Definition of "vug"

The Bureau explored on both the Crystal Spar and Calcium groups. An adit was driven 128 feet on the Crystal Spar group to intersect vug 1, which showed in the outcrop of the vein. The adit penetrated the vug 57 feet below the outcrop and at this level found that it was filled with material that had rolled in from the surface and sloughed off the walls. Only a few small crystals were found in the mud above the adit level. A winze 20 feet deep was then sunk in this vug to explore it below the adit level to make sure no valuable crystals were overlooked, but only small noncommercial crystals were found. A station was cut 28 feet from the face of the adit and a crosscut was driven 39 feet northerly to intersect the vein west of the vug 1, but only small pockets of bony calcite were found. A 40-foot crosscut was then driven easterly to intersect the vein on the east side of the vug 1. After hitting the vein, this working was continued 74 feet in bony calcite to intersect vug 2 below Burch's and Cartwright's old workings. Upon encountering the vug, the drift was continued another 76 feet. It was necessary to spile through the vug, as it was filled with mud. A raise was driven 55 feet to the surface in this vug for ventilation, and it was completed just as the demand for optical calcite ceased. The underground drifts were left well timbered, and mining of this deposit could be started with very little preliminary work.

1944 United States. Bureau of Mines • War Minerals Report 386. Google books