Dimension stone, i.e. natural rock extracted for cutting and/or shaping to a specific size, has been used for a long, long time. It’s the stuff that was used to build the Pyramids around 2800 B.C. and the Hanging Gardens of Babylon in 600 B.C.
There are many reasons why natural stone is still favored today as a building material. Stone ages beautifully, it’s low-maintenance, it’s durable and resistant, it bestows a perception of value and quality, it’s unique and varied in availability, etc.
There is huge demand for dimension stone and the value of the tonnage sold has been steadily rising over the years.
In 2016 producers in the U.S. used or sold 2.46 million tons of dimension stone valued at $468 million. In 2015, 2.63 million tons was used or sold in 2015; this was valued at $461 million.
Between 2012 and 2017 the industry revenue was $18 billion. Over the next five years revenue is expected to grow albeit at a slower rate. The expected areas of growth are the sustained demand for commercial and residential construction, and increased road, street and highway infrastructure construction.
The global stone construction market is expected to grow at a CAGR of 9% between 2016 and 2023 for more or less the same reasons.
Getting into this industry is rather difficult.
You basically have to identify and explore a potential mining site, get a concession for the area, apply for the required licenses and permits, and then think about preparing the site and purchasing the required equipment.
You’re not mistaken if you think dimension stone quarrying is solely the reserve of big companies.
Nevertheless, at the tail end of this post, is a brief introduction to the production of commercial building blocks using stone-cutting machines. This can be a viable idea for typical entrepreneurial individuals.
Once you have everything in place for your dimension stone quarrying small business, all you’ll have to do is ensure you can keep up with the demand.
Here’s what you must know:
1. The definition of dimension stone and qualities for suitability
Dimension stone can be defined as natural rock material that is quarried for the purpose of obtaining slabs or blocks of specified size (width, length and thickness) and shape.
It can also be defined as rock that is extracted from its original site to be used with minor alteration (rough stone), and rock that is broken, sawn, and/or ground and polished (cut or dressed) for use as building and/or ornamental stone.
The color and grain structure of dimension stone contribute to its price and marketability.
Suitable dimension stone also has several qualities that make it desirable including strength, hardness, toughness, and resistance to environmental damage.
The value of dimension stone is therefore pegged on its dimensions and appearance, and underlined by a set of minimum physical properties.
Various types of igneous, metamorphic and sedimentary rocks are used as dimension stone. Nevertheless, there are five principal rock types that are used for this purpose i.e. granite, limestone, sandstone, marble and slate.
The main uses of rough stone are in building & construction and monumental. Dressed stone’s largest uses are ashlars and partially squared pieces, curbing, flagging and monumental.
2. Considerations for the exploration of a potential dimension stone quarrying site
Prior to opening up a quarry, various preparations must be made and these are basically premised on making a thorough geological study of a location.
Nevertheless, considering that dimension stone is quite like other basic construction materials, in terms of being common and widely abundant in nature and available at low depths, the methods of geological study and the investment required for these are not as complex and huge as is the case for metallic ores or hydrocarbon deposits.
The decision to investigate a particular site is informed by considering the relevant properties of a successful dimension stone.
It’s worth appreciating that the aesthetics of a dimension stone strongly inform the decision to use a given stone as a construction material.
With color and texture being the main determinants of a dimension stone’s market value, it can be appreciated that any minor variations in these two qualities, in the deposit, will have a significant impact on the production’s profitability.
Additionally, since the quarrying of dimensional stones requires the extraction of large blocks without fissures and cracks, the distribution and spacing of fractures within a deposit is hugely important.
Accordingly, a dimension stone’s quarry evaluation takes into account three factors:
1. Appearance — The color and pattern of the stone should be as uniform as possible across the deposit so that different blocks can be identified in the market as being from the same deposit
2. Deposit soundness — This takes into account the stone’s use and the demands of the processing industry. For example, if a dimension stone is used for construction and the blocks extracted are sawn using gangsaws having specified dimensions, it follows that the deposit’s fractures should have a certain minimum spacing.
3. Market demand – For the deposit itself, general, geological and industrial features are considered:
- Ownership (landowners, mining rights)
- History of operation
- General environmental issues, land use
- Size of quarry / concession area
- Regional setting and occurrence
- Geometry and structure
- Size (realistic depth and area of workable part of the deposit)
- Petrographic characterization (minerals, texture and fabric)
- Presence of imperfections
- Fractures and faults
- Commercial value, market (color, market concept)
- Access and logistics
- Use of the stone
- Workability (cutting directions, production properties)
- Working facilities
- Area for present and future movement of machinery, explosive magazines, statutory safety zones and basic amenities
- Area for disposal (far from deposit / near to workings)
- Availability of semi-skilled and skilled personnel in the region
3. Exploration of a potential dimension stone quarrying site
For dimension stone exploration it is advisable to proceed in phases.
The idea here is to gather as much information as possible from each phase that will allow you to make an informed decision as to whether you should proceed to the next phase.
