The Impact of the Linked Factors of Provenance,Tectonics and Climate on Potash Formation:An Example from the Potash Deposits of Lop Nur Depression in Tarim Basin,Xinjiang,Western China

Potash deposits commonly accumulate in highly restricted settings at the final stage of brine evaporation. This does not mean that potash deposits are formed simply as a result of the evaporation concentration of seawater or lake water, but rather as a coupling result of particular provenance, tectonics and climate activities. In this paper, we focus on the formative mechanism of the potash deposits of Lop Nur depression in Tarim Basin to interpret the detailed coupling mechanism among provenance, tectonics and climate. In terms of the provenance of Lop Nur Lake, the water of the Tarim River which displays ＂potassium-rich＂ characteristics play an important role. In addition, the Pliocene and Lower-Middle Pleistocene clastic beds surrounding Lop Nur Lake host a certain amount of soluble potassium and thus serves as ＂source beds＂ for potash formation. During the late Pliocene, the Lop Nur region has declined and evolved into a great lake from the previous piedmont and diluvial fan area. Since the mid Pleistocene, the great-united Lop Nur Lake has been separated and has generated a chain system consisting of Taitema Lake, Big Ear Lake and Luobei Lake which has turned into the deepest sag in Lop Nur Lake. Dry climate in Lop Nur region has increased since the Pliocene, and became extreme at the late Pleistocene. The study implies that potash formation in Lop Nur Lake depends on the optimal combination of extreme components of provenance, tectonics and climate during a shorter-term period. The optimal patterns of three factors are generally characterized by the long-term accumulation and preliminary enrichment of potassium, the occurrence of the deepest sub-depression and the appearance of an extremely arid climate in Lop Nur region. These factors have been interacting synergistically since the forming of the saline lake and in the later stages strong ＂vapor extraction＂ caused by extremely arid climate is needed to trigger large scale mineralization of potash deposits.

A Cretaceous Desert-Playa Sedimentary System Controlled the Potash Formation in the Simao Basin

Objective The Simao Basin in Yunnan Province has developed Cretaceous evaporite-bearing clastic deposits, including the Mangang and Mengyejing Formations which were originally interpreted as fluvial and lacustrine deposits. The Mangang Fm. composed of well-rounded quartz sandstones, were commonly considered as the bottom part of the Mengyejing salt series. Dttring last decades,

The Drifting History of the China Main Blocks during Specific Periods and their Tectonic Constraints on Marine Potash Formation

1 Introduction Most of the world well know potash mines are deposited in marine environment.Regarding the serious potash shortage,no significant progress has been made in marine potash in China,while the terrestrial potash

The Analysis on Comparison of Forming Condition with Abroad Palaeo-Epicontinental Marine Basin and Possibility of Potash Formation in North China

1 Introduction Currently,all six different continents have discovered potash deposits and potash-bearing salt lake saline water.However,the distribution is extremely uneven,which is mostly concentrated in Canada,Russia,Middle-Asia and

Features and Formation Mechanism of Faults and Potash-forming Effect in the Lop Nur Salt Lake,Xinjiang,China

The Lop Nur Salt Lake, located in the eastern part of the Tarim Basin, Xinjiang, China, has become a playa in the Quaternary. Rhombic in shape, the Lop Nur depression is mainly controlled by the NE-striking and nearly N-S-striking sets of faults. Since 1995, a superlarge brine potash deposit with potash resources of 2.50×10^8s t has been found in the Luobei subbasin in the northeastern part of the Lop Nur. We intensively studied the features and formation mechanism of faults inside the Lop Nur through satellite images, geomorphologic survey and continuous conductivity imaging and found seven subparallel graben faults formed under the action of nearly N 10° E principal compressional stress during deposition of the Lop Nur Salt Lake. These faults are up to 〉60 km long and 1-4 km wide and may extend downward for 1000 m or more. It is just under the action of these tensional faults that potash subbasius formed. The largest subbasin is the Luobei subbasin and the smaller ones are the Luoxi hollow, Erbei hollow and Tienan hollow. Investigation also indicates that the graben faults in the Lop Nur not only control the origin of the potash subbasins, but they themselves are also good brine reservoir structures, in which abundant potash-rich brines are stored. Therefore, The faults had played an important role in the potash formation of the Lop Nur.

