CONTINENTAL IRONSTONES OF THE KIREEVSK OCCURRENCE (OB-TYM DEPRESSION): MINERAL FORMATION AND GEOCHEMISTRY

Abstract

The relevance of the work consists in absence of a multifactor model of a change of geochemical iron cycle in the continental environment led to accumulation of iron-bearing sediments. The scientific issue covers questions about formation conditions of iron precipitation in Pliocene continental deposits of Ob-Tym depression. The main aim of this work is to reveal mineralogical and geochemical features of ironstone sedimentation on the example of Pliocene Kireevsk occurrence to assess metal sources, the mechanisms of their migration and mineral formation. Methods include field observation, petrographic analysis, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), X-ray fluorescence analysis (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). Results. Siderite and chamosite are predominate in situ minerals of channel ironstone deposit. They indicate to suboxic conditions of mineral formation in the alluvial plain. The major metals precipitation, including iron, could occur in the stable suboxic conditions in the bottom environment due to a carbon dioxide production. This depends on a microbial decomposition of detrital organic matter regularly inputted by river watercourses. This factor indicates the aleurosand accumulation with ironstone in waterlogged lakes conditions. The studied continental ironstone occurrence belongs to the interfluve of the Ob and Tom rivers, which is located in the eastern part of the West Siberian Plate. The Ob-Tuim lowland completely inherits the Mesozoic-Cenozoic negative structure – the Ust-Tym uplift. The ironstones are localized in the sedimentary sequence of the Kireevsk ore deposit. Iron-bearing layers occur at the top of the Kochkov Formation, which is composed of Neogene and Pleistocene sediments.

Keywords

• ironstones
• channel deposits
• authigenic minerals
• mineral formation
• geochemistry
• western siberia