| The Bayinhanggai area is located at the north-western margin of the Chuanjing Depression in the Erlian Basin,with the Solunshan Uplift to the north,the Baoyintu Uplift to the west,and the Bayinhanggai Bulge to the south.The study area is located in the combined part of the Erlian Basin and Bayin Gobi Basin,where several large and medium-sized sandstone-type uranium deposits have been found,showing favorable mineralization conditions.In this paper,based on the systematic collection and analysis of previous data and results,detailed core observation and description,logging data analysis and controlled-source audio geomagnetic measurements,combined with the research results of previous spore powder samples,the stratigraphy of the Saihan Formation has been redefined and delineated,and the lithology,rock geochemical environment and stratigraphic characteristics have been analyzed.The spatial distribution of stratigraphy,distribution of oxidation zones and sand bodies,as well as their constraints on sandstone uranium ore formation,were clarified.The main understanding and conclusions are as follows.1.Uranium source conditions and Th/U values indicate high uranium content in the eroded source area,indicating significant uranium migration.Petrographic analysis shows medium sortability and medium structural maturity of the sandstone lithologies of the Saihan Formation,reflecting strong hydrodynamics and fluvial deposition on a braided river delta.2.Based on the results of spodumene analysis,the target layer of the drilling encounter in the study area is mainly the lower section of the Lower Cretaceous Saihan Formation,of which the third sublayer of the lower section of the Saihan Formation is the target layer of the mineralization search.The resistivity of the target sandstone layer ranges from 10 to 26?·m,and the controlled source audio geomagnetic bathymetry profile shows the third electrical layer,which is lenticularly distributed as medium-resistance clumps on the cross-sectional map,and the inverse resistivity is 8 to 25?·m,which is comprehensively interpreted as the deltaic sand body of the lower section of the Saihan Formation.3.Stratigraphic parameters such as thickness,sand content and oxidation rate of the borehole sands in the study area were counted and their contours were drawn.The sand body is spreading in the north-east and north-east direction.The variation of sand-bearing rate in this area is characterized by a slow south-north steepness and a slow east-west steepness.The braided river deltaic plain subphase is mainly developed along the side near the southern edge of the Bayinhangai occultation project,and large-scale braided river channels,transgressive banks and abandoned river channel deposits are developed.The lower oxidized zone of the Saihan Group is mainly distributed in the south of Bayinhangai and on the side of the Bayinhangai occultation,forming a redox transition zone of several kilometers wide at the front of each oxidized zone,spreading in a north-east,north-east-east and east-west direction.4.The uranium mineralization anomalies are concentrated in Bayinhangai and Dezhis sections,where the average thickness of the sand body is 80?160m,the sand content is 50%?80%,and the oxidation rate is between 30%?80% for easy mineralization.The matching of uranium mineralization main factors such as uranium source,sand body and post-generation oxidation are the main factors limiting the mineralization of sandstone uranium in the study area.5.The sandstone uranium ore formation model of diving to interlayer oxidation and diving to oxidation in Bayinhangai area was established,and the ore formation potential of Bayinhangai and Deiris areas were compared,and the analysis of favorable ore formation factors such as thickness of sand body,sand content rate and oxidation rate contour interval were integrated,and three ore formation prospective areas such as southwest of Zhunga Shun,north of Deiris and south of Ulan Hodug were pointed out as the key directions for the next uranium exploration. |
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