt. This beneficial geotectonic location of Bolnisi district which is part of Artvin-Bolnisi belt, reflected by its geological and facies diversity, volcanism type, and mineral deposit distribution. The Late Cretaceous (~87--71 Ma) silicic-dominated bimodal volcanism in this region resulted in mafic and felsic rock types, the latter being a major host of the ore deposits and prospects, and being defined locally as the felsic Mashavera and Gasandami suites. The existence of caldera structures in this region has been mentioned by various scientists. Our new study in Bolnisi district was focused on a new mapping project based on field and facies-oriented analyses. Different types of ignimbrites are described by the author in this region: welded, mon-welded, slightly welded, and crystal-rich ignimbrites. Thickness varies from several m up to 400-500 m maximum. Gas-escape pipes and accretionary lapilli horizons are observed in this thick ignimbrite. Pumice tuff with different sizes of pumice and sometimes with transition zones to fine ash material, ash fall, and accretionary lapilli thick (up to several meters) horizons is outcropping in this region; different types of breccias including the phreatomagmatic, phreatic, volcanic and sedimentary is observed and mostly connecting with explosive character.  Explosive breccia and pumice-bearing rocks (including different types of ignimbrites and pumice tuffs) are good permeable rocks for fluid, where mineralization is mostly localized.