The epithermal Obichnik deposit is located in the Southeastern Rhodopes. It is a part of the ZvezdelPcheloyad ore field, which includes hydrothermal Pb-Zn and Au-Pb-Zn mineral occurrences and deposits associated with the Oligocene Zvezdel volcano. The ore mineralization is hosted by felsic, intermediate to mafic volcanic, volcano-sedimentary, and intrusive rocks. The gold presence in the area is known from many previous explorations. The most large-scale one has begun in 2019. So far, insufficient data on the mode of occurrence and composition of the gold in the deposit have been reported. This study reveals that gold associates with the minerals of quartz-sulphide stage of the mineralization. It mainly occurs as irregular grains and occasionally as isomorphic grains in fracture or cavity mainly in pyrite and marcasite, and rare in galena. The electron-microprobe analyses of gold detected only gold and silver and its fineness ranges from 870 to 915 parts per thousand.

The colloform pyrite variety incorporates many trace elements that are released in the environment during rapid oxidation. Colloform pyrite from the Chiprovtsi silver–lead deposit in Bulgaria and its oxidation efflorescent products were studied using X-ray diffractometry, scanning electron microscopy, electron microprobe analysis, and laser ablation inductively coupled plasma mass spectrometry. Pyrite is enriched with (in ppm): Co (0.1–964), Ni (1.8–3858), Cu (2.9–3188), Zn (3.1–77), Ag (1.2–1771), As (8179–52,787), Se (2.7–21.7), Sb (48–17792), Hg (4–2854), Tl (1.7–2336), Pb (13–7072), and Au (0.07–2.77). Gypsum, anhydrite, szomolnokite, halotrichite, römerite, copiapite, aluminocopiapite, magnesiocopiapite, coquimbite, aluminocoquimbite, voltaite, and ammoniomagnesiovoltaite were identified in the efflorescent sulfate assemblage. Sulfate minerals contain not only inherited elements from pyrite (Cr, Fe, Co, Ni, Cu, Zn, Ag, In, As, Sb, Hg, Tl, and Pb), but also newly introduced elements (Na, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Mn, Ga, Rb, Sr, Y, Zr, Sn, Cs, Ba, REE, U, and Th). Voltaite group minerals, copiapite, magnesiocopiapite, and römerite incorporate most of the trace elements, especially the most hazardous As, Sb, Hg, and Tl. Colloform pyrite occurrence in the Chiprovtsi deposit is limited. Its association with marbles would further restrict the oxidation and release of hazardous elements into the environment.

Chiprovtsi silver-lead and Martinovo iron mines represent the biggest mining area in Northwestern Bulgaria, which was operated till 1999. Their long-lived operation leads to proved pollution of the environment in the vicinity of the mines, especially water and soil. Seasonal monitoring of heavy metal (Cu, Zn, Cd and Pb) and metalloid (As and Sb) concentrations in mine, surface (river) and drinking waters was carried out during May and August 2006 to determine the level of contamination of the Chiprovska Ogosta river basin resulting from the long-lived mining activity and whether these abandoned mines continue to be potential source for water pollution. This study proves significant As concentrations in mine (up to 170 μg/l) and surface waters (between 50 and 621 μg/l). The presence of other heavy metals, such as Cu, Cd, Zn and Pb, and metalloid — Sb is also recorded. Among them, Pb was found in considerable concentrations - up to 1456 pg/l during May 2006 sampling exhibiting great concentration variability between dry and wet sampling seasons. Sb is also determined in mine waters (up to 25 pg/l), but not exists in surface and drinking waters. Drinking waters are proved to be free of heavy metals and metalloids.

Three types of ore veins are observed in the low-grade metamorphic host rocks (phyllites, quartz-sericitic schists) of the Vezhen pluton in the upper levels of the open pit of the Elatsite porphyry copper deposit, differing in their strikes, dips and mineral composition. The low-grade metamorphic rocks are not affected by the granitoids of the Vezhen pluton. The hydrothermal alterations style is

The Milin Kamak gold-silver deposit is located in Western Srednogorie zone, 50 km west of Sofia, Bulgaria. This zone belongs to the Late Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic and metallogenic belt. The deposit is hosted by altered trachybasalt to andesitic trachybasalt volcanic and volcanoclastic rocks with Upper Cretaceous age, which are considered to be products of the Breznik paleovolcano. Win Kamak is the first gold-silver intermediate sulfidation type epithermal deposit recognized in Srednogorie zone in Bulgaria. It consists of eight ore zones with lengths ranging from 400 to 1000 m, widths from several cm to 3-4 m, rarely to 10-15 m, an average of 80-90 m depth (a maximum of 200 m) and dip steeply to the south. The average content of gold is 5.04 g/t and silver -13.01 g/t. The styles of alteration are propylitic, sericite, argillic, and advanced argillic. Ore mineralization consists of three stages. Quartz-pyrite stage I is dominated by quartz, euhedral to subhedral pyrite, trace pyrrhotite and hematite in the upper levels of the deposit. Quartz-polymetallic stage II is represented by major anhedral pyrite, galena, Fe-poor sphalerite; minor chalcopyrite, tennantite, bournonite, tellurides and electrum; and trace pyrrhotite, arsenopyrite, marcasite. Gangue minerals are quartz and carbonates. The carbonate-gold stage III is defined by deposition of carbonate minerals and barite with native gold and stibnite.Fluid inclusions in quartz are liquid H2O-rich with homogenization temperature (T-h) ranging from 238 to 345 degrees C as the majority of the measurements are in the range 238-273 degrees C. Ice-melting temperatures (T-m) range from -2.2 to -4.1 degrees C, salinity - from 3.7 to 6.6 wt.% NaCI equiv. These measurements imply an epithermal environment and low-to moderate salinity of the ore-forming fluids.delta S-34 values of pyrite range from -0.49 to +2.44 parts per thousand. The average calculated delta S-34 values are 1.35 parts per thousand. The total range of delta S-34 values for pyrite are close to zero suggesting a magmatic source for the sulfur. (C) 2017 Elsevier B.V. All rights reserved.

