First data on rare earth mineralization in acid rock varieties of the Shatak complex (Southern Urals)

Abstract

Research subject. Acid rock varieties of the Shatak complex were studied. Materials and methods. The reseach object included the previously unknown abundant mineralization represented by rare earth minerals. The concentration of petrogenic oxides was determined by the X-ray fluorescence method at the IG UFRC RAS (Ufa) using a VRA-30 spectrometer (Carl Zeiss, Germany) with an X-ray tube with a W-anode (30 kV, 40 mA). The amount of rare earth elements in the rocks of the studied area was determined by the ICP-MS method at the Central Research Institute of VSEGEI (St. Petersburg). The mineralogy was studied using a Tescan Vega Compact scanning electron microscope equipped with an Xplorer Oxford Instruments energy-dispersive analyzer (IG UFRC RAS, Ufa). Results. The studied rocks were diverse in chemical composition, varying from alkaline varieties (trachydacites) to low-alkaline rhyolites. These rocks belong to a highalumina type characterized by potassium specialization and a low agpaitic coefficient. It is assumed that the felsic varieties are subvolcanic formations, and the term “rhyolites” in this case characterizes the chemical composition of the rocks, but not their genesis. The amount of rare earth elements in the studied rocks is subject to significant fluctuations, varying from 60.81 g/t to 1625.39 g/t; moreover, their distribution is characterized by significant differentiation. In general, the rocks belong to a contrasting basalt-rhyolitic series, and their genesis is due to the differentiation of magma in the intermediate chamber. Numerous rare-earth minerals were found in the rocks, inlcuding allanite-(Ce), monazite-(Ce), monazite-(La), nioboeshinit-(Y), aeschinite-(Y), talena-(Dy), talena-(Nd), synchisite-(Ce) and Ce–La–Fe oxide. Conclusions. The presence of paragenetic associations of rare-earth minerals, such as allanite-(Ce) + aeschinite-(Y) + nioboaeschinite-(Y) and allanite-(Ce) + talena-(Dy) + talena-(Nd), indicate the formation of rare-earth mineralization in the course of a single process. The described type of mineralization has no analogues on the western slope of the Southern Urals, which substantiates the need for further research.