Industrial Minerals

Intro

Industrial minerals currently mined in Colorado include quarry aggregate (crushed stone), sand, gravel, industrial gas (helium and carbon dioxide), limestone, gypsum, shale, nahcolite (sodium bicarbonate), and dimension and decorative stone. Sand, gravel, and quarry aggregate play an important part in Colorado’s infrastructure because they are used to produce concrete, asphalt, road base, and construction fill for our roads and other construction projects. Limestone is used primarily to produce cement which is also key to construction activities across the state. Gypsum (used to produce drywall or sheetrock), clay (for the production of bricks), and shale (used to construct lightweight aggregate) are also important parts of the construction industry in the state.

The CGS creates geologic maps through our STATEMAP program that, among other goals, define the locations of specific rocks that contain industrial mineral resources. These maps are used by public and private entities to locate deposits suitable for removal and processing, to determine what resources should be set aside during land-use planning, and to provide field data for future resource supply-and-demand planning and modeling. It is important to know where these resources are so these areas can then be set aside for future development. For example, if local sources of aggregate are depleted, the cost to transport this material will be passed on to local, state, and federal agencies and ultimately, the tax payer. Information from geologic maps are used to create derivative maps that rate geological units for their general potential to contain certain industrial minerals, hazards, or other geological properties. This allows non-geologists to easily determine the potential location for these properties. The CGS maintains a general mineral potential (derivative) map for the geologic quadrangles that we otherwise field map in detail.

Sand and Gravel

The primary uses of sand and gravel is for concrete aggregates, road base and coverings, road stabilization, construction fill, asphaltic concrete and other bituminous mixtures, and other concrete products. Other uses include plaster and gunite sands, snow and ice control, filtration, railroad ballast, and roofing granules. Crushed stone is primarily used for construction material especially in road construction/maintenance and cement manufacturing. For a description of the geology of sand, gravel, and quarry aggregates, the CGS published ON-007-05 Colorado Aggregate Resources that shows the locations, geology, and descriptions of these natural deposits.

Colorado uses a large amount of aggregate to build and maintain infrastructure. Colorado quarry operators produced 51.81 million tons of aggregate (sand, gravel, and crushed stone) in 2018. The estimated 2018 production value was $284 million for sand and gravel and $141 million for crushed stone (see IS-82 for more information). The cost of aggregate to the user is highly dependent on aggregate transportation costs. Locating quarries close to population centers helps lower overall costs. However, residential and commercial development near an aggregate source can make permitting a new or expanding quarry a challenge.

Special Publication 5A and 5B, Sand Gravel and Quarry Aggregate Resources, Colorado Front Range Counties will assist local Front Range governments identify potential sources of sand, gravel and quarry aggregates. Digital versions of the aggregate resource maps may be found in OF-00-09 Atlas of Sand, Gravel, and Quarry Aggregate Resources, Colorado Front Range.

Aggregate Resources

Sand, Gravel, and Quarry Aggregates

Naturally occurring aggregates, such as sand, gravel, and crushed stone are produced in Colorado. Aggregates are used in several applications including construction fill, concrete, asphaltic mix/concrete, road base, other concrete and asphalt products. Other uses of aggregate include rip-rap, plaster and gunite sands, snow and ice control, filtration systems, railroad ballast, hydraulic fracturing, and roofing granules. Aggregates are generally defined as granular materials that are: 1) used with a cementing medium to form concrete or mortar or 2) used as a construction material, meeting the requirements of road, paving, or other construction applications (modified from ASTM C125-18 and D8-18, 2018).

Geology

Sand, gravel, and crushed rock are all quarried for use as aggregate in the state. Crushed rock can include igneous, sedimentary, and metamorphic rocks. This natural rock material must be blasted and crushed to the desired aggregate size. Igneous rocks form from molten rock or magma and include intrusive rocks (magmas that cooled at depth) and extrusive rocks (rocks produced by eruptions onto the earth’s surface). Igneous rocks that are typically quarried for aggregate include granite and basalt.

Sedimentary rocks are formed by deposits of eroded igneous and metamorphic rocks as well as material produced by living organisms. Limestone, sandstone, and other sedimentary rock types are mined in Colorado for aggregate. Limestone is primarily mined and crushed for use as concrete aggregate while well-indurated sandstones (difficult to break with a hammer) can also be a good source for crushed stone.

Metamorphic rocks include rocks that were subsequently transformed after being exposed to heat and pressure. Metamorphic rock types that are typically mined for aggregate include gneiss and schist. Several quarries in the Front Range mine gneiss and provide crushed rock to the Denver metropolitan area.

Sand and gravel deposits are typically unconsolidated or weakly cemented sedimentary deposits formed by several different natural processes including:

• fluvial (streams, also known as alluvial deposits)
• lacustrine (lakes)
• marine (oceans)
• glacial (glaciers)
• eolian (wind) processes.

