streamworks

A streamwork is a mine site established in or beside a watercourse to extract alluvial tin ore, mainly cassiterite, from the unconsolidated sediments deposited over millennia. Unlike hard rock mining, which sinks shafts into solid bedrock, streamworks exploit the natural sorting action of flowing water that has already concentrated heavy ore minerals in predictable layers and pockets along stream floors and ancient terraces.

The geology underlying a streamwork is straightforward: granite or other igneous rocks containing tin ore weather and erode upstream; tin-bearing minerals, being heavy, settle faster than lighter silicates and clays, accumulating in the streambed along bends, behind boulders, and in bedrock depressions. The useful layer, called the tin ground, often sits 2 to 10 metres below the modern stream surface, buried under overburden of clay, sand, and gravel. Streamworks reached their peak in Cornwall and Devon from medieval times through the 19th century, and remain active in parts of Southeast Asia and South America.

Working a streamwork traditionally involved driving the watercourse aside with leats or temporary dams, then excavating the exposed tin ground by hand or, later, with mechanical diggers and water pumps. The ore-bearing sediment was then washed and jigged to separate cassiterite from waste material. This method is efficient where alluvial concentrations are rich enough but water and ground conditions are accessible; it becomes uneconomical where the overburden is thick, the deposit is diffuse, or environmental constraints restrict water management.

Streamworks and stream tin mining

The term streamworks covers both formal, organized operations and small-scale or artisanal workings. Organized streamworks typically held a formal claim or lease; in Cornwall, these were overseen by the Stannary Courts. Informal stream tin mining, sometimes called tinning or panning, remains common in developing countries where individual miners work creek beds without formal tenure, using gravity separation on a much smaller scale. Modern large-scale alluvial tin mining in places like Indonesia and Myanmar uses draglines and dredges; these are industrial descendants of the streamwork principle, though they operate at scales and with equipment the medieval tinners could never have imagined.

The name reflects the geography: stream refers to the watercourse itself, and works