According to modern metallurgic processes, Some metals when alloyed with Antimony and Arsenic, can produce a very strong alloy, both in hardness and tensile strength. Some people have speculated that Arsenical Bronze, or Arsenic Antimony Bronze is the real world basis for Tolkien's Mithril. Incidentally Tetrahedrite is an ore of Copper and Antimony. Tennanite happens to be an ore of Copper and Arsenic.
Some bronze-age weapons were actually Copper/Arsenic alloys, and they were much stronger than the Copper/Tin variant, and they held much better to the test of time than tin bronze. Plato probably referred to this alloy when he was talking about Orichalcum(Which translates to "Mountain Copper, or Mountain Metal"). A reason why this might be the case is Haephestus, and how he is portrayed as lame. Arsenic poisoning can attribute to such.
Ideally you can add Tennanite as a rarer copper ore that appears only in mountain areas and, when smelted and alloyed with Tetrahedrite, produces another steel-grade or better metal, be it called Orichalcum or Mithril or even Onolgusil. Just as a way for those whom can't find iron and/or flux can have an alternative to steel.
When diseases are added to the game, smiths who produce this new metal can, over time, gain the effects of arsenic poisoning and eventually will need crutches. Eventually they'll die of arsenic poisoning, but such is the price of producing Onolgusil.