EPITHERMAL GOLD MINERALIZATION IN THE KRASSEN DEPOSIT, PANAGYURISHTE ORE DISTRICT, BULGARIA

Gold mineralization in the Krassen high-sulphidation epithermal deposit, Panagyurishte ore district, Bulgaria, has been studied in respect to mineral assemblages, gold grain size, fineness and trace elements based on EPMA and LA-ICP-MS studies. Part of the gold in the early massive pyrite dominated ores is submicroscopic in size (< 0.1 µm) and could be attached to the so called “invisible” gold. Later fracturing of the early massive pyrite, followed the deposition of Cu-pyrite ore bodies enriched in chalcopyrite, enargite, bornite, galena and sphalerite accompanied by deformation and recrystallization is suggested as a reason for Au and Ag migration to cracks and gold grains coarsening. The electrum fineness in individual grains varies between 882 and 998 ‰. Most commonly observed trace elements in the native gold, electrum grains and gold hosting sulphide minerals are: Cu, Fe, Hg, Sb, Te, Bi, As and Se. The Au content in pyrite varies from 0.35 to 7.83 ppm and in chalcopyrite from 0.97 to 2.78 ppm. BiTe-Se and Ga-Ge-In trace elements signature is characteristic feature of the ore minerals and indicator for Au enrichment

Late Cretaceous porphyry Cu and epithermal Cu-Au association in the Southern Panagyurishte District, Bulgaria: the paired Vlaykov Vruh and Elshitsa deposits

Vlaykov Vruh-Elshitsa represents the best example of paired porphyry Cu and epithermal Cu-Au deposits within the Late Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic and metallogenic belt of Eastern Europe. The two deposits are part of the NW trending Panagyurishte magmato-tectonic corridor of central Bulgaria. The deposits were formed along the SW flank of the Elshitsa volcano-intrusive complex and are spatially associated with N110-120-trending hypabyssal and subvolcanic bodies of granodioritic composition. At Elshitsa, more than ten lenticular to columnar massive ore bodies are discordant with respect to the host rock and are structurally controlled. A particular feature of the mineralization is the overprinting of an early stage high-sulfidation mineral assemblage (pyrite ± enargite ± covellite ± goldfieldite) by an intermediate-sulfidation paragenesis with a characteristic Cu-Bi-Te-Pb-Zn signature forming the main economic parts of the ore bodies. The two stages of mineralization produced two compositionally different types of ores—massive pyrite and copper-pyrite bodies. Vlaykov Vruh shares features with typical porphyry Cu systems. Their common geological and structural setting, ore-forming processes, and paragenesis, as well as the observed alteration and geochemical lateral and vertical zonation, allow us to interpret the Elshitsa and Vlaykov Vruh deposits as the deep part of a high-sulfidation epithermal system and its spatially and genetically related porphyry Cu counterpart, respectively. The magmatic-hydrothermal system at Vlaykov Vruh-Elshitsa produced much smaller deposits than similar complexes in the northern part of the Panagyurishte district (Chelopech, Elatsite, Assarel). Magma chemistry and isotopic signature are some of the main differences between the northern and southern parts of the district. Major and trace element geochemistry of the Elshitsa magmatic complex are indicative for the medium- to high-K calc-alkaline character of the magmas. 87Sr/86Sr(i) ratios of igneous rocks in the range of 0.70464 to 0.70612 and 143Nd/144Nd(i) ratios in the range of 0.51241 to 0.51255 indicate mixed crustal-mantle components of the magmas dominated by mantellic signatures. The epsilon Hf composition of magmatic zircons (+6.2 to +9.6) also suggests mixed mantellic-crustal sources of the magmas. However, Pb isotopic signatures of whole rocks (206Pb/204Pb = 18.13-18.64, 207Pb/204Pb = 15.58-15.64, and 208Pb/204Pb = 37.69-38.56) along with common inheritance component detected in magmatic zircons also imply assimilation processes of pre-Variscan and Variscan basement at various scales. U-Pb zircon and rutile dating allowed determination of the timing of porphyry ore formation at Vlaykov Vruh (85.6 ± 0.9Ma), which immediately followed the crystallization of the subvolcanic dacitic bodies at Elshitsa (86.11 ± 0.23Ma) and the Elshitsa granite (86.62 ± 0.02Ma). Strontium isotope analyses of hydrothermal sulfates and carbonates (87Sr/86Sr = 0.70581-0.70729) suggest large-scale interaction between mineralizing fluids and basement lithologies at Elshitsa-Vlaykov Vruh. Lead isotope compositions of hydrothermal sulfides (206Pb/204Pb = 18.432-18.534, 207Pb/204Pb = 15.608-15.647, and 208Pb/204Pb = 37.497-38.630) allow attribution of ore-formation in the porphyry and epithermal deposits in the Southern Panagyurishte district to a single metallogenic event with a common source of metal

Composition of some major mineral phases from the Plavica epithermal gold deposit, Eastern Macedonia

