RARE EARTH ELEMENT GEOCHEMISTRY OF SADAT CITY (EGYPT) GROUNDWATERS

Groundwater samples were collected from wells in Egypt’s largest industrial cities, Sadat City.  Samples were taken from monitoring wells in three sectors: industrial, residential and agricultural.  These circum-neutral to alkaline groundwaters are representative of the groundwater resources in the region.

Overall, there is little variation between samples when rare earth element  (REE) composition is normalized to chondrite.  Chondrite-normalized patterns show significant light rare earth element (LREE) enrichment.  The LREE enriched patterns are in stark contrast to average river water and carbonate buffered groundwaters.  Samples represent well-oxidized fluids as evidenced by the presence of a negative cerium anomaly in all but two samples.  All samples possess, to varying degrees, positive europium anomalies.

Shale normalized REE patterns show both the LREE enrichment as well as the positive Eu-anomaly.  If Eu is excluded, several samples show a variable loss in middle rare earth elements (MREE).  The presence of the Eu-anomaly is likely inherited from the aquifer material and soils through which the groundwater is recharged.  Soil samples also show positive Eu-anomalies.  Interestingly, soil shale-normalized REE patterns are nearly the mirror image of the groundwaters.  Soil REE patterns are heavy rare earth element (HREE) enriched and LREE depleted and positive Eu-anomalies.

Based on the results of this preliminary study we suggest the following:  groundwaters in this region recharge slowly and are therefore significantly fractionated from the aquifer material and soil compositions.  Eu-anomalies are likely an inherited characteristic.  The LREE enrichments indicate that these fluids may not carbonate buffered.  The loss in MREE from the groundwaters may be due to phosphate co-precipitation.   Overall the REE in this region do not record substantial compositional or spatial variation and therefore, by themselves, cannot be used to trace flow in the region.  However the unique character of these groundwaters shed light on the recharge rates and water-rock interactions within this highly industrialized region.