Marble
Site visit: CEVALOR Headquarters and the Galrão Group marble quarry, Borba and Vila Viçosa, Portugal
The semi-arid landscape of the Portugal’s Alentejo region blankets an earth crust rich in pink and white stone. Hidden within the unassuming rolling hills are a number of marble and limestone quarries that dive deep into the ground. I visited the area in the height of summer, when the quarry operations had slowed, to learn more about the pits.
I was hosted by Tânia Peças of CEVALOR, the Technological Centre for Portuguese Natural Stone, an industry organization that provides laboratory testing, technical assistance, applied research, natural stone promotion and human resource development for Portuguese stone companies. Our tour began at the Galrão Group’s marble quarry in Pardais where we met Joaquim Palma, manager of the site. The pit is one of Galrão’s two quarries and, according to its website, has an annual extraction capacity of 7500 cubic meters. Galrão shares the open pit quarry with two other manufacturers. Cut lines in the pit roughly divide it into thirds, demarcating each company’s domain.
To extract the massive stone blocks, Galrão uses the standard quarrying technique of drilling and then horizontal and vertical cutting with diamond wire. The wire saw slices clean orthogonal planes in the earth as if cutting into a block of cheese.
The stone is extracted and then transported to the company’s factory where it is divided into smaller, commercially sized pieces. The blocks and slabs are used primarily in construction for dimensional or ornamental applications. The majority of the Portuguese stone is exported internationally, largely to Europe and the Middle East.
After visiting the quarry, Tânia and I drove to CEVALOR’s headquarters in Borba. The center includes a training facility, workshop, and gallery exhibiting the wide range of Portuguese stones, both calcareous (marble and limestone) and siliceous (granite and slate). We toured the laboratory where the stone is tested for its material properties, including flexural strength, compression strength, friction and permeability. Afterwards, Tânia showed me around CEVALOR’s factory and workshop, a small-scale version of many commercial production facilities.
A large quantity of water is used, both at the quarry and in the factory, to lubricate the stone during cutting. Water use is of environmental concern for two reasons — first, to minimize the total quantity of water consumed, and second, to properly manage and treat the wastewater. The CEVALOR facility has an onsite water recycling system similar to that which is used by most larger commercial factories. The system enables about 80 percent of the process water to be re-circulated in the factory, minimizing the demand for water from offsite. [1]
Management of the dirty wastewater is of concern because when it contains stone dust and residual waste from the cutting process. Once separated from the recycled water in the treatment system, this fine powdery slurry is often taken to landfill for disposal. However, in an effort to minimize waste, CEVALOR and the organization’s European industry counterparts are investigating new ways of recycling the byproduct. They are testing methods of drying the material for construction applications, such as bricks and pre-cast concrete members.
Separate from the slurry waste coming out of the process water, there is a large amount of stone waste generated in the extraction and manufacturing processes. Next to each quarry, Galrão’s pit included, stands a large pile of discarded marble. This growing landfill is the destination for the material that does not meet the commercial quality standards. According to CEVALOR’s literature, waste from a quarry can be as much as 50–95 percent of the total material extracted, depending on the quality and consistency of the stone. An additional 20–40 percent of waste is generated in the factory, due to irregularities in shape, size and color. While the quantity is high, the waste is mostly put to use for small applications or crushed for use as aggregate and fill. [2]
Driving away after the tour, I realized that masses in the landscape that I first thought to be hills were in fact the unassuming piles of discarded marble. Each one serves as a visual marker of a quarry hidden in the ground, revealing the number of pits in the area. Imagining the earth’s surface dimpled with these enormous quarries, the magnitude and richness of the natural geology beneath our feet became vividly clear.
Thank you to CEVALOR and the Galrão Group for allowing me to visit, and particularly to Tânia Peças for her time. The thoughts and information in this post are based on my visit to CEVALOR and the Galrão Group quarry and have not been externally verified unless otherwise noted.
All photos and video by Irmak Turan.
Citations:
[1] CEVALOR (2015). Introduction on Geology and Quarrying Techniques and Block Cutting And Slab Processing [PowerPoint slides].
[2] Ibid.
