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БЪЛГАРСКО ГЕОЛОГИЧЕСКО ДРУЖЕСТВО, Национална конференция с международно участие „ГЕОНАУКИ 2016“BULGARIAN GEOLOGICAL SOCIETY, National Conference with international participation “GEOSCIENCES 2016”

Field features of magmatic hydrothermal injection breccias from Bulgarian Antarctic Base area (BAB), Livingston Island, AntarcticaГеоложки особености на магматично-хидротермални инжекционни брекчи от района на Бългаската Антарктическа База (БАБ), о-в Ливингстън, АнтарктикаStefan Velev1, Docho Dochev1, Kamen Bonev2

Стефан Велев1, Дочо Дочев1, Камен Бонев2

1 Sofia University, FGG, 1504 Sofia; E-mails: velev@gea.uni-sofia.bg; dochev@gea.uni-sofia.bg 2 Bulgarian Antarctic Institute, 1504 Sofia; E-mail: bonev.kamen@gmail.com

Keywords: Livingston Island, magmatic hydrothermal injection breccias, high sulfidation ore systems.

IntroductionWillan (1994) described hydrothermal veins and brec-cias exposed on Hurd Peninsula, Livingston island. Based on field data obtained in Antarctic season 2016 we proposed for the first time morphological and ge-netic classification of hydrothermal breccias, based on the classification of Corbett and Leach (1998).

Geological settings of BAB areaThe sedimentary sequences exposed on the Hurd Peninsula composed mainly of terrigenous and aleuro-pelitic mixed rocks, formed in different depositional environments are grouped in Myers Bluff Formation (Campanian–?Paleogene). The formation consists of five members (as follows from bottom to top): South Bay Member, Johnson Dock Member, Sally Rocks Member, Napier Peak Member and Moores Peak Member. The sedimentary rocks exposed in BAB area consist of medium- to coarse grained mas-sive sandstones, alternating with thick mudstones and fine-grained sandstones are part from South Bay Member – the host sediments of magmatic hydrother-mal breccias.

Geologic description and systematic of magmatic hydrothermal injection brecciasDuring our investigation ore-related hydrothermal breccias around BAB are systematized and described in details. We distinguish chiefly magmatic hydrother-mal injection breccias, according to classification of Corbett and Leach (1998). These kinds of breccias are

related to hydraulic breccias (Willan, 1994) and form by injection of mineralized magmatic fluids, typically in high sulfidation ore systems.

Magmatic hydrothermal injection beccias in stud-ied area comprise host rock fragment, mainly sand-stones and mudstones (Fig. 1a–d) set in a matrix of minerals deposited by magmatic hydrothermal fluid: quartz, carbonates and ore minerals (pyrite, chalco-pyrite, galena and malachite) (Fig. 1a). The observed injection breccias are with vertical dimensions and thickness of several cm to 2–3 m (Fig. 1d). In some cases these braccias form in dilational structural en-vironments derived by movement on controlling structures, and so display transitional relationships to the dilational breccias. Tectonic faulting assists fluid pressures in fracturing host rocks, and creation of open space which becomes filled by hydrothermal minerals.

These breccias are classified as rotational (Fig. 1c), mosaic (jigsaw) (Fig. 1a, b) and fluidized breccias. Rotational breccias are characterized by substantial fragment rotation or transport in association with fluid injection. Mosaic or jigsaw breccias are distinguished by fragments which are separated, but have not un-dergone substantial transport. Rock fragments in these breccias may be joined back together by removal of the matrix. Fluidized breccias contain milled fragments in a transported matrix, to form dike-like bodies.

InterpretationThe formation of the magmatic hydrothermal breccias is an integrated element of the evolution of the mag-matic hydrothermal system. They are formed by the explosive release of overpressured magmatic fluids from the fluid saturated magma.

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ReferencesCorbett, G., T. Leach. 1998. Southwest Pacific Rim Gold-

Copper Systems: Structure, Alteration and Mineralization. – Soc. Econ. Geol., Spec. Publ. 6, 236 p.

Willan, R. C. R. 1994. Structural setting and timing of hydro-thermal veins and breccias on Hurd Peninsula, Livingston Island, South Shetland Islands: A possible volcanic-epith-ermal system in deformed turbidites. – Geol. Mag., 131, 4, 465–483.

Fig. 1. a, mosaic breccias with secondary copper mineralization (malachite); b, mosaic breccia; c, fragments of mudstones in ro-tational breccias; d, mosaic brecciated hydrothermal vein; e, ide-alized cross section through a magmatic hydrothermal breccias