New Mexico Mineral Symposium — Abstracts

The Buckhom mine is in the Red Cloud mining district, Gallinas Mountains, Lincoln County, New Mexico. The district contains alkaline igneous rocks with associated base-metal and rare-earth mineralization. The Gallinas Mountains are one of a series of alkalic igneous intrusive centers that form stocks, laccoliths, dikes, and sills of middle to late Tertiary age along and near the margin between the Great Plains and the Rocky Mountains or Basin and Range physiographic provinces in New Mexico.

Intrusive igneous rocks of Oligocene age in the Gallinas Mountains include rhyolite, trachyte, latite, intrusive breccia pipes, and a few dikes of andesite and basalt. Host rocks include Precambrian granite and gneiss and the sedimentary Abo, Yeso, and Glorieta Formations of Permian age. Mineral deposits in the Gallinas Mountains include limestone-replacement iron deposits and veins and breccias that contain concentrations of copper, lead, fluorine, barium, and rare-earth elements, with some anomalous amounts of gold and silver. The intrusive breccias and adjacent country rocks in the district show evidence for several types of alteration, primarily fenitization (introduction of K- and Na-feldspar, sodic pyroxenes, and sodic amphiboles) and carbonatization (replacement by calcite). Apatite, zircon, pyrochlore, monazite, thorite, pyrite, and rutile occur in the ferrite veinlets.

The Buckhom mine, about 2,000 ft east of Rough Mountain in the southeastern Gallinas Mountains, consists of one adit, three shafts, and several prospect pits along a northwest-trending breccia zone. Primary ore minerals include cavity-filling galena, tennantite, argentian tennantite/frei¬bergite, and proustite, plus K-feldspar, xenotime, zircon, fluorite, barite, quartz, calcite, and pyrite. Secondary alteration of the tennantite and sulfide minerals has produced other sulfides (covellite, digenite); silicates (chrysocolla, shattuckite); carbonates (malachite, azurite, cerussite); sulfates (brochantite, cyanotrichite); a sulfate-halide (spangolite); arsenates (adamite, cuprian austinite, comubite, duftite, arsentsumebite); a chloroarsenate (mimetite); and a late-stage copper-bearing clay mineral. An unusual feature is the presence of secondary silver halide minerals including iodargyrite (AgI) and a silver-mercury-sulfide-iodide mineral, possibly related to perroudite,
Hg_5-xAg_4+xS_5-x(Cl,I,Br)_4+x, or capgaronnite, HgAgS(Cl,Br,I). The iodargyrite occurs as thin prismatic crystals (<30 microns long) within rims of shattuckite and chrysocolla that surround proustite. The Ag-Hg-S-I phase occurs as <5-micron crystals around altered tennantite.