**4.1 Map preliminary geothermal gradient Northern Algeria centre**

The geothermal gradient map sets from the temperature data stored in oil drilling during logging operations. It shows a geothermal anomaly of about 4° C/100 m in the Djelfa region (**Figure 5**). It serves as a support base for future projects in the applications of geothermal energy [3].

## **4.2 Hydrogeochemistry of hot springs**

The study area is characterized by the emergence of numerous hot springs area linked to major geological accident (faults) [4–6]. The temperature of these sources usually varies from 20 to 64° C. The chemical composition dominant is sodium chloride-sulfated.

**Figure 5.** *Map preliminary geothermal gradient northern Algeria Centre.*
