punctuation - Is this use of the dash correct?

"But--" Boris tapped his pocket-- "your hotel."
Is this use of dashes correct? Donna Tart uses this construction all the time. The speaker is interrupted with a dash, then the narrator is interrupted with a dash, then the speaker finishes. Not a PAIR of dashes, but two singles. Here's another:

"Yes, but--" wiping his nose--"global warming, I suppose."
"That said--" he closed his eyes-- "I cannot say about those guys."