MineralTrue width is measured perpendicular to the boundaries of the mineralised body. A downhole interval measures the path through that body along the drill hole. The two lengths are equal only in the appropriate perpendicular geometry.
An oblique hole can travel farther inside the same body, producing a longer downhole interval. Hole angle by itself is insufficient to convert the interval; the orientation of the mineralisation also matters.
The JORC 2012 reporting checklist asks authors to state the relationship between geometry and drill-hole angle when known, and to disclose when only downhole lengths are available.
Do not infer a missing width
Where the issuer has not established the geometry, preserve the reported interval and label true width as unknown. A simple trigonometric estimate cannot resolve folding, irregular contacts or changing orientation.
For a straight interval crossing parallel, planar contacts, estimated thickness = downhole interval × sin(angle between hole and body plane). A 20 m interval crossing at 30° gives 10 m. The input is the angle to the mineralised plane, not the collar dip.