Abstract:The unique geographic and climatic conditions of Lop Nur during the Quaternary generated the deposition of the world’s peculiar glauberite giants and the accumulation of large- scale intercrystalline potassium- rich brine. Therefore, the evolution of saline lake and genesis of brine potash deposits in Lop Nur have attracted widely attention of geologists. It has been over 20 years since the super large- scale brine potash deposits in the Luobei depression was discovered in 1995 and considerable progress has been made in terms of scientific research, investigation and exploitation for potash deposits. And the world’s largest production base for high quality K2SO4 fertilizer has been built in Lop Nur. This paper reviews and summarizes the important research results in terms of sedimentary evolution of saline lake, formation conditions and theory, and exploration of potash deposits since the discovery of potash deposits in Lop Nur, with an attempt to understand the relationship of the potash- formation innovation and exploration breakthrough. The theoretical studies for formation of potash deposits in Lop Nur can be summarized as follows: ①based on the recognition of basinal separation and ore- migration along with tectonic movement, a model of “high mountaindeep basintectonic migration” was proposed after “high mountain- deep basin” model, leading to the discovering of the Luobei potash deposits. ②Based on discovery of enormous glauberite deposit, a “three- stage brine- crystallization potash formation” model has been reshaped to “two- stage potash formation” model, leading to the large- scale exploration in Luobei and its surroundings. ③According to the discovery of graben- type fault- subsidence zone, the “brine- bearing wall” model for reservoir formation was established, guiding prospecting in “vertical reservoir” from “horizontal reservoir”, which has resulted in discovery of the deep brine aquifer. In summary, each theoretic innovation of potash formation in Lop Nur has correspondingly brought up breakthrough in potash exploration. Further research on formation regularity of potash deposits in Lop Nur is still required to form new understandings and new directions for potash exploration.

Abstract:Detrital zircon U-Pb age analyses for the samples from the first scientific potash exploration drill core in Lop Nur were conducted to reveal the potential source area of the Quaternary salt lake and stage tectonic evolution of the depression in Lop Nur. Th/U ratios show that the detrital zircons are dominantly magmatic origin, with minor metamorphic zircons. Zircon ages are concentrated mainly in the ranges of 209~240Ma, 265~304Ma, 320~385Ma, 406~446Ma, 705~880Ma and 2376~2405Ma. Combined with the rock nature and age range of the potential source area, it can be preliminarily concluded that the pre-Cambrian materials mainly sourced from the Kuruktag area, and the Caledonian sources derived from the Altyn and South Tianshan tectonic belts. 276Ma of age peak records a representative event of Permian large igneous province (LIPs) in the Tarim basin and South Tianshan is likely the major provenance. Indosinian and Cenozoic detrital zircon ages imply that the Beishan block and East Tianshan, even distant Pamir and West Kunlun, were the potential source areas. Due to largescale weathering and leaching, widely exposed K-rich rocks in the periphery of the depression were transported to Lop Nur, providing important materials for the Quaternary potash formation in Lop Nur. In addition, sediment compositions transported by drainage system of the Tarim basin were also major provenance, with limited amount from the orogenic belts in northern and northeastern Lop Nur. The vertical variety features of detrital zircon ages suggest an obvious tectonic uplift in the north part of Lop Nur, probably resulting in the formation of the Luobei depression.

Abstract:Lop Nur is a typical inland dry salt lake in the eastern end of the Tarim Basin within the interior of Eurasian continent. Thick evaporite was developed in the northern depression since the middle Pleistocene, and this was active response to global cooling and uplift of the Qinghai- Tibet plateau. In this study, carbonate content, carbon and oxygen isotopic compositions were analyzed for 203 samples of evaporite series from the first deep core (LDK01) in the Luobei depression to reveal evolution features of paleoenviroment in Lop Nur since the middle Pleistocene. The research indicates that: (1) δ18O and δ3C values show an obvious synchronous increasing trend, and the evaporation and precipitation ratio has the most significant influence over δ18O of water in the lakes, especially in the arid region; (2) Periodic fluctuation of δ18O and δ13C indicates an environment of alternating wet and dry paleoenvironment and the variations of the runoff into Luobei depression; (3) Rapid aridification of Lop Nur should not be driven solely by global climate change, and be the joint result of cooling of global climate and uplift of the Tibetan Plateau.

