Metallogenic characteristics and genesis of the Tengchong sandstone-type uranium deposit.

Tengchong is the first area in China where the ground leaching experiment of sandstone type uranium ore has made a breakthrough, but the origin of uranium ore is still controversial. This paper takes the core of 10 boreholes constructed in Hanbazhai area of Longchuanjiang Basin and Langpuzhai area of Lianghe Basin as the main research materials. Through the research of core sedimentary facies recording, geochemical analysis and electron probe test, it is concluded that: Uranium is mostly adsorbed in Hanbazhai area, and the uranium minerals are mainly nano scale unnamed minerals with chemical formula generally close to Ca₂U₄(SiO₄)₃(PO₄)_3. Uranium mineralization is controlled by "fault-hydrothermal- bottom-organic rich layer". Uranium in Langpuzhai area is mostly in adsorbed state and form of uranium minerals, such as uranophenite, calcium-uranite, uranite, pitchblende, and uranium-titanite. Uranium mineralization is influenced by the "fault-hydrothermal-bottom-rich organic matter layer" and the emplacement of basic rocks (veins). it is also found that uranium is not only still being enriched and metallogenic in the shallow strata strong reduction zone by deep reducing fluid transport along the fault, but also that uranium mineralization is basically coupled with the basic volcanic rocks (veins) with the geochemical characteristics of intraplate basalt. Combined with the preliminary understanding that the Li-U-Au symbiont enrichment in Tengchong hot spring indicates that there may be "modern mantle plume" in Tengchong, it is proposed that the sandstone type uranium deposits in Tengchong may belong to "Earth core source - mantle plume" origin. i. e., the nature uranium in the outer core in the form of uranium hydride or uranium alloy hydride upward migration along the mantle plume, shallow fault hydrothermal (reduction fluid) and basic rock (vein) introduction, enrichment and mineralization in the favorable structure-lithology position.