Back in 2012, Metallica’s Kirk Hammett said that he’d churned out 400 riffs in preparation for the metal group’s 10th album.

It appears that many of them have been lost forever however, as the guitarist has revealed that his iPhone, which contained 250 of those ideas, has gone missing.

“I put riffs on my iPhone, but something very unfortunate happened to me about six months ago. I lost my iPhone [containing] 250 musical ideas. And I was crushed. It didn’t get backed up,” Hammett told Jamey Jasta (via Blabbermouth ).

He continued: “I can only remember, like, eight of [the ideas]. So I just chalked it down to maybe it just wasn’t meant to be and I’ll just move forward with it.”

While Hammett pieces back together his back catalogue of ideas, the follow-up to 2008’s Death Magnetic does appear to be taking slow but certain shape, with the guitarist suggesting that veteran producer Greg Fidelman will be involved. “We love working with him,” said Hammett. “And for me, his whole attitude toward working is so right on, man. I can’t wait to get into the studio and work with him. He’s not a ballbuster, but he is a slave driver.”

He also described new material as “super riffy, super heavy” and added, rather vaguely, that “it’s a lot similar to Death Magnetic but different in certain parts. And you know, there’s a couple of songs that remind me of something on And Justice for All, but the album doesn’t sound like And Justice for All.”

Metallica headline Reading and Leeds in 2015.