Common beginner error.  Miners always have a wide range of production costs.  The production cost that is publicly reported is an average.  But the standard deviation is significant.

That means as prices fall below the average “cost of production” the top quartile producers go broke.  Meanwhile the bottom quartile producers are still highly profitable and pumping out product.  

The average cost of production falls as the price falls as inefficient producers are driven to the wall, often with little or no impact on global output.  It is not unusual for major miners to take advantage of this market pressure and actually step up production to squeeze out the competition, further depressing price.  

So you are a fool to rely on “production costs” to prop up commodity prices.