The phases are as follows:
a. Desktop study — This is done by thoroughly investigating the available geological maps and reports, with focus on the desired rock types. To aid the study, satellite imagery and aerial photographs are used, in addition to the maps. The geologist doing the study should take into account factors like the dimension stone’s market demand, market trends, and availability of infrastructure in the area.
b. Field evaluation — The dimension stone’s general soundness and appearance are defined. Color is the first concern in this phase of study; if it’s not acceptable then the project can be discarded at this stage. The second concern has to do with the rock outcrop’s formation to ensure that commercial size blocks can be produced. Thirdly, samples of stone from various points of the deposit should be collected, cut and polished. They should then be used to collect feedback from the market that will inform potential demand and expected price.
c. Detailed mapping — This follows after it has been proven that the deposit has potential economic viability. Here mapping traverses are planned, cleaned, and then measured and mapped in detail on a scale between 1:100 and 1:250 according to the deposit’s size. Samples should again be collected, preferably from along the traverses.
d. Geophysical methods — All the previous phases are an assessment of the deposit from a surface point of view. This step’s intention is to make a thorough three-dimensional assessment before bulk sampling and test quarrying can be done. It also reveals the discontinuous and varied nature of a deposit’s geological features in 3-D. Ground-penetrating radar (GPR) and very low frequency electromagnetic/radio frequency electromagnetic (VLF-EM/RF-EM) techniques are used.
e. Drilling — This stage follows and is done in order to demarcate the ore deposit and also provide information about the formation’s vertical extent and possible defects with depth. Diamond core drilling is generally preferred as information about color consistency and presence of defects e.g. banding, joints and veins will be acquired.
f. Bulk sampling — This stage involves the removal of several blocks of dimension stone in order to test market acceptance. The number of blocks to be extracted is informed by the market strategy and whether or not you as the prospector have access to a factory that can cut the blocks into slabs.
g. Test quarrying — Having found success in all the preceding steps, you can now begin test quarrying. Your aim here will be to fully evaluate the recovery of saleable blocks and therefore determine whether full-scale mining will be economically viable. This will also allow you to evaluate what implications various extraction methods have on the quarrying economics.
After finding success in the exploration process you should proceed to make an application for and then purchase a concession for the quarry area.
4. Summary of the quarrying operations application process
Having secured the concession, your next step will be to start the typically lengthy process of applying for licenses and permits from the local, state and federal governments.
This process varies from country to country but will generally involve the following stages:
In your consultations with the Planning Authority, discussions can be expected to cover the following:
- Whether the proposed development will be in harmony with the development plan for the area
- Your awareness about the public concern that extractive industry developments can elicit. As such, the onus will be on you to approach the Planning Authority at the earliest opportunity and explain your proposal, and also ensure that for subsequent planning applications you will fully address the required planning and environmental concerns
- At this pre-application stage you’ll be required to describe vital operational issues including working hours and traffic volumes. Later, at the design stage, you’ll need to describe your plans for rehabilitating the extraction site.
- Prior to preparing an EIA (Environmental Impact Assessment) you should request the Planning Authority to provide you with Terms of Reference (TOR) for the EIA
Submission of your application
Your application will likely include the following:
- Proof of ownership
- Map(s) showing (a) total site area, (b) area to be excavated, (c) any ancillary proposed development, (d) all dwellings or other development — within one kilometre of site
- Description of the aggregate(s) to be extracted, method of extraction, equipment to be used, stockpiles, storage of soil and overburden, storage of waste materials, settling ponds
- Total and annual tonnage of excavated aggregates, expected life of the excavation, maximum extent and depth of working — drawings should include sections across the site, including hedgerows and other natural features — phasing program
- Description of development works — buildings, fixed and mobile plant, roads, fuel tanks, water supply and drainage, earth mounds, boundary treatment
- Estimated traffic volumes
- Environmental Impact Assessment (EIA)
- Rehabilitation plan
- Proposed hours of operation
- An Environmental Management Plan, EMP, including project description — construction, operation, decommissioning, growth, associated developments — environmental impacts — effects on humans, plants, fresh water and marine resources, flora — and possible mitigation measures to control impacts.
5. Launching your dimension stone quarrying small business operations (open pit mining)
After securing the necessary permits and licenses from the concerned authorities you can now start making the actual preparations for your dimension stone quarrying operations.
Depending on the nature of your site you may need to make a raft of preliminary preparations.
For example, before you can be able to access the stone you may be required to remove the overlying dirt and vegetation, i.e. overburden, a process that can last a few months. Constructing of roads to ease access to the quarry may be another thing you need to do.
(There are, of course, other quarry types i.e. the Hill-slope, Boulder, Underground, Hill and Top-hill varieties.)
