Consider the last time you were at a dinner party, a fancy restaurant, or in a swanky, downtown hotel lobby. You may remember the conversation, the beverages, or the meal, or possibly the golden ding of the receptionist bell. Perhaps you even noticed the highly polished stone that adorned the bar, the walls, or the floor. The qualities that catch the eye, such as color and texture, are a result of the geological properties of the rock from which this decorative stone was sourced. Elaborate colors, streaking foliations, and flecks of variegated minerals provide beauty in a material sense. In the mining industry, these variations tell a rich story of deposition, deformation, and skill of production. What is the origin of that fantastic bar countertop you observed? What uses are there across industries for dimension stone? Where should you seek to produce dimension stone as a commodity?
Dimension stone has many industrial and decorative purposes. In addition to the variable use of cut stone, there is a multitude of stone types sourced from different rocks all over the world. The stone utilized in the construction of the most important buildings of downtown Salt Lake City, Utah only traveled 20 miles. The stone’s source in Little Cottonwood Canyon provided the elegantly gray quartz monzonite slabs. This is a common theme throughout the United States and across the world, however, the most valuable and desirable stone can be economically transported at great distances. The Lincoln Memorial in Washington, D.C., is composed of Georgia marble. As far back as the Roman Empire, Italian travertine slabs were transported across Europe for the construction of temples and civic buildings. Today, we pay respects to the marble, granite, or sandstone memorials of passed-on loved ones.
As a commodity, dimension stone seems straightforward. You’ve seen large, natural outcroppings of rock along the highway, in parks, or along the wave-cut benches of California. However, there are many considerations in developing a valuable dimension stone quarry. Namely, these considerations are qualities of the stone: appearance, suitability for rectangular block production, and transportation costs. All (or most) of these characteristics must align in a positive way to result in a marketable and economic product.
The first step in dimension stone exploration is to identify suitable rock in close proximity to a well-defined market. Transportation costs can quickly become the barrier to an otherwise economic quarry. An intrepid explorer could possibly identify a world-class deposit of highly desirable stone that can overcome transportation costs, but this is extremely rare. More often, a reasonable stone with desirable characteristics can be produced and reach markets at an optimal cost. The major geological controls on a viable dimension stone quarry include color, structure (including folds, faults, and joints), and technical properties such as the potential for fracturing along bedding planes. Rock types that are suitable for dimension stone production include, but are not limited to, granite, limestone, marble, sandstone, slate, greenstone, and basalt.
Once a potential rock unit has been located on federally controlled land and you wish to investigate its potential, you must contact the Bureau of Land Management to negotiate a lease of the salable mineral. Essentially, you will pay a per ton cost to the BLM to produce the stone. Proper permitting must be followed to do a thorough geological exploration. In some cases, such as with calcium carbonate-rich rocks (limestone or marble) a set of lode claims could be established to utilize hand tools such as augers and backpack drills to do initial exploration. Ultimately, the resource must be investigated for geologic factors. The following sections will cover the key geological characteristics that result in an economic dimension stone quarry.
Color is the single most important characteristic for quality dimension stone production. Unusual colors are the most desirable, and customers will pay top dollar for these materials. A single-color stone is called homogeneous and often is a pearly marble, a tan sandstone, or black traprock (basalt). Granites and gneissic rocks may contain migmatic swirls from the partial melting of the rock as they were metamorphosed. Variegated and foliated stone provide unique textures that attract the eye and a customer’s wallet. Multi-colored stones are typically metamorphic rocks and may contain vibrant, eye-catching compositions that are also highly desired.
As you evaluate your potential deposit, fracture density and spacing of joints that are natural to the compressional and extensional forces exerted on the rock over time dictate the size of blocks and the ease of production. Evenly spaced fractures can be a great boon to a producer. These natural features provide an inherent cost-saving addition to the geological controls on production. In most cases, a solid quarry site will contain fractures set in a way to produce 3m3 blocks to be sent off for fabrication. Stone featuring orthogonal fractures that cut across bedding planes or primary fabrics are extremely difficult to produce. Theycan quickly squash a potential resource as uneconomic.
Another key characteristic of evaluating a potential dimension stone quarry is the overall size and scope of the deposit. This includes all criteria discussed earlier but brings in a scale factor. Several tens of cubic meters of immaculate marble may seem attractive to a developer or investor, but the lateral and vertical variation of rocks must be investigated either through outcrop studies, field mapping, and drilling. Hopefully, your area of interest has sufficient material to justify a serious investment into the production of dimension stones.
The ultimate evaluation of a deposit prior to production involves investigating the technical properties of the stone. This includes microscopic variations, mineral composition, the form and distribution of these minerals, as well as the deformation contained within the rock and its associated weathering profile. Many of these criteria can be investigated with field observations, however, the microscopic characteristics require a trained eye to identify the overall mineral variations and other qualities such as porosity, permeability, and micro-fracture density.
Once a resource has been evaluated for these characteristics, and after it has been deemed an economic prospect, producers can begin test quarrying a section of the deposit and begin pilot production. Overall, dimension stone is a lucrative investment, and the demand for construction and finishing grade materials has never been higher in the USA. With Burgex in your corner, we have the field experience, technical skills, and economic/financial expertise to help you identify, evaluate, and develop a world-class dimension stone quarry. Contact our team today!
References
Selonen, O., Luodes, H., and Ehlers, C., 2000, Exploration for dimensional stone ̶ implications and examples from the Precambrian of southern Finland, Engineering Geology, v. 56, p. 275-291.
Dolley, T.P., 2003, Dimension stone, Mining Engineering, v. 55, no. 6, p. 23-25.
Ashmole, I., and Motloung, M., 2008, Dimension stone: the latest trends in exploration and production technology, in Proceedings of the International Conference on Surface Mining, The South African Institute of Mining and Metallurgy, v. 5, no. 8, p. 35-70.
Mosch, S., Nikolayew, D., Ewiak, O., and Siegesmund, S., 2011, Optimized extraction of dimension stone blocks, Environmental Earth Science, v. 63, p. 1911-1924.
Mustafa, S., Khan, M.A., Khan, M.R., Hameed, F., Mughal, M.S., Asghar, A., and Niaz, A., 2015, Geotechnical study of marble, schist, and granite as dimension stone: a case study from parts of Lesser Himalaya, Neelum Valley Area, Azad Kashmir, Pakistan, Bulletin of Engineering Geology and the Environment, v. 74, no. 4, p. 1475-1487.
