The northern zone of the abandoned Sb–As–Tl–Au Allchar deposit in North Macedonia is characterized by high concentrations of thallium (Tl), iron (Fe) and arsenic (As), which are distributed among mining waste, technosols and soils (Djordjevic et al., 2021; Vanek et al., 2024). The high concentrations of Tl and As in carbonated, buffered environments have led to the formation of secondary minerals that are more widespread than is currently documented. Therefore, a detailed assessment of Tl- and As-rich legacy tailings is important to understand the behavior of these pollutants, as they are exposed to changes in conditions, which can play an important role in reducing the dispersion of Tl and As from sources of contamination. As part of the current study, we have begun investigating orpiment-rich tailings near Adit 25 in the northern part of the Allchar deposit. Tailings material was collected at four different areas of the tailings and bulk chemical, and mineralogical analyses were performed using powder X-ray diffraction (PXRD), Raman spectroscopy and inductively coupled plasma mass spectrometry (ICP- MS). The preliminary results indicate the following: (i) Tl is present in amounts ranging from 210 to 3,950 ppm, with an average value of 2,035 ppm; (ii) As is present in amounts ranging from 6,750 to 210,000 ppm, with an average value of 124,550 ppm; (iii) Fe is present in amounts ranging from 6,500 to 50,500 ppm, with an average value of 34,700 ppm. Locally the samples show elevated concentrations of Sb (up to 1,150 ppm) and Hg (up to a maximum of 500 ppm). The main sources of As are the primary minerals, orpiment (As2S3) and realgar (As4S4), followed by secondary minerals such as scorodite (FeAsO4·H2O), minor Fe-sulfate arsenates and calcium arsenates. The sources of Fe are pyrite (FeS2), marcasite (FeS2), goethite (Fe3+O(OH)), scorodite, amorphous Fe-oxides, as well as minor Fe-sulfate arsenates. The major sources of Tl are Tl-bearing sulfosalts, such as vrbaite (Hg3Tl4As8Sb2S20) and simonite (TlHgAs3S6), which also serves as the sources of antimony (Sb) and mercury (Hg). Further dominant phases are gypsum, dolomite, quartz, calcite, muscovite and kaolinite, and barite in the heavy fraction (density >2.9 g/cm3). While the present study is based on bulk chemical and mineralogical analyses, ongoing and planned micro-, nano-scale electron microscopy and pH-leaching experiments will extend these results by investigating the interactions between Tl and As with the initial surface mineralogy, and how these were altered into the current metastable phases.