J.F. Benedict | USGS Science

USGS1994

Simulation of ground-water flow and potential land subsidence, upper Santa Cruz Basin, Arizona

A numerical ground-water flow model of the upper Santa Cruz basin in Pinal, Pima, and Santa Cruz Counties was developed to evaluate predevelopment conditions in 1940, ground-water withdrawals for 1940-86, and potential water-level declines and land subsidence for 1987-2024. Simulations of steady-state ground-water conditions indicate 12,900 acre-feet of ground-water inflow, 15,260 acre-feet of outflow, 53,000 acre-feet of pre- development pumpage, 29,840 acre-feet of mountain- front recharge, and 34,020 acre-feet of streamflow infiltration in 1940. Simulations of transient ground-water conditions indicate a total of 6.6 million acre-feet of net pumpage and 3.4 million acre-feet of water removed from aquifer storage for 1941-86. A difference of 1.2 million acre-feet between estimated and net pumpage is attributed to increased recharge from irrigation return flow, mine return flow, and infiltration of sewage effluent. Estimated natural recharge represents 40 percent of pumpage for 1966-86 and averaged 63,860 acre-feet per year for 1940-57 and 76,250 acre-feet per year for 1958-86. The increase in recharge after 1958 was coincident with above- average winter streamflow in the Santa Cruz River for 1959-86. Increased recharge after 1958 and decreased pumpage after 1975 contributed to decreased water-level declines or to recoveries after 1977 in wells near the Santa Cruz River and its tributaries. The results of projection simu- lations indicate that a maximum potential subsi- dence for 1987-2024 ranges from 1.2 feet for an inelastic specific storage of .0001 ft to 12 feet for an inelastic specific storage of .0015 ft. The simulations were made on the basis of pumpage and recharge rates from 1986 and by using a preconso- lidation-stress threshold of 100 feet. A permanent reduction in acquitard storage can range from 1 to 12 percent of the potential loss of 3.9 million acre-feet in aquifer-system storage for 1987-2024.

Water-Resources Investigations Report↗

USGS1982

Geologic reconnaissance and geochemical sampling survey of molybdenum mineralization near Schiestler Peak, Temple Peak Quadrangle, Sublette County, Wyoming

A brief geologic reconnaissance and geochemical survey of molybdenum mineralization near Schiestler Peak, Sublette County, Wyo., indicates that molybdenite occurs in this area as disseminations and blebs in granitic or quartz monzonitic rocks intruded by felsic dikes of similar composition. Samples of stream sediments, panned concentrates from stream sediments, soils, rocks, and water were collected in the geochemical survey. Analytical results show that in reconnaissance, panned concentrates are the best of the sample types used in this study to detect molybdenum mineralization. More detailed analysis of the distribution of the molybdenum is best achieved through the collection of rock samples. Hydrothermal alteration is generally not conspicuous in the study area; however, rock samples that contain molybdenite are usually slightly enriched in silver, copper, lead, and in several instances, gold. Conversely, there appear to be negative associations between molybdenum and zinc and between molybdenum and several of the rare-earth elements. Mo concentrations in the rock samples with no visible molybdenite range from undetectable at a sensitivity of 5 parts per million (ppm) to 700 ppm. Mo content in rock samples containing visible molybdenite ranges from 10 ppm to greater than 2,000 ppm. Stream-sediment values range from undetected to 15 ppm; panned concentrates from undetected to 15 ppm; soils from undetected to 20 ppm. Analyses of the water samples indicate Mo concentrations from 0.8 parts per billion (ppb) to 4.8 ppb. As currently understood, this deposit is not extensive or continuous, but drilling to provide information on the vertical extent of mineralization may alter this opinion.

Open-File Report↗