New Mexico Geological Society Annual Spring Meeting — Abstracts

The Waldo-Graphic Mine is a zinc-lead deposit hosted by the MississippiaI. Kelly Limestone and the Pennsylvanian Sandia Formation. The ore bodies are localized near the contact with the Nitt monzonite stock and in north-trending fractures related to the development of the Cenozoic Magdalena and Socorro cauldrons. Mineralization occrs as both open-space filling and limestone replacement. The igneous rock exhibits prophyllitic and argillic alteration and the limestone has been altered to chlorite and skarn minerals.

The paragenesis encompasses: a skarn stage, formed above 320°C and includes the formation of hedenbergite, actinolite; quartz, specularite-magnetite aggregate; a sulfide stage, formed in the temperature range of 310-170°C and with formation of pyrite, dark colored sphalerite, chalcopyrite, galena, and minor quartz; and a carbonate stage, formed below 200°C,which contains calcite, barite, quartz, and minor light-colored sphalerite.

Fluid inclusion measurements from quartz, sphalerite, and barite show that the fluids responsible for are deposition had low salinity (0.2 to 7.4 eq. wt. % NaCl) and a Th range from 110°C to 367°C.

The theoretical pH values, calculated from fluid inclusion salinity and temperature, of the dark sphalerite fluid inclusions are in the range of 5.0 to 5.9; of light colored sphalerite, 5.8 to 6.3; of pre-ore quartz, 4.6 to 5.6; and of post-ore quartz, 5.9 to 7.3. Geochemical modeling of the fluids suggests an appropriate Zn depositional mechanism to be cooling, perhaps aided by slight rise in pH resulting from water-rock reaction.