A sheet of mineralised rock filling a fracture — narrow, often high grade, and the classic underground target.
A sheet-like deposit of minerals that fills a fracture or fault in rock. Many gold deposits occur in quartz veins where gold was deposited from hydrothermal fluids. Veins can range from millimeters to meters in width.
Veins produce spectacular assays and modest tonnage. The question is never whether the grade is good, it is whether there is enough of it and whether it holds together at depth and along strike.
Narrow veins carry the worst dilution. A one-metre vein cannot be mined at one metre, so the grade delivered to the mill is always below the grade in the drill hole.
108 terms have their own page: the definition, why it matters to an investor, where it shows up in practice, and the mistake people make with it.