Abstract The first part of the day covers Precambrian stratigraphy and industrial mineral deposits in the Van Horn area. The Tumbledown Mountain talc deposit is situated on the northwestern flank of Beach Mountain, both of which are located a few miles north of Van Horn. The Milwhite talc deposit is reached by an unpaved road that traverses Red Valley and Hackberry Creek and crosses the Van Horn Sandstone, Hazel and Allamoore formations. In addition to the talc deposit in the Allamoore Formation, the complex structures in Tumbledown Mountain can also be observed. The lower Paleozoic Bliss, El Paso and Montoya Formation, and the Permian Hueco Limestone are well exposed in adjacent escarpments and fault blocks in this area. Thereafter, a visit will be made to the Texas Architectural Aggregate underground brucitic marble mine at Marble Canyon in the Sierra Diablo. The route is then retraced to Van Horn and the second part of the day is spent traveling westward on 1-1 o. Stops will be made at the Precambrian Carrizo Mountain Group, GiffordHill road metal quarry and Hillside fault, the type locality of the Texas Lineament. Further to the west a stop will be made at the Pioneer-Apache talc plant, and also to discuss the inactive fluorite deposits located to the south in the Eagle Mountains. Further to the west-northwest, along 1-1 0, the route crosses Eagle Flat and a final stop will be made to view the Sierra Blanca rhyolitic laccoliths and contained beryllium prospect. To the south of this locality is the Quitman Mountains, ring dike and intra-cauldron volcanic pile. The final part of the excursion route follows the Rio Grande Valley in a northwesterly direction to El Paso.

Abstract The Allamoore talc district comprises about 100 square miles of west-central Culberson and east-central Hudspeth Counties in Trans-Pecos Texas. Talc-bearing rocks occur within the late Proterozoic Allamoore Formation and crop out in a discontinuous belt about 20 miles long from Tumbledown Mountain, about 8 miles north-northwest of Van Horn, to the Streeruwitz Hills, about 5 miles northwest of Eagle Flat (Fig. 1). Talc production began in 1952. Annual district production for the past decade has ranged from about 200,000 tons to about 400,000 tons of talc (Fig. 2) with the latest available data for 1988 showing 261,000 tons of talc with a value of almost $4.5 million (Virta, 1988). The Allamoore district generally ranks third among domestic talc producers, accounting for about 20% of total production. There are four active talc producers in the Allamoore district: Milwhite, Pioneer, Texas Talc (Dal Minerals), and Southern Clay. The Milwhite property is located at Tumbledown Mountain, whereas the other open pit operations are located in the Allamoore area, eight miles west of Van Hom. The Milwhite beneficiation plant is six miles east of Van Horn, and the Pioneer plant is located at Allamoore.

Abstract During the' first part of the day, the route follows US 585 southward from Carlsbad to Orla and then takes FR 652 westward to the Pennzoil Culberson sulfur mine, located within the Permian Delaware Basin. From there the route proceeds southwestward on dirt roads across the western Delaware Basin to the site of the abandoned Elcor sulfur-derived-from-gypsum plant, where the Castile Formation is well-exposed in a nearby quarry. From this locality the route continues southwestward to the Seven Heart Gap barite deposit that is located between the Delaware Mountains and the Apache Mountains on the southwestern edge of the Delaware Basin. The final part of the route is accomplished by paved FR 2185 descending southward into the Salt Flat graben, traversing Wild Horse Flat, an irrigated farming area, to Van Horn.