New Mexico Geological Society Annual Spring Meeting — Abstracts

The San Luis gold deposit is located about 5 miles northeast of the town of San Luis in Costilla county. It is owned by the Battle Mountain Gold Company. The indicated reserves are 11,021,000 tonnes of ore at 1.4 g/t gold in two mineable zones.

The study of the deposit is designed to charecterise the mineralogy, to determine the mineral zonation, the geochemical environment ofore deposition, type of deposit and establish the evolution and genesis of the deposit.

The gold mineralisation occurs as tabular bodies, in hydrothermally alterd zones in Precambrian biotite gneiss breccia, and to a lesser extent in biotite gneiss cataclasite, within and below a lowangle fault zone. The fault zone is preserved as unmineralised clay fault gouge which marks the upper extent of economic mineralisation. The hosting Precambrian rocks are overlain by a Precambrian gneissic granite and Tertiary-Quaternary sediments. Tertiary flows and dikes of felsite and andesite are present in the mine.

Alteration studies indicate that gold grade is associated with silicification and quartz-sericite-pyrite alteration. The peripheral areas to ore bodies are dominated by illite--chlorite--calcite and hematite-specularite alterations, which carry low-grade to non-detectible gold values. Sulfidization, sericitization, silification and carbonitization are indicated to have operated during the development of the ore deposit. Mineralogy and paragenesis studies indicate that the district, consisting ofseveral ore bodies, was mineralised by the same hydrothennal event.Trace element studies show that gold correlates with silver, lead and copper. This indicates that the gold deposition at San Luis was part of a polymetallic mineralising event. Both lateral and vertical fluid flow in the district is confirmed by wall-rock alteration.

Fluid inclusion measures in progress will be reported. Comparitve studies of the district are in process.