Geoscience Reference
In-Depth Information
Sea Water
Saline mineral
Undersaturated inflow
Calcite
Anhydrite
Gypsum
Halite
Epsomite
Kainite
Sylvite
Carnallite
Borates/celestite
CaCO 2
CaSO 4
CaSO 4 .2H 2 O
NaCl
MgSO 4 .7H 2 O
KMgCISO 4 .3H 2 0
KCl
KMgCl 3 .6H 2 0
SrSO 4
II
III
I
II
I
calcite
Bitterns
Gypsum
Mg + Ca
rich HCO 3
poor water
Ca + Mg
free HCO 3
rich water
Mg - calcite
dolomite
magnesite
Brine type
Saline mineral
Mg-silicate
Ca-Mg-Na-(K)-Cl
Antarcticite
Bischolite
Camalite
Halite
Sylvite
CaCl 2 .6H 2 O
MgCl 2 .6H 2 O
MgCl 2 .KCl.6H 2 O
NaCl
KCl
Gypsum
IIIA
IIB
IIA
Mg + Ca rich
Mg >> Ca
HCO 3 poor water
Ca + Mg poor
Mg >> Ca
HCO 3 bearing water
I
CaCl 2 .2MgCl 2 .12H 2 O
CaSO 4 .Na 2 SO 4
CaSO 4 .2H 2 O
NaCl
Na 2 SO 4 .10H 2 O
Na 2 SO 4
Na-(Ca)-SO 4 -Cl
Tachyhydrite
Glaubrite
Gypsum
Halite
Mirabrite
Thenardite
Ca-Na-Cl
brine
Bristol Dry Lake
Cadiz Dry Lake
Na-SO 4 -Cl
brine
Saline Valley
Death Valley
Mg-silicate
Na-CO 3 -SO 4 -Cl
brine
Alkali Valley
Mono Lake
Mg-Na-(Ca)-SO 4 -Cl
Bischotite
Bloedite
Epsomite
Glauborite
Gypsum
Halite
Hexahydrite
Kieserite
Mirabite
Thenardite
MgCl 2 .6H 2 O
NA 2 SO 4 .MgSO 4 .4H 2 O
MgSO 4 .7H 2 O
CaSO 4 .Na 2 SO 4
CaSO 4 .7H 2 O
NaCl
MgSO 4 .6H 2 O
MgSO 4 .H 2 O
Na 2 SO 4 .10H 2 O
Na 2 SO 4
IIIE
Na-CO 3 -SO 4 -Cl
brine
Deep Springs
Searles Lake
Gypsum
Mirabilite
IIIB
IIIC
IIID
Na-CO 2 -Cl
Halite
Nahcolite
Natron
Thermonatrite
Trona
NaCl
NaHCO 3
Na 2 CO 3 .10H 2 O
NaCO 3 .H 2 O
NaHCO 3 .Na 2 CO 3
Sulfate reduction
Na-Mg-Cl
brine
Great Salt Lake
Mg-Ca-Na-Cl
brine
Dead Sea
Mg-SO 4 -Cl
brine
Basque Lake
Hot Lake
Na-CO 3 -SO 4 -Cl
Burkeite
Halite
Mirabilite
Nahcolite
Natron
Thenardite
Thermonatrite
Na 2 CO 3 .2NaSO 4
NaCl
Na 2 SO 4 .10H 2 O
NaHCO 3
Na 2 CO 3 .10H 2 O
Na 2 SO 4
NaCO 3 .H 2 O
Na-CO 3 -Cl
brine
Lake Magadi
Lake Natron
I =
II =
III =
HCO 3 » Ca + Mg
HCO 3 « Ca + Mg
HCO 3 ≥ Ca + Mg
Figure 15.8 (a) Geochemical pathways and classification for brine evolution with progressive evaporation (after Hardie, Smoot
and Eugster, 1978, and Rosen, 1994). Several lakes are given as examples for each pathway. (b) Common evaporative minerals
associated with sea water and the five principal nonmarine brine types (after Eugster and Hardie, 1978 and Chivas, 2007).
saturation occurs at around 200-350 g/L, while other
common salts include trona (Na 2 CO 3 ·
by the thermodynamic activity of the water (Langmuir,
1997); for any given set of pressure and temperature con-
ditions an increase in dissolved ions reduces of the ability
of the water to evaporate. This relationship, expressed by
the Pitzer equations (Pitzer, 1987), suggests that the evap-
orative potential of concentrated brine is about half that of
pure water. There are also variations in the precipitation of
individual salts, with those minerals of retrograde solubil-
ity, such as gypsum, anhydrite and calcite, precipitating at
high temperatures, while sodium and magnesium chloride
become supersaturated as temperatures fall. This leads to
variations in salt populations on diurnal to seasonal scales
(Yechieli and Wood, 2002).
In broad terms the increasing concentration of brine
leads to a zonation of the evaporites by solubility. In indi-
vidual salt pans this leads to a 'bulls eye' effect of lateral
zonation of facies from carbonates at the edge, through
NaHCO 3 ·
2H 2 O),
thenardite
(Na 2 SO 4 ),
epsomite
(MgSO 4 ·
7H 2 O)
and
burkeite (Na 2 CO 3 ·
2Na 2 SO 4 ). Where sodium-rich brines
come into contact with deposits of gypsum or calcite, dou-
ble salts, such as glauberite (CaSO 4 ·
Na 2 SO 4 ) or gaylus-
site (Na 2 CO 3 ·
CaCO 3 .5H 2 O), may be formed. Less com-
mon evaporites are potassium and magnesium chlorides
(e.g. carnallite), which are found in the Qaidam Basin
of China (Yuan, Chengyu and Keqin, 1983; Chen and
Bowler, 1986; Bryant et al. , 1994a), and nitrates, as in the
saltpetre-rich Matsap Pan of South Africa (Wellington,
1955). The three pathways (I, II and II in Figure 15.8) are
generally found to be characteristic of volcanic terrains
(path I), seawater (path II) and the recycling of ancient
carbonate or evaporates (path III).
Evaporation and salt precipitation rates represented in
 
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