First published by Money Metals here: https://www.moneymetals.com/news/2019/06/14/silver-miners-average-yield-falls-001795

The top primary silver miners in the world saw their production yield fall to the lowest level ever in 2018. Since 2005, the average yield from the top silver miners has fallen nearly in half. And along with rising oil prices, has pushed up the total cost to produce silver by an additional $10 an ounce. So, for those who still believe in the fantasy that it cost $5 an ounce to produce silver, that data shows otherwise.