Sulphur, selenium, tellurium, haloids (fluorine, chlorine, bromine, iodine)

Sulfur (S) Universe: 500 ppm (by weight) Sun: 400 ppm (by weight) Carbonaceous meteorite: 41000 ppm  Earth's Crust: 420 ppm  Seawater: 928 ppm

Sulfur in magmatic processes Native sulfur reacts with water under hydrothermal conditions to form a complex mixture of dissolved sulfur oxyanions, hydrogen sulfide, and polysulfides. Native sulfur is formed as condensates in and around fumaroles, as a precipitate in crater lakes, as a microbial alteration product of gypsum or anhydrite in sediments (most notably associated with saltdomes) and as a weathering product of metal sulfides. It forms decomposition of sulfur-bearing organic matter in waste dumps of coal mines. However the most sulfur are in sulfide and sulfate compounds.

Sulfur in magmatic processes The sulfides concentrated firstly in the early magmatic differenciates. Large masses of chalcopyrite, pyrrhotite, pentlandite etc. occur in these processes. In magmatic rocks sulfur is an uncommon element. There are a few silicates, which contains it in form of sulfate anion, e.g. Noseán - Na8Al6Si6O24(SO4)•H2O, Haüyn - (Na,Ca)4-8 Al6Si6(O,S)24(SO4,Cl)1-2. The most sulfides, sulfosalts appear in post-magmatic processes (we had any information about it at the metals or semimetals).

Sulfur in weathering and sedimentary processes The global sulfur cycle is a complex network of processes that transfer sulfur between four main reservoirs: the ocean, the ocean floor basalts, evaporite deposits and reduced marine sediments (the latter are the largest reservoir of sulfur). By comparison, the atmosphere, rivers, lakes, aquifers, soils and biomass are far smaller sulfur reservoirs which act essentially as links in the transfer of sulfur from the continents to the ocean. As sulfur cycles through these various reservoirs, it changes in oxidation state from predominantly S(VI) in aerobic environments to S(-II) or S(-I) in anaerobic environments. Rivers, and to a small extent groundwater, transport sulfur in the form of sulfate from the continents to the ocean.

Sulfur in weathering and sedimentary processes Weathering of metal sulfides, the dissolution of gypsum and anhydrite, and sea-salt sulfate account for most of the natural riverine flux. In the oceans, sulfate is primarily removed via sulfate reduction and evaporite deposition. The reduction of sulfate in marine sediments leads to the formation of pyrite and organic compounds containing sulfur. This process is mediated by sulfate-reducing bacteria that oxidize organic matter. Sulfate is also extracted from seawater by seawater-basalt interaction at mid-oceanic ridges. As seawater interacts with basalt, most of the sulfate is precipitated as anhydrite upon heating of the seawater.

Sulfur in weathering and sedimentary processes One of the main sulfur compounds, the formation of sulfate requires relatively oxidizing conditions, and sulfate minerals are therefore particularly common in oxygenated surface environments. They are also common precipitates from oxidizing hydrothermal systems, and anhydrite (CaSO4 ) may crystallize as a primary mineral phase from oxidized, sulfur-rich magmas. Some of sulfate minerals may be found in hydrothermal deposits either as primary precipitates (e.g. barite, celestine), or as oxidation products of sulfide minerals during secondary (supergene) alteration (e.g. anglesite, brochantite).

Sulfur in weathering and sedimentary processes The hydrated sulfate gypsum (CaSO4 • 2H2O) shares many of the occurrences of anhydrite, and is an important evaporite mineral. Gypsum is also common in the supergene alteration zone of sulfide mineral deposits, along with other hydrated sulfates such as chalcanthite (CuSO4 • 5H2O), melanterite (FeSO4 • 7H2O), and epsomite (MgSO4 • 7H2O). Hydroxylated sulfates are a diverse group of minerals, and include the important end-members alunite (KAl3 [SO4 ]2[OH]6), jarosite (KFe3[SO4] 2[OH]6), antlerite (Cu3[SO4][O]4), and brochantite (Cu4 [SO4][OH]6). All of these minerals are characteristic of near-surface oxygenated conditions, and are common supergene alteration products of sulfides.

Selenium (Se) Universe: 0.03 ppm (by weight)  Carbonaceous meteorite: 130 ppm  Earth's Crust: 0.05 ppm  Seawater: Atlantic surface: 4.6 x 10-8 ppm     Atlantic deep: 1.8 x 10-7 ppm

Selenium in magmatic processes Minerals of selenium include selenides (Se2-), native selenium (Se), selenites (MxSeO3, Se4+) and selenates (MxSeO4, Se6+). The relative stability of these phases depends on Eh and pH conditions. In reducing environments, selenium isomorphically substitutes for sulfur in sulfides, the selenides are rare. In selenium-rich environments, however, complete solid solution between sulfide and selenide end-members (e.g. galena (PbS) and clausthalite (PbSe) solid solution. In most igneous rock types, selenium is a trace component in accessory sulfides. Trace to minor concentrations of selenium are found in native sulfur associated with volcanic exhalations and oxidized sulfide deposits.

Selenium in weathering and sedimentary processes Rare selenites and selenates are in association with oxidized sulfide ores and vent formations associated with burning coal seams. The formation of selenites and selenates is limited by a number of factors: selenite ions are strongly adsorbed to mineral surfaces and selenates require a combination of highly oxidizing, alkaline, and arid conditions. Selenite and selenate are stable over a broad range of conditions that cover most natural surface waters, where selenate dominates in alkaline, oxidized waters. Selenium is an essential nutrient at trace concentrations but is toxic at elevated levels.

