Analysis Of Metallogenic Conditions Of Sandstone-type Uranium Deposits Of Longchuanjiang Basin In Western Yunnan

The Longchuanjiang basin is located on the Tengchong microplate in western Yunnan and is a cenozoic basin with great prospecting potential in southwestern china.So far,several medium-small sandstone uranium deposits have been discovered in the Longchuanjiang basin,such as 381,382,384,50,and 506 deposits.However,due to the remoteness of the basin,its proximity to national borders,and its complicated topography,the overall degree of exploration is relatively low.In recent years,with the advancement of the exploration of sandstone-type uranium deposits in southwestern china,a certain amount of investment has been made in the basin's ore prospecting work,and the study of the ore-forming conditions of the basin's sandstone-type uranium deposits has continued to deepen.This thesis collects and organizes data systematically,field geological surveys,borehole core cataloging and sampling,indoor microscope physical property analysis,and electronic probe micro-area composition analysis.The second stage of the Neogene Mangbang formation in the prospecting target layer of sandstone-type uranium deposits The layer(N₂m^1-2)has been studied in terms of sedimentary facies and microfacies,sandstone-type rock types,diagenesis-metagenetic alteration,and the existence form of uranium.Based on the tectonic evolution,petrographic paleogeography,uranium source,paleoclimate,and hydrodynamic conditions of the study area,the controlling factors of sandstone-type uranium ore deposits were discussed,the ore-forming laws were summarized,and ore-forming models were established.The following achievements have been achieved:(1)Observation in the field,analysis of measured geological sections,combined with borehole logging curves and core observation analysis analysis,it is concluded that the second layer(N₂m^1-2)of the sand body in the lower section of the Mangbang formation,which is the main ore-bearing layer in the Longchuanjiang basin,mainly develops fans.Delta-lake sedimentary system.From the edge of the basin to the center of the basin,fan delta plains,fan delta fronts,front fan deltas,shallow lakes,and other subfacies are developed in turn.The lakes in the center of the basin are relatively small,and the fan delta plains and the leading margins are favorable sand bodies formation environment.(2)According to field surveys,drilling catalogs,and core observation statistics,it is concluded that the second layer(N₂m^1-2)of the lower section of the Mangbang formation in the Longchuanjiang basin for ore prospecting targets has low component maturity and structural maturity.The main types are sandstone and feldspar debris It is dominated by complex sandstones,with a small amount of litho-quartz complex sandstones,which have near-source sedimentary characteristics.The source of sandstone mainly comes from the uplift orogenic belt around the basin,and part of it comes from the arc source area of magma island.(3)The existing forms of uranium in the uranium ore of the Longchuanjiang basin are mainly independent uranium minerals,that is,two types of uranium stone and pitch uranium ore.They are mainly distributed in the form of granular,fine-grained,gelatinous,etc.around pyrite,between detrital particles,or adsorbed on the surface of clay minerals.Secondly,there are uranium gangue,monazite and other uranium-containing minerals in the form of heavy minerals.The formation of uranium minerals is closely related to reducing substances such as pyrite and organic matter.In short,by comprehensively analyzing the petrological characteristics of sandstone petrophysical characteristics,uranium mineral characteristics,comprehensive basin tectonic evolution,paleoclimatic conditions,sand body sedimentary environment,hydrogeological conditions,uranium source conditions,and redox environment in the Longchuanjiang basin.Analysis shows that the Longchuanjiang basin has good ore-forming conditions and prospecting prospects for sandstone-type uranium deposits.