So just how scarce -are- metals in Zalanthas? Who would have access? Would it be ridiculous for a wealthy merchant to have a copper ring, or normal? Also, what types of metals are on Zalanthas? I know there's copper... what about iron, gold, silver?
There's some metal, just not much. The only obvious places your average commoner would see it would be places like the statue above the gates, or noble signet rings.
Beyond that I'm pretty sure it's something you need to find out ic.
In part, especially on copper and especially recently, it depends where you live. However:
Merchants outside of the GMHs are almost as unlikely as anyone else to ever see metal not on a noble's finger. If one were both lucky enough to obtain it, and foolish enough to flaunt it, one would not live long.
Merchants in GMHs have a little bit more political and economic power. I'd imagine at their highest levels the Houses all have a metal-crafter of some kind or another, but you still wouldn't see them flaunting a ring or earrings without VERY good reason and VERY good connections.
Templars and nobles, well now, that depends.
Regarding geological scarcity, I prefer to believe Zalanthas as a whole and even large swaths of the Known World abound in all manner of metallic ores, but that knowledge of mining and refining techniques was snuffed out by the fall of the Empire (or perhaps before then). That any metal that Zalanthans DO have access to comes from small deposits near the surface just supports this idea.
Owning metal is not about being wealthy.
It's about having enough power to back it up.
For that reason, no, I don't think a 'wealthy' merchant would have metal jewelry--unless they also had significant rank and influence in a large merchanting organization.
As far as types of metal...
Allanak has a large steel dragon atop its western gate that I'm pretty sure most people there know about.
Nobles and templars wear signet rings made of silver, and sometimes other metals. Again, also an obvious IC example.
There are other examples of other metals, but I think exploration of that is best handled IC.
The Great Merchant Houses do have metal, but most of these items are signs of their highest offices, too. Like others said, it's as much about the ability to prevent people (templars or nobles included) from taking it from you. Don't think Tuluk would allow a commoner to walk around with metal jewelery. Thieving is licensed, remember? Allanak wouldn't be half so polite.