Jökull - 01.12.1977, Side 58

m moles/kg
14
1.4
1.2
1.0
o 0.8
o
o
0.4
0.2
0
200 220 240 260 280 °C 200 220 240 260 280 °C
Fig. 5. The relationship o£ gas concentrations (A) and gas ratios (B) with aquifer temperatures
in wells 4 to 9. The plotted points are averages ior samples collected during 1973—1974. In this
period trends in the gas compositions were not observable. The averages are believed to demon-
strate Itetter the relationship in question than individual analyses do, because they level out the
erratic distribution o£ the former.
Mynd 5. Samband gasinnihalds (A) og gaslilutfalla (B) við hitastig i vatnsceðurn hola 4 til 9.
Einstakir punktar á línuritunum samsvara meðaltali fyrir sýni, sem safnað var á timabilinu 1973—
1974. A þessu tímabili voru ekki sjáanlegar breytingar á gasinnihaldi einstakra hola. Talið er, að
meðaltölin sýni betur þau sambönd, sem um rœðir, en einstakar valdar efnagreiningar gerðu, þar
sem þau jafna út óreglulegar sveiflur i gildur einstakra efnagreijiinga.
B
• H2/H2S
° C02/H2S
o
• %
o
1978) and pyrite and pyrrhotite. The removal of
carbon dioxide and hydrogen sulphide from
solution by such precipitation will lower the
total gas content of the steam-water mixture.
Conductive cooling will also lead to pyrrhotite
and pyrite precipitation but not to calcite pre-
cipitation because the solubilities of pyrrhotite
and pyrite decrease with falling temperature
but that of calcite increases. It seems possible
that the relatively high CO2/H0S ratios in the
cooler and more gas deficient waters, has re-
sulted from removal of sulphide from solution
by pyrrhotite and pyrite precipitation during
conductive cooling. At the same time the hydro-
gen concentrations would decrease through the
following reaction:
56 JÖKULL 27. ÁR
S— + 4H20 = SO4— + 4H2
Oxidation of hydrogen sulphide would have
the same effect as pyrrhotite precipitation.
Which of these two processes is the most im-
portant cannot be deduced from the available
data.
DISCUSSION
The variable gas content o£ the well dis-
charges at Námafjall can be explained by the
following model: The major upflow zone
underlies the Námafjall hyaloclastite ridge and
sicleways movement of water to the west sup-
plies the wells. Steam formation in the upflow