To produce metallic colours using process…

P871 = C20 M25 Y60 K25
P872 = C20 M30 Y70 K15
P873 = C30 M30 Y60 K10
P874 = C0 M20 Y50 K30
Another popular mix is
C30 M40 Y100 K5
If you want les black in the mix (from Gracol 2006 Coated1), try these
P871 = C48 M49 Y82 K5
P872 = C50 M53 Y82 K6
P873 = C46 M53 Y80 K4
P874 = C50 M58 Y79 K5
Remember these are not going to get you the metallic feel of the colours, metallic ink has metallic flecks tht sparkle, but these should get you in the right ball park.
3 more useful mixes are:
Silver = C47 M37 Y36 K2
Gold = C44 M46 Y78 K19
Bronze = C40 M52 Y73 K19