Mineralogy and paragenesis of the McAllister Sn-Ta-bearing pegmatite, Coosa County, Alabama

The McAllister Sn-Ta deposit (Alabama) is localized in a complex pegmatite that contains large zones of mineralized late-stage replacement-type saccharoidal albite and nearly monomineralic muscovite 'greisen-like' pipes. The dyke is at least 450 m long and averages approximately 9 m in thickness. At least two 'greisen-like' pipes, as much as 7.6 m by 4.5 m in cross-section and extending at least 76 m down a steep easterly pitch, occur near the center of the dyke. The dyke is hosted by an approximately 300-Ma-old pluton of a group referred to as the Rockford Granite, a mesozonal to epizonal two-mica, peraluminous tin-bearing granite. The pluton is genetically affiliated with a well-defined sequence of simple to complex pegmatite dykes and quartz-casiterite veins that occur near its margin and within the immediately adjacent metasedimentary rocks of the Wedowee Group.