New Mexico Geological Society Annual Spring Meeting — Abstracts

The intersection of the Capitan Lineament (CL) and the Lincoln Country Porphyry Belt (LCPB) is a region of intense volcanism, plutonism, and mineralization. The CL is an E-W structure that focused volcanism, plutonism, and mineralization across central NM. The diversity of igneous rocks and mineral deposits in this region suggests highly fractionated and differentiated magmas. The existing K-Ar and ⁴⁰Ar/³⁹Ar ages* indicates that magmatism occurred during multiple pulses, rather than one single event.

The eastern-most intrusion along the CL is the 27.9 Ma Railroad dike, whereas the calderas in the Socorro and Magdalena Mts (24.3-32.1 Ma*) define the western limit. The LCPB is a N-S belt of Tertiary porphyritic calc-alkaline to alkaline rocks that were emplaced in three pulses: 36-5-38.2 Ma, 26-30 Ma, and 26-28 Ma and are associated with Au-Ag-Te veins, REE-Th-U veins, Fe (±Au) skarns, and porphyry Mo deposits. Three compositionally complex stocks intrude the Sierra Blanca volcanics (36.5-38.2 Ma): Bonito Lake (26.6 Ma), Three Rivers (36.36 Ma*), and Rialto (31.4 Ma). The 28.8 Ma* Capitan pluton forms the eastern part of the LCPB and is the largest Tertiary intrusion in NM. The zoned Capitan pluton is associated with Fe skarns and REE-Th-U-Au vein deposits.

The unmineralized Carrizozo lava flow (near Carrizozo) is the youngest of the volcanic rocks along the CL (3-4, 10-11 ka). The E-W trending Jones Camp dike south of Chupadera Mesa is 27.9 Ma and the NE-SW trending Chupadera Mesa dike (southern Torrance Co) is 30.2 Ma. Additional dike swarms are found throughout the Chupadera Mesa area.

East of Socorro several small deposits of Cu-Ag-U (±Fe, Au) and Rio Grande rift (RGR) barite-fluoritegalena deposits are found along faults, are not directly associated with igneous activity, and could represent migration of mineralizing fluids along rift structures. 40Ar/39Ar ages and field relationships suggest that RGR deposits formed during the last 12 m.y. coincident with the later stages of rifting in central NM. Most of the available ages of igneous activity are K/Ar dates; detailed, high precision geochronology will be required to fully understand the relationships between regional volcanism, plutonism, and mineralization.

* denotes ⁴⁰Ar/³⁹Ar ages from NM Geochron Laboratory. All other ages are K-Ar ages from literature.