Известия Томского политехнического университета: Инжиниринг георесурсов (May 2019)
Genetic features of native iron and products of its oxidation in devonian granitoids of the Aleysk-Zmeinogorsky complex (north-western area of Rudny Altai)
Abstract
The relevance of researching the native iron-ore mineral formation is determined by identifying mineralogical and physical and chemical criteria for potential ore bearing of the polyphase Aleysk-Zmeinogorsky granitoid complex which occupies the most north-western part of the Russian Rudny Altai territory. The aim of the research is a detail and comprehensive description of morphology, chemical composition, occurrence, paragenesis and time of native iron metallides segregation in the course of evolutionary development of a fluid-magmatic system. Research methods include conventional mineralogical and petropgraphical methods, as well as mineragraphic methods targeting at investigation of the accessory native iron and its associated minerals obtained from crashed granitoid samples according to a common procedure. To carry out analytical studies, the author used the X-ray spectral analysis methods performed on an electronic scanning microscope JSM-6510LV (Jeol Ltd) fitted with an energy-dispersive spectrometer INCA Energy 350+ in a laboratory of the Geology and Mineralogy Institute of the Siberian branch of the Russian Academy of Science (Novosibirsk) (by an analyst M. V. Khlestov). Research outcomes. The author identified the presence and distribution of accessory native iron microspheres in rocks of successive phases of the granitoid complex formation and singled out two microsphere varieties by chemical composition, i. e. iron with Ti and Mn impurities and pure iron (ferrite); thoroughly studied the structure, chemical composition and breakdown structure of a xenogenic crystal of ferrokaersutite genetically related to a metalized gabbroid silicate melt supplied to the hypabyssal crystallization chamber by plagiogranitic melt in plagiogranitic rocks of the main intrusion phase. Paragenetic associations of native iron, as well as location and conditions of native Fe phase segregation out of a silicate melt of the native phase was identified. Conclusions. A liquation separation of a metallic phase of iron, including iron with Ti, Mn impurities, clearly manifested itself at an early magmatic stage of a gabbroid melt formation in an intermediate vent under the effect of a reducing intratelluric hydrogen-carbonic fluid together with active action of potassium. The limited occurrence of native Fe globules in derived granitoid melts, especially in finishing leucogranit differentiates, are related to weakening the reducing character of mantle fluids which are displaced by the hyperalkaline fluids with increased potential oxygen. The obtained new data have high petrological importance and practical value for identifying a potential productivity of a granitoid complex for iron-titanium ore mineralization.
