Abstract
Stara Planina (also known as the Balkan mountain range) is known for numerous occurrences and deposits of uranium and associated radionuclides. It is also famous for its geodiversity. The geologic framework is highly complex. The mountain is situated between the latitudes of 43° and 44° N and the longitudes from 22°16′ to 23°00′ E. Uranium exploration and radioactivity testing on Stara Planina began back in 1948. Uranium has also been mined in the zone of Kalna, within the Janja granite intrusive. The naturally radioactive geologic units of Stara Planina are presented in detail in this paper. The main sources of radioactivity on Stara Planina can be classified as: 1. Granitic endogenous—syngenetic–epigenetic deposits and occurrences; 2. Metamorphogenic—syngenetic; and 3. Sedimentary, including occurrences of uranium deposition and fluctuation caused by water in different types of sedimentary rocks formed in a continental setting, which could be classified under epigenetic types. The area of Stara Planina with increased radioactivity (higher than 200 cps), measured by airborne gamma spectrometry, is about 380 square kilometers. The highest values of measured radioactivity and uranium grade were obtained from a sample taken from the Mezdreja uranium mine tailing dump, where 226Ra measures 2600 ± 100 Bq/kg and the uranium grade is from 76.54 to 77.65 ppm U. The highest uranium (and lead) concentration, among all samples, is measured in graphitic schist with high concentrations of organic (graphitic) material from the Inovska Series—99.47 ppm U and 107.69 ppm Pb. Thorium related radioactivity is the highest in granite samples from the Janja granite in the vicinity of the Mezdreja granite mine and the Gabrovnica granite mine tailing dump, and it is the same—250 ± 10 Bq/kg for 232Th, while the thorium grade varies from 30.82 to 60.27 ppm Th. In gray siltstones with a small amount of organic material, the highest radioactivity is related to potassium—2080 ± 90 Bq/kg for 40K.
Highlights
The objective of this paper is to provide an overview of the naturally radioactive geologic units in known areas of Stara Planina
In gray siltstones with a small amount of organic material, the highest radioactivity is related to potassium—2080 ± 90 Bq/kg for 40 K
The objective is to provide answers to the questions: which are the particular geologic units? What are their petrologic, mineralogic, geochemical and radiometric characteristics? How did they come about? The paper presents the outcomes of research conducted in the part of Stara Planina in Serbia
Summary
The objective of this paper is to provide an overview of the naturally radioactive geologic units in known areas of Stara Planina ( known as the Balkan mountain range). Mezdreja and Gabrovnica (abandoned mines in the Janja granites), graphitic schists of the Paleozoic “Inovo Series”, and early Triassic sedimentary units in the Dojkinci–Jelovica area. These occurrences are known and have been described in papers, reports and books, largely from the perspective of Minerals 2018, 8, 6; doi:10.3390/min8010006 www.mdpi.com/journal/minerals. The origin of natural radioactivity is from various rocks enriched with radio elements (uranium 238 and uranium 235, thorium 232 and potassium 40), generated in stars and from cosmic rays [1].
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