Most sand and gravel quarried in the state occurs within the floodplain and underlies low terraces of modern streams that may contain less weathered aggregates. Terraces are remnants of former floodplains that formed when a stream was at a higher elevation prior to down cutting and forming a new lower floodplain. Other deposits include upland gravels and alluvial fans which are fan-shaped wedges of sediment that form where a stream emerges onto an open plain from an area of higher elevation. Upland gravel deposits are associated with ancient stream courses and may or may not occur near modern streams and their tributaries. Both upland gravels and alluvial fans can be quarried for aggregate but upland gravel deposits typically are more weathered and may not be suitable for specific uses. Eolian sand deposits cover a large portion of eastern Colorado and are dominantly comprised of sand and silt. Glacial sand and gravel deposits occur in former glaciated areas at higher elevations in the Rocky Mountains.

Engineering

Many factors determine what constitutes a viable sand, gravel, or crushed rock aggregate resource including:

• material composition, size, size distribution, color, shape, texture, and weight
• vertical and horizontal extent of the deposit
• overburden thickness
• material strength, durability, soundness, porosity, water adsorption, reactivity, specific gravity
• the presence of fines, sulfates, calcium carbonate, and other minerals
• environmental and mine permitting
• community relationships
• local supply and demand
• distance and transportation to the source
• available land for lease/purchase.

Although a natural aggregate deposit may meet many of these factors, developing these resources can be limited by issues associated with one or more of these elements. Also, one sand and gravel deposit may meet construction specifications for one type of application but may not meet the requirements for another. For example, sandstones and other sedimentary rock types may not meet engineering specifications for use in asphalt and concrete but could be used for road base or fill.

Land-Use Planning

Colorado uses a large amount of aggregate to build and maintain needed infrastructure. The cost of aggregate to the end user is highly dependent on the cost of transporting aggregate. Locating quarries close to population centers helps lower overall costs. However, residential and commercial development near an aggregate source can make permitting a new or expanding mine a challenge.

The demand for aggregate is regional but land-use planning and permitting for aggregate supplies is done on a local level. Balancing the need for readily available and reasonably priced aggregate with other regional, social, and environmental priorities is not an easy task for local governments. A 1973 state law recognized the need to balance competing interests in urban areas and counties with a population of least 65,000 residents, which must now develop a master plan for the extraction of industrial mineral deposits. The intent of this state law is to allow for the extraction of aggregates—as well as other commercial mineral deposits—while protecting the environment and public safety.

To help local Front Range governments identify potential sources of sand, gravel and quarry aggregates, the CGS created “Special Publication 5A and 5B, Sand Gravel and Quarry Aggregate Resources, Colorado Front Range Counties”. Digital versions—GIS datasets—of the aggregate resource maps are available in OF-00-09 Atlas of Sand, Gravel, and Quarry Aggregate Resources, Colorado Front Range.  The contents of  these reports are also available as an online map.

Projected population growth in other counties throughout Colorado have prompted local governments in these areas to create mineral extraction plans in conjunction with future land use planning. Mineral extraction plans may prevent quality aggregate resource areas from being lost to other land uses.

Cement

Portland cement in Colorado is used primarily in the production of concrete. Concrete consists of a mixture of aggregates and paste. Sand, gravel, or crushed stone is mixed with water and cement. According to the Portland Cement Association, cement is created by heating lime, silica, alumina, iron, and other materials at high temperatures which creates small round pellets called clinkers that are ground, mixed with limestone and gypsum, and used to make concrete.

In 2018, three Portland cement plants operated in Colorado. All three mining companies sourced the Upper Cretaceous Niobrara Formation as feedstock for their cement products. Like the aggregate business, the production of cement is largely tied to the construction industry. Estimated Portland cement production (e.g. shipments from Colorado) in 2018 was 2.5 million tons. Production and average cement prices are shown in our annual Mineral and Energy Activities reports.

Gypsum

Gypsum mined in Colorado is used for the production of wallboard, as an ingredient in cement production, as a soil conditioner, and for other industrial uses such as glass making and smelting. In 2018, Colorado was one of the top six states in the U.S. that accounted for 67% of the total gypsum mine output. American Gypsum Co. operates a large quarry and fabrication plant for wallboard in Eagle County, near the town of Gypsum, and is the fifth largest producer of gypsum wallboard in North America. Gypsum is also mined in Larimer and Fremont counties. Pete Lien & Sons mines gypsum for the cement industry and soil amendment from the Munroe Quarry north of Fort Collins in Larimer County. As reported by the USGS, crude gypsum production in the U.S. increased about 1.4% in 2018 and was estimated at 23.1 million tons. Production information on Colorado gypsum is unavailable for proprietary reasons.

