Mineral Occurrence Characteristics Of Shallow Solid Potassium Ore After Water Solution Mining In Mahai Salt Lake,Qaidam Basin

Mahai Salt Lake is located in the Saishiteng Sag of the fault block belt on the northeastern margin of the Qaidam Basin.It is the second largest potash production area in Haixi Prefecture of Qinghai after Qarhan Salt Lake.It is stored in the J_?potash deposit in the northern section of the mine.There are nearly 1.2×10⁷t low-grade solid potash ore.Since there is no clear understanding of the type,content,and occurrence law of the solid potassium salt after the dissolution mining project is implemented,it has greatly affected the degree of KCl recovery.Therefore,this article has carried out the cataloging of 32 drill cores.Core observation,rock and mineral identification,geochemical testing and analysis,etc.,in-depth study of the types,contents,and spatial distribution of ore and minerals after long-term water-dissolution mining in the 4 dissolution mining areas of the 67-79 exploration line in the northern section of the Mahai mining area.According to the results of the investigation of the current situation of resources,the effect of water-soluble mining is analyzed and evaluated.The study found that the shallow solid potash ore in the Mahai mining area is mostly low-grade ore,with poor continuity of the ore body.There are 3,2,3,and 6 potassium-bearing peak horizons in No.8,9,13,and 17 dissolution mining areas,respectively.Except for the average KCL content of some potassium peak layers in the No.17 dissolution mining area,which reached the boundary grade,the potassium peak layers in the other dissolution mining areas all reached the industrial grade.However,the average KCl content of representative boreholes in No.8,9,13,and 17 dissolution mining areas are 1.43%,1.98%,1.66%,and 0.96%,respectively,which are all lower than the industrial grade,confirming the shallow solid potassium in the Mahai mining area.The discontinuity of the mine,the potassium ion content in most formations is low,and it is a low-grade solid potassium mine.Using three technical means of thin slice identification,XRD and ESM,12 kinds of salt minerals were identified,and the potash minerals in the study area were determined to be polyhalite,carnallite and sylvine.Polyhalite is mostly in the form of flakes,felts,fibers and granules.The aggregates are mostly petal-like and radial-fibers,and they are mostly distributed among the rock salt crystals and debris.Carnallite is mostly in other shapes,granular,cracked and molten,and is mainly contained in the debris,co-existing with polyhalite and potash.Sylvine is mainly euhedral-subhedral cubic monomer,and it is mostly contained in carnallite crystals.The main potash minerals in the No.8 solution mining area of the study area are carnallite,followed by polyhalite;the main potash minerals in the solution mining areas 9,13,and 17 are polyhalite,followed by carnallite.Sylvine is distributed in a relatively small area,mainly concentrated in the vicinity of exploration line72 in the No.9 dissolution mining area,and there are also sporadic distributions in the No.8and 13 dissolution mining areas.Geochemical studies have shown that the average value of potassium ions in different boreholes in the study area varies greatly,ranging from 0.08%to 1.09%.The average potassium ion of the borehole located in the No.17 dissolution mining area is 0.08%-0.50%,and the No.8 dissolution mining area is 0.35%-0.75%.The average value of potassium ions in boreholes located in No.9 and No.13 dissolution mining areas is more than 0.70%.K⁺?Mg²⁺?Ca²⁺?SO₄^2-in the dissolution mining areas 9,13,and 17 have peaks in most of the same horizons,which further proves that polyhalite is the main potash mineral in the above blocks.Through statistics and analysis of the remaining KCl resource reserves of different grades in the No.8 and No.13 dissolution mining areas,it is found that although the average grade of KCl in most deposits has been reduced,the degree of recovery is quite different.The mining degree of each ore layer in No.13 dissolution mining area is very low.For the emergence of the above situation,the following assumptions are made:(1)The lithology of No.8 and 13 dissolution mining areas is quite different.The former is mainly thick rock salt layer,and the latter is mainly rock salt containing detritus.The high water insoluble matter results in the formation of a large amount of sedimentation during the dissolution mining process,which reduces the permeability of the ore bed and the dissolution mining efficiency.(2)The porosity,water supply,and permeability of the ore bed in No.13 dissolution mining area are relatively low.In addition,there is no clear hydrological unit boundary between the dissolution and mining areas,causing the magnesium sulfate subtype brines of different compositions to flow slowly and slowly here,converge and dope,and the brine is mixed to precipitate potassium-containing minerals such as polyhalite.Resulting in little change in the reserves of potassium chloride resources before and after mining.