Markers and Genetic Mechanisms of Primary and Epigenetic Oxidation of an Aeolian Depositional System of the Luohandong Formation, Ordos Basin

Abstract

Uranium exploration breakthrough was extremely rare in an aeolian depositional system. In order to know the complicate characteristics of oxidation associated closely with uranium mineralization in the aeolian depositional system, petrology and mineralogy markers of the oxidation and its genetic mechanisms are identified and illustrated by fieldwork, thin section analysis and scanning electron microscopy test, based on 2 field outcrops in Zhenyuan County in the southwest of the Tianhuan depression in the Ordos Basin and the core of 2 wells in the north and south of Ordos Basin. The results showed: the typical macroscopic indicator of primary oxidation was the red fine sediments in the aeolian interdune with a thickness of 10–50 cm, and the microscopic characteristics of primary oxidation were the minerals such as hematite, ilmenite, and the irony matrix rich in fine-grained dolomite and biotite; the phreatic oxidation was manifested as the red sandstone with limonite horizontal layer with a thickness of 1–4 cm and a width of 60 cm–1 m, and the circular limonite nodules with a diameter of 3–7 cm, in which there was intergranular limonite cement; the interlayer oxidation was characterized by lenticular tongue and tapered red sandstone with a length of 1–10 m and a width of 10 cm–5 m, in which detrital particles are coated with hematite and hematite was distributed inside the rhombus dolomite. The paleoclimate of the sedimentary period, the water-table movement and the pore and permeability conditions of the sand body were the key factors for the formation of different oxidation types in the aeolian depositional system.

Keywords

Ordos Basin / aeolian depositional system / primary oxidation / epigenetic oxidation / sandstone-type uranium exploration / ore deoposit geology

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