ABSTRACT

A suite of unusual boron minerals is present in upper Louann Salt and immediately overlying Norphlet Shale in Clarke County, Alabama. Core samples come from a depth of about 12,000 feet in a well located on the flank of a non-piercement salt dome. The suite consists of calcium and magnesium borates similar to those occurring in the Zechstein salt deposits of Germany. Well developed, micron- to millimeter-size crystals were recovered from water-insoluable residue from the salt. The minerals identified include:

Tabulated data; refer to PDF file.

Associated minerals are anhydrite, gypsum, magnesite, phlogopite, talc and quartz.

Boracite and hilgardite have boron isotopic compositions indicative of marine evaporite deposits (Swihart et al, 1986).

Danburite, CaB₂(SiO₄)₂, occurs in irregular nodules up to 2 cm in diameter in the overlying Norphlet Shale. the nodules constitute up to 30 percent of the Norphlet immediately adjacent to the Louann, but disappear within about one meter from the contact. The danburite appears to be the result of boron-rich fluids, derived from the underlying marine evaporite sequence, infiltrating and reacting with the shale.