August 2017 Issue Table of Contents
Naturally occurring borates are the major economic source of boron. Borates were first used over 4,000 years ago in precious-metal working and are now essential components of modern industry. Although borates have been exploited from other sources, three minerals from non-marine evaporites now form the major commercial sources of borate – borax, colemanite and ulexite. These major commercial deposits are associated with Neogene volcanism in tectonically active extensional regions at plate boundaries. The most important continental borate provinces are located in the USA, Argentina, Chile, Peru, and China, with the largest borate reserves in the world being found in western Anatolia (Turkey).
Keywords: economic borate deposits, non-marine evaporites,
Turkish borate deposits
Borates are the most important economic source of boron and have been used for millennia. Borax (see Table 1 for borate mineral formulae) was first used in Babylon (ancient Mesopotamia, now in modern Iraq) more than 4,000 years ago; indeed, its name is derived from the Persian burah (boorak). At that time, the Babylonians brought borax from the Himalayas for use in the manufacture of jewellery. The Egyptians used borax in mummification, and by ~300 AD the Chinese were familiar with borax glazes, as were the Arabs three centuries later. Borax was first brought to Europe in the 13th century by traders from Tibet and Kashmir (Ozol 1977; Travis and Cocks 1984; Kistler and Helvacı 1994; Smith and Medrano 1996; Garrett 1998; Helvacı 2005, 2015).
By the 1770s, the French had sourced borax from Purbet Province (India) and, at about the same time, natural boric acid (sassolite) was discovered in hot springs in the Maremma region of Tuscany (Italy). The discovery and commercial development of borate deposits accelerated during the 19th century. Chile started to mine borate from the Salar de Ascotán [salar means ‘salt flat’ in Spanish] in 1852, accounting for a quarter of the world’s annual supply of ~16,000 tonnes. In 1856, John Veatch discovered borax in Clear Lake, California (USA) (Kistler and Helvacı 1994). In Turkey, borate mining extends back to Roman times, but modern mining began in 1865 when borates were extracted from the Aziziye mine (Sultançayır) in the Balıkesir province and was shipped to France for processing (Travis and Cocks 1984).
Economic Mineralogy Of Boron
‘Borate’ has the industrial definition of, ‘Any compound that contains or supplies boric oxide (B2O3)’. But of the many known boron minerals only three are currently major commercial sources of borate: colemanite, ulexite and borax. All three are found within non-marine evaporites (Smith and Medrano 1996; Garrett 1998) (Table 1). Deposits containing these minerals are mined in a limited number of countries and are dominated by the United States and Turkey, which together supply 90% of the world’s borate (Table 2).
Borax is by far the most important mineral for the borate industry. This reflects the fact that borax is the most widely distributed and abundant borate mineral, with large tonnages present in the deposits at Boron (California, USA), Kırka (Turkey), and Tincalayu (Argentina) (Kistler and Helvacı 1994). In addition, borax crushes easily and dissolves readily in water, so processing costs are relatively low.
Ulexite is a mixed Na–Ca borate that has similar mineral processing properties to borax and is the usual borate found worldwide near the surface in playa lakes of Recent to Quaternary age. However, the only deposits specifically exploited for ulexite are the Neogene deposits in the Bigadiç and Kestelek Basins of Turkey.
Colemanite is a Ca-borate that has low solubility in water and requires acid dissolution during processing. It is, however, the preferred source of boron for the production of high-quality sodium-free glass for the fiberglass industry. While colemanite was historically produced in Death Valley (California, USA), large-scale production of high-grade colemanite is now restricted to the Emet Basin of Turkey (Helvacı and Alonso 2000; Helvacı 2005; Orti et al. 2016).
Origin of Borate Deposits
All the world’s major economic borates are found in non-marine evaporite deposits located in extensional basins formed during the collision of tectonic terrains (Fig. 1) (Ozol 1977). Most of the commercial borate deposits in the USA, Argentina, Chile, Peru and Turkey are associated with continental sediments and acidic volcanism of Neogene age (Smith and Medrano 1996; Helvacı 2005). Many borates in Turkey, the USA and Argentina are also covered by carbonate cap rocks that aided their preservation (Helvacı 2005).
The Precambrian borate deposits of Liaoning Province (China) were initially classed as skarn deposits on the basis of their mineralogy (suanite, szaibélyite and ludwigite), but detailed field studies and boron isotope data indicate that they, too, are likely metamorphosed non-marine evaporites (Peng and Palmer 2002).
Borates have also been mined from skarn deposits (e.g. datolite from Dalnegorsk, Russia), active geothermal fields (e.g. sassolite from Lardarello, Italy) and marine evaporites (e.g. inderite from the Inder, Kazakhstan). However, none of these sources are currently of more than local significance (Kistler and Helvacı 1994).
