New Mexico Mineral Symposium — Abstracts

The Jomac mine is located on Brown's Rim, in the White Canyon mining district of San Juan County, Utah. It has recently become the type locality for a uranium-carbonate mineral named blatonite. A second new uranium mineral from the mine has recently been submitted to the International Mineralogical Association for approval. The Jomac mine is the world's second reported location for the minerals swamboite and mbobomkulite. The mine saw most of its ore production in the 1950s and had an active claim until 1985. Obviously, the mine was a wonderful source for interesting minerals. Unfortunately, the mine lies within the boundaries of the Glen Canyon National Recreation Area, and it was reclaimed in 1992. Mineral collecting since then has not been allowed.

The Jomac mine's three adits lie in the Shinarump Conglomerate Member of the Triassic Chinle Formation. Petrified wood, coal, and sooty black organic debris are scattered throughout the conglomerate. The organic remains, apparently setting up a reducing environment, make the sediments more amenable for the precipitation of primary minerals. Uraninite and the sulfide minerals pyrite, chalcopyrite, and sphalerite were deposited. Tiny specks of cuprite are very common in a basal siltstone, but cuprite may or may not be a primary mineral. Oxidation of these minerals led to the formation of an unusual assortment of mostly copper and uranium minerals. The minerals hematite, jarosite, hydronium jarosite, and limonite are common. Also, common in the conglomerate are coconinoite and metazeunerite. A mixture of asbolan-birnessite occurs as dendritic smears on fracture surfaces.

The basal siltstone is the host for most of the mine's minerals. They are found as microscopic crystals locally concentrated in two different assemblages, a copper sulfate assemblage and a blatonite assemblage. Minerals found in the copper sulfate assemblage include anhydrite, carbonate¬cyanotrichite, antlerite, malachite, azurite, serpierite, alunite, sparse smithsonite, boltwoodite, and very rare brochantite. The blatonite assemblage can have sparse amounts of the minerals found in the copper sulfate assemblage, but has a greater amount of carbonate mineralization. This latter assemblage has blatonite; uranopilite; increased amounts of malachite and smithsonite; sparse amounts of swamboite, sklodowskite, rutherfordine, schoepite, metaschoepite, meta-autunite, and mbobomkulite; the recently submitted uranium mineral; an unidentified orange uranium mineral; and some fine-grained, yellow uranium minerals. Impurities in the minerals cause various changes in their habits, making identifications challenging. Cobalt and nickel are common in trace amounts in most of the secondary copper minerals.

The Jomac mine's portals were sealed with mortar and backfilled, and the access road has been blocked with boulders. Despite the reclamation efforts, previously recovered specimens are producing interesting results. Two of the remaining unidentified uranium minerals have unique X-ray diffraction (XRD) patterns.