Study On Metallogenic Model Of Nongle Polyhalite Deposit In Sichuan Province And Metallogenic Prediction

As one of the three elements of fertilizer,potash is an important strategic scarce resource to guarantee the steady development of national agricultural production and economy.Polyhalite?K₂SO₄·MgSO₄·2CaSO₄·2H₂O?is a kind of mineral potassium sulfate type,its theoretical potassium?K₂O?up to 15.6%.It is a soluble potassium salt and sulfate mineral.It is usually associated with hard gypsum and rock salt,and can be used directly as composite potash fertilizer.In Sichuan basin,there are abundant polyhalite resources,but it has not been fully exploited for a long time because of its particularity and complexity.Based on this circumstances,this paper studies the metallogenic environment and metallogenic model and summarizes the metallogenic elements through the investigation on the Sichuan Nongle Polyhalite deposit.Based on the comprehensive interpretation of borehole logging data,this paper makes a prediction of the favorable area in the Sichuan basin.It is located in the north part of the north section of Huayingshan anticline,which is located in the south part of the anticline,and is the first of China to be identified as a polyhalogen deposit.The occurrence of polyhalite is the second member of the lower Triassic Jialingjiang Fomation(T₁j^5-2)and the first member of the middle Triassic Leikoupo Fomation(T₂l^1-1).Polyhalite ores are mainly associated with gypsum and anhydrite,a small amount with carbonate?dolomite?.The main types of polyhalite ores are lumps,streaks,laminates,thin layers halogen,clumps of polyhalite,etc.All the polyhalite deposits are stable and stratified,and the boundary between them is clear.The stratification is in parallel with the adjacent paste rock,and the deformation of the fold is synchronized.Therefore,it is concluded that the ore body of the polyhalite is mainly formed by primary sedimentation.At the same time,,there are spots and clumps of polyhalite in the anhydrite,indicating that the sedimentary process is accompanied by the metasomatism.Volcanic eruption occurred during this period,then the formation of sedimentary of potassic bo crumbs tuff?commonly known as"green-bean rocks"?.This provides an important source of metallogenic material?K⁺?for the sedimentary heterohalite during the gypsum deposition process.The polyhalite is buried deep in Sichuan basin,usually between 1000m and3000m.In order to improve the prediction accuracy,we collect the data of oil and gas drilling in Sichuan basin.By summarizing the logging response characteristics of the polyhalite in Sichuan basin,a comprehensive interpretation of the collected data of more than 100 boreholes.The results show that there are 66 boreholes showing the response characteristics of polyhalite.These boreholes are mostly distributed in the central and northeast of the Nanchong salt basin and in the northeast of China,the anticline and the padded salt basin,which indicate the direction of the favorable area for the mineralization of the polyhalite.The arid and hot climate in the early and middle Triassic in Sichuan basin has developed a large basin of salt basins,providing a favorable sedimentary environment for the formation of polyhalite.There are 6 salt periods in the basin,two of which have polyhalite sedimentary,T₁j⁴-2-2 and T₁j^5-2-T₂l^1-1.In this paper,through summarizing polyhalite ore-forming elements,mainly lithofacies palaeo geography,tectonic setting,ore-bearing characteristics and hydrogeological characteristics is complementary,combined with drilling material collection and comprehensive information of the logging data interpretation of polyhalite,explore a set of polyhalite metallogenic prediction method.This method is used to predict the ore-forming in Sichuan basin and to divide into three areas.