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“Tear drop pattern” potash deposits in lacustrine facies

  • Sun Dapeng
Article

Abstract

It is well known that there are two patterns of potash deposition in lacustrine facies: “tear drop pattern” (the Dabsan saline lake is a typical example) and “bull's eye pattern”. Potash-forming in tear drop pattern is still continuing.

The 2,678 m A. S. L. lake in the middle of the Qarhan playa in the Qaidam Basin covers an area of 210 km2, and has an average depth of 0.39 m. Its MgCl2 type surface brine is 280–340 g/l in salinity and mainly consists of Na, K, Mg and Cl. As a rule, the potash deposits occur as evaporite distributed in tear drop pattern at the northern and northeastern lakeshore zones. They mostly consist of carnallite and halite, occasionally sylvite. The deposition is very unstable and controlled principally by the varying supply of deposit materials from the Golmud River in the south.

The potash deposits were formed when concentration of the surface brine reached a certain degree in the main evaporating season. Their forming process followed some crystalization paths in the phase diagram for the Na, K, Mg/Cl H2O equilibrium system.

Such a sedimentary model of potash deposits in the lacustrine facies is relatively common in nature. Under the extremely arid climate, differential concentration of the nonhomogeneous potassium-rich surface brine produced the potash deposits. Qarhan Salt Lake also had the same pattern of potash depositions and so, in a sense, the Dabsan saline lake is the continuation of the Qarhan salt lake in terms of potash formation.

Schmalz (1970) put forward two distributive patterns for evaporite: “tear drop pattern” and “bull's eye pattern”. These patterns exist in both marine and continental salt-bearing basins (including recent salt lakes), and are controlled by the conditions of physical geography, hydrogeology, sedimentology and climatology of each basin. In his works (Sun, 1981; 1984; 1986; 1988) on the origins of potash deposits, the author always referred to them as two models of potash formation.

The “tear drop pattern” is one of the salt-forming models and also an important potash-forming model. This paper deals with the formative mechanism of the tear drop pattern potash deposition by presenting the Dabsan saline lake as an example and elucidates on the distributive characteristics and formative processes of potash deposits in the lake.

Keywords

Halite Evaporite English Abstract Qaidam Basin Differential Concentration 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Schmalz, R. F., 1970. Environment of marine evaporate deposition,Miner. Ind.,35 (8): 1–7.Google Scholar
  2. Sun Dapeng, 1981. On origins of potash deposits in continental potash-bearing basins.Kexue Tongbao 26: 815–820.Google Scholar
  3. Sun Dapeng, 1984. Distribution and formation of salts and their relationship with petroleum generation in Qaidam Basin,Oil and Gas Geology 5(2): 132–139 (In Chinese, with English Abstract).Google Scholar
  4. Sun Dapeng, 1986. The origins of potash deposits in continental potash-bearing basins.Minerals and rocks.6 (2): 34–45 (In Chinese, with English Abstract).Google Scholar
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  8. Valyashko, M. G., 1962. Geochemical Regularity for the Formation of Potash Ore Deposits, Moscow University Press, pp. 311–312 (In Russian).Google Scholar

Copyright information

© Science Press 1990

Authors and Affiliations

  • Sun Dapeng
    • 1
  1. 1.Qinghai Institute of Salt LakesAcademia SinicaXining

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