METEORIC VERSUS MAGMATIC-HYDROTHERMAL CALCITES IN LICK CREEK CAVE, LITTLE BELT MOUNTAINS, MONTANA, USA

摘要

Lick Creek Cave in northern Montana, USA, is hosted in limestones of the Lower Carboniferous Madison Group near Tiger Butte, an Eocene quartz-syenite porphyry intrusive dome. The cave is located within the zone of contact metamorphism of the dome that crops out ~ 300 m from the cave entrance. The cave consists of two genetically distinct cave systems separated by a fracture zone: (i) a ~ 80 x 50 m dome-shaped cavern in breccias of a Carboniferous palaeocave, and (ii) anastomosing conduits ~ 2-10 m across, parallel to the bedding of the Madison Group and extending 100 m updip to the present cave entrance. The conduits are further subdivided into a tectonized and a maze zone and are variably decorated in several combinations by phreatic isopachous calcite spar cements, with crystals up to several cm long, and with vadose speleothems, including stalactite-stalagmite pairs, flowstone, corallite (cave popcorn), and moonmilk.