The title sets up a metaphor: the speaker is a prospector, someone who digs for valuable things. But what they dig up isn't gold. It's "cries," raw sounds of pain that once, it seems, were turned into words and now sit inside a lung. The image suggests that grief or distress lives in the body, in the breath, long after anyone has spoken it.
The speaker finds these cries and then does something with them: gives "the remains to a book." The word "remains" makes the writing feel a little like a burial, or like sorting through what's left after a loss. Whatever can be saved from the cry goes onto the page.
The last line, "work all night," is plain and tired. It doesn't dramatize anything. The mood is quiet, solitary and serious, with a sense of patient, necessary labor. Writing here isn't glamorous; it's a night shift spent turning pain into something that can be kept.