Minerogenic Theory of the Superlarge Lop Nur Potash Deposit, Xinjiang, China

Located in the eastern part of the Tarim basin, Xinjiang, the Lop Nur was an ultimate water catchment area of the Tarim basin during the Quaternary. Through nearly ten years of investigation and research, the authors have found a superlarge brine potash deposit in the Luobei subbasin—a secondary basin of the Lop Nur depression. The deposit has been mined now. On that basis, the authors propose new theories on the genesis of the potash rock deposit. In the tectonic and geomorphologic contexts, the Tarim basin lies in a 'high mountain-deep basin' environment. At the beginning of the Quaternary, influenced by the neotectonic movement, the Lop Nur evolved into a 'deep basin' in the Tarim basin. At the end of the middle Pleistocene, neotectonic migration began to take place in the interior of the Lop Nur and a new secondary deep basin—the Luobei subbasin—formed gradually. Despite its small area, it is actually the deepest subbasin in the Lop Nur depression, where brines of the Lop Nur Salt Lake gather and evaporate, thus providing materials for the formation of a superlarge brine potash rock deposit. With respect to the phenomenon of brine concentration and change with deepening of the lake, the authors propose a model of 'high mountain-deep basin' tectonic migration for potash concentration. In the sedimentological context, the honeycomb-shaped voids developed in glauberite rock in the subbasin are good space for potash-rich brine accumulation. Study indicates that the deposition of glauberite requires recharge of calcium-rich water. In the Tarim area the calcium-rich water might come from deep formation water or oilfield water, and the river water recharging the Lop Nur Salt Lake was rich in sulfate radicals and other components; in addition, the climate in the area was very dry and the brine evaporated steadily, thus resulting in deposition of substantial amount of glauberite, potash accumulation in intercrystal brine and final formation of the potash deposit. Generally, potash formation in a salt lake undergoes a three-stage process of 'carbonates—?sulfates (gypsum and glauberite)—^chlorides (halite etc.)', but in the study area there only occurred a two-stage process of 'carbonates—>sulfates (gypsum and glauberite)'. The authors call this new geological phenomenon the 'two-stage potash formation' model. In conclusion, the superlarge Lop Nur potash deposit is the result of combined 'high mountain-deep basin' tectonism and 'two-stage potash formation'.

Regional Distribution and Prospects of Potash in China

China was formed by amalgamation of several small continental blocks （cratons）, micro, blocks and orogenic belts in different paleoclimatic settings. It may be correlated with other continental blocks but has its own specific characteristics; therefore the tectonic environments of China＇s marine and continental saline basins and salt, and potash, forming environment have some specific characteristics： multiple phases of salt formation, difference in salt, forming ages, migration and concentration of salt, forming processes and diversity of component materials, as well as small sizes of marine saline basins and great changes of saline basins in the late stage and occurrence of abundant liquid mineral resources. The nature of the tectonic basement exerted a key controlling effect on the formation of potash basins. The stable tectonic region was favorable for potash concentration in a quasi, stable region, and quasi, and the quasi-stable region was favorable for salt concentration and potash formation in a local stable tectonic region. Most China＇s major ancient saline basins occur in ＂quasi, cratons （continental block）＂; especially all the marine saline basins occur in continental blocks with the Precambrian basement. These regions are the key ones for potash search. Most relatively large, scale soluble salt deposits are developed in relatively stable continental nuclei. According to the characteristics of the tectonic domains where China＇s salt, forming basins are located, the North China, Yangtze and Tarim, Qaidam salt minerogenetic domains and the northern Qiangtang, western Yunnan salt minerogenetic belt may be distinguished. Their salt and potash prospects will be discussed separately.

New insights on the age of the Mengyejing Formation in the Simao Basin,SE Tethyan domain and its geological implications

Knowledge on the origin and mechanism of the large potash formation in the southeast Tethyan tectonic domain are still under debate,one of which mainly due to the controversial ages of the potash-bearing strata.Here we present a detailed detrital zircon U-Pb geochronologic-magnetostratigraphic study of the potash-bearing Mengyejing(MYJ)Formation(Fm)from the Simao Basin.948 paleomagnetic cores and 4 detrital zircon U-Pb samples were collected from a 932-m thick Jiangcheng section.Thermal demagnetization isolated 857 primary characteristic remnant magnetization(ChRM)directions,indicated by positive reversals and fold tests and petrologic examinations.Seven normal and seven reversed polarity zones were identified and correlated well with chrons C27r to C34n of the geomagnetic polarity timescale(GPTS2012),yielding the first known age sequence of>112 to~63 Ma for the MYJ Fm.The ages for the potash bearing strata in the Simao commenced~20 Ma earlier than those in the adjacent Khorat basins,opposite to the traditional viewpoint that the former would rather correspond to the middle and lower parts of the latter.Given the paleogeographic reconstruction of likely a pan-Simao-Khorat basin during the Cretaceous,~85 Ma would be another important potential period for future potash exploration in the Simao Basin.

Genesis and geological significance of carbonate in Changdu Basin,Xizang,China:Constraints from geochemistry and C-O isotopes

Research on the origin of carbonates in Changdu Basin holds significant importance for understanding the regional potash formation model.Based on a comprehensive review of previous studies,field geological surveys,and laboratory investigations,this study analyzes the origin and properties of carbonates within the context of regional potash formation.Petrographic studies show that magnesite deposits,with the characteristics of sedimentary origin.The results of elemental geochemical analysis show that the carbonates in this area were formed in the sedimentary environment via evaporation followed by concentration,and the formation of magnesite was possibly caused by the substitution of calcium in the dolomite with magnesium-rich brine.Theδ^(13)C values of carbonats in the study area are between5.9‰and 9.1‰.Theδ^(18)O values of magnesite samples range from-7.3‰to-1.3‰,and theδ^(18)O values of dolomites range from-10.3‰to-8.4‰.All the calculated Z values of oxygen isotopes of carbonates greater than 120.A comprehensive analysis of carbon and oxygen isotopes indicates that the magnesite was formed in a highly concentrated Marine sedimentary environment and does not show any relation with the metasomatism of hydrothermal fluids.The results on the correlation of magnesite with seawater and its sedimentary origin provide key information for explaining the migration direction of brine between the Changdu and Lanping-Simao Basins.The residual metamorphic seawater in the Changdu Basin migrated to the Lanping-Simao Basin,where potash underwent deposition.Whereas,magnesite and dolomite in the early stage of potash formation were left in the Changdu Basin.