Ag-Pb-Sb Sulfosalts and Se-rich Mineralization of Anthony of Padua Mine near Poliˇcany—Model Example of the Mineralization of Silver Lodes in the Historic Kutn á Hora Ag-Pb Ore District, Czech Republic

: Signiﬁcant selenium enrichment associated with selenides and previously unknown Ag-Pb-Sb, Ag-Sb and Pb-Sb sulfosalts has been discovered in hydrothermal ore veins in the Anthony of Padua mine near Poliˇcany, Kutn á Hora ore district, central Bohemia, Czech Republic. The ore mineralogy and crystal chemistry of more than twenty silver minerals are studied here. Selenium mineralization is evidenced by a) the occurrence of selenium minerals, and b) signiﬁcantly increased selenium contents in sulfosalts. Identiﬁed selenium minerals include aguilarite and selenides naumannite and clausthalite. The previously unknown sulfosalts from Kutn á Hora are identiﬁed: Ag-excess ﬁz é lyite, ﬁz é lyite, andorite IV, andorite VI, unnamed Ag-poor Ag-Pb-Sb sulfosalts, semseyite, stephanite, polybasite, unnamed Ag-Cu-S mineral phases and uytenbogaardtite. Among the newly identiﬁed sulﬁdes is argyrodite; germanium is a new chemical element in geochemistry of Kutn á Hora. Three types of ore were recognized in the vein assemblage: the Pb-rich black ore (i) in quartz; the Ag-rich red ore (ii) in kutnohorite-quartz gangue; and the Ag-rich ore (iii) in milky quartz without sulﬁdes. The general succession scheme runs for the Pb-rich black ore (i) as follows: galena – boulangerite (– jamesonite) – owyheeite – ﬁz é lyite – Ag-exces ﬁz é lyite – andorite IV – andorite VI – freieslebenite – diaphorite – miargyrite – freibergite. For the Ag-rich red ore (ii) and ore (iii) the most prominent pattern is: galena – diaphorite – freibergite – miargyrite – pyragyrite – stephanite – polybasite – acanthite. The parallel succession scheme progresses from Se-poor to Se-rich phases, i.e., galena – members of galena – clausthalite solid solution – clausthalite; miargyrite – Se-rich miargyrite; acanthite – aguilarite – naumannite. A likely source of selenium is in the serpentinized ultrabasic bodies, known in the area of “silver” lodes in the South of the ore district, which may enable to pre-concentrate selenium, released into hydrothermal ﬂuids during tectonic events. The origin of the studied ore mineralization is primarily bound to the youngest stage of mineralization of the whole ore district, corresponding to the Ag-Sb sequence of the ‘eb’ ore type of the Freiberg ore district in Saxony (Germany) and shows mineralogical and geochemical similarities to low-sulﬁdation epithermal-style Ag-Au mineralization. Several hundred BSE seventy polished examined and conclusions regarding associations and parageneses drawn. The succession of minerals in individual samples was determined where possible. Several trends, general features and repeated patterns were observed. The general succession follows the trend from Pb-rich phases to Pb-poorer (Ag-richer) phases. The earliest mineral in all three types of ore is galena.


Introduction
Kutná Hora was one of the best-known mining centres in Europe in the Middle Ages. In the first stage of mining (in the 13th and 14th century), the ores of silver-rich lodes in the southern part of the Kutná Hora ore district ( Figure 1a) were mined extensively. By means of the so-called fire-setting mining technique 500 m depth below the surface was reached as early as before the end of 14th century [1,2]. Before the end of the 15th century, mining activity moved from the silver-rich southern part of the Kutná Hora ore district (especially Oselské pásmo Lode) to the northern part of this district, which had silver-bearing sulfide "pyrite-rich" ores (especially Staročeské pásmo Lode at Kaňk, north of Kutná Hora) (Figure 1a). The ores of the northern lodes (ore zones) were poorer in silver (200-300 g/t silver), but the veins were more massive and ore-abundant. Continually increasing operating costs and the discovery of cheaper silver from American deposits caused a decline of mining in Kutná Hora at the turn of the 16th and 17th century [2].

Kutná Hora Ore District
The Kutná Hora Ag-Pb-Zn ore district (60 km east of Prague, Central Bohemia, Czech Republic) represents a hydrothermal vein type mineralization of Variscan age [26]. The ore district covers the area of 10 × 5 km in N-S direction. Ore veins are clustered in so-called ore zones or lodes ("pásmo" in  [25]. Each lode ("pásmo" in Czech, "Zug" in German) consists of several veins. (b) map of Anthony of Padua mine, Kutná Hora, adapted from Koutek and Kutina [26]. The blue-marked sections are ore-mineralized. The small Anthony of Padua Mine, located near the village of Poličany in the southern part of the Kutná Hora ore district, has been preserved to this day owing to the renewed exploration mining during the World War II. Thus, the mine represents a unique opportunity to study in detail the mineralogy of Ag-rich ores both in dump material and also in situ, sampled in the ore veins uncovered inside the mine. Therefore, it is a very appropriate model example, providing a large abundance and variety of new information on the mineralogy of the southern part of the Kutná Hora ore district, including the newly discovered, previously unknown selenium mineralizations from Kutná Hora.

