It's my understanding that the Mt Milligan deposit is polymetallic and according to this early Placer Dome Filing the deposit contains higher concentrations of silver.
MINFILE No 093N 194
At the Creek zone, a diamond-drill hole intersection across 1 metre assayed 4.4 grams per tonne gold and 82.0 grams per tonne silver (Assessment Report 16966). The carbonate-quartz rich veins, which contain sphalerite, galena and pyrite, occur in propylitically altered latitic volcanics northwest and northeast of the MBX stock.
One would assume that the mine floatation circuit would also accomodate recovery of the trace minerals to offset production costs. No mention of it in any economic reports.
Here's the link to Placer Dome's pre-Terrane feasability study............