Question is;

What does it cost to proces on site?
What does it cost to ship directly

Proces on site means you have to build the installation
Ship directly involves only shipping costs as you use a processer somwhere else.

I can imagine that if there is enough they will start building a concentrator ?? onsite but in the meanwhile ship the goodstuff to make money and pay for the concentrator.

By the time you reach the lower grades you can economicaly process them onsite.