Литосфера (Jun 2019)
Trace-elements in minerals from unusual rocks of the Southern Urals
Abstract
Research subject. This articles presents the data obtained in the course of 75 analytical studies on a wide range of minerals (amphiboles, pyroxenes, garnets, spinels, olivines, anorthites, corundums, epidotes, apatites, clinochlore, dolomite, calcite, zircon) contained in igneous and metamorphic Southern Urals rocks. In addition, information is provided about the content of trace elements, including rare earth (REE) ones, in these rocks. The data on the content of trace elements in some minerals are presented for the first time (höegbomite, sapphirine, zoisite, clinozoisite, gedrite, cummingtonite, anthophyllite, potassium-magnesiohastingsite). Materials and methods. A petrographic analysis of rocks containing the minerals under study was carried out. A particular attention was paid to petrographic analysis of rocks containing the minerals under study was carried out. A particular attention was paid to “fresh” rocks, containing the mineral under study which rarely occur in the Urals. These rocks feature inclusions of serpentinite melange in the form of plates and lenses among the metamorphic strata (schists, gneisses, and amphibolites) and are characterized by the preservation of primary structures, relative chemical homogeneity, as well as the presence of simultaneous growth surfaces between most minerals. Of particular research interest were minerals from rocks, the composition of which had been relatively poorly studied (pyroxene-amphibole anorthite gabbro and gabbro-amphibolites, scapolite rocks, hornblendite, gedrite-cummingtonite-anthophyllitic crystallo-schists and amphibolites, ore-less carbonatites). The composition of mineral samples was determined using a scanning microscope REMMA-202 M equipped with an energy dispersive console and a mass-spectrometer Agilent 7700x (ICP-MS and LA-ICP-MS methods). Results. Petrographic characteristics of the rocks containing the minerals under study are given. The geographical coordinates of locations, where mineral sampling was performed, are provided. The content of trace elements is shown to vary greatly within related species of minerals (amphiboles, garnets, pyroxenes, olivines, epidotes, spinels, mica, etc.), with the fluctuations being independent of the alkalinity of host rocks or their geological nature.Conclusions. For the first time, a significant role of zoisite and clinozoisite in the process of concentrating trace elements, including REE, has been revealed. The role of apatite as one of the main mineral concentrators of REE has not been confirmed either in the main and ultrabasic rocks, or in some calcite-dolomite carbonatites.
Keywords
