Gold veins vary in width or thickness from 0.10 m to 20 m. They may pinch or widen at intervals in their downward course. The widest mother veins are not always the most productive, although they may be very persistent in length and sometimes in depth. In some veins of quartz the development of gold mineralization is not good and the valuable minerals are scattered in them, and the development is less easy than narrow veins where gold is more concentrated.
It has been noted that as a fault fissure in its downward course usually pursues a zigzag rather than a straight course with smooth surfaces on either side of the crack, the inequalities of one face of the crack are brought into opposition to the inequalities on the other face, as one or the other side of the fault slips up or down, producing pinches and wide cavities, which modify the vein width and tend to go to the pinches. In some circumstances, a fissure vein may have advantages over other forms of vein occurrence, from its persistency and comparatively regularity to great depths.
Basically, prospectors must not expect that a vein will continue equally rich or poor throughout its course. There may be comparatively spots with low and high mineralization, pinches and widening, local combinations of richer or poorer varieties of gold bearing minerals. But the vein is not likely to entirely disappear easily. In some deposits was noted that gold veins grow less rich and strong with depths, although strong veins may indicate weak mineralization to a greater depth than mining can ever reach. Basically, deep mines have been worked through alternate zones of richness and very low grade due to orebodies are scattered irregularly and the lower grade zone is at the bottom. On the other hand, some of the most celebrated gold mines derived their wealth from rich zones found near the surface and have proved most disappointing with depth.
According to some geologists, atmospheric action for a long period has often reduced the ore to its richness compound, and when the hard material is reached, leanness set in. This is the typical case of many gold veins. Essentially, the richness of gold mines is derived from their decomposed compounds, as the surface crust can be so little explored, it is important to keep in mind that the erosion by glaciers and water has removed thousands of meters of the vein. It means that gold prospectors may detect a small fraction of the gold deposit and unknown quantities lies in the depths below. Some gold deposits are characterized veins occurring in clusters and forming nearly parallel groups and they be grouped forming a belt. In this way, it is possible to have different belts carrying different minerals such as auriferous pyrite belt, argentiferous galena belt or golf-silver belts.