A root in The Etymologies of the 1930s, first glossed “copper” and then “metal”, with derivatives ᴹQ. rauta/N. rhaud “metal” and serving mainly to explain names like N. Angrod and N. Finrod (Ety/RAUTĀ). It might have reappeared in the name S. Rodëol “metal of Eöl” from later Silmarillion drafts (WJ/322), but by 1957 Tolkien was explaining the final element of S. Finrod as S. raud “noble” (PE17/49, 118), so I think it is likely that ᴹ√RAUTA “metal” was abandoned.
Neo-Eldarin: For purposes of Neo-Eldarin, I’d use Q. tinco (LotR/1122) and its cognate [N.] tinc (Ety/TINKŌ) for “metal” words. For “copper” I'd use derivatives of √(U)RUS (VT41/10).
An unglossed root in The Etymologies of the 1930s with the derivative Ilk. rost “plain, wide land between mountains”, an element in the names Ilk. Nivrost “West Vale” and Ilk. Radhrost “East Vale” (Ety/ROS²). In later versions of The Silmarillion these names became S. Nevrast “Hither Shore” (S/119) and S. Talath Rhúnen “East Vale” (S/124), making it likely that ᴹ√ROS “✱plain” was abandoned.