Borate Deposits of Turkey
The world’s largest and best-studied borate deposits are those of western Anatolia (Turkey) (Helvacı 1995, 2015; Orti et al. 2016; Helvacı et al. 2017). The borate deposits themselves lie in an area covering 300 km east–west by 150 km north–south in western Anatolia, south of the Marmara Sea (Fig. 2). The main districts include the Bigadiç colemanite and ulexite deposits (Ca and Na borate); Sultançayır priceite deposits (Ca-type); Kestelek colemanite deposits (Ca-type); Emet colemanite deposits (Ca-type); and Kırka borax deposits (Na-type) (Figs. 2–4) (I nan et al. 1973; Helvacı et al. 1993, 2017; Helvacı 1995; Helvacı and Orti 1998; 2004; Garcia-Veigas et al. 2011; Garcia-Veigas and Helvacı 2013; Orti et al. 2016).
In Anatolia, the ultimate source of the boron is calc-alkaline volcanic rocks that were enriched in boron as a consequence of metasomatism and melting of the lithospheric mantle during continental collision (Ersoy et al. 2010). The boron was then leached from the volcanic rocks by geothermal waters that collected and evaporated in playa lakes within extensional basins (Fig. 5).
The mineralogy of the borate deposits reflects the composition of the geothermal fluids that are, in turn, dependent on the local geology (Helvacı 1995). For example, boron isotope data from the Kırka deposit suggest that colemanite precipitated from fluids of low pH (~8.2) compared to ulexite (pH ~8.6) and borax (pH ~8.8) (Palmer and Helvacı 1995). Strontium isotope data from across the Turkish borate province indicate that Ca-rich borates likely formed from the evaporation of geothermal fluids that had interacted with basement limestones (Palmer and Helvacı 1997; Floyd et al. 1998).
Turkey is currently the largest producer of borates and has the world’s largest reserves (Table 2). Production has more than doubled since 1980 to over one million tonnes per year, and further increases (particularly of borax from Kırka) are likely to lead to Turkey dominating world markets. Turkey is already the major world producer of colemanite, much of which comes from the Emet Valley.
Exploring for Borate
Borate exploration uses all the tools available to the exploration geologist, with the recognition of trends of favourable host rocks and structures being an important guide to areas of possible interest. Borates are highly soluble, hence post-depositional dissolution of borate deposits by circulating meteoric water can lead to their dissolution. On the plus side, the mobility of borates also means that water sampling (from the surface and from wells) and vegetation surveys can yield useful information (Kistler and Helvacı 1994; Floyd et al. 1998; Helvacı 2005).
Geophysical surveys, particularly gravity and magnetics, are used to outline target basins or structures beneath sedimentary basin fill. Once geophysical, geological and geochemical surveys have identified promising targets, soil and rock-chip sampling techniques are used in exploration drill programs, with Sr, As, and Li as a common suite of elements to be assayed alongside boron (Helvacı et al. 1993, 2004; Palmer et al. 2004). Unlike most other elements, simple field assays of B2O3 can be undertaken using the original flame test and the simple wet-chemistry turmeric/curcumin test. Although layered evaporite deposits of borax, colemanite and ulexite are not generally sought at depths >500 m, boron-rich brines, particularly those associated with other salts of value, can be extracted from greater depths under certain circumstances (Kistler and Helvacı 1994).
Mining of Borate
Borate extraction and transport has a colourful history. For example, workers would wade into Himalayan lakes to harvest the lake “floor” and then transport the borax in saddlebags on sheep across the Himalayas to markets. There was borate extraction from what was known as the “Dante’s Inferno” of the Larderello (Italy) boric acid fumaroles. And there were the famous 20-mule teams used to transport borax from Death Valley to the Pacific coast in the western United States (Kistler and Helvacı 1994).
Most of the world’s commercial borate deposits are now mined from open pits (Fig. 4). For example, the Boron mine in Kramer (California, USA) and the Kırka mine in Turkey are huge open pits that are mined by massive shovel excavators and trucks, plus front-end loaders for ore mining and overburden removal. The borate ores and overburden are first drilled and blasted and then a belt conveyor is used to move ore from the in-pit crusher to a coarse-ore stockpile from which it is reclaimed by a bucket wheel that blends the ore before it is fed to the refinery.
The Tincalayu deposit in Argentina is also mined from open pits. Here, the ore is transported 400 km by truck and rail to the Salta refinery. Some South American and Chinese salar (i.e. salt flat) operations also use hand labour to mine thin salar borates, generally after stripping of the overburden with a small bulldozer.
