It has been established that the structural characteristics of gold deposits indicate how was deposited the gold and where can be found, and the gold veins form a key aspect. A fissure gold vein is a mineral mass tabular in form as a whole, though often irregular in detail, filling or accompanying a fracture or series of closely set and intimately related parallel fractures in the enclosing rock, the mineral mass having been formed later than both the country rock and the fracture, either through the filling of open spaces along the fracture or through chemical alteration of the adjoining rock.
A gold lode is a zone of fissuring that contains roughly parallel mineral masses of the general type of fissure veins, usually connected by cross veins and mineralized breccias to such a degree that over certain portions the whole width constitutes a single orebody. A ledge is an irregular mass of altered rock, containing ore bodies, the alteration of which is due to and characteristic of the action of mineralizing solutions. A gash vein is a gold vein of superficial character, widest near the surface and narrowing to extinction in depth. Gash veins are usually the results of solution and deposition along joints or small fissures by surface waters, and are of secondary origin. The term has been less correctly applied to lenticular gold that, prominent at the surface, die out in a similar manner in depth. The usual occurrence of gash veins is in sedimentary rocks. The typically short length of this type of gold vein should not lead to an expectation of continuity in depth, even if the origin is not suspected from study of the outcrop.
A gold bed vein is a vein that follows a bedding plane of an enclosing sedimentary rock, less frequently a plane between layers of volcanic rocks. Bed veins are commonly thought to be less persistent than veins that cut across the strata of enclosing rocks; many cases are known, however, where bed veins are both persistent and contain important values. Blanket vein is often used as a synonym for bed vein, but actually refers to a horizontal or nearly horizontal position only. A bed vein in unaltered rocks is sometimes distinguished with difficulty from a stratum whose mineralization was contemporaneous with its own deposition. In the examination of an unaltered bed, an opinion may usually be based upon the closeness with which the mineralization follows the minute bedding planes as well as the larger bed divisions; if the mineralization follows the larger bedding features and does not penetrate the relatively solid intervening strata, it is probably later in origin than the bed itself.
Fragments of country rock or the presence of cross or branching stringers are definite signs of a later origin. Furthermore, a mineralization that is not relatively continuous through a certain stratum, but is transferred to strata above and below without corresponding lateral extent, is later than the containing bed. For example, In the old deposit of Coeur D'Alenes, Idaho, a majority of the auriferous quartz veins are of the bed-vein type. These veins in some places occur singly, but more commonly they occur in groups, individual veins being separated by a few centimeters or a few meters of slaty country rock. An overlapping arrangement is common; one vein gradually pinching out while a parallel vein between adjacent beds becomes correspondingly thicker. Although certain individual gold veins persist for hundreds of meters without cutting across the planes of stratification, such crossings may be observed here and there and cross-cutting stringers of quartz that link neighboring veins are numerous.