Kutná Hora Ore District
The Kutná Hora Ag-Pb-Zn ore district (60 km east of Prague, Central Bohemia, Czech Republic) represents a hydrothermal vein type mineralization of Variscan age [26]. The ore district covers the area of 10 × 5 km in N-S direction. Ore veins are clustered in so-called ore zones or lodes ("pásmo" in Czech), each 1 to 3 km in length and 100-500 m in width (Figure 1a). A detailed description of the geological and mineralogical situation of the Kutná Hora ore district is given in [25][26][27]. The genetical, geological, mineralogical and chemical similarities of the ore districts of Kutná Hora and Freiberg (Germany) have been studied and pointed out by several authors, e.g. [28,29].
The pyrite-rich assemblage comprises pyrite, arsenopyrite, sphalerite, Ag-bearing galena, pyrrhotite, marcasite, chalcopyrite, stannite, freibergite and Pb-Sb-Bi-Ag) sulfosalts in quartz gangue without kutnohorite. The presence of Bi and Sn (each from a different mineralization sequence) is typical, while it is completely absent in the former, silver-rich assemblage. The pyrite-rich assemblage yields a rich suite of Ag-Pb-Bi-Sb sulfosalts, recently studied by Pažout [22,23].   Chemical composition of freieslebenite is relatively uniform and close to ideal formula ( Table 2)  Ag-excess fizélyite (AEF) is by far the most abundant of all andorite minerals (ca. 770 analytical points compared to ca. 100 points of all other andorite minerals put together- Figure 3). It is fairly frequent among microprobe analyses in polished sections. It occurs as anhedral grains, occasionally as semi-euhedral or column-like aggregates, usually up to 100 µm, in exceptional casesup to 1500 µm (Figure 4), in black ore (i), most frequently associated with galena, boulangerite, jamesonite, owyheeite, other andorite group minerals and miargyrite (Figure 2b,d,e, Figure 5a-d). AEF usually replaces andorite IV, itself being replaced by freibergite and miargyrite. frequent among microprobe analyses in polished sections. It occurs as anhedral grains, occasionally as semi-euhedral or column-like aggregates, usually up to 100 μm, in exceptional casesup to 1500 μm (Figure 4), in black ore (i), most frequently associated with galena, boulangerite, jamesonite, owyheeite, other andorite group minerals and miargyrite (Figures 2b,d,e, 5a-d). AEF usually replaces andorite IV, itself being replaced by freibergite and miargyrite.  Ag-excess fizélyite was described for the first time on the basis of chemical analyses as "miné ral F" from Les Farges (France) by Moëlo et al. [41] and later from the Lill mine in Příbram (Czech Republic) by Plášil et al. [42]. Structurally, it was defined by Yang et al. [43] in samples from Van Silver mine, Canada. It significantly differs from fizélyite in its higher Ag content. The excess silver is situated at the Ag2 site in the structure [43], which remains unoccupied in "normal" fizélyite. Higher Ag contents result in a shift of calculated Nchem (the width of the blocks of octahedra separated by Pb atoms in trigonal prismatic coordination) to higher values above 4. The mineral from Van Silver mine [43] shows calculated values of Nchem in the range of 4.31-4.59, mean 4.42. AEF from the Anthony of Padua Mine (Table 3) shows a wider range of Nchem values of 4.27-4.91, mean 4.54 ( Figure 4). The determined range of the andorite substitution (Ag + Sb = 2Pb) varies between 57.6 and 67.4% (mean 63.7). Apart from sulphur, the anion contains significant selenium content up to 4.48 apfu (4.69 wt.%) ( Figure 6), which is considerably higher than in all other andorite group minerals. The empirical formula for studied Ag-excess fizélyite on the basis of 88    , which is subsequently replaced by andorite VI (Ad6; ragged edges). Ag-excess fizélyite is further replaced by freieslebenite (Frs; right side of the grain); (c) galena (Gn) replaced by boulangerite (Bou) and owyheeite (Ow), both minerals subsequently replaced by Ag-excess fizélyite (Aef);(d) earliest galena (Gn) replaced by owyheeite (Ow), Ag-excess fizélyite (Aef) and diaphorite (Dia). All back-scattered electron images. Analyses are ordered according to increasing Se content. in kutnohorite of black ore (i) is replaced by andorite IV (Ad4), which is subsequently replaced by andorite VI (Ad6; ragged edges). Ag-excess fizélyite is further replaced by freieslebenite (Frs; right side of the grain); (c) galena (Gn) replaced by boulangerite (Bou) and owyheeite (Ow), both minerals subsequently replaced by Ag-excess fizélyite (Aef);(d) earliest galena (Gn) replaced by owyheeite (Ow), Ag-excess fizélyite (Aef) and diaphorite (Dia). All back-scattered electron images.
Ag-excess fizélyite was described for the first time on the basis of chemical analyses as "minéral F" from Les Farges (France) by Moëlo et al. [41] and later from the Lill mine in Příbram (Czech Republic) by Plášil et al. [42]. Structurally, it was defined by Yang et al. [43] in samples from Van Silver mine, Canada. It significantly differs from fizélyite in its higher Ag content. The excess silver is situated at the Ag2 site in the structure [43], which remains unoccupied in "normal" fizélyite. Higher Ag contents result in a shift of calculated N chem (the width of the blocks of octahedra separated by Pb atoms in trigonal prismatic coordination) to higher values above 4. The mineral from Van Silver mine [43] shows calculated values of N chem in the range of 4.31-4.59, mean 4.42. AEF from the Anthony of Padua Mine (Table 3) shows a wider range of N chem values of 4.27-4.91, mean 4.54 ( Figure 4). The determined range of the andorite substitution (Ag + Sb = 2Pb) varies between 57.6 and 67.4% (mean 63.7). Apart from sulphur, the anion contains significant selenium content up to 4.48 apfu (4.69 wt.%) ( Figure 6), which is considerably higher than in all other andorite group minerals. The empirical formula for studied Ag-excess fizélyite on the basis of 88 apfu (mean of 767 analyses) can be expressed as (Ag 5 Fizélyite occurs only rarely in polished section (determined in only seven samples) as euhedral grains of tabular shape with hypoparallel intergrowth. It occurs as inclusions of up to 50 µm in jamesonite enclosed in boulangerite which replaces galena. It also occurs as individual grains in quartz up to 100 µm associated with jamesonite and miargyrite. It is also associated with owyheeite, boulangerite, other andorite minerals and diaphorite (Figure 2a). It is found only in black ore (i), as with all andorite group minerals.
The classification of fizélyite and Ag-excess fizélyite comes from the following assumptions. The formula of fizélyite is Ag 5 Pb 14 Sb 21 S 48 , which gives N = 4.00 and L% = 62.49. The formula of Ag-excess fizélyite is Ag 6 Pb 14 Sb 21 S 48 , which corresponds to N = 4.46 and L% = 64.85. Considering that AEF defines one more Ag atom compared to fizélyite [43], the borderline between fizélyite and Ag-excess fizélyite must be guided by the content of 0.5 Ag atom more against fizélyite, i.e., by the formula Ag 5.5 Pb 14 Sb 21 S 48 , which yields the values of N = 4.22 and L% = 63.76.
Chemical composition of fizélyite and corresponding chemical formulae are given in Table 4. In comparison with Ag-excess fizélyite (Figure 3), the determined range of N chem values is centred around an ideal N value equal to 4 and ranges from 3.90 to 4.19 (mean 4.09). Determined values of the Ag + Sb = 2Pb substitution between 57.7 and 62.2% are slightly lower than 62.5 published for ideal fizélyite [41,43]. Found contents of Se do not exceed 1.17 apfu (1.20 wt.%) ( Figure 6) and are significantly lower than those found in Ag-excess fizélyite. Another difference against AEF is the presence of minor elements, namely iron. All fizélyite analyses show increased Fe between 0. 38

Fizélyite Ag5Pb14Sb21S48
Fizélyite occurs only rarely in polished section (determined in only seven samples) as euhedral grains of tabular shape with hypoparallel intergrowth. It occurs as inclusions of up to 50 μm in jamesonite enclosed in boulangerite which replaces galena. It also occurs as individual grains in quartz up to 100 μm associated with jamesonite and miargyrite. It is also associated with owyheeite, boulangerite, other andorite minerals and diaphorite (Figure 2a). It is found only in black ore (i), as with all andorite group minerals.
The classification of fizélyite and Ag-excess fizélyite comes from the following assumptions. The formula of fizélyite is Ag5Pb14Sb21S48, which gives N = 4.00 and L% = 62.49. The formula of   Andorite IV is the second most frequent andorite mineral (10 samples, 70 point analyses). It is most often found as grains and inclusions up to 300 µm in Ag-excess fizélyite which is replaced by andorite IV, and also as worm-like relict aggregates associated with andorite VI, occasionally mutually intergrowing, associated with boulangerite, owyheeite, jamesonite, freieslebenite and diaphorite in black ore (i) (Figure 5a,b). Andorite IV is sometimes as lamellae as much as 150 µm long and 30 µm wide. According to the degree of replacement, only amoebic relics, frayed or ragged at the edges, remain. The earliest mineral in the association is galena, followed by andorite IV, which is replaced by andorite VI, which are corroded by owyheeite and fizélyite. Thus, this is an opposite trend to the general succession.

Andorite VI, AgPbSb 3 S 6
Andorite VI is much less frequent than andorite IV (17 point analyses of four samples). It was found in black ore (i) as anhedral grains up to 80 µm in earlier Ag-excess fizélyite, which is replaced by andorite IV, which is then replaced by andorite VI, and, occassionally, as anhedral grains up to 250 µm in earlier Ag-excess fizélyite with all or most of andorite IV being replaced by andorite VI (Figure 5b). It is the mineral with the highest andorite substitution (2Pb = Ag + Sb), i.e. the lowest Pb and highest Ag and Sb contents, and it appears as the latest mineral in the association of andorite group minerals.
Chemical composition of andorite VI and corresponding chemical formulae are given in Table 6. Owyheeite occurs as massive needle-like steel to lead grey aggregates up to 2 cm long in quartz and kutnohorite associated or intergrowing with massive boulangerite, miargyrite and pyrite. It occurs in black ore (i) associated with galena, Pb-Sb sulfosalts (boulangerite, jamesonite) and Ag-Pb-Sb sulfosalts (andorite group minerals, freieslebenite and diaphorite) (Figure 5c,d). It is frequent in polished sections (160 point analyses). It was found as elongated lamellae up to 100 µm in length and 20 µm in width forming massive grains several hundred microns across.
The chemical composition of owyheeite (Table 7) is close to ideal formula Ag 3 Pb 10 Sb 11 S 28 proposed by Moëlo et al. [44], with a slight deficit of Pb and an excess of Sb. Figure 7 shows that contents of main elements Ag, Pb and Sb do not correlate significantly and the 2Pb  Owyheeite occurs as massive needle-like steel to lead grey aggregates up to 2 cm long in quartz and kutnohorite associated or intergrowing with massive boulangerite, miargyrite and pyrite. It occurs in black ore (i) associated with galena, Pb-Sb sulfosalts (boulangerite, jamesonite) and Ag-Pb-Sb sulfosalts (andorite group minerals, freieslebenite and diaphorite) (Figure 5c,d). It is frequent in polished sections (160 point analyses). It was found as elongated lamellae up to 100 μm in length and 20 μm in width forming massive grains several hundred microns across.
The chemical composition of owyheeite (Table 7) is close to ideal formula Ag3Pb10Sb11S28 proposed by Moëlo et al. [44], with a slight deficit of Pb and an excess of Sb. Figure 7 shows that contents of main elements Ag, Pb and Sb do not correlate significantly and the 2Pb↔Ag + Sb substitution presented by Moëlo et al. [45] is not the dominant factor in the chemical composition of owyheeite. The determined contents of selenium in the studied mineral are relatively low (0. 12 Ag + Sb substitution presented by Moëlo et al. [45] is not the dominant factor in the chemical composition of owyheeite. The determined contents of selenium in the studied mineral are relatively low (0.12-1.    contents of main elements Ag, Pb and Sb do not correlate significantly and the 2Pb↔Ag + Sb substitution presented by Moëlo et al. [45] is not the dominant factor in the chemical composition of owyheeite. The determined contents of selenium in the studied mineral are relatively low (0. Pb+Fe (apfu) 9  The Ag-poor part (with Ag contents lower than in the case of owyheeite) is an interestingand so far not a well-known part of theAg-Pb-Sb-S system,with only two approved minerals-questionable zoubekite [45,46] and tubulite-with unusual tubular morphology and crystal structure [47]. We identified mineral phases with 0.7-4.3 at.% Ag (0.87-5.12 wt.% Ag), which can be divided into four groups of compositions (Table 8)  The substitution scheme can be expressed as Pb as massive needle-like steel to lead grey aggregates up to 2 cm long in quartz iated or intergrowing with massive boulangerite, miargyrite and pyrite. It ) associated with galena, Pb-Sb sulfosalts (boulangerite, jamesonite) and ndorite group minerals, freieslebenite and diaphorite) (Figure 5c,d). It is ctions (160 point analyses). It was found as elongated lamellae up to 100 μm width forming massive grains several hundred microns across. position of owyheeite (Table 7) is close to ideal formula Ag3Pb10Sb11S28 al. [44], with a slight deficit of Pb and an excess of Sb. Figure 7 shows that ents Ag, Pb and Sb do not correlate significantly and the 2Pb↔Ag + Sb by Moëlo et al. [45] is not the dominant factor in the chemical composition of ined contents of selenium in the studied mineral are relatively low (0.12-1. Ag + Cu vs Sb + As (apfu) (a) and Ag + Cu vs Pb + Fe (apfu) (b) for owyheeite.

