Question

A 20 m thick orebody is dipping at an angle of \(75^\circ\). The orebody and host rock are strong. It is proposed to deploy a 150-200 mm diameter drill for production. The suitable stoping method is

• A. block caving
• B. long hole stoping
• C. shrinkage stoping
• D. post and pillar stoping

Hint:

Match the method to a steep, thick, strong orebody drilled with large diameter blastholes, think about which method uses that kind of production drilling.

Answer 1

The Correct Option is B

Step 1: List the deposit conditions that decide the stoping method.
The choice of stoping method mainly depends on dip, thickness, and the strength of the orebody and the host rock.
Here the orebody is 20 m thick, which is a wide orebody, it dips steeply at \(75^\circ\), and both the ore and the host rock are strong. A large 150-200 mm diameter drill is planned for production drilling.

Step 2: Check what a steep, thick, strong deposit calls for.
A dip of \(75^\circ\) is steep enough for broken ore to flow down by gravity, so the method should take advantage of that.
Because the deposit is thick, at 20 m, and strong, open stopes can be cut wide without needing the ore to be left in place as a working floor, and the walls can stand without immediate support.
Large diameter, 150-200 mm, blastholes are the mark of mechanised longhole, or sublevel, drilling, drilled in long parallel rows from sublevels above and below the stope and blasted in one go, then the broken ore is drawn from the bottom.

Step 3: Rule out the other options.
Block caving needs the ore, and usually the host rock, to be weak or moderately jointed so that it caves and breaks up on its own once undercut, a strong ore and strong host rock will simply not cave, so option (A) does not fit.
Shrinkage stoping uses the broken ore itself as a working platform and is drilled with smaller diameter jackleg or stoper drills, it also becomes hard to manage in a 20 m wide stope because so much broken ore has to be held in the stope at once, so option (C) does not fit either.
Post and pillar stoping is meant for flat to gently dipping deposits, where pillars can be left standing under gravity, a steep \(75^\circ\) dip makes this impractical, so option (D) is ruled out.

Final Answer:
Long hole stoping fits a steep, thick, strong orebody with strong host rock and large diameter production drilling.
\[ \boxed{\text{Long hole stoping}} \]