GEOLOGIC SETTING The mining district lies in the Laramide Arizona-Sonora-New Mexico porphyry copper belt. It is the oldest porphyry copper deposit in the state; although the Piños Altos pluton is ca. 74.4 Ma (McDowell, 1971) and a Georgetown monzonite dike has been dated as ca. 71 Ma (McLemore, 1998), both of which have associated Cu-Au-Ag skarn or Ag carbonate-hosted replacement deposits.
The Twin Peaks monzonite porphyry in the Burro Mountains is 72.5 Ma (Hedlund, 1980) and a hornblende andesite in the Hidalgo Formation in the Little Hatchet Mountains is 71.4 Ma (Lawton et al., 1993). Polymetallic veins and alteration suggests that a porphyry may underlie the Lordsburg district (57.4 Ma, McLemore et al., 2000a). Porphyry copper deposits are not known to occur in these areas, but certainly the possibility exists that deposits may occur undiscovered in the subsurface.
Geology indicates that this epithermal ore vein occurrence is the result of the halo effect caused by a nearby “porphyry” deposit. It is well known that “Porphyry” deposits exist throughout the district. Our consulting geologist has identified evidence of an undeveloped ‘Porphyry’ deposit quite close or beneath this property.