Abstract:Potash deposit in the Luobei depression is a large-sized underground liquid potash deposit, and contains seven aquifers of potassium-rich brines, with the first (W1) being K-rich brine aquifer and others (W2, W3, W4, W5, W6 and W7) being confined brine aquifers. At present, the main mining target concentrates on phreatic brine aquifer which is shallow buried and easily mined, and elastic yield in part of confined aquifer. With expanding production scale and increasing annual yield for brine in the mining area, some area will face difficulty in mining the deep confined aquifers with poor water. But confined brine layers often occur in relatively tight salt crystallization layers or pore or solution cracks of detrital layers. Their hydrological parameters are lower than that of phreatic brine aquifer (W1), which causes much difficulty in mining the deep potassium-rich brine. In this study, a large-scale pumping test was carried out in the deep confined aquifer in different hydrogeological areas of the Luobei depression by using blasting method and atmospheric connection method. The reasonable and economic mining method was determined for deep confined brine in different hydrogeological areas, and the deep confined brine（W2,W3,W4）resources have been effectively mined. This method turned unrecoverable deep confined potassium-rich brines into available resources, improving utilization rate of deep confined potassium-rich brine.

Abstract:The Tarim basin was the eastern extension of the Paratethys Sea during the Paleogene, with the Kuqa sub- basin located in the northeastern part of this basin. It experienced a sedimentary evolution from shallow marine, marine terrigenous to continent, resulting in deposition of giant evaporites. It has become an important base for oil- gas production and a key exploration area for potash deposits, thus having attracted wide attention from a large number of geologists. However, there are still some controversies and uncertainties about the source and degree of evaporation and concentration of Eocene ancient brine in the Kuqa Basin. Therefore, this study, based on observation of petrology and mineralogy, analysis of XRD and SEM- EDS and stable isotope characteristics, analyzed depositional environment, supply origin and degree of evaporation and concentration of the evaporite. Petrography analyses of evaporite show that it deposited in a salt lake environment mixed with addition of proximal mud. The anhydrite δ34S values are characteristic of certain marine source supplement. The δD and δ18O values of primary fluid inclusions from halite range from -118.1‰ to -95.3‰ and from 2.5‰ to 5.7‰, respectively, and the evaporation trend line indicates that the ancient brine had a high degree of evaporation and concentration. Although experiencing three transient freshwater influxes, the evolution of the ancient salt lakes did not affect the precipitation of potassium and magnesium saline minerals with continuous evaporation of ancient salt lakes, and the corresponding potassium saline minerals were precipitated when the δ18 O values were positive. It can be speculated that Eocene salt- bearing series strata in the Kuqa basin has favorable potential for potash formation.

Abstract:Hightemperature, highpressure and high- salinity brine in the Jiangling depression of Jianghan basin is rich in K, Li, B, I, Rb and Cs elements, contents of which have reached the industrial grade or exceeded the comprehensive utilization grade. But this K- and Li- rich brine deposit has long faced difficulty in locating its position. The relationship between enrichment of K- and Li- rich brine and structure of ore field has not been identified. With the guide of modern ore field geology, the paper analyzed the ore field structure of brine and ore field mineralization based on geophysics, wells and fields data. Affected by tectonic locations, each area of the Jjiangling depression shows very different local structures developed in different periods. The orderly distribution and superimposition of these local structures forms abundant structural traps, which provide favorable places for the enrichment of LiK brine. During the deposition period from Shashi Formation of Paleocene to Xingouzui Formation of Early Eocene, the high temperature and dry paleoclimate of Jianghan basin was favorable for the evaporation of salt lake, and K- and Li- bearing materials from volcanic activities provided base for the enrichment of Li- K brine. Structurereservoir coupling accumuation mode of K- rich brine in the Jiangling depression and deposition characteristic of salt lake have determined that a large amount of brine accumulates in the strata. The biggest reservoir space for brine is sandstone pores. Tectonic movement resulted in the formation of a large amount of fractures in mudstone and igneous rock, which become the ideal places for brine accumulation. Due to structural fold and burial diagenesis, brine migrated from salt crystal to sandstone pores, finally into fractures and volcanic system.

Abstract:A set of evaporite strata consisting of calcium glauberite and rock salt (halite) developed in the early Eocene Xingouzui Formation in the southern margin of the Jiangling depression. The mineralogical and mineralogical evidence shows that the main salt minerals in the salt- bearing strata include rock salt, calcium glauber and anhydrite, which all formed in the environment of perennial salt lake. Calcium glauber is a primary- quasi-synthetic salt mineral. According to the type of mineral salts and sedimentary characteristics and typical warm saline minerals (native) calcium mirabilite extensive development, Yanjing-Shenjindu sub- depression can be inferred in the sedimentary period of Xingouzui formation in the ancient climate for type. According to extensive development of salt minerals (such as calcium glauber) and their depositional type and characteristic, it can be inferred that the climate in the Yanjing- Shenjindu sub- depression was warm during the deposition of the Xingouzui Formation. The δ34S composition of calcium mirabilite is 25‰~33‰, much higher than that of the seawater sulfur isotope (17~19‰) in the same period, suggesting that calcium mirabilite may have undergone bacterial modification. In addition, during the period between Late PalaeoceneEarly Eocene, sulfates in the Yanjing-ShenJindu subdepression may originate from the older sulfite formation in the west.

