A summary of the geology, geochemistry and tin occurrences in the Black Range, New Mexico
Ted L. Eggleston and David I. Norman
Tin deposits in the Black Range occur in Tertiary topaz-rhyolite lavas known as the Taylor Creek
Rhyolite. The deposits consist of hematite–cassiterite–wood-tin veinlets near exteriors of the host rhyolite
domes. Fluid inclusions in cassiterite and associated topaz and quartz are large vapor inclusions and unique
five-phase inclusions consisting of glass, vapor, and three daughter minerals at room temperature. At about
350°C the glass melts to form liquid-vapor inclusions that homogenize to a liquid at about 680°C. Quartz
associated with tin mineralization has an oxygen-isotopic composition of +7.5 permil. Fluid inclusions in
gangue minerals which include quartz, calcite, fluorite, and a number of fluoroarsenates homogenize at 130-
300°C and have salinities of about 0.5 equivalent wt% NaCI. Spatially and temporally associated zones of
intense vapor-phase recrystallization in the host rhyolite have del18O values of 8 permil.
The Taylor Creek Rhyolite is enriched in SiO2, F, Rb, and lithophile elements and depleted in TiO2, CaO,
Fe203, Sr, Ba, and V. Chondrite-normalized rare-earth-element pattems are flat, with large negative Eu anomalies.
Initial S87/Sr86 ratios are 0.708 and 0.710.
These data indicate that tin mineralization was deposited in a fumarolic environment from high-temperature
magmatic fluids in response to extreme thermal gradients. Quartz, calcite, and fluorite gangue minerals were
deposited from a short-lived, meteoric-water-dominated hydrothermal system at much lower temperatures. The
mineralizing fluids originated from the host rhyolites due to extreme differentiation in a shallow magma chamber.
This period of extreme differentiation is responsible for concentrating tin in the fluid phase of the rhyolite
magma. The magmas originated in either the upper mantle or lower crust.
- Eggleston, Ted L.; Norman, David I., 1986, A summary of the geology, geochemistry and tin occurrences in the Black Range, New Mexico, in: Truth or Consequences region, Clemons, R. E.; King, W. E.; Mack, G. H., New Mexico Geological Society, Guidebook, 37th Field Conference, pp. 173-177.