Abstract:

The Lanping-Simao basin in the southwestern China is located at the junction of the Eurasian and Indian Plates, and
adjacent to a large potash deposit of Khorat Basin and Sakon Nakhon Basin in Thailand and Laos. Chinese scientists thought that the
potash deposit in Lanping-Simao basin should be as large or important as that in Khorat Basin and Sakon Nakhon Basin. The
relationship between Mengyejing potash in Lanping-Simao basin and potash deposits in the Sakon Nakhon Basin and Khorat Basins has
long been discussed in many respects such as tectonic belt, depositional features, salt minerals, geochemical elements, and forming era.
Many scientists thought that they had similar brine origins, and hydrothermal fluid was one important origin for the potash deposit.
However, the ideas have received no supporting evidence. The type of hydrothermal fluid was not clear either. This study presents δ18O
and δD of halite inclusions from a ZK2893 core in Laos to provide isotopic evidence for the idea. The values of δ18O are from -2.3 to
9.5‰ with an average of 2.9‰ , while those of δD are from -78 to -150‰ with an average of -108.6‰ . Most of δD was less
than -90‰. The relationship between δ18O and δD shows that the hydrothermal fluid is metasomatic hydrothermal fluid which was
originated from reactions between rainwater and surrounding rocks. Surrounding rocks are important origin for potash deposits. Most
data were plotted near to the 150℃-curve in the δ18O-δD diagram. The possible forming temperature of halite inclusion in Laos could be

about 150℃. On the other hand, the forming temperature of halite inclusion in Lanping-Simao Basin was about 145℃ with the highest
value of 170℃. The similar temperatures provide new evidence for their similar brine origins of the two basins.

Key words: potash deposit, halite inclusions, oxygen and hydrogen isotope