Has your approach to controlled blasting failed?
In today’s times, when money appears to be the dominating factor of how we conduct our business, focusing on the result can often be sidetracked by the costs and not the overall effect. Within the explosives industry, there is a drive to push every cost factor down to the lowest possible denominator without the commensurate diminishing results. This has led some Mines to believe that the cheapest method of extracting the rock is the best; there is little to no thought put into the result of what is left behind. Moving like a successful proverbial bull in a china shop, ploughing through the dirt and giving that hungry Mill the stock it needs.
However, is this the way we should be going?
In our efforts to please two masters, we sometimes forget that the primary aim of MINING is to extract the ore in the most cost efficient method. Taking a holistic approach to the extractive methods would show us that removing more ground than planned is going to cost us twice the money: once when we take it out of the pit or portal and the second time when it dilutes the ground going into the Mill.
We need to focus on the cost drivers, not the costs!
Extracting rock from underground costs money, so why do we continue to focus only on advance without paying attention to the surrounds? Overbreak is one of the highest money pits in the industry but, despite there being methods to combat this, it falls into one of two baskets:
1) The too hard to fix right now
2) Too costly and/or time-consuming
Attention to detail is often lost in the brutal world of mining so why would we stop to think about overbreak?
Overbreak means different things to surface and underground. If underground is taken, for example, and the very first part of the Mine is the portal – what does it look like? The entrance to some ancient cave, the subject of many dollars to bring it in line with safety and design parameters or was it cut in a professional manner requiring minimal remedial work before mining could continue?
Are you taking the King Kong approach to your ground?
At what point does the cheaper explosive become, the most expensive option? Filling a hole with explosives, irrespective of the nature of that explosive, will impart a shock energy into the surrounding rock that will erode the stability of the roof. All explosives produce gas, and these gasses are used to best effect when there is 100% coupling – it is the way they are designed to operate; so why would you try to put all the available energy into the rock when all you are aiming to achieve is to move the rock away from the back.
Decouple your charge
If 100% coupling means the gasses have the opportunity to migrate into the back, then decoupling the explosive will eliminate the effect of the intimate contact zone. JOHNEX’s ECONOTRIM Buttbuster was designed with this in mind and has evolved over the years into a product that has been used in over 12 million holes to great effect in Australian (and now Canadian) Mines. It is overdriven which reduces the production of gas, producing the crack we need and not the heave; gravity will do that for us.
The benefits of controlled blasting in the perimeters of a tunnel outweigh almost all input costs. The cost savings come from various segments of the development cycle;
· Remedial work (shotcrete, bolting meshing, etc.)
The design for the heading allows for a 4-5% window, which is necessary to get the next jumbo in without re-blasting, and any rock created more than this is MONEY going out of the portal – with your permission.