The largest primary silver mine in the world saw its average yield fall to the lowest level ever in 2015. Matter-a-fact, the primary silver mine’s yield fell nearly 16% compared to last year.
This is a substantial decline in productivity from the world’s largest mine in Mexico that starting production in 1824.

http://www.silverseek.com/commentary/largest-primary-silver-mine-productivity-falls-lowest-ever-15370