Lithium, boron, and barium in formation waters and sediments, Northwestern Gulf of Mexico Sedimentary Basin



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Lithium, boron and barium, found in varying abundances in formation waters of the Gulf of Mexico Sedimentary Basin (Gulf Basin), have contrasting origins and are useful in assessing the open or closed nature of hydrocarbon-producing aquifers in Texas and Louisiana. Dissolved barium concentrations are controlled primarily by barite. Barium contents of sandstones show that either the barium content of dissolved or albitized detrital feldspars was considerably higher than in detrital feldspars which remain unaltered or that the original feldspar content of the sandstones was higher than that of the least altered sandstone analyzed. Boron and lithium contents are more difficult to attribute to local diagenesis. Most formation waters contain low concentrations of lithium (less than 10 mg/L) ascribable to feldspar diagenesis, except that whole-rock sandstones increase in lithium content with increasing diagenetic alteration. Formation waters from deep reservoirs contain very high concentrations of lithium for which there is no apparent local source. These waters do not resemble waters residual from either marine or non-marine evaporite deposition. Boron in most formation waters cannot originate exclusively from organic matter unless organic matter contents are much higher than have been measured, nor does it come from volcanic sediments because these are abundant only in the South Texas region while high boron contents are not geographically restricted. Formation waters from deep reservoirs contain very high concentrations of boron which probably come from deeper in the Basin because clay minerals, the major reservoir of boron, show no systematic decrease in boron content with depth. The 𝛿¹¹B of these waters is light (to +11%₀) and shows that the boron is not seawater boron (+40%₀) or boron from Jurassic evaporites (+31%₀). The 𝛿¹¹B of other formation waters lies between the value for sea water and the light boron. The Gulf Basin is nearly open with respect to lithium and boron but closed with respect to barium. The high concentrations of lithium and boron probably originate deeper than the sampled part of the Gulf Basin and may be products of metamorphic processes. The source of the barium in formation waters is detrital feldspars.