NATURAL DISTRIBUTION OF δ81BR IN FORMATION WATERS IN SEDIMENTARY AND CRYSTALLINE ENVIRONMENTS

Bromine has two stable isotopes (⁷⁹Br and ⁸¹1Br) and 29 radioactive isotopes. The two stable isotopes are by far the two Br dominant isotopes with Atomic Masses of 78.9183379 and 80.916291, respectively. The relative abundances of the two stable isotopes (⁷⁹Br and ⁸¹Br) are 50.69 % and 49.31 %, respectively.

Although the attempts to measure and use bromine stable isotopes were carried out as early as 1920, it has not been utilized until very recently due to the complexity of the analytical protocol and the associated poor accuracy and precision. The recent development of a more accurate and precise methodology made it possible to examine and determine δ⁸¹Br compositions of formation waters from several sedimentary and crystalline environments around the world.

The δ⁸¹Br compositions obtained to date from more than 250 formation waters revealed a total range of bromine stable isotopes between -1.43 ‰ and +3.35 ‰ relative to SMOB. The sedimentary formation waters illustrated a larger range of isotopic variation (-1.43 ‰ to +3.35 ‰) in comparison to the formation waters from the crystalline environments (+0.01 ‰ to +2.04 ‰). The summary of all known δ⁸¹Br samples shows that the vast majority of samples (95.69 %) fall between -1 ‰ and +2 ‰.