New Mexico Geological Society Annual Spring Meeting — Abstracts

A finite difference ground-water flow model has been developed for the area surrounding Tyrone, New Mexico, to determine the effects of
dewatering an open-pit copper mine and pumping adjacent wells on regional water levels and stream flows.

The open-pit mine straddles the Continental Divide at the eastern edge of the Big Burro Mountains in southwestern New Mexico. The model area includes a portion of the Big Burro Mountains which are composed primarily of granite and associated rocks along with the Tyrone quartz monzonite stock, the Little Burro Mountains, and intervening valley areas which are underlain by the Gila Conglomerate. The model includes portions of two ground-water basins managed by the state engineer: the Mimbres and the Gila-San Francisco basins.

Initial estimates of hydraulic parameters for the flow model were developed on the basis of the hydrogeologic characteristics of the formations and aquifer tests. The parameters were refined within the empirically estimated range through two transient calibration simulations. The simulations were performed over the period April 1952 to June 1953, during which time four wells were pumped and water levels were monitored in nearby wells, and the period January 1971 to February 1985, during which time the mine was in operation and for which pumping, tailings pond seepage, and water level records were available. The model was then used to calculate the drawdown at nearby existing wells and the depletion in the flow of Mangas Creek which would result from proposed pumping at the mine.