streamwork

Streamwork is an alluvial tin operation worked in or near watercourses, targeting cassiterite deposits that have been concentrated by natural water movement over geological time. Unlike hard rock mining, which requires shaft sinking and underground extraction, streamwork exploits tin that has already been liberated from bedrock and redeposited in gravel beds, sand layers, and clay horizons within riverbeds, flood plains, and ancient stream channels. The ore is typically loose or weakly cemented, making extraction mechanically simple but dependent on hydrology and seasonal water availability.

Streamwork sites range from small artisanal operations working a single riverbed section with hand tools and gravity separation, to larger mechanised workings using dredges, draglines, or bucket-wheel excavators. Water is essential: it is used both for moving overburden and for washing and concentrating cassiterite. Many streamwork operations in Southeast Asia, Cornwall, and West Africa have operated continuously for centuries, with evidence of tin recovery in alluvium dating back to pre-industrial periods.

Working deposits and environmental constraints

Cassiterite in alluvial deposits occurs alongside other heavy minerals, magnetite, ilmenite, and zircon, all of which settle together in the same sedimentary environments. Grade varies widely: alluvial tin ore may run 0.01% to 0.5% tin by weight, depending on the degree of natural concentration and the volume of barren overburden. The deposits are finite and non-renewable on a human timescale, and extraction necessarily removes the entire gravel column, leaving behind open pits or ponds. Streamwork therefore alters drainage, removes riparian vegetation, and generates heavy sediment loads in receiving watercourses.

The name reflects the literal geography: tin is worked from the stream itself or from alluvium deposited by stream action. The term is most common in Commonwealth mining usage and older colonial literature. Modern regulations in most jurisdictions now require environmental impact assessment and restoration plans before streamwork is permitted. Where alluvium is thick and tin values are sufficient, however, the low extraction cost and absence of underground hazards still make streamwork economically attractive compared to underground tin mining.