This study focuses on a well-exposed section of the Ar tvin-Bolnisi zone located in the open pit of the Madneuli ore deposit, Lesser Caucasus, Georgia. Detailed field and petrographic obser vations of the main volcano-sedimentary lithofacies of its Upper Cretaceous stratigraphic succession were carried out. Whole rock geochemistry studies suppor t the interpretation of intense silicification of the rocks, and suppor ts our petrographic studies of samples from the Madneuli open pit, including lobe-hyaloclastite described in detail during this study. A par ticular focus concerned lobe-hyaloclastite exposures in the Madneuli open pit, singled out for first time in this area of the Lesser Caucasus. Two types of hyaloclastite arerecognized at the Madneuli deposit: hyaloclastite with pillow-like forms and hyaloclastite with glass-like selvages. The petrographic description shows a different nature for both: hyaloclastite with glass-like selvages represented by devitrification of volcanic glass, which is replaced by quartz and K-feldspar overgrowth of crystals in the groundmass and elongated K-feldspar porphyry phenocrysts. Perlitic cracks were identified during thin section obser vation. The hyaloclastite with pillow-like forms consists of relicts of volcanic glass and large pumice clasts replaced by sericite. Key obser vations are presented in the case of lobe-hyaloclastite and their immediate host volcano-sedimentary environment to constrain their depositional setting. A paleoreconstruction of their environment is proposed, in which hyaloclastite record the interaction of magma emplaced in unconsolidated volcano-sedimentary rocks associated with a submarine rhyodacite dome, emplaced during several magmatic pulses. Our study shows that the predominant par t of the host rock sequence of the Madneuli polymetallic deposit was deposited under submarine conditions, which is in agreement with volcanogenic massive sulfide models or transitional, shallow submarine magmatic to epithermal models that were proposed by previous studies.