| Abstract (english) | The 3rd stop comprises a group of smaller Palaeogene bauxite bodies located in the valley of the Mirna river in Istria, called Minjera bauxites. Compared to other Palaeogene bauxites from Istria, they are characterised by their complete or partial reduction and subsequent pyritization. Such pyritized bauxites have been documented throughout the Jurassic and Palaeogene in the Mediterranean bauxite belt, with the best examples found in Montenegro (DRAGOVIĆ, 1989; RADUSINOVIĆ & PAPADOPOULOS, 2021), Hungary (BARDOSSY, 1982), and Greece (ECONOMOU- ELIOPOULOS et al., 2022; LASKOU & ECONOMOU- ELIOPOULOS, 2007, 2013). This pyritization phase is epigenetic in all these deposits as well as in the Minjera bauxites and is related to the transgression that succeeded the bauxitization phase. This unique grey bauxite from the Minjera locality was mined in the past for the production of alum and vitriol, which were obtained by processing pyritized bauxite. Only the grey bauxite was used as ore, while the mined non-pyritized red bauxite, which occurred in some Minjera bauxites, was left on tailing heaps in the area. Mining in Minjera probably dates back to the 16th century, but was historically documented from 1784 to 1824 (D’AMBROSI, 1926), when the mine was in operation. The Minjera bauxite deposits are of great importance as they are the first locality where bauxite was mined in the world. There are visible differences in the type of mining between the individual bauxite bodies, as many larger bauxite bodies contain adits indicating underground mining, while some of the smaller bauxites do not contain adits and were probably surface mined. Most of the deposits are present as large and sub-vertical canyon-type ore bodies (20–30 m thick), while the rest are smaller (< 5 m thick) and have mainly sinkhole morphology. The main part of the canyon-type deposits is located on the northern side of the Mirna River in this area, while the sinkhole type and smaller canyon-type deposits are found on the southern side, indicating the variability of the palaeotopography during the formation of the Minjera bauxites.. |
