On-sale date from Amazing Heroes #49, with shipping date of 1984-06-12.
This issue is a variant of Thor (Marvel, 1966 series) #348 [Direct].
There exist further variants:
Thor; Roger Willis; Balder; Agnar; Norns; Odin; Warriors Three [Fandral; Hogun; Volstagg]; Malekith; Wormwood; Dark Elves; Surtur; Karnilla; Algrim; Silverhoof (Balder's horse)
Synopsis
Thor and Roger save Lorelei, but fail to keep Malekith from opening the Casket of Ancient Winters. The Norns convince Balder that life is better than death. Surtur begins his advance.