| The controlling factors of uranium mineralization in the sedimentary and key metallogenic stages of the paleo-valley area in the central part of Erlian Basin are analyzed by using various geological indicators.Starting from the synsedimentary and metallogenic stages,the characteristics of depression stage and the mechanism of structural control of uranium reservoir development are analyzed.The restraints of structural inversion and denudation on uranium mineralization during metallogenic stage are analyzed and their regularities are analyzed.This paper summarizes the genesis and relationship of several uranium deposits in the uranium ore belt,and establishes a uranium metallogenic model controlled by tectonics.To lay a foundation for revealing a new uranium metallogenic model and enriching the geological theory of sandstone-type uranium deposits,it is of great significance for expanding the search for similar types of uranium deposits.1.The study shows that the central part of Erlian Basin has experienced four stages of evolution:Early-Middle Jurassic rifting stage,late Jurassic-Alshan formation episode I rifting stage,Tengger-Saihantala formation episode II rifting stage,post-Cretaceous thermal subsidence stage and late Paleogene-Neogene rifting stage.The Saihantala Formation is at the end of Tengger-Saihan rift episode II,which is an important stage of structural transformation.It has the characteristics of weak fault depression,symmetrical deposit,low accommodation space,rapid filling,overburden deposit and material source system changing from lateral to vertical.It controls large-scale alluvial-river,large-scale braided river-braided delta uranium ore-forming sand of Saihantala Formation.Body development.In the central part of Erlian Basin,there are mainly single-fault super-fault and warping-fault structural styles.The structural landform of type A in series is the dominant geomorphic condition for sand body development.2.According to lithostratigraphic characteristics,regional lithostratigraphic structure characteristics,age discrimination of biostratigraphy,paleomagnetism synthesis and sequence stratigraphy comprehensive analysis,the uranium-producing horizon of Bayan Ura uranium field is Saihantala Formation,and the main horizon of Bayan Ura uranium field is the upper Seihantala Formation.It is considered that the lower Seihantala Formation and the upper Seihantala Formation are three-level sequences.Three first-level marker layers and five second-level marker layers were identified.3.Through the compilation of a series of sand dispersion system maps,it is revealed that the"belt"sand bodies of the Saihantala Formation in the central Erlian Basin are the combination of multiple provenance systems;the"belt"sand bodies of the Saihantala Formation are the residual sand bodies after erosion;the"lateral"provenances are actually the main provenance directions of the"belt"sand bodies,not the"lateral recharge"provenances;and the multi-provenances and"lateral recharge"provenances of the Saihantala Formation.The characteristics of denudation residues actually reflect the characteristics of the Saihantala Formation in the Erlian Basin,and the area where the"lateral"provenances overlap with the axial sand body is an important part of mineralization.Braided River and braided river delta depositional systems are mainly developed in the upper part of Saihantala Formation.4.Erlian fault depression basin is a residual denudation basin after sedimentation of Saihantala Formation in Lower Cretaceous,which has not only uplifted and denuded as a whole,but also reversed the main faults.The Saihantala Formation in Bayanwula area has been denuded intensely,and the phreatic-interlayer oxidation zone and uranium mineralization have been developed in the remaining Saihantala Formation.The main contribution of inversion faults to uranium mineralization in Bayanwula area lies in the formation of structural slopes on one side of the faults,and the denudation of large-scale sand bodies in the upper part of Saihantala Formation exposed to the surface,forming a complete uranium metallogenic system and uranium mineralization.5.Uranium ore bodies of industrial value in Bayanwula area occur in the lower system tract of the upper Saihantala Formation,and a small amount occurs in the lower Seihantala Formation sequence.There are three small sequences in the upper section of Saihantala Formation in Bayanwula area.Uranium mineralization is mainly concentrated in small sequence Ps1 and Ps2.According to the law reflected by sand dispersion system chart and conglomerate thickness chart,the optimum uranium metallogenic location is that the sand body becomes finer and thinner,the sand content changes,and the lithology changes from coarser to finer.The Bayanwula deposit and its periphery are mainly braided river delta plain deposits,in which the main braided distributary channel,secondary braided distributary channel and interdistributary bay can be identified.Industrial uranium ore holes in the deposit are mainly distributed at the intersection of the main braided channel and the secondary braided distributary channel.6.The Bayanwula deposit is related to the phreatic-interlayer oxidation zone caused by tectonic slope and denudation formed by late uplift and tectonic inversion.During the Late Cretaceous-Eocene,the Saihantala Formation suffered from denudation for a long time,weathering denudation and leaching,which resulted in the formation of denudation zones and phreatic-interlayer oxidation zones.In the Saihantala Formation,the precipitation of uranium is related to organic matter,pyrite and other reducing media.The main carriers of sandstone-type uranium deposits are grain size pore of sand body and adsorption of organic matter.The distribution area of industrial ore holes corresponds well with the coal seam in the lower section of Saihantala Formation.The main types of kerogen in Bayanwula deposit are type III and type IV,which should be terrestrial plant origin and have low S content.There is no characteristic of organic matter participating in mineralization caused by oil and gas spillover.Therefore,the main reducing medium of Bayanwula deposit should come from strata themselves.The heterogeneity of sand body and the change of reducing medium caused by the phase transformation of sedimentary environment are the most fundamental factors for uranium mineralization.7.During the metallogenic period?K2-E1?in Bayanwula area,the strata of Saihantala Formation were denuded as a whole.Because of the reversal of F1 fracture,a large area of sand body in the upper part of Saihantala Formation was exposed to the surface,and a phreatic-interlayer oxidation zone developed and mined.After the interruption of sedimentation,the mudstone of Eocene Erding Manha Formation?E2y?of Paleogene was deposited and covered,which played an important role in mineral preservation. |
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