Architecture of Upper Cretaceous rhyodacitic hyaloclastite at the polymetallic Madneuli deposit, Lesser Caucasus, Georgia

Abstract

This study focuses on a well-exposed section of the Artvin-Bolnisi zone located in the open pit of the Madneuli ore deposit, Lesser Caucasus, Georgia. Detailed field and petrographic observations of the main volcano-sedimentary lithofacies of its Upper Cretaceous stratigraphic succession were carried out. Whole rock geochemistry studies support the interpretation of intense silicification of the rocks, and supports our petrographic studies of samples from the Madneuli open pit, including lobe-hyaloclastite described in detail during this study.A particular 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 are recognized 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 observation. The Hyaloclastite with pillow-like forms consists of relicts of volcanic glass and large pumice clasts replaced by sericite. Key observations 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 part 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.

Long-lived, stationary magmatism and pulsed porphyry systems during Tethyan subduction to post-collision evolution in the southernmost Lesser Caucasus, Armenia and Nakhitchevan

“…1), and include the operating Cu-Au-polymetallic Madneuli deposit, the precious metal Sakdrisi deposit, and the polymetallic Beqtakari prospect (Gugushvili, 2004;Migineishvili, 2005;Popkhadze et al, 2014). To the west, the Artvin-Bolnisi volcanic arc extends into the VMSporphyry-epithermal districts of the Turkish Eastern Pontides ( Fig.…”

Felsic magma-water interaction in shallow intrusive environments: Timing between fluidal peperites and intrusive hyaloclastites in a jurassic cryptodome from the eastern Deseado Massif (patagonia, Argentina)

“…Finally, and although the intrusion of magmas into wet sediments may give rise to significant hydrothermal systems (McPhie, 1993;Cathles et al,1997;McPhie and Orth, 1999;Skilling et al, 2002), and thus lead to substantial hydrothermal alteration and/or mineralization (e.g. Sillitoe and Bonham, 1984;Cas, 1992;Boulter, 1993;Wallace et al, 2003;Gifkins et al, 2005;Popkhadze and Moritz, 2014A), the lack of detailed geochronological studies at the Don Nicolas Mine precludes us to directly link the studied intrusion with the gold-bearing mineralization found at mine. Still, the presence of widespread intrusive hyaloclastite and peperites prove that water saturation conditions may have prevailed in the pyroclastic sequence for a significant amount of time.…”

“…In these breccia envelopes, clast geometry, clast/matrix ratio and the nature of the matrix itself, along with the distribution and geometry of the different facies, have been proven to be useful tools in order to assess the intrusion mechanisms, providing also information on the consolidated vs. unconsolidated nature of the host rocks, the viscosity of the intruding magma among other parameters (e.g. Goto and McPhie, 1998;Stewart and McPhie, 2003;Popkhadze et al, 2014B;Páez et al, 2018;Goto and Tomiya, 2019;Cole et al, 2020).…”

Jurassic to Cenozoic Magmatic and Geodynamic Evolution of the Eastern Pontides and Caucasus Belts, and Their Relationship With the Eastern Black Sea Basin Opening

“…The Bolnisi district (Figure 3) is located at the northeastern most portion of the SK in southern Georgia, mainly characterized by Late Cretaceous volcanic and sedimentary sequences emplaced between the Khrami and Loki massifs (Adamia et al, 2011; Zakariadze et al, 2007). These sequences are divided into six suites interpreted to be between Cenomanian and Maastrichtian in age, unconformably overlain by Maastrichtian limestone and marl (Apkhazava, 1988; Gambashidze, 1974; Gugushvili et al, 2014; Popkhadze et al, 2014). An early Eocene formation consisting of terrigenous sedimentary rocks and middle Eocene volcanic rocks unconformably covers the older rocks.…”