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How does blast mining work?

The most common way to get rock from the ground or mountains is by blasting and drilling. There are some locations where there are literal mounds of lose rock (that have formed naturally) but these are not as common, and when they do form there is not enough in quantity to supply all the area’s construction needs. 

Survey

The process starts off with a geologic survey done to determine if the mountain is viable as a source for the desired type of rock (as not all mountains contain the same type of rock), and for how long (you want years and years of supply before committing to an operation as expensive as mining). 

Drilling

Track carriages mounted with drills will then be moved to the mountain’s face, where they will bore holes deep into the face of the mountain, however deep as necessary, from 15 feet and beyond. Holes are drilled 6-15 feet apart for small blast holes, and 30 feet apart for large blast holes.

These drill-mounted track carriages are ideal since they can freely move on jagged rock surfaces, from one drilling location to another, like a tank.

As the drill drills through, air is blown down into the hole. This keeps the drill bit cool and also allows debris to be blown out & removed. The rate at which the drill can drill through the rock can be from 20 to 100 feet per hour.

Explosives

The most common explosives used in blast mining are dynamite and ANFO.

Dynamite

  • Most sensitive, nitro-glycerin based and most expensive

ANFO

  • Most commonly used, liquid mix of ammonium nitrate, and number 2 diesel. It can only be detonated with special primers and is therefore safer.  

Blasting

Dynamite isn’t just thrown haphazardly and randomly at the mountain. There are several factors that must be taken into consideration.

One of them being the shape of the mountain. The blasting needs to be done so that: 1) the resulting rubble is accessible for collection 2) the remaining structure of the mountain is in a stable shape, 3) the next round of drilling and blasting will not be hindered

To achieve this, think of the mountain as a Thanksgiving Turkey. You’re shaving off pieces of meat from the outer-most part of the turkey, one thin slice at a time.

It’s similar with blast-mining. You approach the outer-most part of the mountain (the face), and that is the part that you blast off, and then keep working backwards from there, effectively carving off slices of the mountain.

To achieve this, sections are blasted off in carefully measured rows, so that each blast is an even slice off the mountain.

It’s vital that the explosions are controlled and planned in order to:

  1. Minimize flyrock (rock flying away and thus lost)
  2. Dust
  3. Unwanted damage to the mountain

Processing

After the rock is blasted the rubble will be processed by crushing it and feeding it into various sized screens, collecting batches for each type of size, from large man-sized boulders to small 1inch gravel.

Why do companies do blast mining?

Put simply, it is the most inexpensive way to go about fracturing rock. Let’s face it, construction requires a lot of raw materials, and if the gravel had to be drilled by hand, the man-power needed would be unimaginable. By using explosives, the costs for rock are kept low.

Where should you get your rocks?

We have several quarries serving the NZ, AZ and CA regions. At Kalamazoo we’ve got what you need, and the most gorgeous colors in the area. Visit our catalog to see for yourself!


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