10Be-9Be in the Salton Sea Geothermal System (U.S.A.)

Abstract

Fluids from well Fe #5 and deep hole SSDP California State 2-14,as well as rocks from the deep hole were analyzed for 10Be and 9Be. In the solid samples 10Be concentration ranges from 9.44 to 259 x 10/6 at/g and 9Be from 0.36 to 2.52 ppm. The 10Be concentration in the geothermal waters ranges from <1 to 10/3 to 4.9 x 10/6 at/g and 9Be form 0.7 to 16.6 ppb. Compared to steady state inventory expected from rain deposition, the 10Be inventory is the deep core is 3 orders of magnitude higher indicating that most 10Be is inherited and that the sediments 3250 m are young, less than a few million years old. In the core, 10Be/9Be ratios exhibit a strong decrease at depths close to both aquifers(1837 m an 2956. A reverse trend dis observed in the fluids. 10Be and 9Be distribution coefficients (Dds) decrease form surface to bottom (3333 to 48 for 10Be and 727 to 393 for 9Be). Leaching is more active at depth where pH is <5.3 and salinity high. 10Be is more easily removed from the metamorphosed sedimentary rocks, due to its occupation of absorption sites. In addition, during the flow tests mixing with more concentrated brine and/or with ultrafine solid particles is observed.