Boulangerite, Pb 5 Sb 4 S 11
Boulangerite occurs as abundant lead grey felt-like aggregates and needle crystals in quartz cavities up to 1 cm or as massive grain needle-like aggregates several cm in size associated with galena and miargyrite in black ore type (i). In polished sections (170 point analyses), it occurs as needle-like and column-like crystals up to 80 µm in length and 10 µm in width associated with galena, freislebenite, jamesonite, andorite group minerals and pyrite (Figure 2a,b, Figure 5c, Figure 8, Figure 10a,b) of black ore (i). Also occurs as lenses in white quartz of ore (iii) consisting of massive fibrous and needle-like grains associated with jamesonite and galena. It belongs to the earliest minerals in the observed mineral associations, next to galena.    The chemical composition of boulangerite (Table 9) is close to ideal stoichiometry; only traces of Fe, Mn and Ag were identified. In anion, contents of Se up to 0.63 apfu (2.69wt.%) ( Figure 11) were observed, which is significantly more than in other Pb-Sb sulfosalts (jamesonite, semseyite). Its average composition (167 analyses) is possible to express by the empirical formula (Pb 4.89 Fe 0.01 Mn 0.01 ) Σ4.92 Sb 4.03( S 10.89 Se 0.12 ) Σ11.01 on the basis of 20 apfu.    Semseyite was found in a similar association as boulangerite, but is much rarer, it usually occurs as needle-like or tabular grain up to 20 µm in length and 15 µm in width (Figure 10b). The chemical composition of semseyite (Table 10) corresponds to ideal stoichiometry of this mineral phase; Ag content in one point analysis (0.19 apfu) can be influenced by the surrounding phases. Unlike other Pb-Sb sulfosalts, semseyite is virtually Se-free ( Figure 11). Its empirical formula (mean of 4 analyses) is (Pb 8.91 Ag 0.05 ) Σ8.96 Sb 7.95 S 21.08 on the basis of 38 apfu. Jamesonite occurs as needle crystals in quartz gangue or as massive grain needle-like aggregates up to 2 cm in black ore (i) and ore (iii). In the polished section, it was found as long needles up to 150 µm in length and 20 µm in width. It usually replaces galena and grows together with boulangerite, freibergite and pyrite (Figure 2c, Figure 8). It belongs to the earliest minerals in the association.
The chemical composition of jamesonite (100 point analyses) is relatively uniform (Table 11) and close to ideal formula; only minor contents of Mn (up to 0.11 apfu) and Se (up to 0.27 apfu) were identified ( Figure 11). The observed range of SeS −1 substitution is distinctly lower than in boulangerite ( Figure 11). The empirical formula for studied jamesonite on the basis of 25 apfu (mean of 84 analyses) can be expressed as Fe 0.95 Mn 0.02 ) Σ0.97 Pb 3.94 Sb 6.05 (S 13.94 Se 0.07 ) Σ14.01 . Miargyrite is by far the most abundant silver mineral in the Kutná Hora ore district, together with freibergite. Short column-like grey-black crystals of miargyrite up to 10 mm in size in cavities of milky quartz gangue (ore (iii)), or quartz-kutnohorite gangue (ore (ii)) are famous from this locality [36]. Frequently, miargyrite forms massive grain aggregates and lenses in all three types of ore of several centimetres in size, often intergrowing with other Ag minerals such as pyrargyrite, diaphorite, freibergite and freieslebenite. In polished sections, it was found as groups of anhedral grains several hundred µm in size and occasional euhedral crystals into cavities. It appears in two generations at least, the latter being characteristic of a considerably smaller size of grains (up to 20 µm), higher selenium content ( Figure 12a Table 12 due to increased Zn content from neighbouring sphalerite. The more significant contents of Se in miargyrite were so far described only by Nekrasov, Lunin [51] and Yunfen et al. [52]. The representative chemical analyses of both miargyrite generation and corresponding empirical formulae are given in Table 12. second-generation Se-rich miargyrite (lighter, 5% Se). (b) miargyrite (Mia) embedded in sphalerite (Sp). An argyrodite (Agd) inclusion is on the boundary between sphalerite and pyrite (Py), both minerals (miargyrite and argyrodite) replace sphalerite. Both back-scattered electron (BSE) images.
Chemical analyses of miargyrite (175 points) revealed interesting Se contents (Figure 13 a,b), otherwise it is close to the ideal formula. Determined traces of Pb, Cu and Fe in some of analyses are probably caused by microscopic intergrowths with other phases; irregular contents of As do not exceed 0.01 apfu (0.19 wt.%). The prevailing earlier generation of miargyrite contains up to 0.08 apfu (2.29 wt.%) of Se; the later generation of miargyrite shows a considerably larger extent of the SeS-1 substitution, usually between 0.11 and 0.35 apfu, corresponding to the maximum Se content of 8.79 wt.%. Two exceptionally high Se contents were measured in small anhedral grains of miargyrite in sphalerite of red ore (ii), belonging to the later generation. These show 0.57 and 0.62 apfu Se (14.54-15.34 wt.% of Se)-not included in Table 12 due to increased Zn content from neighbouring sphalerite. The more significant contents of Se in miargyrite were so far described only by Nekrasov, Lunin [51] and Yunfen et al. [52]. The representative chemical analyses of both miargyrite generation and corresponding empirical formulae are given in Table 12.
S ( apfu)   Pyrargyrite crystals up to 5 mm in size and massive grain aggregates several cm in size, occurring (less abundantly than miargyrite) in milky quartz gangue associated with miargyrite and freibergite of ore (iii) or in cavities of the kutnohorite-quartz gangue of red ore (ii), associated with other Ag-Sb sulfides and pyrite. Only three samples of pyrargyrite were found in black ore (i) (Figure 2a Table 13. In comparison to miargyrite and stephanite (Figure 13b), the determined range of SeS −1 substitution in pyrargyrite is limited, maximum is 0.13 apfu (1.82 wt.%) in one analysis, but in all others does not exceed 0.70 wt.%). The found As contents in pyrargyrite (solid solution with proustite) are very low (up to 0.02 apfu, i.e., 0.21 wt.%), similar to As contents in all primary sulfosalts of the hypogene mineralization in Kutná Hora.
occurring (less abundantly than miargyrite) in milky quartz gangue associated with miargyrite and freibergite of ore (iii) or in cavities of the kutnohorite-quartz gangue of red ore (ii), associated with other Ag-Sb sulfides and pyrite. Only three samples of pyrargyrite were found in black ore (i) (Figure 2a). In polished sections pyrargyrite was found in nine samples (40 point analyses) as anhedral grains up to 30 μm. It often forms thin veinlets as much as 200 μm in length and 20 μm in width. It occurs as a filling of thin fissures in miargyrite in a close vicinity of Au-rich silver. It also occurs in drop-shaped inclusions of galena in pyrite of red ore (ii) where it replaces galena ( Figure  14a). The chemical composition of pyrargyrite and the corresponding chemical formulae are given in Table 13. In comparison to miargyrite and stephanite (Figure 13b), the determined range of SeS-1 substitution in pyrargyrite is limited, maximum is 0.13 apfu (1.82 wt.%) in one analysis, but in all others does not exceed 0.70 wt.%). The found As contents in pyrargyrite (solid solution with proustite) are very low (up to 0.02 apfu, i.e., 0.21 wt.%), similar to As contents in all primary sulfosalts of the hypogene mineralization in Kutná Hora.  Orange to bright red leaflets and coatings of pyrostilpnite on fractures of quartz gangue were described by Vepřek [53]. Later, Mrázek and Zeman [17] found orange-red elongated transparent crystalas up to 4 mm in length with intensive lustre in cavities of quartz gangue from the Vein I and Vein A (ore (iii)), determined by X-ray diffraction.
In backscatter electron images, pyrostilpnite was not distinguished from its isochemical dimorph, pyrargyrite. However, orange crystals of pyrostilpnite under veinlets of pyragyrite were observed in optical microscope.

