General geology of Chloride mining district, Sierra and Catron Counties, New Mexico
— Richard W. Harrison

The Chloride mining district has been an area of intermittent precious- and base-metal mining activity for the past hundred years. Metal values in excess of $18,000,000 have been produced from the district. Tertiary volcanic and volcaniclastic rocks of the Mogollon–Datil volcanic field host epithermal vein-type deposits. The oldest Tertiary unit in the Chloride district is the Rubio Peak Formation. Rubio Peak overlies Paleozoic rocks with angular unconformity and is divisible into a lower, sediment-dominated sequence overlain by a volcanic-dominated sequence. Very large exotic blocks of Paleozoic rocks occur as landslide deposits within the lower Rubio Peak Formation. Overlying Rubio Peak are Kneeling Nun Tuff, sandstone of Monument Park–Caballo Blanco Tuff–tuff of Koko Well, basaltic andesite of Poverty Creek, tuff of Little Mineral Creek– tuff of Stiver Canyon, and Moccasin John Rhyolite. Strike–slip faulting along north–northeast trends cut only Rubio Peak and older rocks. High-angle normal faults along north, northwest, north–northeast to northeast and east trends cut the entire stratigraphic section. Epithermal vein deposits occupy all fault trends. Vein deposits consist of quartz, calcite, (fluorite, barite) gangue material with sulfide mineralization occurring in structurally controlled shoots. Sulfide mineralization occurred in two stages in the southern portion of the district; an older stage of Pb, Zn, Cu, (Ag) mineralization, followed by stage of Cu, Ag mineralization. A single stage of Ag, Au, (Cu) mineralization occurred in the northern part of the district. Vein mineralization is spatially and temporally related to emplacement of Moccasin John-type intrusives.