News.bytes Extra, issue 355

Blasts close hazardous "Southern Belle" abandoned mine

Two years ago, the BLM constructed a bat-compatible gate on one shaft of the abandoned Southern Belle mine. But that left 17 more openings at three sites. The openings were so unstable – because of  extremely brittle rock and crumbly soil surrounding them -- that it was impossible to construct bat-compatible gates. The openings were too large and on too steep a slope to carry foam for a solid closure.

One option: blasting the openings shut. (text continues below)

An unstable opening is blocked temporarilly with chicken wire, before the blast
 

First, bats were excluded from the sections of mine being blasted.  Then, approximately 2,000 pounds of explosives were placed strategically, and linked with 200 feet of detonating cord and 75 blasting caps.

The resulting blast closed 4 openings completely on “site 3” -- the largest  area.  The rest of the openings are now stable – that is, there are no unstable roofs or backs and can be closed safely with backfill or foam.

The Southern Belle mine and mill site saw production of gold and silver from 1893 through 1937, according to U.S. Bureau of Mines production records. The mine workings have several portals connected by more than 3,900 feet of shafts, tunnels and other underground structures. Surface workings include numerous pits. The New Year shaft is reported to be 260 feet deep with development on three levels.

Boxes of explosives were placed strategically inside the mine openings


A worker lays detonating cord across the rocks

A hazardous opening before the blast...

...and after:
 

- Cheryl Seath, geologist, BLM-California Bishop Field Office, 10/28/08

BLM-California News.bytes, issue 355