Carbonates Evaporites (2012) 27:71–85 DOI 10.1007/s13146-012-0085-6 ORIGINAL ARTICLE Activity diagrams of borates: implications on common deposits Rezan Birsoy • U¨ nal O¨ zbas¸ Accepted: 24 January 2012 / Published online: 15 February 2012 Ó Springer-Verlag 2012 Abstract Most of the world’s borate minerals are found depicted and expectant paragenetic phases can be predicted in Neogene deposits and Quaternary lake deposits. Only a in any deposits. few of the borates are common geologically and com- mercially. A series of equilibrium activity diagrams were Keywords Activity diagrams Á Common borates Á calculated for the common as well as some rare borate Geochemical conditions Á Diagenetic trend Á minerals in the systems of (1) Na2O–B2O3–H2O, (2) Stability fields Á Paragenetic relations CaO–B2O3–H2O ± CO2, (3) MgO–B2O3–H2O ± CO2, (4) CaO–Na2O–B2O3–H2O, and (5) CaO–MgO–B2O3–H2O. Stability diagrams constructed with respect to variables Introduction n of log[aMbnþ =ðaHþ Þ ] and log[aMbnþ =aMcðnÀ1Þþ ðaHþ Þ] versus both log[a ] and log[a ] showed that some rare There are over 230 borates are in the upper crust occurring H2O BðOHÞ3 borates are thermodynamically not stable (tertschite, in- in igneous, sedimentary, and metamorphic environments. derborite) at all in these systems. Still some common Among borates, few of them occur in large quantities and phases are thermodynamically occurred as metastable some of them are very rare and only present in a few phases (tincalconite, meyerhofferite) in some deposits. On particular locations. Borate minerals, which are extensively the contrary, some thermodynamically stable phases can used in industry, are found in great amounts in the deposits form kinetically slower than the others and not found as of Turkey, South America, and United States of America. common phases (inyoite). Some common and uncommon All of these deposits are found in tectonically active minerals such as ulexite, aksaite, and gowerite have small extensional terrains and associated with continental sedi- stability fields indicating that they can form at very limited ments and volcanic soil of Neogene. However, only a small thermodynamic conditions. Some phases such as pander- number of Ca-, Na-, Mg-, CaNa-, and CaMg-borates mite, ginorite, ascharite, and suanite being structurally are common geologically and commercially, such as complex phases, form after less complex precursor colemanite, borax, kernite, ulexite, probertite, and boracite. minerals at the end of diagenesis due to burial and/or Some of the borates are found in the compositional series, increasing temperature. Concentrations of cations and such as inyoite, meyerhofferite, and colemanite; borax, boron, pH, evaporation rate are other controlling variables tincalconite, and kernite; probertite and ulexite; suanite and of diagenetic processes. Through these diagrams, observed ascharite; gowerite and nobleite; inderite and kurnakovite; paragenetic relations and geochemical conditions can be somehow only one or two of them are found as preferred phases in most of the deposits. There have been many studies on their crystal structures (Christ and Clark 1977; Hawthorne et al. 2002) textural and mineralogical relations R. Birsoy (&) Á U¨ .O¨ zbas¸ (Foshag 1921; Kistler and Helvacı 1994; Garsia-Veigas Department of Geological Engineering, et al. 2011), geological settings (Helvacı and Firman 1976; Faculty of Engineering, Dokuz Eylu¨l University Tınaztepe Campus, 35160 Buca, Izmir, Turkey Alonso et al. 1991; Helvacı and Alaca 1991) and their e-mail: [email protected] formation sequences and transformation mechanisms. 123 72 Carbonates Evaporites (2012) 27:71–85 Some of the borate minerals are precipitated from solution methods of Mattigod (1983) and Li et al. (2000). Matti- such as ulexite (Alonso 1986) and the others are products god’s method provided the closest results to the experi- 0 of diagenesis and post diagenetic reactions. According to mental DGf; 298 values. So Mattigod’s (1983) structural experimental, textural, and structural data, colemanite were 0 empirical method was used to calculate DGf; 298 values of said to be formed as primary (Kistler and Helvacı 1994)or borates. This method involves each of the borate minerals secondary phase (Christ and Garrels 1959). According to as a reaction of the type: textural and structural data of borates in Kırka Deposit of Turkey, inyoite and ulexite were transformed to coleman- xBOHÀ aMmþ jHþ mH O ðÞ4aqÂÃðÞþ ðÞaq þ ðÞaq þ 2 ðÞliq ite. Borax transforms to tincalconite, and ulexite replaces ¼ Ma BxOyðÞOH z Á nH2OðÞSolid borax (I˙nan et al. 1973). Ulexite and colemanite appear to be primary (Helvacı 1977) in Emet deposit of Turkey. where x, y, z, a, and n are the stoichiometric coefficients All borates structurally contain combinations of B(OH)3 of boron, oxygen, hydroxyl, cation and structural water in - and B(OH)4 in their structures. Also thermodynamic the borate polyanion in the solid, respectively. Major ? ? ? 