New Mexico Geological Society Annual Spring Meeting — Abstracts

The Gold Hill mining district occurs approximately 20 km northeast of Lordsburg, New Mexico. Gold-bearing quartz veins, found throughout the district, are most numerous in the central part. The majority of these veins occur along diabase dikes that strike N400 W to N, and dip 20°-60°. Host rocks are upper amphibolite grade supracrustals of the Bullard Peak Series (minimum age 1550 m.a.l), Burro Mountain granite (1450 m.al), and diorite and quartz monzonite of unknown age. Diabase dikes are not foliated, but some are intensely fractured parallel to strike. Near vertical basaltic and rhyolitic dikes, striking N60 E to E, crosscut the diabase dikes. Quartz veins along basaltic and rhyolitic dikes are nearly barren of mineralization.

Veins range up to a meter in width, but most are less than quartz, minor pyrite, and Fe-Mn oxides. Oxidized vein material, found almost exclusively on dumps, has a gossan texture and consists of Fe-Mn oxides and quartz. Values of unoxidized veins range up to .37 oz. Au/ton and up to .90 oz. Ag/ton. Nealryall host rock Au and Ag values are below detection limits (10 ppb and 5 ppm, respectively). Mineralization has been dated as early Cenozoicl, and may be related to Laramide intrusive activity in the Region.