Some more on the mechanics of the Iron Range occurrences:
It happens where the bedding dip is low and the friction angle on the bedding planes also is low. If there isn't enough relief, as for example when the last shot wasn't fully mucked out, the blast can wedge rock layers behind the shot...
I posed your question to a friend with much blasting experience; this is his reply:
"I've actually seen it happen in the Iron Range a few hundred feet back from the blast. Usually happens at the back of a blast and is due to poor relief on the blast. Of course if it is stability related...
Be more specific. Many people use the terms borehole and blast hole interchangably, in which case the only difference could be what's put into the hole rather than how it's drilled.
The short answer is "in many ways". Check out the following reference/course books for a bit more detail:
+ Introductory Mining Engineering, by Hartman & Mutmansky (1st and 2nd editions)
+ SME Mining Engineering Handbook, edited by Hartman
+ Underground Mining Methods, edited by...
Contact Robert King of the Colorado School of Mines (www.mines.edu) Engineering Division. He has had numerous graduate students work on mining robotics and automation of mining equipment over the past couple of decades.
The best job market for mining engineers in the US is in aggregates and construction materials. The industry has been consolidating like mad and really needs trained and/or experienced mining engineers. There are very few counties/parishes that don't produce construction materials of several...