Tuba dike is a monchiquite dike approximately 2 miles long which crops out in the lower Jurassic along the northern edge of the Painted Desert 12 miles northeast of the Cameron uranium mining district. The dike strikes almost due north and forms a low spinelike ridge rising out of the blow-sand-covered sedimentary strata.

The dike has a porphyritic texture consisting of olivine and calcite- and chlorite-replaced olivine phenocrysts in a matrix of unterlocking augite blades. Fractures filled with calcite parallel and crosscut the dike. Two carbonate-filled pipes lie just west of the center of the dike. The sandstones of these vents have been heavily impregnated by introduced calcite which has also invaded a large part of the sediments between the dike and the vents. Argillic alteration of montmorillonite to illite, concentrated in the sediments immediately adjacent to the dike, has produced relatively resistant borders of a wall-like nature at the dike contact.

Deuteric alteration, calcitic impregnation, and argillic alteration indicate considerable hydrothermal activity associated with the formation of the dike. The dike and accompanying alteration represent possible sources of hydrothermally introduced mineralization.

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