Bi. Pisarskii et al., Alkaline carbon dioxide hydrotherms and strontium-containing travertines in the Songwe River valley (Tanzania), GEOL GEOFIZ, 39(7), 1998, pp. 934-941
This paper considers the thermal water of a group of springs in the Songve
River valley, located 7-10 km downstream from the Panda Hill carbonatite ma
ssif, and calcareous tuffs formed from this water. The authors relate these
hydrotherms to the latest, Quaternary, alkaline magmatism which covered th
e entire East-African rift system, including the Rukwa graben, along which
the Songwe River flows.
The thermal water contains carbon dioxide, alkalies, silicon, carbonates, a
nd hydrocarbonates, mineralization being 3.3-3.4 g/l. By some geochemical c
oefficients (Li/Rb, Sr/Li, Sr/Rb, rNa/rCl), this water differs from the the
rmal water of other continental rift systems, in particular the Baikal Rift
water.
Using a microprobe permitted study of the carbonate minerals of the tuffs:
main - calcite and aragonite and secondary dolomite and strontianite. The c
alcites are characterized by extraordinarily high contents of Sr (up to 5.6
wt.% SrO) and Mg (up to 5 wt.% MgO). The aragonites also have high content
s of Sr (11.5-36.8 wt. % SrO) and low contents of Mg (0.05-0.17 wt.% MgO) a
nd form an isomorphous series with Ca-strontianite (46.8-54.2 wt.% SrO).
Sometimes the tuffs contain terrigenous grains of quartz and feldspar and i
mpurities of trona, halite, and hydromicaceous minerals.