Mother Lode and Sierra Nevada Batholith

A mineralized and silicified zone which dips more gently than the wall rock and is accompanied by reverse faulting or thrusting is denned as a "mother-lode structure." The western border of the Sierra Nevada batholith is accompanied by a belt of such structures. A tripartite arrangement which coincides with three distinctly different portions of the batholith can be recognized in this belt: (I) a southern portion of scattered lodes within the boundaries of the widest portion of the batholith; (2) a medial continuous zone (the Mother Lode proper) west of the batholith; and (3) a northern extension of scattered, rich lodes which are closely related to the contacts of scattered and small massifs. The divisions of the batholith are believed to be accidental and due to a northward plunge of the mass; lower levels are exposed in the southern region and higher levels in the north. Gold production and mining values increase from south to north and seem to be highest where the shallowest levels of the batholith are encountered. The plunge of the pluton would explain why the southern area is almost devoid of paying gold deposits. The first appearance of a uniform Mother Lode trend is indicated by a series of intrusions which accompanied a post-Carboniferous and pre-Jurassic orogeny.