A Hydrothermal Origin Story
Deep beneath Myanmar's Shan Plateau, geology performed a remarkable feat of chemistry. The Ngwe Taung silver deposits are a direct result of scorching, salty water forcing its way through ancient rock. The process began with hydrothermal fluids, superheated to 250°C, moving up from deep within the Earth's crust along faults and fractures. These were not pure water; they were a concentrated brine containing about 15% salt, making them four times saltier than today's oceans. This high salinity was important, as it allowed the fluids to dissolve and carry significant quantities of metals, including lead, zinc, and silver.
The target for these metal-rich fluids was the Wunbye Formation, a thick sequence of limestone and dolomite deposited in a shallow sea during the Ordovician Period, over 450 million years ago. This carbonate rock is highly reactive to acidic solutions. As the hot, slightly acidic brine percolated through the limestone, it dissolved the calcium carbonate (CaCO₃) of the host rock. This created voids and dramatically changed the local chemistry, causing the dissolved metals in the fluid to precipitate out of solution. The result was a replacement-style deposit, where the original limestone was chemically swapped for an entirely new set of minerals.