In contrast, changes in total CO, dur-
ing storage fell within the analytical
error of 2.5 percent. The curves (Fig.
1) were calculated for 25°C from the
data of Lagerstrom (//), as verified by
Ingri (72), for equilibrium constants
of silica species in solution.
According to Fig. 1, our data can be
divided into four groups: (a) concentrated, intracrustral high-pH brines from
Lake Magadi and Alkali Valley; (5)
concentrated brines from open pools in
Alkali Valley and Lake Magadi, from
the brine pool north of Abert Lake, and
from the closed sag pond of Deep
Springs Valley; (c) brines of intermediate concentration, interstitial to saline
muds from Albert and Magadi takes;
and (d) Abert Lake, plus saline springs
and interstitial fluids from adjacent mud
flats, inflow brines from springs of the
Lake Magadi area, and brines from the
area of Deep Springs Lake. No systematic correlation exists between silica
content and temperature at the time
of collection of each brine, although
some of the scatter (Fig. |) may be
due to temperature differences.
Groups
(a)
and
(d) are
under-
saturated with respect to amorphous
silica, group (c) is of intermediate pH
and near saturation, while group (5) is
close
to
supersaturation
or
substan-
tially supersaturated. The only other
nongeothermal water reliably reported
to have a very high pH andsilica content, from Aqua de Ney Springs, Cali-
fornia (/3), plots very near the satura-
tion curve for amorphous silica. The
correlation between pH and SiO. for
each group can be explained by their
special history. We believe that the enrichment in silica in the brines is primarily due to evaporative concentration.
Points of group (a) show a high pH
because of the depletion in HCO,-,
caused by trona precipitation; the pH
has increased more rapidly than evaporative concentration of SiO.; exchange
The brines in contact with saline
muds,
containing abundant silicates
[group (c)], plot near saturation with
respect to amorphous silica. Higher
SiO., values are from samples of bottom
sediment near the water-mud interface;
lower values, from interstitial waters
deeper in the sediment. This fact suggests that initial equilibrium is established with respect to an amorphous
surface layer on silicates (14); subsequent recrystallization lowers SiO, content.
The compositions of the springs of
Lake Magadi [group (d)] are governed
by their underground history. A reverse
trend appears to exist between pH and
SiO. and probably reflects adsorption of
with the atmosphere is apparently too
silica on freshly precipitated sesquioxides (/5). The other points of group
(¢d) are for waters of Abert or Deep
The open pools of group () are
either undersaturated with respect to
have been concentrated from waters
having distinctly lower SiO, content.
slow to checkthis trend.
sodium carbonate minerals or saturated
with natron (NA.CO,:10H.,O). Evaporative concentration of SiO., is apparently more rapid than nucleation and
precipitation of silica.
Springs Lake: they are either dilute or
If silica is indeed concentrated by
evaporation, this concentration should
be reflected in a correlation between
SiO., and sodium, the predominant cation of these brines (Table 1). As Fig.
Table 1. Representative alkaline brines from Alkali Valley (Alkali Lake, AIL) and Abert Lake (AL) basin, Oregon, Deep Springs Lake (DSL)
and sag pond, Calif. (Deep Springs Valley, DSV), and the Lake Magadi (LM) area, Kenya. Included are brines with relatively high contents of
CO:, even though chloride or sulfate may in fact dominate the anions. Little Magadi Lake, Kenya, LML.
Sample
pH
Contents (ppm)
Collece W
i
tion
temp..
time (°C)
Field Labora-
120°03’°W ,42°S7‘N
8~6-63
25
9.97
Surface brine from
pothole near log
road on SW side,
AIL playa
120°03'W ,42°S7°N
8-6-63
40
At gage, AL
120° 117W,42°36’N
7-22-64
23
9.75
At mouth of Chewaucan River, surface, AL
120°15’°W 42°3 VN
7-25-64
30
9.82
Brine from within
very porous salt
crust, central DSL
118°02°W,37°17’N
8-18-63
41
8.9
Closed sag pond, DSV
118° L.5°W,37°17VN
8-15-61
33
Interst, brine from
bottom mud, $
end, near W shore,
AL
120° 15’°W ,42°32’N
8-6-63
22
9.05
Interst, brine from
bottom mud, SW
end, AL
120°15'W ,42°33’N
8-6-63
22
8.65
148
Interest, brine from
bottom mud, near
mouth of Chewaucan River, AL
120° 15’°W,42°3 WN
@-8-63
36°16°E,01°44’S
6-66
Saturated brine, LM
36° 15’E,01°54’S
6-66
Saturated brine, LM
36° 17°E,01°S0’S
6-66
Description
Brine from
pit
next to
pothole near log
road on SW side,
AIL plava
Hot spring, LML
1312
.
Source
coordinates
9.90
22
81
(COs)
fate
(SOx)
Chioride
1
(C1)
Dis(ane)
trace
99,500
20,200
19,800
237,000
8080
trace
133,000
25,000
27,900
318,000
15,200
604.
3840
6920
792
12,700
39,300
2360
112
758
972
135
2190
6220
78
108.000
22,000
4990
20,700
56,200
120,000
332,000
§24
119,006
10,900
3630
66,160
90,900
41,000
330,000
211
19,500
1360
10,200
6370
949
16,900
50,300
20.800
1350
14,600
4780
1270
16,800
§2,300
1200
4280
35180
1860
13,800
42,700
12,606
239
45,600
3540
147
5950
30,200
tory
Silica
1).
(SiO2)
Sodium
otas
;
bonate
10.0
590
91,400
5090
10.4
1270)
121,000
9.65
128
9.85
48
10.0
9,25
162
16,100
sum (HCO;)
cate“
solved
id
9.05
9.05
90
34
11.06
10.25
1055
132,000
2280
trace
106,060
219
84,400
324,000
36
10.11
o.5
383
110.000
1530
trace
95,600
97
50,700
247,000
SCIENCE, VOL, 158