Abstract:The Dianjiang salt basin, located in the eastern part of Sichuan basin, is one of the most important Triassic salt basins in eastern Sichuan basin. However, the metallogenic condition of marine potash formation has long been in dispute. This paper carried out an analysis for the halite samples from Gaotan well 1 and Changping well 3 in the Changshou area using microscopic observation, scanning electron microscope, X- ray power diffraction and chemical components. The results show that the core samples from Changping well 3 contain high K+ concentration up to 3.82% and a large number of polyhalite and minor amount of sylvinite were found at depth between 2749 meter to 2778 meter in Changping well 3. Br×103/Cl coefficients of the samples from two wells suggest that the brines reached the deposition state of sylvinite. Study of the paleoclimate conditions, materials source and tectonic conditions in the Changshou area shows that this area was characteristic of high paleo- seawater temperature and hot climate during the early Middle Triassic, both of which were beneficial to the formation of potash deposit. The materials of potassic salt were mainly derived from seawater, which provided plentiful sources for potassium ion. There might exist a secondary sag in Baohe village. Good structural condition helped the formation and preservation of potash deposits. Therefore, this area will be the target for exploration of potash deposits.

Abstract:The Dianjiang depression of eastern Sichuan basin is one of the most important salt basins in the Triassic. However, there exist some disputes about whether the paleo- brine reached potash deposition and whether preferential metallogenic conditions for marine potash formed. In this paper, we carried out chemical analysis for salt samples from Changping well 3, Gaotan well 1, and ZK001 Jialingjiang Formation in the Dianjiang depression, and chlorine isotopic analysis for the salt samples from Changping well 3 to determine depositional stage of paleobrine and formation condition. The results indicate that all chlorine isotopic values o the Triassic Jialingjiang halite are negative, lower than -0.32‰, with the lowest value of -1.18‰, and most Br/Cl ratios are higher than 0.31, with coefficient of bromine chloride in some samples exceeding 0.45. There features imply that during the Jialingjiang period paleo- brine in the Dianjiang depression had reached the precipitation stage of sylvinites, which is consistent to analysis result of inclusions in halite. Combined with analysis of climate, provenance and tectonic factors, it can be concluded that the Dianjiang depression was hot, abundant in potash source, existence of sub-depression, and excellent tectonic condition, all of which determined the great potential for the formation of marine potash.

Abstract:The salt basin of north Shannxi province (Shanbei) during the middle Ordovician was located in the junction of the North China Sea and the Qilian Sea, where developed a huge thickness of evaporite- carbonate sediments. The fifth Member (M5) of the Majiagou Formation is lithologically characterized by mediumand thinlayered muddy or fine grained dolomite and anhydrite, medium- thick layered coarse- grained dolomite and limestone, medium- thick layers halite and anhydrite, and anhydrite and halite with mudstone. In this paper, we carried out a systematic analysis of sulfur isotope compositions for anhydrite from the M5 evaporite- carbonate layers. The study shows that the sulfur isotope values of the M5 anhydrite in the Shanbei salt basin are generally high, ranging from 25.03‰ to 29.25‰, and fall within the sulfur isotope area of Ordovician global seawater spectrum. And sulfur isotope values are closely related to the sedimentary lithology, with limestone/dolomite section (average value is 27.28‰; 25.77‰～29.25‰) >mudstone section (average value is 26.22‰; 25.49‰～28.08‰) >rock salt section (average value is 25.41‰; 25.03‰～26.04‰). Many factors resulted in isotopic differences of anhydrite in evaporite basins. In the study area, high δ34 S values during transgression phases were affected mainly by marine sedimentation, paleoclimate, MSR function under the anoxic condition and others; relatively low δ34S values during regression phases were influenced by the formation of the closed cycle of brine and the addition of the mixed brine formed by dissolving in situ sulfate minerals.

