The Sweet Home Mine, Alma, Colo., is closed for good. Bryan Lees, owner of The Collector’s Edge Minerals Inc. in Golden, Colo., and the driving force behind reopening the 132-year-old mine in 1991, made the announcement on Oct. 18, 2004. The Sweet Home Mine had been the source of the world’s finest transparent rhodochrosite mineral specimens (see “Sweet Home Rhodochrosite,” JCK, June 2003, p. 103).

The mine’s history dates back to 1873. It was a silver mine, and the rhodochrosite was a byproduct of silver-ore production. Early mining techniques—i.e., pickax and dynamite—left few crystals untouched, so much of the broken gemmy material was traded for drinks at the local saloon. The crystals that survived intact were carved, faceted, or left as mineral specimens that ended up in museums and private collections.

The mine was worked off and on throughout the last century, but its most important history began in 1991. Bryan Lees leased the mine from principle owner Leonard Beech to look for rhodochrosite—not silver.

Lees faced three tasks: Raise money to open the mine and keep it operating while looking for rhodochrosite, find good mineral specimens of rhodochrosite, and recover these specimens without damaging the crystals.

In 1991 Lees used old mine records to determine which locations had contained rhodochrosite. Although he was successful at discovering more rhodo, techniques for locating new pockets were 100 years old: drilling and blasting. Early on, Lees added a slight modification to the old method called probing—drilling to discover a pocket beyond the mine face.

Lees enjoyed a good start, but following old silver veins and using the tried and true hit-and-miss technique left him frustrated. In 1992 he added a hydraulic splitter to crack and break the rock around a vein, resulting in little or no damage to the crystals.

Lees’s crew spent time mapping the geology of the mine site, garnering clues about where to search next. These geological maps helped them systematically start knocking off target pocket areas—with some success. Then they added a diamond chainsaw to extract entire blocks of rock, plates of rhodo specimens. But they were still drifting on bad targets. They needed different ways to explore.

By 1995 they were examining the fluid inclusions inside rhodochrosite, when Lees and his crew made an astounding discovery. They realized that the gemmy red material was formed at a higher temperature than the lighter, less-gemmy pink material. They also discovered that the red material contained large amounts of arsenic, and that the pink material had large amounts of antimony. Now, they would go back into the mine and look for high-temperature veins and sample for arsenic and antimony.

This proved successful, and in 1998 they struck important finds of rhodo, pyrite, and fluorite. In 2000, they even worked through the winter. After examining three-dimensional maps of known discoveries in the mine, they could map the direction of more potential pockets.

In 2003 they hit the top of the rhodochrosite ore zone where a fault line had occurred. So they started mining downward. Lees discovered that these ore zones were fairly well-contained cigar-shape zones at angles of about 30 degrees. And he discovered one more thing—that they had mined them all.