Sam, the narrators husband, is a the miner has died in a cave in. the other miners help to dig him out, and at the same time, one has stolen ore (nick it). the law (english)is that if one person can steal three 'dishes'-a measure of ore- from a mine, he has, in fact, 'claimed the mine' a stowe is what in california/US west would call a claim.

Miner can stake a claim(US english!) by finding ore, and paying a tax in ore to the crown, and keep the mine as long as they can work it. but if someone else can steal three dishes of ore, and the 'owner' doesn't challenge (by producing his own ore dish,) the person can 'nick the stowe'.

the meaning of the words is often made clear by the narritive, but there are many words in the book that i have never encountered!