Jökull - 01.12.1987, Side 8

compositions. This may either be due to equilibration in
the basalt sheet intrusions or that the same alteration
minerals form in the acid and basaltic volcanics despite
the difference in their composition.
Gas geothermometers developed by D’Amore and
Panichi (1980), Arnórsson and Gunnlaugsson (1985) and
Arnórsson (1987) have been used to estimate subsurface
temperatures in the Torfajökull field (Table 3). The
correlation between the results of individual geother-
mometers is shown in Fig. 2. C02-temperatures lie most-
ly in the range 240-290°C. C02-N2-temperatures cover a
larger range and towards lower temperatures. The
steam samples giving low C02-N2-temperatures contain
high nitrogen concentrations. These low temperatures
can, therefore, be attributed to atmospheric contam-
ination of the steam samples or partial condensation of
the steam in cold water. The steam heated water would
be degassed in the process, thus adding N2 to the remain-
ing steam phase.
Geothermometry temperatures obtained from the
TABLE 3.
Results on the gas geothermometry and steam condensation in the upflow of the Torfajökull field.
Geothermometry temperatures % steam cond.
Sample no. n o H2S h2 co2-h2 co2-n2 Ab Zc zbd
11 240 (225) 169 169 122 213 231 47 31
12 273 (278) 241 259 250 287 352 -59 -16
13 287 (283) 227 264 245 277 292 26 12
14 240 (194) 220 230 227 179 296 74 64
15 246 (193) 215 236 234 177 326 78 70
16 257 (257) 232 246 242 256 334 -4 -1
17 236 (181) 200 135 <100 168 151 76 69
18 246 (206) 221 274 299 190 392 73 61
19 265 (264) 212 249 240 261 318 8 4
20 253 (256) 223 256 262 259 371 -24 -8
21 265 (266) 231 266 269 265 395 -4 -1
22 332 (316) 285 301 261 300 372 71 45
23 304 (299) 280 288 270 294 (400) 31 13
24 272 (143) 238 255 245 137 344 95 93
25 269 (247) 217 256 250 228 322 66 47
26 249 (178) 249 236 231 165 325 84 79
27 256 (239) 218 238 229 224 323 54 36
28 276 (271) 226 250 231 262 314 33 16
29 281 (237) 242 263 249 212 338 84 73
30 293 (247) 230 267 244 221 310 88 77
31 247 (203) 224 223 210 186 299 75 64
32 275 (276) 215 244 222 278 293 -13 -4
33 246 (238) 235 249 256 228 360 33 19
34 281 (280) 209 222 179 278 246 9 4
35 280 (278) 228 238 207 277 287 7 3
36 344 (336) 277° 284° 259° 326 194 50 23
37 358 (337) 277° 292° 265° 319 197 75 48
a Values in parenthesis indicate C02-temperatures corrected for condensation according to Zb. bGeothermom-
eter of D’Amore and Panichi (1980). 'Assumes conductive heat loss. dAssumes mixing of 100°C steam with 5°C
water. Tunctions corresponding with saline waters and waters above 300°C were used (see Arnórsson and
Gunnlaugsson 1985). Sample locations are shown in Fig. 1. Analyses of samples 11-24 are given by Arnórsson and
Gunnlaugsson (1985), Table 6, in the same sequence as here.
6