Gold veins were courses of water, more are less heated and alkaline channels whose formation is related to hot ore springs carrying earthy minerals and metals in the same solution and depositing them, partly by cooling and sometime by chemical precipitation and mainly by relief of pressure in such openings or weak places. It has been noted that the origin of these openings and weak places is not simple. The class of great fissures holding fissure veins, cleaving our mountains from top to bottom to an unknown great depth was produced by the fracturing and faulting of rocks. In the gradual process of folding upwards, and elevation of the mountain system, there is process so slow and gradual that it may be even progressing with one noticing it.
The relief of extreme tension from folding results finally in faulting. The fault fissure may extend to very great depths gradually. Also, from time to time, the shock produced a fissure in a slip of only few inches may grow. Basically, a great severe fault fissure was likely to be accompanied by minor adjacent faults and by small incipient fissures or loose fractures of the rocks, producing parallel fissures and zones of fissure veins. Other opening occupied by fissure veins may be compared to those joints common to all rocks, the results of contraction and shrinkage of the granitic or volcanic rocks from soft, semi plastic condition to one more solid and compact. In some cases, the fissures now occupied by veins 5 to 30 m wide were modified with the time. Rather than cracks fitting very tightly together by enormous lateral pressure such as that produced in fault cracks.
These narrow cracks were under alkaline and acid solutions and enlarged the process; the rock gradually was replaced by gangue and metals carrying gold. The process is further assisted by the shattered character of the rock commonly present near a fault. This cavity was sooner or later replaced by minerals. Some of the broken rocks being not consumed were left forming fragments in the vein, which when small are called breccia and when large are called horses. The great fissures in volcanic veins are formed by cooling and contraction of the lava.
In some gold deposits forming bedded deposits in limestone find the formation in solution through the vertical joints common to all water formed rocks, resulting from contraction in consolidating from a soft, muddy condition. Such veins and fissures are short and act like channels to a more important line of weakness occupied by the main body of the gold deposit, the dividing line between one stratum and another. Another line of weakness for the attack of mineral solutions is at the juncture of a dyke with some other rock. The interval between them is often occupied by a contact vein. The heat of volcanic compounds with stream may have influenced the solutions.