There are a number of open pit mining design parameters you’ll need to consider:
- Ultimate pit depth — This is the maximum depth that the pit will reach at the end of its life and is decided by economic reasons and a break-even point. It’s basically a depth beyond which continuing won’t be economically viable
- Bench height — This is typically decided by the economic reach of the mining equipment to be used. (Rule of thumb: Bench height = economic bucket height of an excavator (e.g. loader or shovel) + 3 metres.)
- Bench slope — Decided by geo-technical conditions of the overburden and orebody.
- Overall pit slope — Also decided by the geo-technical stability of the rocks in the mine, bench height and bench slope. Pit slope is always less than bench slope.
- Bench width — Decided by space required for equipment operation
- Haul road width and slope — Depend on operating parameters of the trucks and other hauling equipment; it’s always wider than bench width
- Bench length — Depends on the production rate; the higher the production rate the longer the bench.
These parameters are illustrated in the open pit mine cross-section below:
It is also at this stage that you will require the assistance of an experienced quarry manager.
It is this manager who will inspect the veining and coloration of the dimension stone and then, based on the observation made, control the extraction of material.
Primarily, the manager will be looking for the stone’s “flow” through the quarry.
Note that the same stone will look different depending on how a block is cut from the wall and later processed.
If the block is cut in the direction of the source stone’s flow it’ll be described as a “Vein Cut”; if cut against the flow it’ll be described as a “Cross-Cut”.
Once the manager decides how the extraction will be done, quarrying can begin proper.
6. Quarrying of dimension stone
For the extraction of dimension stone from the open pit mine you can use one of two methods:
- Extraction of a primary block from the solid rock — This block will typically be cubic and may measure up to 4000m³. This is the main technique used in granite and marble quarries.
The process can be illustrated as follows:
Primary phase — Primary block is extracted from the bench
Secondary phase — The block is divided into smaller secondary blocks
Splitting — These secondary blocks are then divided into smaller transportable blocks
Squaring — The blocks are trimmed into the desired final shape
- Directly cutting commercial blocks from the rock body. This is the technique used for the production of sandstone building blocks.
Techniques for primary block extraction from the rock bench
There are three main techniques employed for the extraction of primary blocks from the mine walls:
Sawing method — The main sawing techniques include:
- Diamond wire sawing — This technique involves using a wire coated with diamond beads to do the cutting. The diamond wire is looped around the rock mass and then the sawing machine, which is mounted on a rail, is gradually pulled backwards. Vertical, horizontal and inclined cuts are made this way. This technique can be used for virtually all rock types including granite.
- Chain saws — The chain saw looks like a huge power saw. Its mobile arm carries a toothed chain to which abrasives (can be diamond beads or tungsten carbide beads) are attached. Cutting depth can be as high as 6m. The technique is mainly applicable for soft stones.
- Disc saws — They are not frequently used for extraction. These saws are typically run on rails or mounted on excavators, and are mainly used for making vertical cuts. The technique is only used for softer rock types.
Drilling method — You can use this extraction technique:
- in combination with splitting techniques
- for continuous channeling (considered to be an expensive method)
- to make holes for diamond wire cutting
You can either go for pneumatic or hydraulic drill equipment; the latter is preferable as it’s faster, more powerful, and consumes less energy.
Blasting method — The use of blasting has steadily declined thanks to the introduction of improved sawing methods. Even so, there are still situations and rock types for which blasting is still considered to be the most efficient technique. A successful blast can move a primary block 5–50 centimeters away from the rock face without significant damage to it.
Wedging/Splitting techniques — There are a couple of techniques here:
- Plug and feathers method — This is a manual method that involves drilling a hole into the rock surface, inserting two “feathers” in this hole, and then inserting a “plug” in between the “feathers” and hitting it with a heavy hammer resulting in the splitting of the rock.
- Hydraulic splitting — This involves using hydraulic wedges affixed to a tractor. The principle here is similar to that of the manual technique but it’s much faster and can be efficiently employed over a large quarrying area.
- Splitting with expanding mortar — This is a slow method of wedging. Expanding mortar is placed into drill holes and as it expands it splits the rock. However, this technique is expensive, and also results in some mortar “escaping” into open fractures and cavities in the rock.
Jet burner technique — This involves using a high temperature jet frame to cut channels in granite. This technique’s use is in decline thanks to the rise of wire sawing, and not to mention the unwanted characteristics of the procedure i.e. extreme noise, much dust, and the inability to do any other work in the quarry when channeling is ongoing.
Directly cutting commercial blocks from the rock body
The stone-cutting machine used for this technique comprises of circular blades to which diamond abrasives have been attached. A single machine can have two or three blades for making vertical cuts and one or two blades for making horizontal cuts i.e. on the top and bottom surfaces of the commercial blocks.
Production starts with a thorough preparation of the quarry site. The dimension stone bed is adequately leveled such that the rail on which the machine runs can lie flat on the surface.
When everything has been set up the operator can begin running the machine along the rail. As it moves it cuts out equally sized commercial blocks which are then collected and transferred to storage or loaded into trucks.
This is a video demonstrating this process: