Frozen.

How long can it lead the charts?
Beyoncé is doing very well every week.

But I'm wondering how long her weekly sales can stay ahead of Lorde. Perhaps one more week?
Lorde will reach 1.9 million next week assuming another 70,000 which should be easy enough with her US tour starting this week.
Of course Beyoncé is touring in the UK at the moment, so that should help her too.