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The beryllium silicate minerals phenakite and bertrandite have been identified in granitic pegmatite dykes of the beryl-columbite subtype of Variscan age (~340−355 Ma), associated with S- to I-type granitic rocks of the Tatric Superunit, Western Carpathians (Slovakia). The two beryllium silicates and associated minerals were characterised by electron microprobe analysis, back-scattered electron petrography and cathodoluminescence imagery, X-ray diffraction and micro-Raman techniques. Phenakite and bertrandite form euhedral-to-anhedral crystals and aggregates in irregular domains and veinlets replacing primary magmatic beryl. A detailed textural study revealed a close genetic association of phenakite and bertrandite with secondary fine-grained quartz, K-feldspar and muscovite. Locally, clay phyllosilicate minerals, (with compositions similar to those of Fe-dominant hydrobiotite, beidellite, nontronite and saponite) occur as the youngest minerals. During the post-magmatic (hydrothermal) stage of the pegmatites, infiltration of aqueous K-bearing fluids at T ≈ 200–400°C resulted in the breakdown of magmatic beryl to secondary assemblages containing phenakite and bertrandite.

The sediment-hosted As-Sb-Tl-Pb +/- Hg +/- Au Janjevo occurrence is located in the southern part of the KizhnicaHajvalia-Badovc ore field, in the Trepca (Trepca) Mineral Belt (TMB) in Kosovo. The As-Sb-Tl-Pb +/- Hg +/- Au mineralization is hosted by Upper Triassic marbles and occurs in the form of quartz-stibnite veins and dolomitized irregular pockets associated with jasperoid rocks. The main sulfide most widespread in the mineralization studied is pyrite which is the main carrier of thallium. A wide range of techniques was used to characterize the geochemistry and textural evolution of pyrite/marcasite from Janjevo: polarized reflected-light microscopy, electron microprobe (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), X-ray powder diffraction (XRPD), MOssbauer spectroscopy, and isotopic studies. The study of 42 thin and polished sections resulted in the identification of 4 generations of pyrite/marcasite. The first generation of pyrite related to the pre-ore stage occurs as framboidal pyrite with different degrees of evolution (Py1a), as well as recrystallized pyrite/marcasite (Py1b). Au-enriched pyrite (Py2) occurs as elongated fibrous aggregates and is genetically associated with the formation of stibnite veins (Sb stage). As-Tl-Sb-Hg pyrite (Py3) forms irregular colloform aggregates which fill the stylolites and also overgrow older generations of pyrite. The youngest generation is represented by marcasite (Py4), which forms euhedral crystals. Co/Ni ratio < 1 in all pyrite/marcasite generations implies a sedimentary fingerprint. On the other hand, delta S-34 isotopic studies confirm a magmatic sulfur source for As-Tl-Sb-Hg pyrite (Py3), as well as co-occurring stibnite and realgar. The most important minor and trace elements in pyrite/marcasite are As (up to 14.1 %), Tl (up to 3.94 %), Sb (up to 3.73 %), and Hg (up to 0.55 %), which are mainly hosted by Py3. In addition to arsenic, thallium, antimony, and mercury, other generations of pyrite show enrichment in Ni, Co, and Cu (framboidal pyrite Py1), Au, and Se (Au-enriched pyrite Py2), and Se (marcasite Py4). The highest gold content of up to 6.08 ppm was recorded at Py2. Studies on Py3 geochemistry confirm the presence of 2Fe(2+) Tl+ + Sb3+ heterovalent substitution in pyrite. As-Tl-Sb-Hg pyrite (Py3) is the main thallium host mineral in the mineralization studied, with significantly less thallium present in the Pb-Sb +/- Tl +/- As sulfosalts. In addition, the high arsenic content of Py3 is due to the presence of arsenic in the form of As1- and As-0 related to amorphous arsenic-rich nanoparticles. The reported Py3 is the best phenomenon of the crystallization of colloform As-Tl-Sb-Hg-rich pyrite under hydrothermal conditions. Pyrite-rich sediment-hosted As-Sb-Tl-Pb +/- Hg +/- Au mineralization from Janjevo is associated with the distal manifestation of a concealed porphyry system.