Vertical Crater Retreat

Blasthole mining is a general term applied to mining methods that employ long hole drilling for the production of ore. In most Blasthole methods the ore is blasted into a vertical opening. In most blasthole methods the ore is blasted into a vertical opening. The blastholes may be small diameter long hole carbide drill holes or larger diameter holes drilled with in-the-hole (ITH) drills, or they may be a combination of both.

Vertcial crater retreat is a comparatively new method of blasthole mining in which only large diamter ITH holes are used to blast down horizontal slices of ore into an opening below the block of ore being mined. The method on the 'cratering' effect of an explosive charge being blasted close to the end of the hole. Mining retreats vertically as successive horizontal slices are blasted.

In the case of narrow stopes where hole deterioration is a problem, a slot is brought up at one end of the block via cratering and the remainder of the block is slashed into it. Mining retreats horizontally as successive vertical slices are blasted.

Vertical block mining is the term most often used for this method. In VBM the workplace is divided into a series of vertical blocks and the blocks may be nined on a retreat basis working from the ends of the workplace. This may be repeated on several different horizons in an extensive VBM area.

VBM Design

Improvements	Pro's
- Increased productivity - Increased production rate/workplace - Reduced total operating costs - Improved working conditions	- Flexibility to follow changes in Strike/Dip - adaptable to existing workplaces - Maximize ore recovery - Mininize dilution of rock/sand - Improve ground conditions - Minimize secondary mining - Increase equipment utilization - Minimize capital expenditures

Advantages over Cut & Fill Methods

Vertical Block Mining provides 3 distinct advantages over Cut & Fill Methods:

• SAFETY
  - a reduction of the exposure to open ground conditions and an improved workplace environment.
• PRODUCTIVITY
  - increased versatility by providing multiple headings.
• COST
  - a saving of ground conditioning materials

Layout for a Large New Area

Multi-level longitudinal VBM, consists of a bottom sill, several top sills driven as sublevels, a footwall ramp access connecting the sublevels and raise bored ore passes. The bottom sill is a new sill driven through the orebody. The access ramp is driven from the top level in the footwall rock, and connects each sublevel driven through the orebody. Each sublevel is reinforced with grouted cable bolts. Two bored raises are driven from the top level to the haulage level below, intersecting the ramp at various intervals. One serves as a rock pass and one as an ore pass. The mining sequence may be on a retreat pattern from the ends of the orebody; and will be ccled so that several blocks will be in the same phase simultaneously.

EQUIPMENT

Development	Production
Gardner Denver 2 Boom Electric Jumbo Atlas Copco 3 Boom Jumbo Jackleg/Stoper Gardner Denver DH-123 LCD Drills Boart Cable Bolting Drill Carrier Scooptrams Anfo Loader	Mission ITH Drill Ingersoll-Rand ITH Drill GO-60 ITH Drill R.C. Scooptrams L.H.D. R.C. Drill

How the Method Works

The mining cycle of a V.B.M. mining area is divided into 5 steps:

• - Development
• - Production drilling
• - Loading/blasting
• - Ore removal
• - Sandfilling

---

Return to UG Methods