Download Sulfur in weathering and sedimentary processes

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 endmembers 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.