“It's been 30 years since we last recorded an album together. It’s a huge f---ing deal,” says Ozzy Osbourne, in reference to Black Sabbath’s new studio album, 13, which is scheduled for release in June.

Ozzy and bassist Geezer Butler are holding court in a dark, wood-paneled library inside the Osbourne estate, a grand, modern home perched atop a hill in the outskirts of Los Angeles County that overlooks valleys of luxurious ranch houses and thoroughbred horses.

Guitar World is here, sitting on a plush, blue velvet couch (beneath a gold, bat-adorned chandelier, of course) and listening to a preview of 13. Missing from this meeting is guitarist Tony Iommi, who is back home in England undergoing the final round of treatment for lymphoma.

“I spoke to him this morning,” Osbourne says. “He’s havingan infusion. He’s like, ‘I feel a bit tired.’ I’m like, ‘A bit tired?’ F---ing hell. He’s my hero. If I was diagnosed, I’d say, ‘You can kiss my f---ing a-- goodbye. I’m gonna go get myself well.’ ”

Iommi has long been known as a formidable force in heavy metal, but the guitarist’s iron man–like status has risen to legendary proportions during this process. In early 2012, when he received his diagnosis, Black Sabbath were midway through writing new material for 13. Production stopped while Iommi began chemotherapy, but it wasn’t long before he requested the band move operations from L.A. to England so he could work on material between treatment sessions.

“Tony’s the kind of bloke that doesn’t want to let us down,” Butler says. “He wouldn’t let his illness interfere with this album. He wanted to get it done.”

Iommi’s illness was not the only setback to befall Black Sabbath during the creation of 13. Despite spending a year writing with the band, drummer Bill Ward declined to move forward with recording, due to contractual disagreements.

“We’d have loved to have Bill on the album,” Butler says. “But suddenly something came up. I went to Hawaii when Tony started his treatment, and when I came back Bill wasn’t in the band anymore.”

Upon producer Rick Rubin’s suggestion, Sabbath tapped an unexpected source to handle tracking drums: Rage Against the Machine’s Brad Wilk. The band was skeptical at first, but Wilk proved up to the task. “I was really surprised,” Butler says. “He had that Bill Ward kind of jazzy swing feel, rather than heavy metal bashing.”

With Wilk in place and Iommi working around his treatment sessions, the band finally began laying down tracks at Rubin’s studio in California. Sabbath recorded 16 songs, which will get cut to nine or 10 for the final release. Among these are three seven-plus-minute behemoths — “End of the Beginning,” “God Is Dead” and “Epic” — which abound with all the godlike riffs, sinister grooves and apocalyptic choruses you’d expect from the fathers of heavy metal. The group also tackles some fittingly dark topics on 13, such as killing pedophile priests (“Dear Father”) and the scourge of methamphetamine addiction (“Methademic”).

Now with 13 completed and Iommi on the mend, the band will soon start gearing up for a short spring tour across Australia and Japan. But for the moment, Butler and Osbourne are simply enjoying the fact that they’ve come out on the other side of 13 relatively unscathed, especially in comparison to Ozzy’s previous, less-than-stellar outing with the band, 1978’s Never Say Die!

“This was a million times better than that last album,” Butler says with a laugh, “where everyone was coked out of their brains!”

Adds Osbourne, “Never Say Die! should have been called, ‘We Should Be F---ing Dead!’ ”