An industrial-scale chemical reaction
The Monywa copper mining complex, which includes the Letpadaung, Kyisintaung, and Sabetaung deposits, is the site of a massive, ongoing geochemical process. The striking blue water is the result of acid mine drainage, a phenomenon that begins when sulfide minerals deep in the earth are excavated and exposed to air and water. The ore at Monywa contains in copper-iron sulfide minerals such as pyrite (FeS₂), also known as "fool's gold," and chalcocite (Cu₂S).
When rainwater and oxygen interact with these minerals, the iron sulfide oxidizes, releasing sulfuric acid (H₂SO₄) and dissolved iron. This natural process is dramatically accelerated by specialized microorganisms. Chemoautotrophic bacteria, particularly from the genus Acidithiobacillus, thrive in these harsh conditions. They metabolize the iron and sulfur, speeding up the acid-producing reactions by a factor of up to one million. These extremophile bacteria do not need organic carbon energy; instead, they derive it directly from the inorganic chemical reactions that break down the ore. The resulting acidic water can reach a pH as low as 3 or 4, similar to orange juice. This process is harnessed commercially in a technique called bio-heap leaching, where the acidic solution is collected to extract the valuable copper.
The chemistry of color
The intense blue of the pools is not caused by the acid itself, but by the chemicals it dissolves. The highly corrosive sulfuric acid leaches metals directly from the mined rock. One of the main metals released is copper, which becomes aqueous copper sulfate (CuSO₄) in the solution. It is the high concentration of these dissolved copper sulfate ions that gives the blue hue to the water. A similar process occurs with iron, which initially dissolves from pyrite. When the pH of the water later rises through dilution, the soluble iron precipitates as iron(III) hydroxide, an orange-yellow solid known as "yellow boy" that stains rocks and stream beds downstream.
The Monywa mining complex is a massive operation, distributed over an area of 20 square kilometers. The largest deposit, Letpadaung, accounts for about 75% of the total copper reserves. The entire district holds a pre-mining resource estimated at 2 billion tons of ore, containing 7 million tonnes of copper. The extraction process involves three main stages: bio-heap leaching to dissolve the copper from vast piles of ore, solvent extraction to purify the copper-rich solution, and finally electrowinning, which uses an electric current to plate pure copper metal onto cathodes. This method allows for the production of copper that is more than 99.99% pure.