Geology of Quartz-Lined Hypogene Caves of Southeastern Arizona

Abstract

Chiricahua Crystal Cave may be the only known limestone cave in the world that intersects room-sized quartz geodes (up to 16 m across). The cave is a relatively deep, laterally confined network maze, with zones of breakdown and vertical shafts. Large euhedral quartz crystals are found at all levels of the cave, lining vugs that range in size from centimeters to tens of meters. These geodes are crosscut by a network of phreatic tubes and abruptly terminating fissures that show little evidence of top-down flow or connection with surface hydrology. All surfaces of the cave below a certain elevation are covered with a thick coating of calcite mammillaries. The cave reflects a series of distinct geochemical environments. We propose that deep-seated hydrothermal silicic acid initiated the formation of the vugs and deposited a quartz rind as it cooled. Hypogenic (and likely hydrothermal) carbonic acid dissolved the subsequent passages and then vacated the cave. Subaerial conditions prevailed for a time before fluid once again entered the cave. A cooler, calcite-rich pool filled the lower reaches of the cave, depositing mammillaries in a stable environment with slow, steady atmospheric and hydrological mixing. Additional features, such as cupolas, solution pockets, phreatic tubes, corroded and altered surfaces, and vertical pits at the bottom of the cave (possible feeders), are also compatible with bottom-up thermal processes.