cobbing

Cobbing is the process of breaking ore by hand with a hammer and removing unwanted rock or waste material on site, before the ore is hauled away for processing. A miner or cobber sits beside freshly extracted ore and strikes it with a specialized hammer to fracture it along natural planes, then discards the pieces of barren stone that do not contain economically valuable minerals. What reaches the surface as ore is mixed with considerable waste rock, and cobbing reduces haulage weight and improves the grade of material sent to the mill or concentrator.

The cobbing hammer, also called a cob hammer or picking hammer, is typically a long-handled tool with a head weighing 2 to 3.5 kilograms, featuring a pointed or wedge-shaped end on one face and a flat or slightly rounded striking face on the other. The miner uses the point to pry and fracture along grain lines, and the flat face to split pieces cleanly. Different ore types and hardness grades require different hammer weights and striking techniques; granite or siliceous ore calls for heavier impacts, while softer materials like clay-bound deposits can be worked with lighter blows.

Cobbing was historically performed at the pit head as ore was pulled to surface, and later at small sorting stations near open pits or underground mine entrances. The work is labour-intensive and repetitive, requiring good eye for distinguishing mineral-bearing rock from obvious waste. In hard-rock mining, particularly for metalliferous ores, a skilled cobber could remove 40 to 60 percent of waste rock before transport, substantially lowering costs when mines were remote or haulage expensive. Underground, cobbing was sometimes done by lamp-light in the stope itself to reduce the volume of broken ore moved through narrow passages.

Decline and residual use

Mechanical crushers, screens, and later flotation concentrators displaced hand cobbing through the 20th century. Dense media separation and X-ray sorting have further reduced demand for the skill. However, cobbing remains in use at small-scale artisanal and alluvial operations, particularly in emerging mineral districts or where ore grades are highly variable and selective hand-sorting reduces processing costs more than automated methods would. Gemstone mining and placer gold recovery in some regions still employ cobbing for initial grade improvement.

The term derives from the hammer itself, historically called a cob. Its etymology is uncertain, though it may relate to old English usage of 'cob' for a rounded lump or lumpy object. In British mining dialect, 'cobbing' entered standard vocabulary alongside terms like 'balling' and 'picking', all describing manual ore preparation work that preceded mechanical treatment.