New Mexico Geological Society Annual Spring Meeting — Abstracts

Petrographic and geochemical data are presented for a camptonite sill located in northwestern Lincoln County, New Mexico. The sill has intruded the Bridge Creek Member of the Greenhorn Formation (Late Cretaceous) and is well exposed in the roadcut on US-54 twelve miles north of Carrizozo, New Mexico. The phenocryst assemblage consists of: plagioclase, more dominant than orthoclase with no foid-bearing minerals observed; biotite, pseudohexagonal or irregular forms with optical zoning present; pyroxene, mainly as clinopyroxene (augite) and minor orthopyroxene (hypersthene); amphibole (hornblende), pleochroic yellow-green, and olivine. Plagioclase laths occur in the groundmass. The sill is calcalkaline, silica poor and calcium rich with high aluminum and titanium contents. Geochemistry is typical of the camptonite variety for a lamprophyre. This sill is chemically similar to the camponites found in the Sacramento Mountains and the nearby basinites and trachybasalt dikes associated with the Capitan Dike swarm.