A taste of the Tethys Sea
The brine that emerges at Ban Na Ouane is not ordinary spring water. Its chemical signature identifies it as the remnants of an ancient ocean. Geochemical analysis shows the water is a sodium-chloride (Na-Cl) type, a composition consistent with dissolved rock salt, or halite. Isotope ratios of elements like chlorine and bromine confirm that this halite is marine in origin, formed from the evaporation of seawater during the Late Cretaceous period, over 66 million years ago.
The water itself begins as rain and snowmelt in the surrounding mountains. This meteoric water seeps into the earth, circulating to depths between 240 and 570 meters. Deep underground, geothermal energy heats the water to reservoir temperatures ranging from 87 to 137 degrees Celsius. This superheated water then dissolves thick layers of halite left behind when a branch of the ancient Tethys Ocean evaporated. The resulting brine, under pressure, rises back to the surface through fissures in the rock, emerging as the Ban Na Ouane salt spring. The concentration of dissolved minerals is exceptionally high, with Total Dissolved Solids (TDS) in the region's springs measuring from 11.65 all the way up to 311.27 grams per liter.
An ancient industry
For centuries, local communities have used this geological anomaly to produce salt. The method of extraction is straightforward and effective: boiling the brine. This process, a form of forced evaporation, removes the water and leaves behind the crystallized salt. Archaeological evidence from the wider region suggests that this is an ancient practice. A salt-working site in nearby Thailand, Bo Phan Khan, shows evidence of industrial-level salt extraction beginning in the 1st or 2nd centuries CE, supporting a long history of this technology in the area.
The process likely involved collecting the brine in large vessels and heating it over a fire until the water evaporated completely. Historically, this was often done using specialized, thick-walled ceramic pots. The salt crystals would form a solid block inside, and the pot would be broken to retrieve the final product. This method allows for continuous production regardless of the weather, a significant advantage over solar evaporation in a monsoon climate. The salt produced here has been a cornerstone of local trade and food preservation for generations.