Stephanite, Ag 5 SbS 4
Stephanite occurs in red ore (ii) from the Vein B as rare anhedral grains up to 20 µm in size in fractures of miargyrite or as inclusions in miargyrite (Figure 2e), accompanied by exsolutions of pyrargyrite, itself being replaced by acanthite. It belongs to later minerals in the studied association.
It also occurs among drop-shaped inclusions in pyrite of red ore (ii), often rich in selenium (as much as 9.8 wt.% of Se) (Figure 14a,b and Figure 20b) or veinlets in miargyrite of red ore (ii) (Figure 24a).
The chemical composition of stephanite and the corresponding chemical formulae are given in Table 14. One grain of stephanite is characteristic of a very high Se content of as much as 1.11 apfu (9.84 wt.%, not included in Table 14 due to a lower total). Thus, stephanite-together with miargyrite-is the mineral with the highest determined range of the SeS −1 substitution among Ag-Sb-S mineral phases (Figure 13b). The selenium analogue of stephanite-the mineral selenostephanite-was described from two Russian deposits-Rudnaya Sopka, Chukotka [54] and Julietta, Magadan region [55]-and requires 17.3 or more wt.% of Se. Polybasite was found in four grains of two samples (8 point analyses) as very rare euhedral table-like crystals 40 µm in length and 10 µm in width, cutting across galena inclusions in pyrite of red ore (ii) (Figure 15a,b). Polybasite is in a close contact with Se-rich acanthite and both minerals replace galena. Associated minerals forming inclusions in pyrite but not in a direct contact with polybasite include argyrodite, pyrargyrite, aguilarite, clausthalite and naumannite. red ore (ii) (Figure 15a,b). Polybasite is in a close contact with Se-rich acanthite and both minerals replace galena. Associated minerals forming inclusions in pyrite but not in a direct contact with polybasite include argyrodite, pyrargyrite, aguilarite, clausthalite and naumannite. Polybasite differs in minor but essential Cu content from chemically similar stephanite and also by a different (Ag + Cu)/(Sb + As) ratio. Copper contents of only 0.22-0.44 apfu are lower than for minerals of polybasite group in the literature [56]; low contents of copper are characteristic especially of selenium-containing members of this group [57]. Determined contents of Se in the range 0.07-0.76 apfu (Figure 13b) in samples from Padua mine are lower than the minimal limit (>1 Se apfu) for selenopolybasite [57]. The content of the pearceite component in studied sample is low and does not exceed 0.17 apfu As (0.55 wt.%). The chemical analyses of polybasite and corresponding empirical formulae are given in Table 15.  Analyses are ordered according to increasing Se content. Polybasite differs in minor but essential Cu content from chemically similar stephanite and also by a different (Ag + Cu)/(Sb + As) ratio. Copper contents of only 0.22-0.44 apfu are lower than for minerals of polybasite group in the literature [56]; low contents of copper are characteristic especially of selenium-containing members of this group [57]. Determined contents of Se in the range 0.07-0.76 apfu (Figure 13b) in samples from Padua mine are lower than the minimal limit (>1 Se apfu) for selenopolybasite [57]. The content of the pearceite component in studied sample is low and does not exceed 0.17 apfu As (0.55 wt.%). The chemical analyses of polybasite and corresponding empirical formulae are given in Table 15.