Geochemical studies of seasonally collected mine, stream and drinking waters, bottom sediments (mine and stream) and soil samples from all mining sections were carried out in order to assess the rates of pollution in the immediate proximity to underground mining facilities and related waste rock dumps. The determined concentrations of studied elements in water (As, Pb, Cu, Zn and Sb) show spatial distribution corresponding to ore mineralisation in different sections. Arsenic concentrations show gradual decrease in west-east direction, whereas Pb concentrations peak in the central and eastern sections. Arsenic and, to a lesser extent, Pb proved to be major pollutants in mine and surface waters, as well as in bottom sediments and soils. Detailed geochemical study of soils revealed strong spatial relation with host rocks and ore mineralogy. Comparisons with state guidelines for harmful elements revealed that alluvial and meadow soils in close proximity to waste dumps contain As, Pb, Cu, Zn and Cd above maximum permissible levels. It was also found that, compared to other Bulgarian and world alluvial (fluvisol) soils and the upper continental crust, the soils in Chiprovtsi mining district are enriched in Te, Re, W, Pd, Au, Ag, Mo, Ti, Mn, Co, Se, Sb, Bi and Cs. Since the processes of weathering and oxidation of mine waste remaining in the area continue naturally, the pollution with As and Pb will presumably carry on with decreasing effect.

Arsenic (As) is a toxic element which can occur in increased concentrations mainly in areas affected by mining and ore processing activities. To assess the As fractionation in soils from the Ogosta River floodplain, a seven-step sequential extraction procedure (SEP) followed by As determination using ultrasonic nebulization inductively coupled plasma optical emission spectrometry (USN-ICP-OES) was applied. The SEP fractionate between the (1) ionically bound As; (2) strongly adsorbed As; (3) As co-precipitated with acid volatile sulphide, carbonates, Mn oxides, very amorphous Fe oxyhydroxides; (4) As co-precipitated with amorphous Fe oxyhydroxides; (5) extraction in 0,2M NH4-oxalate buffer + ascorbic acid; (6) As associated with crystalline Fe oxides; (7) orpiment and remaining recalcitrant As minerals. No significant differences were found between the pooled amount of As concentrations in each extraction step and the total As concentration measured using a XRF spectrometer (recoveries rate of 90 –110%). Total As concentration in soils varied widely, in the range of 36 72300 mg kg-1. The partitioning of As among the seven fractions in the six soil samples (%, medians and ranges) was: (1) 0.97 (0– 4.8); (2) 12 (0–36); (3) 25 (12–44); (4) 8.7 (2.5–31); (5) 4.0 (0.2–25); (6) 34 (3.6–84); (7) 0.15 (0.02–1.1). Significant differences on As distribution in contaminated and uncontaminated soils were observed, the fractions of mobile species, were found to be predominant in highly contaminated soils in contrast to the low-As soils, where As contents were bound to the matrix.

The Milin Kamak gold-silver deposit belongs to the Western Srednogorie zone in Bulgaria – part of the Upper Cretaceous Apuseni-Banat-Timok-Srednogorie (ABTS) magmatic and metallogenic belt (Popov et al., 2002). The deposit is located 50 km west of Sofia and 2 km south of the town of Breznik in the Bardoto locality. The area has been explored by Trace Resources Ltd. between 2004 and 2012 with100 trenches and 121 drill holes. Eight ore zones of almost identical mineral composition have been established. Based on the results, probable reserves and resources at a cutoff grade of 2 g/t have been estimated. The average content of gold is 5.04 g/t and of silver – 13.01 g/t.

The Srebren gold-silver deposit is located 36 km southern from the town of Velingrad and 10 km northern of the town Sarnitsa, in the West Rhodopes. It occupies the ridge parts of the eponymous peak and covers an area of approximately 1 km2. The deposit was explored between 2004 and 2012 years by Thrace Resources Ltd. Pyrite and arsenopyrite typically contain significant amounts of minor and trace elements including As, Pb, Zn, Sb, Au, Ag, Mn, Bi, Cu, Co, Ni, Ga, Ge, Mo, Sn, Cd, In, Y, Ta, Zr.