Abstract:The Khorat basin, which hosts major potash deposits in Laos, is one of the largest potash ore cluster areas in the world. The main mineral assemblages are rock salt, carnallite and secondary potash. Fissure water is mainly distributed in potassiummagnesium salt layers with a depth of 150 m. Leaking of fissure water has imposed serious threat on production safety. But it is still unclear about origin and evolution process of fissure water. This study carried out hydrochemical and H and O isotopic analysis for 12 samples of waters from orebearing layers and neighboring water bodies. The results show that fissure water is saturated brine with high TDS (368.1-430.7 g/L). The fissure water, similar to salt springs, belongs to chloride- type water. The chemical characteristic coefficients of constant and trace ion contents indicate that the fissure water is affected by dissolution of potassium and magnesium salt minerals. The δD (-64.2‰~-55.2‰ average -60.42‰) and δ18O (-7.75‰~-7.1‰, average -7.34‰) of fissure water are different from that of original brine in rock salt (δD=-144‰~-78‰，δ18O=-1.1‰~4.2‰) and potassiummagnesium salt (δD=-54.75‰~-1.42‰，δ18O=-7.09‰~0.95‰) at the depositional stage, and are plotted close to the global meteoric precipitation line. This suggests that the fissure water is not characterized by original residue brine, but mainly originated from minerals of evaporite, leached by meteoric precipitation. The determination for source of fissure water will provide some basis for understanding groundwater cycle and treatment of leakage of mine water during development process of potash deposits.

Abstract:The Mengyejing potash deposit, which is located in the southern Simao basin of eastern Tethyan realm and approximately 500 km north of the Khorat basin, is only pre-Quaternarya solid potash deposit in China. The Khorat basin contains immense potash deposits occurring mainly in the Maha Sarakham Formation. There has long been dispute about resources amounts and genesis between the Mengyejing potash deposit and the Khorat huge potash basin, especially about the questions below. Controversies still occur over potashforming ages over the late Cretaceous, Paleocene and even Jurassic; potash material sources from continental, marine and multiple sources; and their ore-formation mechanisms. Through summarizing previous research and the results in this study, we suggest that the Mengyejing Formation stratum is Albian to Cenomanian of the Late Cretaceous in age and the primary potash deposited at the same time. The primary potash was affected by multiple hydrothermal fluids during the post depositional stage, especially since 14 Ma, resulting in the formation of secondary vein-type potash. The ore-forming material of potash deposit might be dominantly sea water due to incursion of the Mid-Tethyan Ocean with minor amount of continental water and deep fluids. It can be concluded that the Simao and Khorat basins were isolated lakes in arid desert environment during the Late Cretaceous and the transgression of MidTethys Ocean from west to east resulted in flowing of seawater into Khorat basin, forming a unified Simao-Khorat Sea. This model can interpret the relation between the sources of the potash deposits and genetic link between of Simao and Khorat basins. The formation and latestage alteration of the potash deposits in the Simao basin had been controlled mainly by tectonic activities from initial faulted subsidence to compression and strike-slip by the collision of India and Asia at the post-sedimentation stage.

Abstract:The shallow brine aquifer in the western Qaidam Basin is a multi- coupled dynamic equilibrium system and controlled by hydrodynamic force, climate and chemical factors. The study carried out an analysis for compositions of brine and permeability of brine aquifer in the shallow brine aquifer in different seasons (summer and winter). The results show that the concentrations of major ions in brine vary obviously from summer to winter and the concentrations of K, Mg, Ca and Cl increase correspondingly, with an increasing order of Cl, Mg, K, Ca. While the concentrations of SO42- and Na decrease, with SO42- decreasing more obvious than Na. Calculation results of pumping test suggest that permeability coefficient K in drilling core ZK08 decreases from 178 m/d to 97 m/d from summer to winter. The reason for that is that precipitation of mirabilite（Na2SO4）with decreasing of environment temperature not only improves dissolution capacity of K, Mg and Ca in brine and increases concentrations of K, Mg and Ca, but also decreases the permeability of the aquifer. In addition, the viscosity of brine increases with temperature decreasing. Therefore, it can be concluded that two factors jointly result in decreasing of the aquifer permeability.

Abstract:Pliocene lacustrine facies sequence in the northwestern part of the Qaidam basin in Qinghai Province hosts the inland lake facies evaporite- type celestite ore deposit with the largest reserve in China. The work on this deposit has long focused only on geological exploration and exploitation. But study of the mineral source and genetic models for the Dafengshan celestite deposit is relatively poor. In this paper, we have studied the typical sections of evaporites in the north wing, shaft and south wing of the short axis double anticline. Combined with regional geological setting of the study area and characteristics of strontium isotope data from previous research, this study discussed ore- forming material source and ore genesis of the deposit using the distribution characteristics of strontium in modern river of the Qaidam basin, major element features of evaporite sections and thin section analysis. The main conclusions have been drawn as follows. ①The long- term weathering of felsic bedrock in the periphery of Qaidam basin provides the source of strontium for the formation of celestite ore deposit. ②The significant dissolution and metasomatism of Srrich carbonatic rock, which is orebearing country rock, played an important role in the secondary enrichment of celestite mineral. ③Under the structural background of high mountaindeep basin, volatile drying provides favorable conditions for the dissolution, migration and concentration of strontium in sediments.