tying

Tying is the process of separating minerals from waste rock by washing crushed ore in a buddle, a shallow circular or oval basin with a gentle spiral current. Water and ore pulp flow around the sloped floor, where density differences cause heavy mineral particles to settle toward the center while lighter waste is carried to the outer lip and discharged. The method exploits gravity and fluid dynamics to sort material without chemicals or mechanical crushing.

A typical buddle receives ore ground to 1 to 3 mm mixed with water. The incoming slurry enters tangentially, creating a slow rotating flow; rotation speeds are kept between 5 and 15 revolutions per minute to avoid remixing settled material. Heavier minerals like cassiterite, wolframite, or magnetite accumulate in a central cone; operators rake this concentrate toward a collection point at the basin's lowest point. Lighter silicates and other waste discharge continuously over the outer rim or through a weir.

Tying works best for ores with clear density separation between the mineral sought and its host rock. Cassiterite (tin ore) in granitic host rock is ideal; magnetite concentration from iron-bearing sands is common. However, tying cannot separate minerals of similar density, and fine particles below 0.1 mm do not settle reliably in a buddle's modest depth. Modern flotation and magnetic separation have largely displaced traditional tying, though small-scale and artisanal operators still use buddles for tin and gold in some regions.

Buddle floors suffer steady erosion from the abrasive slurry and continuous raking. Liners of smooth stone, cast iron, or concrete ceramic extend service life, but replacement is frequent. Water supply must be consistent; fluctuating feed rate disrupts the settle pattern and degrades product grade. Operators learn to read the spiral flow by eye, adjusting blade angle and feed rate to maintain the balance between recovery and concentrate purity.

The term tying likely derives from the idea of tying or binding ore particles together in a unified flow rather than dispersing them. Historical sources on Cornish tin mining and Welsh lead mills use the word in this sense, and tying remains standard vocabulary in geology and mining heritage texts, even where the practice itself has become uncommon in industrial operations.