One of the most common words used in natural stone quarries is “recovery rate”. Yet when one explores further and speaks to industry people involved in the quarrying business, one finds what they all mean is not so easy to define. When people from different countries involved in quarrying are talking about recovery rate, they may actually be talking of very different things.
It soon becomes evident that there are different concepts which define the recovery rate. One concept would be restricting it to obtaining dimensional blocks in commercial size according to international practices. But another concept of recovery rate would, in addition, also include using waste stone (defined here as not being dimensional blocks) for gravel crushed stone for industrial purpose like for the paper industry, filters, toothpaste, etc. An even more encompassing concept would also include waste stone being sent to seashores for building breakages or, for example, creating sound barriers to protect against noise in villages close to a roadway. It immediately becomes evident, therefore, that practices in different countries lead to different ways of understanding what is meant by recovery rate in a quarry.
In Finland, for example, the licenses granted in some areas, demand that at least 50% of the material be used. This does not mean that the blocks coming out should be perfectly cut in rectangular sizes, since the geological formation and current technologies can make it impossible for a particular quarry. But it does mean that at least 50% of the material will be used in some way-not just dimensional blocks but also as gravel, for example.
In other countries, however, the recovery rate can be basically defined by the dimensional stone industry from a totally different and opposite perspective. In countries like India, for example, the law may not even allow a company to undertake more than one business- a separate license could be required for activities that are not for obtaining dimensional blocks but for gravel used in paving, for example. When a lease is granted the entire land may have to be used only for ornamental dimensional, blocks, and no other activity. There is, therefore, a complete difference in philosophy.
The Nordics, more environmentally conscious, have also defined and framed the regulations in such a way that not only encourages and promotes environmentally friendly activities, but also makes them feasible.
In places like South India where there are a large number granite deposits, pavestones cannot be made in the same lease areas and have to be transported to a different area. The recovery rate, naturally, is defined by the mining people in India in a much more narrow sense, restricted to dimensional blocks.
There is another element to recovery rate which is, in fact, key to whether the business is viable or not- when recovery rate is defined using economic criteria. Not all blocks have the same commercial value- the tones, the veins, the black spots (mica for the geologist) all these can dramatically affect the sales price of the material once it is being commercialized.
The situation for the quarry owner becomes even more difficult if the dimensional blocks, perfect in every other way, have fissures. It can mean the difference between the mining operation in a stone quarry being a profitable operation or going bankrupt. A block that has fissures can completely break down when being processed in the gangsaws, block cutters or multi-wire machines, and therefore, this block can be totally worthless. How many quarry owners have gone bankrupt during the last two or three decades simply because the material, be it granite or marble or other kind of stone, so commercially attractive and perfect in every way, once they started mining after making huge investments, discovered that most of the blocks that came out had fissures and were total useless? The technology for covering the fissures is now being developed, colloquially it is known as treatment, but it is still in the nascent stage.
All this means that any discussion on recovery rate becomes very complicated. But it can get even more difficult even when there is a certain amount of clarity and consensus as to what constitutes recovery rate and the people involved are highly experienced and knowledgeable people.
One common point of confusion results when someone who says that the recovery rate of his quarry is 40% may not be taking into account that perhaps only 10 to 20 % of that 40% he theoretically recovered has been actually commercialized in the form of dimensional blocks. Another person, talking of the same issue, would say the recovery rate is, therefore, just 4 to 8 %. Whatever be the definition of recovery rate that one may have arrived at, comparing the recovery rate between different quarries is made difficult by the fact that recovery depends on several factors like location and operating conditions. The recovery of the stones mined on earth is different than in quarries with boulders, on hillocks, or quarries on mountains or when deep in the ground - all this when we may be talking of aesthetically very similarly looking materials.
It now becomes obvious that if defining recovery rate is very complicated, relating it to value is even more so.
Blocks with fissures can not only have zero value, they can even be destructive to value, since sometimes the fissures, especially when they are small and located well inside the blocks, are identified only when the block has been processed and breaks up in the factories in the gangsaws, blockcutters or diamond wire machines. This means the factory owner has to undergo the huge expenses of processing the blocks only to find he has come out with nothing- and he obviously asks the quarry owner for compensation. And gravel, obviously, is a very low value product.
In conclusion, any talk of recovery rate to have any meaning at all should first start by clarifying what exactly one is trying to calculate. In which country is the activity taking place, what are the rules and laws of that place, what are the specific ground conditions, these factors are not just important to define in great detail , but constitute the very essence of the words `recovery rate´.