Minerals of the Tetrahedrite Series
Freibergite, Ag 6 [Cu 4 Fe 2 ]Sb 4 S 13−x Freibergite, together with miargyrite, is the most abundant silver mineral observed in the studied material (193 analyses). Freibergite occurs as crystals several mm in size in cavities of quartz-kutnohorite gangue (red ore (ii)) or in cavities of milky white quartz (ore (iii)) or grain aggregates several cm in size associated with miargyrite and pyrargyrite (ores (ii) and (iii)). In polished sections, it was frequently found also in black ore (i), and it forms anhedral grains up to 300 µm in size. The grains are often zonal, growth zones differ by silver content, negatively correlated with the copper content. Freibergite grows together intimately with diaphorite and freieslebenite, usually being replaced by miargyrite. An example of freibergite in black ore (i) is shown in Figure 2c; freibergite in red ore (ii) is shown in Figure 16a,b; and ore (iii) is shown in Figure 2f.
The status of Ag-rich members of tetrahedrite group (freibergite, argentotennantite) and especially their boundaries with tetrahedrite and tennantite, is still being investigated [44]. Some authors have proposed a minimum content for freibergite of 4 apfu Ag [44,58], and a condition of Ag > Cu for argentotennantite (about 5 apfu Ag) [59]. On the basis of the results of crystal structure studies [58,60] and analyses of natural samples [61,62], Ag preferentially occupies the triangular A position with total content 6 apfu, and according to the present rules of mineralogical nomenclature [31], the boundary would be 3 apfu Ag [62].
Two groups of compositions were identified. The majority of analyses (Table 16) represent typical freibergite with more than 4 apfu of Ag. Its chemical composition is fairly monotonous with regard to Fe/Zn and Sb/As ratios. Iron is always dominant, and As is not present, as is the case with all sulfosalts in hypogene mineralization in Kutná Hora. Zonality phenomena are visible in some grains quite profoundly, however, differing only moderately in terms of Ag/Cu ratio. Ag contents were determined from 3.99 apfu (23.33 wt.%) to 7.25 apfu (38.61 wt.%) in freibergite, indicating that the placement of Ag not only in the A position (up to 6 apfu), but also to a limited degree in the B position (up to 1.25 apfu) takes place. Freibergite with as much as 46.4 wt.% of Ag (8.93 apfu) was described from the Rejzské pásmo Lode in the Kutná Hora ore district [18]. This phase corresponds to the newly approved mineral rozhdestvenskayaite [63]. Ag and Cu contents show an excellent negative correlation (Figure 17a), which is in agreement with published results (e.g., [35,64,65]). In the case of freibergite below 6 apfu Ag, the rest of the A position is filled with copper. The B position, in addition to Ag contents (up to 0.40 apfu), is occupied by dominant Cu. In the C position, Fe (1.09-2.02 apfu) prevails over Zn (0.03-0.98 apfu), which is typical of freibergite (Figure 17b). Determined Ag/Cu ratios show no apparent correlation with Fe/Zn ratios. In the X position, the dominant Sb is in a part of analyses accompanied by negligible As, not exceeding 0.09 apfu (0.36 wt.%).
The second group of analyses corresponds to members at the boundary between freibergite and Ag-rich tetrahedrite. This member is very rare and was found only in one sample of black ore (i) as anhedral grains associated with galena, freieslebenite, diaphorite, owyheeite and Ag-excess fizélyite. Ag content varies from 17.41 to 18.48 wt.%, corresponding to 2.93 to 3.15 apfu Ag, which is appreciably less than a typical common member of the tetrahedrite series, which is freibergite on all lodes of the Kutná Hore ore district. The chemistry is similar to freibergite in the respect that iron prevails over zinc, no arsenic substitutes for antimony (Table 17), and the substitution of Se for S is non-existent, although surrounding minerals contain as much as 1.1 wt.% of Se  authors have proposed a minimum content for freibergite of 4 apfu Ag [44,58], and a condition of Ag > Cu for argentotennantite (about 5 apfu Ag) [59]. On the basis of the results of crystal structure studies [58,60] and analyses of natural samples [61,62], Ag preferentially occupies the triangular A position with total content 6 apfu, and according to the present rules of mineralogical nomenclature [31], the boundary would be 3 apfu Ag [62]. Two groups of compositions were identified. The majority of analyses (Table 16) represent typical freibergite with more than 4 apfu of Ag. Its chemical composition is fairly monotonous with regard to Fe/Zn and Sb/As ratios. Iron is always dominant, and As is not present, as is the case with all sulfosalts in hypogene mineralization in Kutná Hora. Zonality phenomena are visible in some grains quite profoundly, however, differing only moderately in terms of Ag/Cu ratio. Ag contents were determined from 3.99 apfu (23.33 wt.%) to 7.25 apfu (38.61 wt.%) in freibergite, indicating that the placement of Ag not only in the A position (up to 6 apfu), but also to a limited degree in the B position (up to 1.25 apfu) takes place. Freibergite with as much as 46.4 wt.% of Ag (8.93 apfu) was described from the Rejzské pásmo Lode in the Kutná Hora ore district [18]. This phase corresponds to the newly approved mineral rozhdestvenskayaite [63]. Ag and Cu contents show an excellent negative correlation (Figure 17a), which is in agreement with published results (e.g., [35,64,65]). In the case of freibergite below 6 apfu Ag, the rest of the A position is filled with copper. The B position, in addition to Ag contents (up to 0.40 apfu), is occupied by dominant Cu. In the C position, Fe (1.09-2.02 apfu) prevails over Zn (0.03-0.98 apfu), which is typical of freibergite (Figure 17b). Determined Ag/Cu ratios show no apparent correlation with Fe/Zn ratios. In the X position, the dominant Sb is in a part of analyses accompanied by negligible As, not exceeding 0.09 apfu (0.36 wt.%). The second group of analyses corresponds to members at the boundary between freibergite and Ag-rich tetrahedrite. This member is very rare and was found only in one sample of black ore (i) as anhedral grains associated with galena, freieslebenite, diaphorite, owyheeite and Ag-excess fizélyite. Ag content varies from 17.41 to 18.48 wt.%, corresponding to 2.93 to 3.15 apfu Ag, which is appreciably less than a typical common member of the tetrahedrite series, which is freibergite on all lodes of the Kutná Hore ore district. The chemistry is similar to freibergite in the respect that iron prevails over zinc, no arsenic substitutes for antimony (Table 17), and the substitution of Se for S is non-existent, although surrounding minerals contain as much as 1.1 wt.% of Se A very interesting thing in the chemistry of freibergite and tetrahedrite is the fact that selenium does not enter the structure of freibergite, even if the grains of freibergite occur in a Se-rich environment, which was documented both in black ore (i) and red ore (ii). While all other associated sulfosalts take in selenium more or less eagerly, freibergite remains Se-free.   A very interesting thing in the chemistry of freibergite and tetrahedrite is the fact that selenium does not enter the structure of freibergite, even if the grains of freibergite occur in a Se-rich environment, which was documented both in black ore (i) and red ore (ii). While all other associated sulfosalts take in selenium more or less eagerly, freibergite remains Se-free.

Acanthite, Ag 2 S
Acanthite occurs as anhedral grains, fillings of other silver minerals, or veinlets 50 µm wide and several hundred µm long, associated with pyrargyrite, allargentum and native silver (Figure 18a) in quartz-kutnohorite gangue of red ore (ii), where it originated from former argentite. It belongs to the latest minerals in the association. This acanthite shows no selenium content. The second mode of occurrence of acanthite is drop-like inclusions of up to 30 µm in pyrite of red ore (ii), which are characteristic of increased Se content with a continual transition to aguilarite and naumannite (Figure 18b-d). Occasionally, inhomogeneous grains with oscillating Se content occur. Grains of acanthite richest in selenium (with composition close to aguilarite) are usually under 10 x 10 µm. In the third mode of occurrence inclusions of galena in pyrite are partially replaced by acanthite, which has a significant selenium content. It is fairly frequent in red ore (ii), associated (but not in direct contact) with naumannite, clausthalite, argyrodite and aguilarite. Acanthite occurs as anhedral grains, fillings of other silver minerals, or veinlets 50 μm wide and several hundred μm long, associated with pyrargyrite, allargentum and native silver (Figure 18a) in quartz-kutnohorite gangue of red ore (ii), where it originated from former argentite. It belongs to the latest minerals in the association. This acanthite shows no selenium content. The second mode of occurrence of acanthite is drop-like inclusions of up to 30 μm in pyrite of red ore (ii), which are characteristic of increased Se content with a continual transition to aguilarite and naumannite (Figure 18b-d). Occasionally, inhomogeneous grains with oscillating Se content occur. Grains of acanthite richest in selenium (with composition close to aguilarite) are usually under 10 x 10 μm. In the third mode of occurrence inclusions of galena in pyrite are partially replaced by acanthite, which has a significant selenium content. It is fairly frequent in red ore (ii), associated (but not in direct contact) with naumannite, clausthalite, argyrodite and aguilarite.
Chemical composition of acanthite and corresponding chemical formulae are given in Table 18. Increased selenium contents are characteristic of the studied acanthite. In most cases, these are up to 0.13 apfu, some very small grains have as much as 0.30 apfu (8.83 wt.%) (Figure 19). With regard to the small size of grains, measured minor contents of Cu, Pb, Fe, Zn and Sb in some analytical points are probably influenced by surrounding phases. Chemical composition of acanthite and corresponding chemical formulae are given in Table 18. Increased selenium contents are characteristic of the studied acanthite. In most cases, these are up to 0.13 apfu, some very small grains have as much as 0.30 apfu (8.83 wt.%) (Figure 19). With regard to the small size of grains, measured minor contents of Cu, Pb, Fe, Zn and Sb in some analytical points are probably influenced by surrounding phases.    Aguilarite was confirmed in one sample as a small anhedral grain 6 × 4 μm in a galena inclusion (25 μm across) in pyrite of red ore (ii) (Figure 18b); aguilarite replaces galena. The galena inclusion was surrounded by (but not in direct contact with) smaller inclusions-or semi-euhedral grains-of

Aguilarite, Ag 4 SeS
Aguilarite was confirmed in one sample as a small anhedral grain 6 × 4 µm in a galena inclusion (25 µm across) in pyrite of red ore (ii) (Figure 18b); aguilarite replaces galena. The galena inclusion was surrounded by (but not in direct contact with) smaller inclusions-or semi-euhedral grains-of acanthite with variable selenium content (from zero to 4 wt.%). Plentiful inclusions in pyrite of this sample are formed-apart from predominant galena and occasional acanthite-by argyrodite, freibergite, (Ge,Se)-rich acanthite, clausthalite, naumannite, polybasite, pyrargyrite and unnamed Ag-Cu-S phases.
The chemical composition of aguilarite exhibitss contents of Se in the range of 1.22-1.28 apfu (Table 19); with regard to the small size of grains, the measured minor contents of Pb and Fe are likely to be caused by surrounding phases. Aguilarite was defined by Bindi and Pingitore [66] as a member of the monoclinic solid solution acanthite-aguilarite with Se>S (more than 16.67 at.% Se), and at the same time, with Se contents below ca. 1.4 apfu (23.33 at.%), which represents a boundary for an orthorhombic S-rich naumannite ( Figure 19). The nomenclature of mineral phases along the Ag 2 S-Ag 2 Se join was published by Bindi and Pingitore [66]. They suggest that two distinct solid solution series could exist: monoclinic "acanthite-type" series including aguilarite in the range Ag 2 S-Ag 2 S 0.4 Se 0.6 , and an orthorhombic "naumannite-type" series between Ag 2 S 0.3 Se 0.7 -Ag 2 Se. The status of members with Se contents in the range 0.60-0.70 (or 1.2-1.4 for 6 apfu of aguilarite), which correspond to two-phase (monoclinic and orthorhombic) field as was described by Pingitore et al. [67] or Pal'yanova et al. [68] is still under debate. According to Kullerud et al. [69], there are two possible explanations-presence of metastable cubic high-temperature phase or mixtures of two submicroscopic phases formed during cooling of homogenous cubic phase below 80 • C. Natural minerals with compositions related to this two-phase field have also been reported [68,69].
The described aguilarite in Table 19 shows Se contents within the above-mentioned range, i.e., between 1.22 and 1.28 apfu, corresponding to 0.61 and 0.64 apfu, if calculated to 3 apfu. However, it is impossible to decide whether a metastable phase or a mixture of two submicroscopic phases is present.

