smelting an iron weight

[frindle]

Hello. Could you tell me what the underlined part means in this context?
Does it mean the speaker was boiling with frustration and anger?
Thank you.

------------
"You coming up the Arcade?"
"I can't."
I watch him go, then turn up the hill and start to run, frustration and anger
smelting an iron weight in my guts.

(The speaker should get his little brother and take care of him. The speaker is in a difficult situation. )

[bhaisahab]

Hello. Could you tell me what the underlined part means in this context?
Does it mean the speaker was boiling with frustration and anger?
Thank you.

------------
"You coming up the Arcade?"
"I can't."
I watch him go, then turn up the hill and start to run, frustration and anger
smelting an iron weight in my guts.

(The speaker should get his little brother and take care of him. The speaker is in a difficult situation. )

That's what it means, yes.

[allenman]

I don't know...none of this sounds like a native speaking.