This is quite a fascinating question, because it contains so many possible nuances.
Presuming that none of the miners were Jewish, the issue is not what is the Halakhah regarding reneging on a promise. It is more an issue of fundamental ethics.
What exactly did they mean by the pact? That they would share nothing, absolutely nothing? Somehow that seems a bit hard to believe. My sense is that they were referring to the stuff that would not reflect well on the group, such as the fistfights.
This agreement, was it entered into by everyone of their own accord, or did one segment impose it on another against their will? That too changes the equation.
And were they all with their full wits when they made this pact, or was this made as a way to ensure solidarity and survival with no one suspecting anyone else of harboring ill intentions?
Another issue - if one person breaks the pact, is the pact now fully broken, such that if others now spill the beans, there is no ethical breach on their part? One could make a solid argument to justify others telling all after the pact was broken, but the ethical high road is to still keep the promise.
Additionally, the matter of how desperate is the situation of the "divulgers" enters into the discussion. Promises are made to be kept, up to but not including life threatening circumstances. I have no idea how bad the poverty situation is, but that can be a mitigating factor.
Finally, a more crucial issue that arises from this breach of promise is the prohibition of bad mouthing others, precisely when it is the truth.
The irony of all this is that by breaking the promise and throwing dirt on each other, these 33 will quickly lose their hero status, thereby jeopardizing any possibility of making money the clean, and "promise kept" way.
Answered by: Rabbi Reuven Bulka