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Abstract

Wolframite-bearing quartz veins that have peripheral greisen-type wall rock alteration products are present in and around the Black Pearl mine (about 18 km northeast of Bagdad, Arizona). The veins are spatially related to a small albitite stock, and the largest vein, which was the only one mined, is at the apex of the stock. On the basis of field relations, this stock is interpreted to be a late differentiate related to the 1400 Ma Lawler Peak Granite, which crops out within 3 km of the mine. Other, similar albitite bodies are common in the Black Pearl mine area. Sharp contacts with country rocks (schist, monzogranite, and granodiorite), relatively unaltered xenoliths, and consistent mineralogy throughout indicate that the albitite bodies are igneous, and have undergone relatively minor postmagmatic alteration.

A thin (1- to 2-m-wide) border pegmatite unit (“stockscheider”) exists at the contact of the albitite of the Black Pearl mine and the country rock. Directional indicators and other evidence indicate that the pegmatite was formed from a volatile-rich phase at the time of magma emplacement. The sudden change from potassium-feldspar-rich pegmatite to fine-grained albitite suggests a pressure-quench of the system, perhaps owing to fracturing of and escape of volatiles up the Black Pearl vein at the apex of the stock. Similar stockscheider textures are typical of the borders of productive plutons in tungsten and tin districts worldwide.

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