The breccia pipes of Cave Peak are located on the eastern flank of the Sierra Diablo of west Texas. Three breccia pipes intruded along a 1-mile-long north-south line. The complex consists of a main pipe, with an associated quartz latite-quartz monzonite porphyry plug, and two smaller breccia pipes, both with associated rhyodacite plugs. The rocks and mineralized zones of the main (northernmost) breccia pipe have been investigated by over 42,000 feet of core drilling.Intrusion began 39 m.y. ago with emplacement of a small rhyodacite plug and breccia pipe. Farther north of this initial system a middle rhyodacite plug and breccia pipe developed, while immediately adjacent and slightly north of this middle pipe, the main Cave Peak breccia pipe ultimately formed. Quartz latite-quartz monzonite porphyry, which forms a plug within the main pipe, has been dated at 36 m.y. Development of multiphase molybdenum mineralized zones followed brecciation in the main pipe. The quartz latite-quartz monzonite porphyry plug, the breccia, and the molybdenum mineralization of the main pipe are all cut by 32-m.y.-old porphyritic quartz monzonite which emanated from a deeper, unexposed stock of molybdenum-bearing biotite granite porphyry discovered by deep drilling.The configuration, genetic sequence, and minerals associated with the multiple molybdenum mineralization events of the main Cave Peak breccia pipe are in many ways similar to molybdenum orebodies described from Colorado.

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