2? 0 concentrations (activity) of H , B(OH)3,Na /H ,Ca / contribution of free energy changes (DGr ) in the above ? 2 2? ? 2 2- - (H ) ,Mg /(H ) ,CO3 , HCO3 and H2O are deter- reaction come mainly from the free energy of polymerization À 0 mining variables of the formation of borates (Christ et al. of BðOHÞ4 ions. In other words, the magnitude of DGr 1967). The study (Birsoy 1990) emphasizing on polymer- would reflect the polymerization of borate minerals. The ization of borates demonstrates the effects of the activity of degree of polymerization value is expressed as an empirical - major cations (Ca, Na, and Mg), B(OH)4 , and pH on the relationship: paragenetic relations of polymers. Nevertheless, extent and 0 2 limits of these variables have not been quantified. Conse- DGr; 298 ¼ 124:26 À 82:37x þ 2:95x quently, the present study for various chemical environ- where x is the number of boron atoms in the polyanion unit. ments has been undertaken to define the stability limits of Then, applying this equation to the dehydration reaction of common and rare borate occurrences through thermo- borate mineral given above results in; chemical calculations. Such work would provide valuable 0 information about the formation and transformation con- DGf; 298ðÞborate mineral ditions, and paragenetic relations for borate phases. Such ¼ DG0 þ xDG0 BOHðÞÀ þaDG0 Mmþ work is also useful to explain some problematic field r; 298 f; 298 4aqðÞ f; 298 ðÞaq 0 0 þ observations and/or to support the given explanations. For þ mDGf; 298H2OðliqÞ þ jDGf; 298H this purpose, borate minerals of Turkey, South America With reference to the above equation, calculation of free and United States, and minor extend of China and energy of aksaite is; Kazakhstan are considered, and those deposits are evalu- À þþ þ ated by activity diagrams (Table 1). 6BðÞ OH 4 þ Mg þ 4H ¼ MgB6O7ðÞOH 6Á2H2O þ 9H2O 0 Method of study DGr; 298 ¼ 124:26 À 82:37ðÞþ 6 2:95ðÞ 36 0 0 ¼ DG Aksaite þ 9DG H2O Thermodynamic data f; 298 f; 298 0 À 0 þþ 0 þ À 6DGf; 298BOHðÞ4 ÀDGf;298 Mg À 2DGf; 298 H Thermodynamic data for some borate minerals have been 0 0 tabulated by Anovitz and Hemingway (2002) and Wagnam DGf; 298 Aksaite ¼263:76 À 9DGf; 298H2O 0 À 0 þþ et al. (1982). However, thermodynamic data for some of þ 6DGf; 298BOHðÞ4 þ DGf; 298Mg the borates are not available. In such cases, empirical and þ 2DG0 Hþ theoretical approaches must be used to predict the ther- f; 298 0 modynamic properties of hydrated borates. Various meth- DGf; 298 Aksaite ¼263:76 À 9ðÞþÀ237:13 6ðÞÀ1153:17 ods are available to model the borate minerals (Mattigod þðÞþ454:8 20ðÞ 1983; Li et al. 2000). In the present study, free energy of ¼5;503:4kj=mol 0 formation (DGf; 298) values for some borate minerals and ionic species were obtained from Anovitz and Hemingway Stability limits of calcite, dolomite, and magnesite, (2002) and Helgeson et al. (1978) respectively. Free energy which contribute as a source of cations and accompany to of formation of some borates has not been found in liter- the occurrence of borates, are also considered. Free ature. To provide internal consistency in thermodynamic energies of all the phases used in the present study are data, all other borates were recalculated applying both given in Table 2. 123 Carbonates Evaporites (2012) 27:71–85 73 Table 1 Mineral assemblages of major borate deposits Deposits Types of deposits Associated minerals (in decreasing amounts) Turkey Kırkaa Playa surface Borax, ulexite, colemanite (hydroboracite, inderite, inyoite, kurnakovite, meyerhofferite, kernite, calcite, dolomite, smectite, illite, erionite) Emetb Permanent playa, lacustrine Colemanite, probertite, ulexite, hydroboracite, meyerhofferite, dolomite, realgar, orpiment, montmorillonite Bigadic¸c Playa setting Colemanite, ulexite, probertite, hydroboracite, montmorillonite, opal-CT Kestelekd Shallow lake Colemanite, ulexite, hydroboracite, smectite, illite, dolomite, quartz, clinoptilolite Sultanc¸ayırıe Playa lake Pandermite (priceite), howlite, colemanite, clinoptilolite, illite, calcite, opal-CT Italy Lardarellof Volcanic lagoon Sassolite, ammonium and magnesium sulfate United States Kramer (Boron, CA)g Shallow-permanent lake Borax, kernite, ulexite, colemanite (probertite, hydroboracite, howlite, sassolite, inyoite meyerhofferite, tunnelite, realgar, and natrolite) Searles Lake CAh Playa lake Borax (trona, halite, hanksite, searlesite and gaylusite) Death Valley CAi Playa setting Colemanite, ulexite–probertite, hydroboracite, gypsum, halite, clinoptilolite, chabazite, phillipsite and calcite