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 (0.1ammoniomagnesiovoltaite 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, 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.Minerals 2020, 10, 12 2 of 25 trace metals, such as thallium, and the production of sulfuric acid. However, its abundance makes pyrite also the major constituent of mine waste and the main contributor to the formation of acid mine drainage in some mining areas. The latter being a result of the high reactivity to oxygen and water. Pyrite oxidation [20][21][22][23][24] leads to the formation of a number of water-soluble sulfates [25][26][27][28][29][30]. Their formation in situ on pyrite-containing wastes in tailing impoundments or other waste storage facilities is more abundant but can be observed during certain environmental conditions, usually employing low humidity. However, the "colloform"/spherulitic pyrite tends to accommodate more trace elements due to the conditions of its formation (supersaturated fluids and rapid crystal growth [31][32][33][34][35][36][37]) and also oxidizes more rapidly to produce efflorescent sulfates due to the larger reactivity area.The phenomenon of sulfate crystallization on samples containing "colloform"/spherulitic pyrite during their laboratory storage gives a unique opportunity of direct observation of this process, and information to what extent the trace elements incorporated in pyrite can be mobilized into the environment and behave as pollutants.In this study, we report data on the trace element composition of colloform pyrite from the Ag-Pb Chiprovtsi deposit (NW Bulgaria) and the mineralogy and trace element composition of the efflorescent sulfates formed during its oxidation in laboratory conditions. The results are interpreted with respect to the partitioning of inherited trace elements among newly formed sulfates and their environmental significance. Geological BackgroundThe Chiprovtsi silver-lead deposit represents the central and eastern part of an ore zone that extends from the outcropping in NW-W direction Sveti Nikola granite to the E of the Zhelezna village in the Western Balkan Mountains (Bulgaria) (Figure 1). The western part of the ore zone is...
A number of Paleozoic gold deposits are situated in the Hercynian terrains of the Balkan Mountain. On Bulgarian territory Govezhda and Svishti Plaz deposits are the most important ones. Neresnitza, Blagoev-Ka nen and Osanitza deposits are located in the Serbian part of the Balkan Mountain. All these deposits are hosted in the Pre-Alpine basement of the Balkanide zone. The orehosting structures are veins, lenses and mineralized fissures related to tension and shear faults. The structural characteristics of the ores are an evidence for tectonic control and tectonic activity during the ore deposition. All stages of ore deposition were accompanied by strong fracturing of already deposited minerals and subsequent precipitation of next portion. The economically important mineral in all these deposits is the native gold, with variable Ag contents. In the two Bulgarian deposits the main ore minerals are arsenopyrite and pyrite. Arsenopyrite is not reported for Serbian deposits, but scheelite is a main mineral there instead. Based on mineral associations, three possible genetic concepts of Au deposition could be expressed. 1) The gold is genetically associated with arsenopyrite and pyrite from stage 1 (Fe-As- Au+W). It is primarily deposited as invisible gold in these minerals. During the next stage of sulfide deposition driven by induced heating, it is remobilized and redeposited in cracks, formed during the cataclastic events of this stage. 2) The gold is genetically connected to the stage 2 (Pb-Zn-Cu-Ag- Au). 3) Dual generation of gold related to both stages 1 and 2. All Balkan Paleozoic gold deposits show lots of similarities to mesothermal gold deposits in shear zones in Archaean greenschists terrains in Canada, Western Australia and Africa, as well as to Hercynian gold deposits in France and Portugal. The similarity especially concerns their connection to granodiohtic magmatism, the mineral parageneses and the gold occurrence and its associations. Despite that the mining in the Balkan gold deposits is already closed, they still have nonexplored and non-operated reserves
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.
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.
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