TEAR DROP PATTERN ' POTASH DEPOSITS IN LACUSTRINE FACIES

摘要

It is well known that there are two patterns of potash deposition in lacustrine fades: " 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 MgCh type surface brine is 280-340 g/1 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 d