Long Hole Stoping: What Actually Holds the Column

In a long-hole stope, some of the holes break through into the next level. This is by design.

Before you load them, the holes needs a bottom — something at the breakthrough for the explosive column to sit against.

There's a long history here, roughly in the order it evolved:

• Wooden dowels/wedges. The cheapest method. Cut to hole diameter, drilled through the center, rope threaded through and knotted, lowered down the hole, then the rope wrapped around rock at the top to hold the dowel or wedge just above the breakthrough.
• Stick powder. Tie a rope around the middle of a stick of packaged explosive, lower it until it falls out the breakthrough, let it flip sideways, then pull back up so it wedges into the hole like a toggle bolt.

Both work. Both are slow, and neither gives you a repeatable seal.

Here's the part that catches people. A broken-through hole is connected to the mine's active ventilation. It's either blowing air out or sucking air down, acting like a chimney.

That moving air works against whatever you put in the hole.

The field test for a seal is simple: kick some dust into the collar. If the dust hovers at the top without moving, the hole is sealed. If it takes off, it isn't.

• BLASTBALL just above the breakthrough. Inflated with air once in place. One method customers use - they'll drop it through, feel it fall out into the lower stope, pull it back up into the hole, then inflate it where they want it. This is a great tool for plugging a breakthrough.
• BLASTBAG AERO for depth - Up holes and down holes. Like the Blastball, it only inflates once you hit it with compressed air, so it goes all the way to position first, then seals in 3 to 15 seconds. Aerosol and chemical bags inflate as they fall, which can be difficult in a deep hole.
• SLUMPSTOPPA at the collar. A bottle-brush plug whose bristles grip the hole wall and hold the column against gravity, while still letting emulsion gas.
• BLASTSHIELD Plus when you're lining. Ripstop woven liner with gussets and carbon strips through the material, so it opens easily at depth and doesn't build static or twist on the way in.

When considering which product to use: AERO and BLASTBALL are packaged differently. Stope development drills through installed ground support mesh, which leaves jagged metal at the breakthrough opening. If Blastbag Aero is dropped through, it can hang up when you try to pull it back into the collar. AERO works great for plugging breakthroughs, but you should lay a depth gauge alongside the air hose and tape it every couple of feet so you can stop it at a known depth just above the opening.

In an uphole the toe is at the top and the collar is the bottom-facing opening at the loading level. Gravity is working against you the whole time.

1. Plug the toe at the breakthrough with Blastball or Blastbag Aero so the toe of the hole is sealed.
2. Load down from there with ANFO or emulsion.
3. Plug the collar using Blastball, Blastbag Aero, or Slumpstoppa at the bottom-facing opening to stop the column slumping back out.

Most sites drill fans of holes, roughly a 10 o'clock to 2 o'clock spread from the center of the stope. The outer holes of those fans sit in the most sensitive ground, because they define the final wall.

In soft geology those outer holes can benefit from air decking to reduce wall pressure and prevent overbreak. At one US gold mine shooting 90 ft up-holes with a soft seam at the 40 (12 m) to 50 ft (15 m) mark, the crew used three BLASTBALLs per hole — one at about 50 ft (15 m), one at about 40 ft (12 m), and one at the collar — creating two charges separated by a 10 ft air deck. Labor intensive, but it solved the overbreak.

That matters more than it sounds. Too much energy into a soft seam causes concave caving, a wider unsupported span, and fracturing that destabilizes ground support well beyond the seam itself.

Gold — Ghana. Open stoping with hole lengths up to 85 ft (26 m) using emulsion. BLASTSHIELD Plus paired with the BLASTBAG AERO eliminated emulsion slumping in up holes, and the holes were charged in one pass where the crew had previously needed multiple reloads.

Underground — Mexico. In development rounds rather than stopes, BLASTBAG AERO used for air decking returned a 14% decrease in dilution (19% down to 5%), a 70% reduction in vibration, and a 15.3% decline in cost per hole, about $72 saved per hole. The mine adopted the AERO for ongoing underground work.

If your crew is still sourcing or cutting dowels and wedges, that's not a failure — it works, and it's cheap. It's just slow, and it doesn't give you the same reliable seal.

Worth knowing before you order: what diameter your long holes are, whether you're loading with anfo, sensitized emulsion, or gassed emulsion, and whether you are plugging the breakthrough from the top or the bottom.

Not sure which one to use? Call us at 606-663-4069.