Barite/celestite/selenite/calcite mineralization at Bell Lake sink, Lea County, New Mexico

Abstract

Sulfur, carbon, oxygen and strontium isotope values of barite, celestite, selenite and calcite at Bell Lake Sink suggest that Bell Lake Sink may be a structure such as a breccia pipe which connects a brine reservoir at depth with the surface. The ultimate source of barium and strontium for the barite and celestite may be the anhydrites of the Castile and Salado Formations and also oil -field brines in the Bell Canyon Formation. Age of mineralization could be late Quaternary. INTRODUCTION AND PAST INVESTIGATIONS Bell Lake Sink is located in sec. 9, T24S, R33E, Lea County, New Mexico. Nicholson and Clebsch (1961, p. 46-47), who first discussed the origin of Bell Lake Sink, thought that it was a "collapse depression" and that the source of gypsum for the selenite dunes in the sink was "ground water seeping upward . . . from the Permian and Triassic formations. . . ." Anderson (1980a, p. 32) reported "large nodules of barite and celestite" occurring in selenite-gypsum dunes around the edge of a Pleistocene playa inside the sink. Anderson believed that Bell Lake Sink had developed due to collapse and that the selenite in the dunes originated from rising sulfate-rich water. Anderson also used Bell Lake Sink as a possible example of deep-seated dissolution and recent upward movement of fluids from a lower evaporite source (i.e., lower Salado and Castile Formations). Barrows et al. (1983) showed a gravity profile of Bell Lake Sink and concluded. that the sink had a complex density structure. Hill (1989a) reported on the celestite-barite-calcite mineralization at Bell Lake Sink to the Environmental Evaluation Group, Albuquerque, New Mexico. This paper is a condensed version of that report. DESCRIPTION OF MINERALIZATION Bell Lake Sink is a collapse structure along which "Mescalero caliche" and "Old Mescalero soil" has downdropped along sink-margin faults (Anderson, 1980b, p. 113, 115). The fault relationships suggest that the sink is younger than the "Old Mescalero sand" (less than about 100,000 years). Bell Lake playa, which is confined within the downfaulted center of the sink, is dry except in times of heavy rainfall. The playa is flanked by caliche and "old red soil," which contains quartzite, chert, basalt and caliche clasts possibly derived from the Ogallala Formation. No barite-celestite-selenite-calcite mineralization was found around the margins of Bell Lake playa. Two smaller playas exist inside the larger playa and are directly surrounded by selenite-clay dunes approximately 5-10 m high. The southern small playa contains water (filled by ranchers for stock?), but the northern small playa is dry. Barite-celestite nodules occur around the dry northern playa at the contact between a red and yellow oxidized zone, located about 2 m above a former water level (small pond) in the playa. Selenite mineralization that composes the surrounding dunes occurs above the zone of barite-celestite mineralization in the playa. This sequence suggests a solubility-transport relationship between the three sulfate minerals, with the more insoluble barite and celestite being deposited nearer to the small pond by upward-moving capillary water, and the more soluble and abundant selenite being transported farther from the pond to a higher level. The selenite at Bell Lake Sink is transparent to translucent, with crystals up to 10 cm long. Selenite roses about 5 cm in diameter are also interspersed within the clay of the dunes. The barite occurs as heavy nodules about 10 cm in diameter. The white, translucent, tabular barite of the nodules surrounds an intergrown core of clear, vitreous, transparent, euhedral celestite, most of which is colorless but some of which is slightly bluish on crystal tips. No calcite was found intergrown with the barite-celestite of these nodules. Celestite also occurs in other nodules as slightly bluish crystals imbedded in a fine-grained matrix of calcite. Celestite crystals extend into the centers of these nodules in a