New Mexico Geological Society Annual Spring Meeting — Abstracts

The Victorio mining district, southwestern New Mexico, hosts tIiree types of mineral deposits that are spatially related (from the outer most zone to central zone): carbonate-hosted lead-zinc replacement, W -Be-Mo skarn/vein, and porphyry-Mo deposits.

There are three types of fluid inclusions found within the different deposits; primary twophase liquid-vapor, primary three-phase inclusions that include liquid CO₂, and secondary three phase inclusions that contained a solid mineral phase. Fluid inclusions that contain liquid CO₂ are primarily found in fluorite and quartz from the granite, the skarn and porphyry deposits. Two-phase liquid vapor inclusions show evidence of dissolved liquid CO₂ and are primarily found in the carbonate-hosted deposits. The inclusions with the solid mineral phases are found in fluorite from the skarn deposits.

The fluid inclusions from the porphyry deposit has a homogenization temperature range of 208 315°C and salinities between 2.0 -11.9 eq. wt% NaCl. The fluid inclusions from the skarn deposits have a range of homogenization temperatures from 180 -350°C and have salinities 2 -22.5 eq. wt% NaCl. The fluid inclusions from the carbonate-hosted replacement samples have a range of homogenization temperatures of 105-289°C and salinities <2 -5 eq., wt% NaCl. The carbonate-hosted replacement deposits contains two types of primary inclusions; one type are liquid-vapor inclusions and the other type are two-phase inclusions that only contain liquid and vapor-CO₂. The presence of two separate primary phases indicates that boiling may have occurred during the mineralization of this deposit. The results from the fluid inclusion analysis indicate the carbonate-hosted replacement deposits are slightly lower in temperature and salinity than the skarn and porphyry deposits.

Gases analyzed from fluid inclusions plot in two different compositional fields. The porphyry, skarns, and siliceous veins from the carbonate-hosted replacement deposits fall between the boundary of magmatic and shallow meteoric waters. The samples that plot in the magmatic and shallow meteoric fields also contain more CO₂ gas and hydrocarbons. Two samples, a breccia pipe sample and a sulfide sample from the carbonate-hosted replacement deposit, plot in the crustal waters field.

Pyrite and molybdenite from the skarns and porphyry samples and galena, sphalerite and pyrite from the carbonate-hosted deposits were analyzed for sulfur isotopes. The δ³⁴S values ranged from 2.9 to 6.0 %0 for the skarns and granite; one pyrite sample value was -11.2%from the skarns. The molybdenum samples in the skarns and granites had values that range from 4.7 to 6.7 %. The carbonate-hosted value for pyrite is 4.8 %0; galena had a value of 4.0 %0; sphalerite values ranged from 4.4 to 4.5 %. Using the fractionation factors for sulfides shows the majority of the calculated δ³⁴S_H2S values for the skarns, granite and carbonate-hosted deposits plot between 2.0 and 6.0%. This indicates calculated δ³⁴S_H2S values for the mineralizing fluid of the skarns; carbonate-hosted deposits and granite are similar and are consistent with the three types of mineral deposits being derived from a similar mineralizing fluid.

Limestone and calcite sampled from drill hole GVM 21, within the skarn deposits, were analyzed for carbon and oxygen isotope values. The results indicate that both carbon and oxygen isotopes values shift from unaltered values with an increased Mo and WO₃ concentrations. This evidence suggests a greater water/rock ratio for the samples with high metals concentrations.

Collectively, the is geochemical and isotopic evidence suggests that the skarns and porphyry-Mo deposits are related to the intrusion of the Victorio Granite, and it is possible that the carbonate-hosted lead-zinc replacement deposits were mineralized during this same event.
These data are consistent with a proposed model for the district which requires a change in temperature and salinity to move from high temperature skarn mineralization to lower temperature carbonate-hosted replacement mineralization.