Naumannite, Ag 2 Se
Naumannite was found in four grains of three samples (9 point analyses). The mode of occurrence is very similar to aguilarite, i.e., in drop-like inclusions in massive pyrite of red ore (ii).
In the first sample, an inclusion of Se-rich miargyrite (8.7 wt% of Se) 100 µm across in pyrite contains an euhedral grain of naumannite 30 µm across and a semi-euhedral grain of clausthalite. Clausthalite and naumannite are not in direct contact and both minerals replace Se-rich miargyrite (Figure 20a). The second grain occurs in a 20 µm inclusion in pyrite formed by clausthalite, Se-rich stephanite (9.8 wt.% of Se) and naumannite. Clausthalite appears to be the earliest mineral, replaced by both stephanite and naumannite. In the third sample, an inclusion in pyrite 30 µm across is formed by Se-rich stephanite (9.1 wt.% of Se), which is replaced by naumannite. The shape of the inclusion is not drop-like, but rather euhedral, following the crystal shape of stephanite (Figure 14b). The fourth sample occurs in a galena inclusion of 140 µm in pyrite. An anhedral grain of naumannite 6 µm across replaces galena at one of its edges.
Chemical composition of naumannite and corresponding chemical formulae are given in Table 20; the range of SSe −1 substitution in naumannite was determined to be 0.01-0.18 apfu (Figure 19). With regard to the small size of grains, minor measured contents of Pb and Fe insome analytical points are probably influenced by surrounding phases. Chemical composition of naumannite and corresponding chemical formulae are given in Table  20; the range of SSe-1 substitution in naumannite was determined to be 0.01-0.18 apfu (Figure 19). With regard to the small size of grains, minor measured contents of Pb and Fe insome analytical points are probably influenced by surrounding phases.  Argyrodite was found in nine grains of three samples (16 point analyses). It occurs as individual anhedral grains up to 40 μm among bubble-shaped inclusions in pyrite of red ore (ii) (Figure 18c). It was also found in sphalerite as a 12 μm grain bordering on freibergite in a galena inclusion of 45 μm (Figure 20b). Argyrodite and freibergite replace galena and are rimmed by pyrite. The replacement progresses from the clean-cut boundary with pyrite towards the centre of the galena inclusion, which is completely enclosed in sphalerite; in sphalerite associated with miargyrite and pyrite (Figure 12b); and as inclusions in freibergite with remnants of members of galena-clausthalite solid solution, which are replaced by freibergite (Figure 16b).
Chemical analyses of argyrodite are complicated due to the small size of the grains; the measured contents of Cu and Fe probably come from surrounding phases. Apart from major elements (Ag, Ge a S), significant contents of Se up to 0.69 apfu (4.93 wt.%) were found. The chemical composition and corresponding chemical formulae are given in Table 21. The discovery of   Argyrodite was found in nine grains of three samples (16 point analyses). It occurs as individual anhedral grains up to 40 µm among bubble-shaped inclusions in pyrite of red ore (ii) (Figure 18c). It was also found in sphalerite as a 12 µm grain bordering on freibergite in a galena inclusion of 45 µm (Figure 20b). Argyrodite and freibergite replace galena and are rimmed by pyrite. The replacement progresses from the clean-cut boundary with pyrite towards the centre of the galena inclusion, which is completely enclosed in sphalerite; in sphalerite associated with miargyrite and pyrite ( Figure 12b); and as inclusions in freibergite with remnants of members of galena-clausthalite solid solution, which are replaced by freibergite (Figure 16b).
Chemical analyses of argyrodite are complicated due to the small size of the grains; the measured contents of Cu and Fe probably come from surrounding phases. Apart from major elements (Ag, Ge a S), significant contents of Se up to 0.69 apfu (4.93 wt.%) were found. The chemical composition and corresponding chemical formulae are given in Table 21. The discovery of germanium in the geochemistry of the Kutná Hora ore district shows another similarity with the Freiberg ore district, which is the type locality for argyrodite.

Ag-Cu-S Phases
Unnamed Ag-Cu-(S,Se) phases were found in five grains of three samples (23 point analyses) and occur in a very similar way to argyrodite as individual inclusions in pyrite, not in contact with any other mineral (Figures 18d and 21a). These phases were found as anhedral grains up to 50 × 30 µm among predominantly galena inclusions in pyrite in red ore (ii) (Figure 21b) and belong to the latest minerals. Similar to selenides and argyrodite, these grains are enclosed in pyrite growth zones with plentiful bubble-shaped inclusions.

Analyses
Ag Elevated levels of Pb, Fe or Zn are caused by surrounding galena, pyrite or sphalerite. Analyses are ordered according to incereasing Se content.

Ag-Cu-S Phases
Unnamed Ag-Cu-(S,Se) phases were found in five grains of three samples (23 point analyses) and occur in a very similar way to argyrodite as individual inclusions in pyrite, not in contact with any other mineral (Figures 18d and 21a). These phases were found as anhedral grains up to 50 × 30 μm among predominantly galena inclusions in pyrite in red ore (ii) (Figure 21b) and belong to the latest minerals. Similar to selenides and argyrodite, these grains are enclosed in pyrite growth zones with plentiful bubble-shaped inclusions. A common feature of all analyses (Table 22) is that the metal/sulphur ratio is between 1.36 and 1.74, while all known Ag-Cu-S minerals have this ratio equal to 2. Higher contents of S + Se in the anionic part suggest a different structural arrangement than in known phases and/or a possible involvement of Cu 2+ cation. The Ag and Cu contents with a clear negative correlation (Figure 22a) were observed. They differ from known phases in the Ag-Cu-S system with respect to: a) the Ag/Cu ratio, and b) higher contents of Se in the anionic part ( Figure 22b); the contents of minor Se were determined to be between 2 and 5 at.%. With regard to the rarity of Ag-Cu-S phases and to the minimal size of grains which does not rule the influence of surrounding phases (especially contents of Fe and Zn), it cannot be decided whether the measured points belong to new mineral phases. A common feature of all analyses (Table 22) is that the metal/sulphur ratio is between 1.36 and 1.74, while all known Ag-Cu-S minerals have this ratio equal to 2. Higher contents of S + Se in the anionic part suggest a different structural arrangement than in known phases and/or a possible involvement of Cu 2+ cation. The Ag and Cu contents with a clear negative correlation (Figure 22a) were observed. They differ from known phases in the Ag-Cu-S system with respect to: a) the Ag/Cu ratio, and b) higher contents of Se in the anionic part ( Figure 22b); the contents of minor Se were determined to be between 2 and 5 at.%. With regard to the rarity of Ag-Cu-S phases and to the minimal size of grains which does not rule the influence of surrounding phases (especially contents of Fe and Zn), it cannot be decided whether the measured points belong to new mineral phases.    Native silver occurs as yellow-white metallic aggregates several mm in size in cavities of the kutnohorite-quartz gangue of Vein B (red ore (ii)), associated with other silver minerals, namely with miargyrite, pyrargyrite and freibergite, and also in ore (iii) associated with pyragyrite, miargyrite and diaphorite. Silver occurs in two varieties, which differ with regard to Sb content: hypogene (primary) Sb-rich silver (Table 23) and later (mobilized) pure Sb-free native silver (Table 24). Polished sections of Sb-free silver were found as grains up to 50 µm in veinlets of Sb-rich silver several hundreds µm long, which form rims of masses of allargentum (Figure 18a). This pure native silver contains only traces of Hg, As, Fe and Cl. The more abundant Sb-rich silver is associated with pyrargyrite, acanthite, allargentum and Sb-free silver. Contents of Sb in the range 0.01-0.03 apfu (1.3-3.1 wt.%) are characteristic of this type of silver (Table 23, Figure 23).    (Table 25) were also identified; the minor contents of S determined are probably caused by surrounding phases. Interestingly, no native silver whatsoever occurs in plentiful bubble-like inclusions in pyrite-all are acanthite-with the exception of Au-rich silver (electrum).    (Table 25) were also identified; the minor contents of S determined are probably caused by surrounding phases.
Members of the Au-Ag solid solution (electrum) have been identified in the past from three lodes of Kutná Hora ore district on the basis of ore microscopy as allotriomorphic grains up 10 μm enclosed in freibergite, pyrargyrite or miagyrite. Only one occurrence was analysed chemically by emission spectral analysis [71].   Members of the Au-Ag solid solution (electrum) have been identified in the past from three lodes of Kutná Hora ore district on the basis of ore microscopy as allotriomorphic grains up 10 µm enclosed in freibergite, pyrargyrite or miagyrite. Only one occurrence was analysed chemically by emission spectral analysis [71].

