ORPIMENT MINERALIZATIONS IN TUFFACEOUS DOLOMITES IN ALLCHAR DEPOSIT-SEM-EDS INVESTIGATIONS

Abstract

Ore mineralization of Sb-As-Tl-Au in the Allchar deposit are localized in diferent type of lithological units like a tuffs, dolomites, silicified dolomites and tuffaceous dolomites. The tuffaceous dolomite (probably from the Tertiar) lie discordantly over the Mesozoic basic rocks in the larger part of the north and south-west parts of the region. The appearances are bright-gray, gray-white to bright-brown colored. They are built up finecrystallined dolomite which contains variable quantities od very fine granulated gray-white volcanic ash or tuffaceous material. Tuffaceous dolomites form massive, bright colored sampled which most frequently appear on the east side of the river. Most of them are strongly tectonized and broken, hydrothermaly changed and rather eroded (due to the physical inhomogenicity) and have psefitic structure. The hydrothermally changed appearances are often corroded by the yellow to yellow-brown iron oxides. These massiv appearances show very small signs of stratigraphic relations with the Pretertiary stratigraphic parts. The mentioned appearances discovered in the central parts of the region, north from the antimony holes, clearly points to their yang volcanosedimentary localization. Here, the massiv tuffaceous dolomites contain local intercalations of fine-grinded tuffs, wet ash or volcanic glass. The layers are about 2 cm up to 3 m thick. Stratigraphic thickniss of the tuffaceous dolomites is unknown, but according to the extent of uncovering in the north parts of the region, the thickniss is estimated to be from 100 to 125 m. Investigations by the SEM-EDS technique is concluded that tuaffaceous dolomites are very common lithological unit for ore mineralizations for arsenic and thalium. Tuffaceous dolomites are mainly composed by the grain of dolomites ond grain of volcanic glass-tridimite.

Keywords: Allchar, tuffeceous dolomites, orpiment, volcanic glass