Application of chemical geothermometers to thermal springs of the Maghreb, North Africa

In order to assess the geothermal potential in the Maghrebian region, several studies have been undertaken in the three countries concerned, Morocco, Algeria and Tunisia, during the past decade. Research programmes have considered the surface evidence (thermal springs) and underground thermal information from deep and shallow wells. The main chemical characteristics of the sampled thermal springs and the results of the application of geothermometers as result from these studies are presented. Of the 238 inventoried thermal springs, 169 have been selected, on the basis of complete water analyses and acceptable ionic balances. Measured temperatures range from 22.5 to 98°C, thermal indexes from 0.5 to 78°C and salinities from 0.13 to 52.5 g/L. Most studied springs are sodium-chloride type waters. These basic data allow identification of the main thermal anomalies in the Maghrebian zone, which are located in regions of the Libyan-Tunisian, Algerian-Moroccan and Algerian-Tunisian frontiers, of northern Tunisia, the Eastern Rif and the northern part of the Saharan Atlas. Several chemical geothermometers have been applied to selected springs: Na-K, Na-K-Ca, Na-K-Ca-Mg, Na/Li, Mg/Li, K2/Mg, quartz, chalcedony (Fournier) and chalcedony (Arnorsson). The Na-K, Na-K-Ca, Na-K-Ca-Mg, Na/Li and Mg/Li geothermometers seem to give unreliable results, while K2/Mg and silica temperatures are apparently reasonable. However, dissolved silica seems to be governed by quartz solubility for some thermal springs and by chalcedony solubility for others. The results are tentatively compared with known geothermal gradients and geological features. © 1998 CNR. Published by Elsevier Science Ltd