Uytenbogaardtite Ag 3 AuS 2
Uytenbogaardtite was found as one semi-euhedrall grain 9 × 6 µm in massive miargyrite of red ore (ii). The image in Figure 25a reveals that the grain contains minute inclusions of Au-rich silver (white spots, one larger one is visible at the left edge of the grain) with 51.0 wt.% of Au and 46.3 wt.% of Ag (corresponding to 35.7 at.% Au), which are probably responsible for the lower sulphur content in the measured points of uytenbogaardtite. The top and right edge of the grain displays a hem resembling a reaction product. However, the hem is formed by uytenbogaardtite with increased Sb content, a possible contamination from surrounding miargyrite. Analyses are ordered according to decreasing Au content.

Uytenbogaardtite Ag3AuS2
Uytenbogaardtite was found as one semi-euhedrall grain 9 × 6 μm in massive miargyrite of red ore (ii). The image in Figure 25a reveals that the grain contains minute inclusions of Au-rich silver (white spots, one larger one is visible at the left edge of the grain) with 51.0 wt.% of Au and 46.3 wt.% of Ag (corresponding to 35.7 at.% Au), which are probably responsible for the lower sulphur content in the measured points of uytenbogaardtite. The top and right edge of the grain displays a hem resembling a reaction product. However, the hem is formed by uytenbogaardtite with increased Sb content, a possible contamination from surrounding miargyrite. This is the first occurrence of uytenbogaardtite in the Czech Republic. Recently, uytenbogaardite was described from the selenium-rich Au-Ag mineralization of the Kremnica Sb-Au-Ag epithermal deposit, Slovakia [72]. The chemistry of uytenbogaardtite from Kutná Hora (Table 26) shows a surplus of silver (3.16-3.33 apfu) and a deficit of sulphur (1.66-1.87 apfu) at all four analysed points. Two analyses show a surplus of gold (1.14 apfu), and two show a deficit (0.77 and 0.87 apfu). We assume that the lower sulphur contents compared to stoichiometry are caused by the fact that the grain is, in fact, a submicroscopic intergrowth of uytenbogaardtite with Au-rich silver, which is visible on the BSE photograph (Figure 25a).  Allargentum (together with Sb-rich silver) is more abundant than native Sb-free silver in the hypogene mineralization. It is found as metallic white-yellow outgrowths, platelets or wire-like aggregates, usually up to several mm in size in the cavities of quartz-kutnohorite gangue of red ore (ii), associated with silver, pyrargyrite and miargyrite. In polished sections, it occurs as anhedral aggregates up to several hundred μm in size in miargyrite, associated with pyrargyrite and acanthite (Figure 18a). This is the first occurrence of uytenbogaardtite in the Czech Republic. Recently, uytenbogaardite was described from the selenium-rich Au-Ag mineralization of the Kremnica Sb-Au-Ag epithermal deposit, Slovakia [72]. The chemistry of uytenbogaardtite from Kutná Hora (Table 26) shows a surplus of silver (3.16-3.33 apfu) and a deficit of sulphur (1.66-1.87 apfu) at all four analysed points. Two analyses show a surplus of gold (1.14 apfu), and two show a deficit (0.77 and 0.87 apfu). We assume that the lower sulphur contents compared to stoichiometry are caused by the fact that the grain is, in fact, a submicroscopic intergrowth of uytenbogaardtite with Au-rich silver, which is visible on the BSE photograph (Figure 25a). Allargentum (together with Sb-rich silver) is more abundant than native Sb-free silver in the hypogene mineralization. It is found as metallic white-yellow outgrowths, platelets or wire-like aggregates, usually up to several mm in size in the cavities of quartz-kutnohorite gangue of red ore (ii), associated with silver, pyrargyrite and miargyrite. In polished sections, it occurs as anhedral aggregates up to several hundred µm in size in miargyrite, associated with pyrargyrite and acanthite ( Figure 18a).
The chemical composition of allargentum is relatively uniform and is close to the ideal formula (Table 27, Figure 23); only traces of Cl were identified. The empirical formula for studied allargentum samples on the basis of 7 apfu (mean of 10 analyses) can be expressed as Ag 5.95 Sb 1.02 Cl 0.02 . Au-rich dyscrasite was found as one anhedral grain 60 x 30 µm in quartz, close to, but not in direct contact with, the massive miargyrite of red ore (ii) (Figure 25b).
The chemical analysis of dyscrasite (Table 28) revealed interesting contents of Au in the range 0.08-0.10 apfu (3.65-4.11 wt.%). A small deficit of Sb observed up to 0.08 apfu (Figure 23) corresponds to the ideal formula Ag 3 + x Sb 1 − x proposed for dyscrasite by Scott [73] on the basis of crystal structure study. Galena is a very frequent mineral in the Pb-rich black ore (i) from Vein B. It occurs as typical lead-grey cleavable grain aggregates several cm in size associated with other sulfides, occasionally as crystals in cavities. In polished sections, it was frequently found as the earliest mineral associated with boulangerite, freieslebenite, diaphorite, owyheeite, andorite group minerals, miargyrite and freibergite (Figure 2a-c,e, Figure 4, Figure 5c,d, Figure 8, Figure 10b, Figure 12a).
It is also frequently found in the red ore type (ii) as plentiful bubble-shaped inclusions in pyrite (Figure 21b), and also as idiomorphic grains; usually, it is the earliest mineral. Very frequently, it occurs as filling of bubble-shaped inclusions in the pyrite of red ore (ii) (Figure 15a,b, Figure 16b, Figure 18b,c,d, Figure 20a,b, Figure 21a,b). It also occurs in ore (iii) (Figure 2f). Increased Se contents (Table 29) were found only in small grains of galena (up to 20 µm across), associated with various Ag-Pb-Sb sulfosalts. Significantly increased Ag contents (up to 12.34 wt.%) were occasionally identified (34 points above 1 wt.% of Ag). These were found to be positively correlated with Sb contents (Figure 26a) and considerably higher than previously reported in the literature from this locality (0.10-0.21 wt.% [13,35]). Ag and Sb enter the structure of galena probably by the same mechanism as Ag and Bi in PbS SS , i.e., galena -matildite solid solution [74,75]. The maximum values of Ag and Sb in the galena grains are 0.22 apfu and 0.23 apfu. Sucha high degree of substitution was observed only in several grains and corresponds to the highest contents of PbS SS ( [74,76,77]. In most studied galena grains, the contents of Ag do not exceed 0.12 apfu; a similar range of Ag + (Bi,Sb) → 2Pb substations in PbS SS are known from other occurrences around the world [23,74,75,77]. Measured contents of Se in galena (Table 29) are substantially higher than previously published data (0.14 wt.% Se [13]) and suggest an unlimited SeS −1 substitution in galena -clausthalite solid solution ( Figure 26b); as mentioned before, higher Se contents were determined for smaller aggregates of galena, usually not exceeding 20 µm. 2Pb substations in PbSSS are known from other occurrences around the world [23,74,75,77]. Measured contents of Se in galena (Table 29) are substantially higher than previously published data (0.14 wt.% Se [13]) and suggest an unlimited SeS-1 substitution in galena -clausthalite solid solution ( Figure 26b); as mentioned before, higher Se contents were determined for smaller aggregates of galena, usually not exceeding 20 μm.  Analyses are ordered according to incereasing Se content.

