Geochemical Characteristics of Deep-Seated Potassium-Rich Brine in the Middle Triassic Leikoupo Formation, Sichuan, China

Brine extremely rich in potassium boron and bromine has been discovered from the Mid-dle Triassic Leikoupo Formation at a depth of 4300 m in Sichuan Province. It contains ~50 g/L of K+, >92 g/L of Na+, >12 g/L of B2O3. >2.36 g/L of Br- and ~0.030 g/L,of I+. The sol-id precipitates during evaporaton at 25℃ include KB5O8.4H2O, K2B4O7.3H2O, MgCl2 -6H2O and KMgCl3. The brine ranges from 2. 2‰ to 2. 8‰ (SMOW) in δ18O, - 38‰- - 53‰ (SMOW) in δD, 15. 6‰ in δ34S, and 13. 5‰ - 15. 1‰ in δ11B. These data, particularly the iso-topic composition of boron,indicate that the brine has a composite derivation from marine and non-marine brines and dissolved marine evaporites in the Triassic system.