lode

A lode is a sheet-like body of ore that fills a fracture or fissure in rock, bounded by walls of country rock on either side. Unlike scattered ore deposits, a lode has defined limits and can be worked systematically. The ore runs through solid rock in a relatively continuous band, which makes it economically mineable when the metal content justifies extraction.

Lodes form when hot, mineral-rich fluids percolate through cracks in cooling bedrock. As temperature and pressure drop, metals precipitate out and accumulate in the fissure over geological time. The width of a lode can range from a few centimetres to several metres, and productive lodes may extend hundreds of metres vertically and laterally. Gold, silver, copper, tin, and lead commonly occur in lodes, often alongside quartz or other gangue minerals.

Underground mining of lodes typically involves sinking a shaft to reach the vein, then driving horizontal adits or cross-cuts to intersect it. Miners then develop the vein by cutting parallel to the lode walls, creating a working space called a stope. The ore is extracted in benches or slices and transported to the surface. The defined geometry of a lode means a miner knows where to look and can plan the mine layout accordingly, unlike open-pit or alluvial deposits.

Lodes can fail when ore grade drops sharply, when the vein pinches out (narrows to nothing), or when it intersects with faulting or dead-weight country rock. Miners who drive into adjacent wall rock waste labour and time. The orientation of the lode, dip angle, and structural stability all affect extraction costs and safety.

The term lode is older than vein in mining English, appearing in Welsh and Cornish mining contexts by the 16th century. It is often synonymous with vein today, though some geologists reserve lode for metal-bearing veins and use vein more broadly. The complementary term lodestar originally meant a guide or standard, derived from the mining sense of lode as a reliable, fixed reference.