Clausthalite
Clausthalite is the most frequently occurring selenide mineral. It was found in both black ore (i) ( Figure 27) (two samples, 10 point analyses) and, even more often, in red ore (ii) (four samples, 10 point analyses). The mineral was found as anhedral grains in fractures in freibergite filled in by miargyrite in red ore (ii) (Figure 16a). This miargyrite shows increased amounts of selenium and belongs to the latest minerals of the association. Other clausthalite grains are observed in bubble-shaped inclusions in pyrite of red ore (ii) (Figure 16b, Figure 20a) in association with Se-rich galena, accompanied by other minerals present in these inclusions (see aguilarite). Clausthalite was identified among compositions corresponding to the galena-clausthalite solid solution in black ore

Clausthalite
Clausthalite is the most frequently occurring selenide mineral. It was found in both black ore (i) ( Figure 27) (two samples, 10 point analyses) and, even more often, in red ore (ii) (four samples, 10 point analyses). The mineral was found as anhedral grains in fractures in freibergite filled in by miargyrite in red ore (ii) (Figure 16a). This miargyrite shows increased amounts of selenium and belongs to the latest minerals of the association. Other clausthalite grains are observed in bubble-shaped inclusions in pyrite of red ore (ii) (Figure 16b, Figure 20a) in association with Se-rich galena, accompanied by other minerals present in these inclusions (see aguilarite). Clausthalite was identified among compositions corresponding to the galena-clausthalite solid solution in black ore (i) as inclusions up to 50 µm in Se-free freieslebenite, which is replaced by clausthalite. Generally, members of the clausthalite-galena solid solution occurring in black ore (i) are accompanied by galena and Pb-Sb-(Ag) sulfosalts. Often a common trend is that smaller grains are Se-rich galena or clausthalite and larger grains of galena are generally Se-free. (i) as inclusions up to 50 μm in Se-free freieslebenite, which is replaced by clausthalite. Generally, members of the clausthalite-galena solid solution occurring in black ore (i) are accompanied by galena and Pb-Sb-(Ag) sulfosalts. Often a common trend is that smaller grains are Se-rich galena or clausthalite and larger grains of galena are generally Se-free. It has to be noted that no sulphur-free clausthalite was found in any of the measured samples. Sulphur contents in clausthalite (Table 30) range between 0.10-0.50 apfu (4.87-6.28 wt.%) ( Figure  26b). An unlimited miscibility among clausthalite and galena was observed in experimental studies of phase relations in this system at temperatures above 300 °C [78][79][80]. The extrapolation of thermodynamic data for end members enables to envisage the existence of a complete solid solution PbSe-PbS up to temperatures of about 100 °C [79,80]. The existence of a complete isomorphous series PbS-PbSe in natural samples was described for the first time by Coleman [81], who studied samples from uranium-vanadium deposits in the area of Colorado Plateau, and later, it was confirmed by the research of samples from the deposits of Niederschlema-Alberoda [82], Moldava [83] and Potůčky [84] in Krušné hory Mountains or Běstvina in Železné hory Mountains [85]. Unlike coexisting galena, clausthalite contains very rarely increased contents of Ag (and Sb), not exceeding 0.11 apfu or 0.04 apfu, respectively ( Figure 28). In Table 30, the contents of Ag and Sb are negligible. It has to be noted that no sulphur-free clausthalite was found in any of the measured samples. Sulphur contents in clausthalite (Table 30) range between 0.10-0.50 apfu (4.87-6.28 wt.%) (Figure 26b). An unlimited miscibility among clausthalite and galena was observed in experimental studies of phase relations in this system at temperatures above 300 • C [78][79][80]. The extrapolation of thermodynamic data for end members enables to envisage the existence of a complete solid solution PbSe-PbS up to temperatures of about 100 • C [79,80]. The existence of a complete isomorphous series PbS-PbSe in natural samples was described for the first time by Coleman [81], who studied samples from uranium-vanadium deposits in the area of Colorado Plateau, and later, it was confirmed by the research of samples from the deposits of Niederschlema-Alberoda [82], Moldava [83] and Potůčky [84] in Krušné hory Mountains or Běstvina in Železné hory Mountains [85]. Unlike coexisting galena, clausthalite contains very rarely increased contents of Ag (and Sb), not exceeding 0.11 apfu or 0.04 apfu, respectively ( Figure 28). In Table 30, the contents of Ag and Sb are negligible.

Succession of Crystalization
The ore mineralization of the whole Kutná Hora ore district originated in several stages, separated by tectonic movements [26]. Each stage is subdivided into mineralization sequences, divided by weaker tectonic events or by distinct metasomatic processes. The similarity of the Kutná Hora [26] and sequence III, with a weaker overprint of Se mineralization; corresponds to 'eq' ore type, Ag-Sb sequence in Freiberg.
The mutual relationship between the three ores (i, ii and iii) is difficult to assess with regard to their occurrences in different veins. The authors of this article are of the opinion that the Pb-rich black ore (i) is the earliest of the three, followed by (ii) and (iii).

Discussion of the Formation Conditions
The Kutná Hora ore district is considered a typical example of postmagmatic sulfide base-metal mineralization of late Variscan age (Early Permian; [87]), analogous to the 'kb + eb' ore types (mineralizations) of Freiberg in Saxony, Germany [28,29]. Silver minerals ('eb', the Ag-Sb sequence in Freiberg) in the whole Kutná Hora ore district occur mostly on independent younger structures (Ag-Sb sequence IIIa) within the vein system; marked differences between the southern (dominant stage III (i.e.'eb' and 'eq' ore type), weaker stage II ('kb') and northern lodes (dominant stage I and II ('kb'), weaker stage III ('eq') are primarily caused by a different geological (petrological, tectonic) structure of both parts [26]. Bernard and Žák [88] suggested that mineralization of Kutná Hora ore district generally originated at high temperatures (430 ± 80 • C + 'kb' stage); younger parts of the mineralization ('eb/eq' stage) were colder (< 190 • C; [89]).
According to Seifert and Sandmann [29] an analogous Ag-Sb mineralization from the Freiberg district ('eb' ore type) originated at temperatures between 300-120 • C. They also mention possible mineralogical and geochemical similarities to epithermal-style Ag-Au mineralization [90,91]. The similarity of the studied Ag-Sb mineralization from southern "silver-rich" lodes of the Kutná Hora ore district with the 'eb' ore type of the Freiberg district is highlighted by the newly discovered germanium-bearing mineral argyrodite and by Au and Se presence in Kutná Hora correlating with the argyrodite occurrence and locally increased Au and Se contents in 'eb' ores of the Freiberg district [29].
The character of the discovered selenium mineralization (i.e., increased selenium contents in Agand Pb-Sb sulfosalts, the occurrence of minerals of galena -clausthalite solid solution, and Se-rich acanthite, aguilarite and naumannite) indicates the formation from hydrothermal fluids with f O2 slightly above or close to hematite -magnetite buffer and the f Se2 /f S2 ratio close to unity. The presence of minerals of galena -clausthalite solid solution shows that the upper values of the f Se2 /f S2 ratio were more likely controlled by the galena -clausthalite buffer, which is still close to unity [92,93]. The occurrence of naumannite and acanthite which was deposited together with silver and Ag-sulfosalts requires conditions close to the native Ag-naumannite + acanthite invariant point [93,94]. Together with observed minerals of the galena -clausthalite solid solution it is possible to define a f Se2 range of −23 to −26 and a f S2 range of −21 to −22, respectively [93,94]. These values correspond very well with conditions published for selenide-bearing Au-Ag epithermal deposits by Simon et al. [93]. Although Kutná Hora ore district including Anthony of Padua mine is not a volcanic low-sulfidation epithermal deposit, the studied mineralization shows many similar features.
The source of selenium is probably in the bodies of (meta)ultrabasic rocks (serpentinites) frequently found by boreholes in southern "silver" lodes both south of town, as well as in its historic centre. The topomineral properties of these rocks may enable to pre-concentrate selenium which was released into hydrothermal fluids during tectonic events. The amphibolite from the quarry of Markovice, 10 km SE of Kutná Hora, known up to now only for the occurrence of zeolites, was recently found to contain selenides, tellurides and native tellurium [95,96]. The origin of selenides and tellurides from this locality is assumed to be related to (meta)ultrabasic rocks cutting through amphibolite rocks. A similar situation is also known from the northern part of the Kongsberg deposit, Norway [97]. (8) The source of seleniumin Kutná Hora is probably related to the bodies of (meta)ultrabasics (serpentinites) frequently found by boreholes in southern "silver" lodes both south of town and in its historic centre. The topomineral properties of these rocks may enable to pre-concentrate selenium which was released into hydrothermal fluids during tectonic events.