Borates are mined underground in the Liaoning Province of China and at the Billie and Gerstley mines in Death Valley. Borate brines are recovered at Searles Lake (California) and in the Qinghai Basin of China. Brines have also been extracted in the Inder region of Kazakhstan.
borate Mineral Processing
Processing techniques for borates are related to the scale of the operation and the ore type, with either the upgraded or refined mineral (borax, colemanite, or ulexite) or boric acid as the final product for most operations. Borax ores (e.g. from Boron, Kırka and Tincalayu) are generally crushed to ~2.5 cm and then dissolved in hot water/recycled borate liquor. The resultant liquor is clarified and concentrated in large counter-current thickeners, filtered, fed to vacuum crystallizers, centrifuged, and then dried. The final product is refined borate decahydrate (borax sensu stricto), borate pentahydrate (tincalconite) and fused anhydrous borax and can be used as a feed for the production of boric acid.
Colemanite concentrates are used directly in glass melts for the non-sodium fiberglass industry or are used as a feed for boric acid plants. Magnesium borates are generally concentrated, dissolved in acid to remove the magnesium, and then converted to boric acid or sodium borates.
Brines from Searles Lake (and also, presumably, from Qinghai) are recovered by either controlled evaporation or carbonation (Kistler and Helvacı 1994). The remaining borate liquor is fed to tanks containing borax seed crystals, which aid in the borate recovery. The resultant slurry is filtered, washed, redissolved, and fed to vacuum crystallizers that produce dehydrated borax products or boric acid.
While evaporite borate minerals and brines have relatively low energy (and, hence, low cost) production methods, borosilicates require much higher energy processing, something that has led to them becoming largely uneconomic. For example, ores from the Bor deposit (Dalnegorsk, Russia) with their relatively low B2O3 grades, are crushed, and then run through a complex plant that includes magnetic separators, heavy mineral separators, and flotation cells (Utekhin 1965). The concentrates are then dried, leached, and calcined before being converted to boric acid or to a sodium borate.
Uses of Boron
Boron is widely used in many industries, so that only a brief summary is possible here: more extensive details are provided in Crangle (2015). Borax pentahydrate and boric acid are the most commonly traded commodities. Boric acid plants are operated by all the major borate producers. Glass fibre insulation is the major end use in the United States, followed by textile glass fibre and borosilicate glass, detergents, and ceramics. Boron fibre–reinforced plastics are used extensively for aerospace frame sheathing where they combine flexibility and light weight with strength and ease of fabrication. Minor uses that will likely increase include those in fertilizers, wood preservatives, alloys and metals, fire retardants, and insecticides (Garrett 1998).
Borates are also used in pharmaceuticals, cosmetics, anti-corrosion compounds, adhesives, abrasives, insecticides, metallurgical processes, and nuclear shielding. More recently, boron has been used in super magnets, where it is combined with rare earths, nickel and iron to produce alloys to make electromagnets for computer drives, high fidelity speakers, starter motors, and household appliances.
Borates are also increasingly used in “green” (i.e. environmentally friendly) applications by aiding recovery of heavy metals from industrial waste streams and by removing impurities from the polymers used in bleaching wood pulp for paper production.
Medical applications of borates include cancer research, where the large capture cross-section of the 10B isotope makes it an excellent neutron absorber that reacts with low-energy neutrons to give off short-range alpha particles that can be used for microsurgery in previously inoperable areas of the brain. Current tests on boron analogues indicate they may also be effective in reducing serum cholesterol and other disease-causing proteins.
Borates were traded at relatively high prices into the late 19th century, but have become a relatively modestly priced industrial mineral commodity in recent years following the development of the large deposits at Boron (USA) and Kırka (Turkey). Prices are directly related to production costs, of which the largest is fuel for drying, dehydrating, and melting the refined ore into the industrial products. Industry prices for most products have held steady with the rate of inflation (Kistler and Helvacı 1994; Helvacı 2005).
Based on recent history, the major world consumers of borates will likely continue to be North America, Europe and Japan. Consumption of borates is expected to increase, spurred by strong demand in the Asian and South American agriculture, ceramic and glass markets. World consumption of borates was projected to reach 2.0 Mt B2O3 by 2014, compared with 1.5 Mt B2O3 in 2010 (Rio Tinto Inc. 2011; Roskill Information Services Ltd. 2010, O’Driscoll 2011).
Known reserves of borate minerals are large—particularly in Turkey, South America, and the USA—and production from Turkey and the USA will continue to dominate world markets (Table 2). Very few modern industries can get by without borates, and very few people can get by without their products. Hence, borates and their products will continue to play a vital role in the global economy.
Barbara Dutrow and Edward Grew are gratefully acknowledged for their constructive reviews and contributions which greatly improved the paper. Mustafa Helvacı and Berk Çakmakog˘lu are thanked for typing and drafting assistance.
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