High-sulphidation epithermal gold has been determined and studied in the Plavica deposit, which is an integral part of the Kratovo-Zletovo volcanic area. Epithermal gold and associated mineral phases have been determined in silicified tuff, secondary quartzite, quartz-pyrite-enargite veins and mainly disseminated within an altered, but mostly silicified volcanic setting. Beside gold within this acidsulphate volcanic environment was determined the presence of contaminated pyrite, zinc-tetrahedrite, enargite, and certainly seligmanite regularly and commonly present copper association led by chalcopyrite, followed by bornite, chalcocite, covellite, as well as slightly higher temperature associations of arsenopyrite and molybdenite. Most of these accessory sulphide mineral phases within this study were observed under state of the art polarized optical microscope, and the electron microprobe, which results are presented in detail in this paper. For illustration we want to emphasize that in pyrite were found increased concentrations of copper and zinc and less silver, then enargite with increased zinc concentrations (0.24– 7.56 Zn), antimony (0.46–1.33% Sb) and silver (0.09–0.54% Ag) , tennantite with increased iron (0.21– 1.55% Fe), zinc (6.24–9.06% Zn) and silver (0.08–0.87% Ag), while within the molybdenite elevated concentrations were detected for sulfur and iron

Mineralogy of gold in the Elshitsa massive sulphide deposit, Sredna Gora zone, Bulgaria

The Elshitsa volcanic hosted massive sulphide deposit occurs in the central part of the Srena Gora metallogenic zone in Bulgaria. The gold-bearing massive sulphide mineralization is considered to be the product of an island arc volcano-plutonic process and hydrothermal activity that took place during the Late Cretaceous. In addition to the major gold-hosted opaque minerals such as pyrite, chalcopyrite, sphalerite and galena there are minor phases of tennantite, gold®eldite, Se-bearing aikinite, native silver and bornite in the massive sulphide lenses and stringer zones. Most of the sulphide minerals are Se-bearing. All of the six mineral assemblages that were deposited during the pyrite and copper-pyrite stages of mineralization are gold-bearing. The gold tenor as a rule is less than 1 g/t. Native gold and electrum occur as blebs or intergranular particles in the sulphide minerals. Gold in the early massive pyrite is of submicroscopic type ( 100 lm) in the late gold-sulphide assemblages. The electrum ®neness in 41 individually studied grains varies between 780 and 992&with a mean of 895&. Native silver was found in association with bornite. Cu, Te, Sb and Bi are the most common traceelements in gold and electrum. The Cu-Zn-Pb association is most important as a Au-Ag-carrier. A model for gold behaviour during sulphide deformation is proposed involving coarsening of gold grain size from the earlier to the later sulphide mineral assemblages

Geochemical constraints on the genesis of the Pb–Zn deposit of Jalta (northern Tunisia): implications for timing of mineralization, sources of metals and relationship to the Neogene volcanism

The occurrence of Pb–Zn deposits of Jalta district (northern Tunisia) as open space fillings and cements and breccia in the contact zones between Triassic dolostones and Miocene conglomerates along or near major faults provides evidence of the relationship between the mineralization and tectonic processes. Pb isotopes in galena from the deposits yielded average 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 18.821, 15.676 and 38.837, respectively, implying a well-mixed multi-source upper crustal reservoir of metals. Magmatism and compressional tectonism during the Alpine orogeny favored Pb–Zn mineralization in the Jalta district. The enrichment in Pb, Zn, Cd and Co of the Triassic carbonates and enrichments in Pb, Zn and Cd in Triassic clayey shales is associated with hydrothermal alteration around faults. Alunite in the deposit has δ34S values (−2.5 to −1.5‰ VCDT), which could have been formed at and above the water table in a kind of steam-heated environment, where fluids containing H2S mixed with fluids containing K and Al. The H2S could have been produced by TSR of sulfates at high temperature at depth and then leaked upward through deep-seated faults, whereas the K and Al could have been acid-leached from Miocene volcanic rocks

Goldeneye project results and impact of mining

Improved use of Earth observation with sensor and positioning data can offer significant exploitation and environmental control benefits and increase the productivity of mines. The EU-funded Goldeneye project has developed a GoldenAI platform, which can fuse high-resolution data from satellites, drones, and in-situ sensors to generate new high-resolution data from an entire mine. This data is being processed and converted into actionable intelligence with new tools developed in the project, offering improvements to exploration, mine safety, environmental monitoring, exploitation, and increasing extraction in pilot mines. The project has combined remote sensing and positioning technologies and taken advantage of Earth observation and Earth GNSS data with data fusion and processing powered by data analytics and machine learning algorithms. The GoldenAI platform and other developed technologies have been piloted in five trial mine sites across Europe and the results are presented in this paper

Golden AI Data Acquisition and Processing Platform for Safe, Sustainable and Cost-Efficient Mining Operations

Improved use of Earth observation, sensor and positioning data can offer additional exploitation and environmental control and increase the productivity of mines. The EU-funded Goldeneye project develops a Golden AI platform to allow satellites, drones and in situ sensors to collect high-resolution data from an entire mine. This data will be processed and converted into actionable intelligence in new tools offering improved safety, environmental observation, exploitation and increased extraction in pilot mines. The project will combine remote sensing and positioning technologies to take advantage of Earth observation and Earth GNSS data together with data fusion and processing powered by data analytics and machine learning algorithms. The benefits of Golden AI platform will be demonstrated in mining pilots in Bulgaria, Finland, Germany, Kosovo and Romania.J. Havisto et al., "Golden AI Data Acquisition and Processing Platform for Safe, Sustainable and Cost-Efficient Mining Operations," 2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS, 2021, pp. 5775-5778, doi: 10.1109/IGARSS47720.2021.9554181

Late Cretaceous porphyry Cu and epithermal Cu–Au association in the Southern Panagyurishte District, Bulgaria: The paired Vlaykov Vruh and Elshitsa deposits

ISSN:0026-4598ISSN:1432-186