A polymetallic anomaly
The Bawdwin deposit is a geological outlier, a volcanogenic massive sulfide (VMS) deposit hosted within early Ordovician rocks. For centuries, this site in Myanmar's northern Shan State has been a source of valuable metals. The name "Bawdwin" itself means "silver mine" in the local Shan language. Early exploitation, dating back to the 15th century, was conducted by Chinese miners who sought silver and discarded the lead. It wasn't until the early 20th century that the mine's full potential was realized.
Under the management of the British-owned Burma Corporation—which counted a young Herbert Hoover as a consulting engineer before he became a US president—Bawdwin became one of the world's largest producers of lead and a major source of silver before the Second World War. The mine's primary ore body, discovered in 1913 and named the "Chinaman Lode," was an immense deposit of argentiferous galena (lead-silver sulfide), sphalerite (zinc sulfide), and chalcopyrite (copper-iron sulfide). At its peak before 1942, the mine produced up to 500,000 tons of ore annually. The complex geology yields a mix of lead, zinc, silver, copper, and nickel.
A legacy in the riverbeds
Decades of intensive mining and processing have left a persistent toxic signature on the area. Waste rock and tailings, laden with heavy metals, have eroded into the local waterways. The contamination flows downstream into the Namtu River, a major waterway in the region. This is not a historical footnote; the metals settled in the riverbeds are an environmental problem.
The primary contaminants are lead (Pb) and zinc (Zn), the main products of the mine, but other dangerous heavy metals like cadmium (Cd) and arsenic (As) are also present in the waste. These metals do not easily break down. Instead, they bind to sediment particles on the river bottom. During periods of high water flow, these contaminated sediments can be resuspended and transported further downstream, extending the zone of pollution. This process creates a mobile reservoir of toxins that can be slowly released into the water column over many years. The metals can also accumulate in the floodplain soils during floods, contaminating agricultural land. Local communities have expressed fears about lead poisoning caused by runoff from the mining projects. The environmental damage from the original mining is compounded by ongoing and planned efforts to re-develop the mine, raising concerns for the health of thousands who live along the Namtu River.