A sheet of mineralised rock filling a fracture — narrow, often high grade, and the classic underground target.
Definition
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.
Why it matters
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.
Where people go wrong
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.
See also
True Width — The actual thickness of a mineralized zone measured perpendicular to its orientation. Drill holes rarely inter…
Dilution — The unavoidable contamination of ore with waste rock during mining, which lowers the average grade of material…
Epithermal Deposit — A mineral deposit formed at shallow depths and low temperatures from hydrothermal fluids. Epithermal deposits …
Orogenic Gold — Gold deposits formed during mountain-building (orogenic) events, typically hosted in quartz veins within metam…
Stockwork — A complex network of small veins or veinlets forming a three-dimensional mesh in rock. Stockwork mineralizatio…