PETROLOGY AND MINERAL RESOURCES OF THE WIND MOUNTAIN LACCOLITH, CORNUDAS MOUNTAINS, NEW MEXICO AND TEXAS
VIRGINIA T. McLEMORE, VIRGIL W. LUETH and TIM C. PEASE
New Mexico Bureau of Mines and Mineral Resources, 801 Leroy Place, Socorro, New Mexico 87801, U.S.A.
JAMES R. GUILINGER
Addwest Minerals, Inc., 5460 Ward Road, Suite 370, Arvada, Colorado 80002, U.S.A.
Abstract
The Wind Mountain laccolith is one of many intrusive bodies found in the Cornudas Mountains. These intrusive bodies comprise the northern
part of the Trans-Pecos alkaline magmatic province in southern New Mexico and southwestern Texas. Ten laccoliths and stocks along with
numerous dikes, sills, and smaller plugs of varying textures have intruded Permian limestone and other sedimentary rocks in the Cornudas Mountains
area. Nepheline syenite predominates, although phonolite, trachyte, and syenite are common. The Wind Mountain laccolith is texturally and
mineralogically zoned, whereas the other intrusive bodies in the Cornudas Mountains seem homogeneous. Wind Mountain consists of
two textural varieties of nepheline syenite porphyry and four textural varieties of syenite porphyry. The zonation is attributed to crystal fractionation,
volatile separation, and cooling history, not to different pulses of magma. Feldspar crystallization under initially hypersolvus conditions can
account for most of the chemical variation in the volumetrically larger nepheline syenite zones. Subsolvus conditions of feldspar crystallization,
coupled with the separation of a volatile phase, was responsible for the chemical and mineralogical variation within the capping syenite units,
which form a rind at the top of the pluton. The Cornudas Mountains have been examined for potential economic deposits of gold, silver,
beryllium, rare-earth elements, niobium, and uranium, but no production has occurred. The nepheline syenite porphyry
at Wind Mountain is being considered as raw material for use in dark-colored glass, flatglass, and ceramics.