International Geologiical Congress - Oslo 2008

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MRB-01 General contributions to industrial mineral deposits

 

Characteristics and formation of the potash deposits in Lop Nur salt lake, Xinjiang, China

 

Chenglin Liu, Chinese Academy of Geological Sciences (China)
Mili Wang, Chinese Academy of Geological Sciences (China)
Pengcheng Jiao, Chinese Academy of Geological Sciences (China)
Yongzhi Chen, Chinese Academy of Geological Sciences (China)
 

 

Lop Nur Lake is located in the southeast of the Tarim Basin, Xinjiang, China. Now it becomes a playa. In 1995, a large potash deposit was discovered in the Lake, which is the second largest potash deposit in China. For a severe short of potash resources in China, this deposit is timely exploited on large scale soon after its discovery.
During the Quaternary period, the western part of the Tarim Basin was uplifted, and its eastern part, i.e. the Lop Nur area sank, so Lop Nur became a catchment of waters from rivers and paleolakes inside and around the Tarim Basin, thus laying a rich material foundation for potash formation.
The Early Pleistocene∼early Middle Pleistocene was a period of a unifying great lake with a brackish-saline environment in Lop Nur. In the Middle Pleistocene, in its south there was still a brackish-saline environment, while in the north glauberite deposits began to appear. In the Late Pleistocene, the northern part of Lop Nur Lake was uplifted and the hollows for potash deposition were formed. In the late Pleistocene, in the north there appeared polyhalite, and in Early Holocene halite started depositing. In the Late Holocene Lop Nur Lake largely dried up.
The dominant minerals of the Lop Nur Lake are glauberite, gypsum and halite with subordinate polyhalite, mirabilite, loeweite, bloedite, kainite and magnesite; minor minerals include syngenite, epsomite, carnallite and halo-sylvite.
The main potash deposits of the Lake are the brine potash, and most of brine occurs in pores of glauberite beds. The brine has an average potassium chloride content of 1.40% and are hydrochemically of magnesium sulfate subtype. In addition, most of the solid potash deposits are polyhalite beds as intercalated ones in thick glauberite layers, and their reserves are very small relative to the brine potash.
The unique characteristic of the salt lake is that glauberite is dominant in salt minerals. And gypsum often occurs as remnants in the inner of glauberite crystals, which means glauberite formed through the replacement of gypsum. The studies show that the Lake was supplied with "sulfate-rich" surface water and possibly with "Calcium-rich" hypogene brine. It is deemed that the potash formation was controlled by glauberite sedimentation: glauberite having rhombohedra-plate shape, lots of pores developed in the glauberite rocks during sedimentation and diagenesis; pores of glauberite rocks reserved brine; and a great deal of glauberite deposited, meaning the removal of Ca2+, Na+ and other ions from the lake water, resulting in the accumulation of potassium in brine. Therefore, enormous quantity of glauberite deposits has an important effect on the formation of potash deposits in Lop Nur Lake.

 

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