Irina Marinova

The low-sulfidation silver-gold prospects in the Eastern Rhodope Mountains, SE Bulgaria, united in the East Rhodopean low-sulfidation gold-silver metallogenic province, contain a considerable precious-metal endowment for current and future mining. For the most promising prospects, geochronological, stratigraphical, biostratigraphical, structural, mineralogical, and stable-isotope data exist, but their origin remains not fully understood. In this paper, we review existing data on geodynamics, metamorphism, magmatism, and their geochronology in the Rhodope Crystalline Massif, as well as data on the geology, mineralogy, stable isotope geochemistry, and formation conditions of low-sulfidation gold deposits from the Eastern Rhodopes, SE Bulgaria. The aim is to provide a synopsis of the existing data to help one construct a new genetic model for this class of economic deposits. The main conclusions which can be drawn from the reviewed literature are the following: (i) geochronological and stratigraphic constraints clearly revealed older age of these de-posits than the local Late Eocene- Early Oligocene magmatism; (ii) there is isotop-ic evi-dence of meteoric origin of the fluids; (iii) there is a seismological evidence of slab rollback since Eocene to Late Miocene-Pliocene in the Rhodope realm, (iv) conveying role of the deeply penetrating detachment fault systems for hot uprising fluids is evidenced by hy-drothermal alteration and silicification, both strong in places; and (v) heating of mete-oric water in the area of high heat flux produced by the Cenozoic crustal extension and as-thenospheric mantle upwelling in the Eastern Rhodopes is seems to be a necessary condi-tion for the formation of these deposits.

This study provides additional data on selected minor and trace elements in pyrite and marcasite from 19 chosen ore samples obtained from drill hole cores within the Sarnak gold deposit (also referred to as the Surnak deposit) presented by SEM-EDX elemental mapping for As, S, Fe, Ag, and Au in zonal pyrite, alongside binary plots. The dataset comprises the same 210 single-spot, time-resolved LA-ICP-MS analyses conducted on marcasite grains and distinct pyrite zones (core, mantle, and rim) discussed before in Gadzhalov et al. (2023).

This study demonstrates that the bladed texture, which is common in epithermal, low-sulfidation (adularia-sericite) precious metal deposits, can serves as exploration vector towards precious metal...

This paper presents a study on boiling assemblages in the Kupel occurrence, as boiling was evidenced by the presence of vein adularia and platy calcite. Fluid inclusion evidence is not available since the present fluid inclusions are very small in size for investigation under optical microscope. Boiling assemblages occur in two types of auriferous mineralization hosted by supradetachment, grey fine-grained arkosic sandstones and presented by (i) veinlets of quartz-adularia and (ii) veinlets of platy calcite. In quartz-adularia veinlets micron-sized electrum aggregates form globular shapes, which reach 800 µm across and are arranged along the veinlet length. In cross-sections electrum aggregates display abundant silicate-filled pores of a few microns in size. Globular geometry of the electrum aggregates and their arrangement along the veinlet length suggest collectively that these globules were flowing particles - flocs but not colloidal particles since the latter are much smaller. In these veinlets electrum is intergrown with micron-sized chalcopyrite, galena, hessite and greenockite. The auriferous calcite veinlets are formed later than the auriferous quartz-adularia ones, since the first clearly has intersected or brecciated the latter. Electrum in the calcite veinlets forms accumulations only in portions of sharp thickness expansions after throttle portions, which are barren. This suggests that electrum has been transported by a flowing fluid, in a particulate form and deposited due to pressure drop during hydrofracturing, as the electrum particles have been arrested in low velocity (expanded) portions of ore conduits. The auriferous assemblages in the Kupel occurrence indicate high effectiveness of boiling for deposition of Au, Ag, Cu, Pb, Cd and Te through collective loss of H₂, CO₂, H₂S and H₂Te what is in complete accord with recent studies on modern terrestrial geothermal fields. Methods used comprise observations under binocular, optical and scanning electron microscope, and electron microprobe analysis.

Divergent drift of Adriatic-Dinaridic and Moesian carbonate platforms during the rifting phase witnessed by triassic MVT Pb-Zn and SEDEX deposits; a metallogenic approach