NotSoQuick, This article is from a year ago but it gives a pretty good explanation about the correlation between the two. 

These fees are charged by smelters for converting mined concentrate into refined metal. They are a good indicator of raw material availability, smelters charging more in times of feast and less in times of famine.

As such, next year’s treatment charges are a clear warning that the world’s copper mines aren’t producing enough concentrates to satisfy smelter demand. 

Here is the full article,

 https://www.reuters.com/article/us-metals-copper-ahome/column-copper-smelters-feel-the-squeeze-as-mine-supply-falters-idUKKBN1Y71JX?edition-redirect=in

herbie1