Copper, silver, or gold MC cartridge coils?

To Add to the list of Coil Wires being used.
Aucurum Wire,
( Gold Plated Six 9's Copper) known to be used by 
Ortofon for approx' 20 Years in some of their designs.

Koetsu Urushi,
( have a model that has a Silver Clad ' not plated'  Six 9's Copper )

I have been impressed with Ortofon Cartridges that have coils wound  Aucurum , as a result I now own a Cadenza Black, that I intend on having rebuilt to a change of Specification.

There are also Cartridge Tag Wire Pins used of different Metals, 
I am sure the combination of Coil Metals and Pin Metal will also have an
Sonic Signature.   
   

Since you asked for ZYX:

 I can say that tried both Silver Coil (Airy 3) and copper (Premium 4D) I think the last one (copper) is better, you can’t go wrong with copper coil from ZYX. 

Silver is definitely not warmer. 

For ZYX  i would prefer copper coils though silver could match rock pop material a bit better.
Never heard any of their gold model so i cannot comment.
@chakster 4D is somehow different to Airy so coil material there would not be easy to compare.
I agree though that you cannot go wrong with copper.

G

Rock music and Pop music is not the same, completely different genres of music. I don’t even understand how one person can listen to rock and pop. Rockers hates Pop music.