Typomorphic features of magnetite from tomtor massif camaphorites

Abstract

Background. The paper presents new data on the material composition and formation conditions of apatite-magnetite rocks (phoscorite and camaphorites) from the Onkuchakh deposit within the Tomtor massif drawing on the study into the typomorphic features of magnetite.Aim. To study the morphology, chemical composition, and relations of magnetite with associated minerals in apatite-magnetite rocks from the Onkuchakh deposit (Tomtor massif).Materials and methods. The study employed core samples measuring 177 m in total length (borehole No. 801, Onkuchakh field, Tomtor massif). In order to determine the composition of recovered minerals, the following instruments were used: JEOL JXA-8230 Electron Probe Microanalyzer (ALROSA, Mirny, Russia); TESCAN MIRA 3 LMU field emission scanning electron microscope equipped with an Oxford Instruments INCA Energy 450+ energy dispersive spectrometer with an XMax-80 detector (ALROSA, Mirny; V. S. Sobolev Institute of Geology and Mineralogy, SB RAS). The measurements were performed according to a standard procedure: accelerating voltage — 20 kV; current — 1 nA; counting time — from 60 s; probe size — 2 μm. Instrument calibration was carried out using a set of characterized artificial compounds and natural minerals; instrument stability was confirmed by measuring Co line intensity.Results. The authors identified the textural and structural features of magnetite ores, as well as ascertaining their relations with the areas of camaphorites characterized by different material composition and host rocks. The impact of superimposed hydrothermal processes was determined. In addition, a detailed morphological characterization was provided for magnetite found to comprise two generations: primary magmatic magnetite and that transformed under the influence of superimposed processes. Finally, representative data on the chemical composition of magnetite were obtained.Conclusion. It is concluded that magnetite is formed through a magmatic process involving crystallization differentiation. The occurrence of noble metal is shown to be related to hydrothermal processes superimposed on magnetite ores. The role of apatite-magnetite ores in the formation of the supergene complex — ferrous phosphate lateritic weathering crusts of the Tomtor massif — is confirmed. It is recommended to consider camaphorites from the Tomtor massif as naturally alloyed iron ores potentially extracted along with a number of valuable components.