Tellurium (Te) Universe: 0.009 ppm (by weight)  Carbonaceous meteorite: 2.1 ppm  Earth's Crust: 0.001 ppm  Seawater:   Atlantic surface: 1.6 x 10-7 ppm     Atlantic deep: 7 x 10-8 ppm

Tellurium in magmatic processes Tellurium is a chalcophile element. It occurs in sulfide minerals of silver, copper, lead, mercury and nickel, replacing sulfur, especially in chalcopyrite, bornite and pentlandite. As a native element it is rarely found in hydrothermal veins. It usually forms independent minerals in sulfide-bearing gold veins (more than 40 minerals are known) mostly tellurides with silver, gold, copper, lead, and bismuth: calaverite AuTe2 , nagyágite Au2Sb2Pb10Te6S12 , petzite Ag3AuTe2 , sylvanite (Au,Ag)Te4 , hessite Ag2Te, etc. All tellurides formed at the low-temperature phase of the hydrothermal process. It has not been detected yet in rock-forming minerals because of its low content.

Tellurium in weathering and sedimentary processes In weathering conditions tellurium may be oxidized to tellurites or tellurates (similar to selenites and selenates), or oxides, which are slightly mobile and usually sorbed by Fe hydroxides. There has been no systematic investigation of tellurium in soils over the world, although it has low mobility in various soil conditions. It is often accumulated in coal as a result of sorption by organic matter.

Fluorine (F) Universe: 0.4 ppm (by weight) Sun: 0.5 ppm (by weight) Carbonaceous meteorite: 89 ppm  Earth's Crust: 950 ppm  Seawater:    Atlantic surface: 1 x 10-4 ppm     Atlantic deep: 9.6 x 10-5 ppm

Fluorine in magmatic processes Fluorine is a common element in igneous and metamorphic rocks. The atomic radius of fluoride is similar to the hydroxyl ion (OH-) and substitutes for it in minerals such as apatites, micas, pyroxenes, amphiboles, tourmalines. In general ultramafic rocks have smaller fluorine contents than those with higher percentages of SiO2 . The most important F-bearing mineral, fluorite (CaF2) concentrates in the post-magmatic stadiums (from pegmatitic till epithermal). There are characteristic mineral in alkaline magmatites: villiaumite (NaF), a RFF-fluorides (yttrofluorite) and cryolite (Na3AlF6).

Fluorine in weathering and sedimentary processes Phosphate and fluorite contain the most concentrated occurrences of fluorine in sedimentary rocks. Phosphate deposits consist of phosphorite, a combination of apatites which contain calcium fluorapatite. Fluorite (CaF2 ) occurs as primary veins and fillings in some limestone and dolomite deposits. The fluorine in sediments have often volcanic origin.

Chlorine (Cl) Universe: 1 ppm (by weight)  Sun: 8 ppm (by weight)  Carbonaceous meteorite: 380 ppm  Earth's Crust: 130 ppm  Seawater: 18000 ppm

Chlorine in magmatic processes Chlorine may occur as a trace element substituting for hydroxyl ions in some hydrous minerals such as micas and amphiboles, sodalite, scapolite. It can be important component in apatites (chlorapatite), similar that fluorine. The F: Cl ratio increases from basic to acidic magmatic rocks. Sal ammoniac (cubic NH4Cl) forms in volcanic exhalations.

Chlorine in weathering and sedimentary processes Evaporitic salts are the most important chlorine-containing rocks, which include mainly halite (NaCl), sylvite (KCl) and carnotite (KMgCl3 • 6H2O). There are some chlorides in the oxidation zone of ore deposits, mainly in arid clime: chlorargyrite (AgCl), cotunnite (PbCl2), nantokite (CuCl), calomel (HgCl).

Chlorine in weathering and sedimentary processes Chlorine entered the oceans over time by weathering and erosion from the rocks. Among other, the chlorine reached near modern concentrations in the oceans by the early Precambrian via volcanic emissions. Volcanism, sedimentation and erosion facilitate chlorine exchange between ocean and continental reservoirs. Tending to remain with the aqueous phase of the cooling magma until the last crystallizing fraction, chlorine may be deposited as salts in hydrothermal fractures and veins in the surrounding country rock.

Bromine (Br) Universe: 0.007 ppm (by weight)  Carbonaceous meteorite: 1.2 ppm  Earth's Crust: 3 ppm  Seawater: 67.3 ppm

Bromine in magmatic and sedimentary processes Bromine is generally associated with volatile components and is most highly concentrated in the upper mantle and crust. The very low concentration in rocks suggests that only a small fraction of bromine is fixed in igneous minerals; most of the bromine is extruded with residual fluids and in the magmatic gases. Close in ionic radius to chlorine, bromide can substitute in structure containing chloride, where most bromine occurs. The most common bromine mineral is bromargyrite (AgBr), which may be found in association with chlorargyrite (AgCI). Halite (NaCI) and other sedimentary rocks may contain up to 0.2% bromine.

Iodine (I) Universe: 0.0001 ppm (by weight)  Carbonaceous meteorite: 0.26 ppm  Earth's Crust: 1.4 ppm  Seawater:   Atlantic surface: 4.89 x 10-2 ppm     Atlantic deep: 5.6 x 10-2 ppm

Iodine in magmatic and sedimentary processes Iodine content appears to be uniform and less than 1 mg/kg in common rock-forming minerals. Sedimentary rocks generally contain more iodine than igneous rocks, and over a broader range of concentrations. Two types of deposit are particularly rich in iodine: phosphate rock (0.8-130 mg/kg) and the caliche (nitrate) deposits with ~400 mg/kg iodine (sometimes in form of iodate compounds). The weathering of rock releases up to about half of the original iodine content as water-soluble compounds, mainly iodide. Soils contain much more iodine than the rocks from which they are derived. Recent marine sediments are particularly rich in iodine (5-200 mg/kg); they are the largest repository of iodine at the Earth's surface.