An Analysis Of Lithofacies Palaeogeography Of Doushantuo Formation-Dengying Formation And Manganese-forming Factors In Chengkou Area

Manganese mining area of Chengkou County belongs to national major metallogenic belt of manganese ore resources.However,there is few orebody or shallow orebody on surface now,which leads market into a dilemma.What's more,the contradiction between supply and demand becomes increasingly prominent,and geological prospecting work has entered into a hard phase.In order to fulfill the requirement of local economic development for mineral resources,we should not only improve the degree of manganiferous ore processing,but also deeply understand the manganese-forming factors,ore-controlling rules,etc.,so that we can give guidance to mineral exploration.This paper is guided by theory of sedimentary petrology,sequence stratigraphy,lithofacies paleogeography,metallogeny,etc.,and with the emphasis on typical mining area and nearby areas in Chengkou,Chongqing.Through the combination of large-scale field measured section and collecting data,the field macroscopic monitoring and indoor micro-analysis,this paper has achieved following results:By a comprehensive analysis of outcrop section,drilling,and etc.,there are some differences between formation lithology and thickness,which in different parts and periods have different results.The Sinian Guanyinya Formation-Dengying Formation has 2 sedimentary systems.The Guanyinya Formation belongs to Coast-Neritic sedimentary systems.In these systems,the coast sedimentary system develops into ice water littoral facies,and the neritic sedimentary system develops into ice water epicontinental neritic facies.The Doushantuo Formation-Dengying Formation belongs to Coast-Ramp-Platform sedimentary systems.In these systems,the coast sedimentary system develops into the tidal flat facies of terrigenous clast,and the ramp sedimentary system develops into carbonate ramp,furthermore,the platform sedimentary system develops into restricted platform tidal flat facies,lagoonal facies,and inter-platform basin facies.It will aslo make a detailed partition upon the features of subfacies,microfacies and different sedimentary facies.The manganese ore layer is located in the inter-platform basin facies,restricted platform tidal flat facies and lagoonal facies of the top of Doushantuo Formation.Based on the sequence identification and system tract division of Guanyinya Formation-Dengying Formation in Chengkou area,there is a supersequence(ZSS1)and 4 third-order sequence(ZSQ1-ZSQ4).And it gives a detailed discussion about each third-order sequence specifically,the sequence characteristics,and the phenomenon that manganese ore is mainly situated in high stand system.Setting ZSQ2-ZSQ4(TST)and ZSQ4(RST)as graphics processing unit,compile some sketches which describe the lithofacies palaeogeography of Early-Late Doushantuoian and Late Doushantuoian – Early stage of Dengying in experimental area by using compression algorithm and the representation of dominant sedimentary facies separately.In Early-Late Doushantuoian,the experimental area mainly belongs to epicontinental marginal sea,in which the Gaopinliang area belongs to the tidal flat facies deposition of theterrigenous clast with higher ground.The Daduxi – Xiuqi area mainly develops into the alternate soaking of inter-platform basin and restricted subtidal platform.Gaoyan area develops into deep-water deposit basin.Mingyue area mainly develops into deep-water inter-platform basin with restricted tidal flat facies.Longtian village belongs to shelf deposit – transition inter-platform basin deposition.And other areas mainly belong to restricted subtidal platform with few inter-platform basin deposition.During the Late Doushantuoian – Early stage of Dengying,the experimental area transform into carbonate epicontinental platform,and the Gaopinliang area becomes the restricted tidal flat facies and mixed tidal flat deposition partly,and the Longtian village becomes platform margin clinothem facies.Besides,the area between Gaopinliang and Longtian village develops into restricted tidal flat facies with deposition.The Mingyue area produces manganese ore in restricted subtidal platform,which is non-dominant deposition.The Gaoyan area produces manganese ore in the slope of inter-platform basin,which is non-dominant deposition.The Dadu Stream – Xiuqi produces manganese ore in lagoon area,which is non-dominant deposition.Based on the above research,this page makes an analysis of manganese ore-forming conditions by combining the different manganese-bearing ore belt and geological characteristics of manganese ore.It turns a result that the Mingyue mining area belongs to the environment of restricted subtidal platform.In this environment,the development of manganese ore is ordinary.It also reflect that the Gaoyan area belongs to the deposit of slope in inter-platform basin,which is good for forming manganese ore deposition,and the manganese in here is abundant.The Late Doushantuoian of Dadu Stream and Xiuqi mining area belong to the lagoon subfacies on restricted platform,which is good for deposition of manganese and phosphorus,and the manganese in here is abundant.The Gaopinliang area belongs to the strandflat,which is bad for the formation of manganese.And lots of terrigenous clasts exist in this place.