Helium

In 2017, helium was primarily used for magnetic resonance imaging, lifting gas (e.g. for lifting high-altitude equipment), analytical and laboratory applications, welding, and other applications. Grade-A helium is produced in Cheyenne County, Colorado. Although the U.S. appears to have abundant reserves, helium was listed as a critical mineral by the U.S. Geological Survey in 2018. That same year, they reported that 42% of U.S. helium production was provided by the federal helium storage facility at Cliffside Field in Texas. However, the Bureau of Land Management (BLM), who manages the federal helium program under the Helium Stewardship Act of 2013, will terminate this program no later than 2021 or when the remaining helium stockpile falls below a predetermined threshold. As reported by the USGS, “By the end of the decade, international helium extraction facilities are likely to become the main source of supply for world helium users”.

Carbon Dioxide

Naturally occurring carbon dioxide gas (CO₂) was produced in 2018 primarily from three areas in Colorado in Montezuma, Dolores, and Huerfano counties. Jackson and Rio Blanco counties have produced it in the past. CO₂ is produced from wells in a similar way to natural gas production and is used primarily in enhanced oil recovery (EOR) in Texas and New Mexico. EOR is the implementation of various techniques for increasing the amount of crude oil that can be extracted from an oil field. EOR is also called improved oil recovery or tertiary recovery (as opposed to primary and secondary recovery). CO₂ is used to extend the life of a well after the initial pressure in the well decreases. Other uses include welding gases, manufacture of dry ice, and in the food and beverage industry. In 2018, Colorado produced an estimated 419 billion cubic feet (Bcf). Montezuma County sourcing accounted for about 90% of the total Colorado CO₂ production.

Sodium Bicarbonate

Sodium bicarbonate (more commonly known as baking soda) is primarily used in food preparation and baking, personal care products, pharmaceuticals, animal feed products, pool and water treatment, and other industrial applications. Natural Soda, Inc. operates a nahcolite solution mine in Rio Blanco County. Nahcolite is the naturally occurring mineral of sodium bicarbonate (NaHCO3). High grade nahcolite (greater than 80%) is recovered from the Boise Bed in the Green River Formation of the Piceance Basin.

Hot water is pumped down a well approximately 1,900 ft (600 m) deep to dissolve the nahcolite. Other wells recover the sodium bicarbonate-enriched solution and pump it to the surface where the solution is allowed to cool and precipitate sodium bicarbonate which is further dried and processed to produce commercial grade product.

Limestone, Calcium Carbonate, and Lime

Limestone is mined in Colorado for aggregate, dimension stone, and quicklime for cement production. Lime is made by calcining (e.g. burning) high-purity limestone to form calcium oxide, commonly called quicklime. Other uses include soil conditioner, water and sewage treatment, and in food products. Limestone occurs in many locations in the state and has been quarried in Boulder, El Paso, Fremont, Garfield, Larimer, and Moffat counties for cement, concrete, and/or other limestone products. Limestone is ground into a calcium carbonate powder at some facilities and is used for a variety of purposes including a filler for roofing shingles, fire suppression in underground coal mines, calcium supplement for liquid animal feed, and other uses.

GIS Data

The following are GIS maps showing specific state-wide industrial minerals resources:

ON-007-01 — Aggregate Resources of Colorado — Naturally occurring aggregates, such as sand, gravel, and crushed stone are quarried throughout Colorado. This interactive map includes the digital versions of our sand, gravel, and quarry aggregate publications for most of the Front Range counties, Garfield County, and includes a statewide map of older quarry locations. This map shows the locations and ratings of these potential resources to assist with land use planning and resource development in the Front Range and beyond.

ON-007-03 — Mineral Resource Potential Derivative Map — The CGS compiled mineral resource derivative maps using 7.5-minute quadrangles published under the current CGS STATEMAP geologic mapping program. These maps show the general location and mineral potential rating of select aggregate and industrial mineral deposits by geological unit as mapped during the STATEMAP program. The maps are created from these geological maps and historic mining/quarry information to provide a general rating as to their potential for containing select mineral resources. Potential mineral resources include sand and gravel, decomposed granite, crushed stone, clay/claystone/shale, fluorspar, gypsum, limestone and dolomite, dimension stone, and others. Derivative maps are generalizations of detailed geological information that are used to assist non-geologists with evaluating complex geological information. 

ON-007-05 — StoryMap: Colorado Aggregate Resources – Geology and Industry Overview — An interactive website that integrates maps, text, and photos about the location and geology of sand, gravel, and quarry aggregates in the state. Includes a description of aggregates, what they are used for, where they are found, how and why the location of these deposits are important to land-use planning, and the general geology of sand, gravel, and rock quarry aggregates.

ON-007-07 — Reconnaissance of Potential Sand Sources in Colorado for Hydraulic Fracturing — An online map of the data provided on the two plates included in this report: RS-47 Reconnaissance of Potential Sand Sources in Colorado for Hydraulic Fracturing. This online map includes over 800 sample locations across the state, photos of each sample location, photomicrographs of samples, geologic descriptions, estimates of rounding and sphericity, estimates of quartz content and friability, mineralogy, sieve results, and resource ratings. 

References