Brass than in brass produced by cementation. These may be "natural alloys" manufactured by smelting zinc rich copper ores in redox conditions. Many have similar tin contents to contemporary bronze artefacts and it is possible that some copper-zinc alloys were accidental and perhaps not even distinguished from copper. However the large number of copper-zinc alloys now known suggests that at least some were deliberately manufactured and many have zinc contents of more than 12% wt which would have resulted in a distinctive golden color. By the 8th–7th century BC Assyrian cuneiform tablets mention the exploitation of the "copper of the mountains"
Native metal more reactive than gold. Natural alloys of the platinum group metals include: native osmium (Os,Ir,Ru), rutheniridosmine (Ir,Os,Ru), ruthenium (Ru,Ir), palladium (Pd,Pt), platinum Pt, and rhodium (Rh,Pt). In addition gold, copper, iron, mercury, tin and lead may occur in alloys of this group. As with gold, salts and other compounds of the platinum group metals are rare; native platinum and related metals and alloys are the predominant minerals bearing these metals. These metals occur associated with ultramafic intrusions and placer deposits derived from those intrusions. Native copper has been historically mined as an early source of the metal. The term Old