71% of silver mined for FREE, 29% mined for $5-$7 per ounce
According to the Silver Institute, only 29% of all silver mined, comes from primary silver mines.
The remaining 71% is mined as an essentially FREE byproduct of other sorts of mining. That means that byproduct silver is just considered to be a waste product of other mining activities and it means that even if silver prices dropped to $1 per ounce, they'd still need to separate out the silver waste from their primary product and they'd still sell it to someone for $1 per ounce, rather than hauling it off to the dump.
The 29% of total mined silver that comes from primary silver mines, cost $5 - $7 per ounce in cash to mine according to data from 2010 and 2011 and those costs are dropping in 2012 with falling oil prices.
Further, the world produces twice as much silver as we use. Much silver mining could be curtailed and we'd still be swimming in excess supply.