Pyrite is formed in all mineral assemblages described in the Martinovo and Chiprovtsi deposits. It is observed as euhedral, cubic to cubic-octahedral, coarse- to fine-grained crystals and spherulitic aggregates. Pyrite associates with molybdenite and scheelite in the retrograde skarn assemblage; with arsenopyrite and lollingite in the later postskarn assemblage; with galena, sphalerite, chalcopyrite, tennantite-tetrahedrite and Ag-Sb sulfosalts in the polymetallic assemblage and with chalcopyrite, tetrahedrite-tennantite, galena and cinnabar in the low temperature assemblage. In all assemblages pyrite is enriched in As. Arsenic contents vary in a wide range - from <0.10 wt. % up to 4.78 wt. %. Pyrite from the retrograde skarn assemblage show enrichment in Ti, Co, Zr, Y, La, Ce, Dy, Yb, Th, U, Bi and Pb. Gold has concentrations between 0.90 and 1.93 ppm. Pyrite from the polymetallic assemblage is enriched in Cu, Zn, Ag, Pb, As and Sb. Spherulitic pyrite is enriched in Co, Ni, Zn, Se, Ag, Sb, Pb, TI and Hg. Chemical composition of pyrite of different mineral assemblages from the Martinovo and Chiprovtsi deposit reflect the gradual change of the elemental composition of the ore-forming fluids in the area.

Numerous papers have considered the potential of pyrite and arsenopyrite to incorporate gold, as so called “invisible gold” (Maddox et al., 1998; Cabri et al., 2000; Morey et al., 2008, etc.). Chemical speciation and distribution patterns of gold in these minerals have been widely discussed in the cited papers as well. So far, X-ray photoelectron spectroscopy (XPS), micro X-ray absorption near edge structure (XANES) spectroscopy, field emission scanning electron microscopy (FESEM) and secondary ion mass spectrometry (SIMS) have shown that the so called “invisible gold” in arsenopyrite occurs as elemental (Au0) and chemically bound (Au1+) species. In some gold deposits, arsenopyrite accommodates a major amount of Au. This poses problems in gold extraction from the arsenopyrite-rich sulfide ores and consequent negative impact on the environment.

The Chiprovtsi mining area is contaminated as a consequence of past mining. The 20-year existing of Goliam Bukovets mine tailings impoundment has affected all elements of its surroundings. As a result elevated concentrations of arsenic and heavy metals in upper soil layers and in grass are established. The low distributions of arsenic and heavy metals in depth allow assuming their low mobility which restricts their unfavourable environmental impact. The sheep’s milk has elevated Zn and Cu contents and so it transfers them to the humans. The carry-over of Pb, Cd and As from grass to the milk is low. Metal concentrations in livestock’s excrements are low and seem not to pose risk for secondary soil contamination if used as organic fertilizer. Although the tailings impoundment is almost recultivated and the dust pollution is finished the contaminated soils of the surroundings contain arsenic and heavy metals and continue to transfer them trough the food chain. Besides, the soil cover of the impoundment is not sufficient to avoid the penetration of grasses root to the mine tailings.

A complex bismuthiferous association is found in the Svishti Plaz gold deposit situated in Central Balkan Mountain. The vein type mineralization is hosted in Paleozoic dioritic, granodioritic and quartzdioritic plutonic bodies and related hornfelses. The ore consists of arsenopyrite, pyrite, native gold, galena, sphalerite, tennantite, pyrrhotite, magnetite. Gangue minerals are quartz and calcite. Four stages of mineralization have been outlined. Bismuth mineralization belongs to the third one. The bismuthiferous association is complex and polyphase. According to microprobe data several groups of bismuth minerals are distinguished: native Bi, bismuthiferous galena, Pb-Bi, Cu-Pb-Bi, Ag(Cu)Pb-Bi and Ag-Cu-Pb-Bi sulfosalts. According to structural relations a exsolution genesis from ISS or primary bismuth sulphosalt is suggested for native Bi, Ag(Cu)-Pb-Bi sulfosalts, Pb-Bi sulfosalts, bismuthinitepekoite and chalcopyrite. Aikinite-friedrichite belongs to the same association but is obviously later than the previous minerals. Later Ag-Cu-Pb-Bi sulfosalts are found as longprismatic needlelike orientated crystals in bismuthiferous galena. They are both considered later than the other Bi-minerals. According to the microprobe analyses two different phases are distinguished: berryite and benjaminite. Galena contains 1.23 to 4.72 wt.% Bi and 1.06 to 1.86 wt.% Ag. Inclusions of unidentified Ag-Cu-Pb-Bi-sulfosalts are observed in a cobalt-pyrite, morphologically very different from the other pyrites in the deposit. Multiple stages of mineralization involving possible reheating, late, high-temperature inflow of Cu, Ag, and Bi, and remobilization of elements (Pb) already presented in the earlier minerals are responsible for the formation of the complex Cu-Pb-Ag-Bi assemblage.