Narrow-vein stoping practice: a United Kingdom perspective

Metalliferous narrow-vein deposits are generally exploited underground and represent worldwide a valuable resource of metals-in particular, gold. In t he United Kingdom a single gold operation remains in Wales, but the Cornish tin-mining industry has left behind it a wealth of practical expertise. Se veral new projects are under development within the United Kingdom. Narrow veins are challenging to evaluate and exploit. They are generally le ss than 3 m wide, discordant and of variable dip and display a complex stru cture and paragenesis. A high degree of geometrical and grade discontinuity (nugget effect) often makes it difficult to assess their shape and reserve s from drill data alone, necessitating expensive underground development an d infill drilling-typically at 30-m centres or less. Detailed geological un derstanding is crucial for effective reserve evaluation and exploitation. Typical extraction methods include overhand shrinkage, cut-and-fill and ree f open stoping (entry methods) and sub-level open stoping (a non-entry meth od). In all cases mining is typified by the drill-blast-muck cycle. The cho ice of method is governed by geology and ground conditions and involves con sideration of efficiency (recovery/dilution), safety and capital and operat ing costs. Among the geological variables that require consideration are th e vein geometry, rock types, tectonic effects, grade distribution, geotechn ical properties and hydrogeology. Mining may represent up to 70% of the tot al operating costs, of which labour forms a large part (up to 40%). However , with strong geological input and close collaboration between the geologis t and engineer at both the feasibility and production stages viable operati ons are possible.