Castle Dome
Special Feature: The Plants and Animals of Castle Dome
Collecting Report, April 2008
Sitting under the majestic Castle Dome Peak, Castle Dome and Hull are sister mines, similar to the relationship of the nearby Red Cloud and Geronimo mines. Castle Dome and Hull are known for fluorescent combinations of Calcite, Fluorite, Willemite, and occasional other minerals. These combinations are distinct from those at Red Cloud and Geronimo in a few ways. First, the specimens at Castle Dome tend to be more solid and heavier, often containing Galena. Second, the arrangement is less often in veins and more often in either a conglomerate or solid Calcite with blebs of Fluorite and Willemite. Third, the Willemite at Castle Dome is often bright green and very phosphorescent, although the yellowish-white variety is also found there.
The Castle Dome district is one of the oldest in Arizona and also one of the most actively-mined over the years. The primary minerals of economic importance were Lead and Silver although lesser quantities of other minerals were also mined. Most of the material was taken before 1900, although mining continued after that sporadically until the mid 1980s. After operations shut down collectors descended on the area and discovered various crystal specimens including Vanadanite, Wulfenite, Barite, and Fluorite.
Fluorescent specimens from Castle Dome and Hull are seldom seen for sale nowadays, partly because the Castle Dome Mine has been closed to collecting for some time. In the past some very nice pieces came from the area so I determined to find out if there was anything left. My recently departed friend George Young, who spent his last years in Yuma, introduced me to the caretaker of the Castle Dome Museum. Although he went as far as offering to take me into the mine itself via rope and harness, I felt much safer just checking the dumps. When I did so I was disappointed to find almost nothing that was worth collecting. I had better luck checking the various prospects in the area surrounding the mine. Even then I found very little of the classic 3-color combinations. What I did find was some nice 2-color Fluorite and Willemite specimens and some oddball combinations such as Fluorite with Hyalite or Caliche.
The Hull Mine, at a hill about a mile further north, was more cooperative with my expectations and did produce some classic-type pieces. There were about 20 different tailing piles at the mine and the surrounding area. I searched all of them thoroughly and found that only two of the piles had any significant amount of fluorescence, one on the north side of the hill and one on the south. The tailings on the south side had obviously been hit by other collectors before as there was not much left. The pile on the north side, however, seemed to have escaped the notice of most collectors and I had some success there. Even so, there was really not a lot to collect and I exhausted what was there without trying very hard.
Most of the pieces are moderate in brightness under shortwave UV, although the Calcite and Fluorite are quite brilliant under midwave UV. The Caliche from this area also responds well to midwave and so some of these combinations are best viewed under a midwave lamp. However midwave UV does not illuminate the Willemite or the occasional occurrence of Hydrozincite, so pieces with those minerals are often best viewed under a combination of shortwave and midwave or sometimes shortwave and longwave.
