PRELIMINARY GEOCHEMICAL ANALYSIS OF THE A-1 EVAPORITE, SALINA GROUP, MICHIGAN BASIN

Untapped potash, lithium, and other critical mineral accumulations of evaporitic origin may be found in the Silurian-aged Salina Group located in the Michigan Basin. Our study compares the A-1 evaporite from three historic cores in the Michigan Basin to identify spatial differences in mineralogy and trace-element geochemistry. More systematic evaluation of temporal and regional variations in evaporites could support potash exploration, as well as identification of potential byproducts such as Li and B.

We sampled three cores at the Michigan Geological Repository for Research and Education. Dalrymple #1-16 from Roscommon Co. spans the base of the A-1 carbonate, the entirety of the A-1 evaporite, and the upper A-0 carbonate. Kalium Hersey KH1054 from Osceola Co. spans the base of the A-2 evaporite, the entirety of the A-1 carbonate, and the upper A-1 evaporite. Borgen #1-30 from Kalkaska Co. spans the base of the A-1 carbonate and the upper A-1 evaporite.

The Dalrymple core contains thinly bedded A-0 carbonate below ~9040’, then halite interbedded with carbonate mud ‘draped’ over euhedral crystals. The base of the A-1 evaporite (~9017’) is made up of massive clear to black halite, largely recrystallized and interspersed with <1 cm thin bands of Mg sulfate. Orange to colorless sylvite intervals starting ~8870’ contain occasional borate nodules <1 cm size. Interbedded halite is colorless to grey, with cloudy, inclusion-rich primary and clear, inclusion-free secondary crystals. The A-1 carbonate starting ~8666’ is finely laminated to massive, dark grey to black. The Kalium Hersey and Borgen cores have similar mineralogy, although the Kalium Hersey core contains elemental sulfur at the A-1 evaporite-carbonate contact.

Preliminary geochemical analysis of the Dalrymple core was conducted using ion chromatography for major anions and ICP-OES for major and trace cations. Clear halite from the base of the A-1 evaporite had 7 ppb Li. Clear sylvite from the first A-1 sylvite bed (8870’) had 19 ppb Li. A layer of Mg sulfate had 312 ppb Li and 1150 ppb B. Future work will explore whether trace element concentrations in clear and inclusion-rich salt increase with increasing paleo-salinity from the base to the top of the A-1 evaporite. In addition to wet chemical analysis, XRD and SEM will be used to identify the Mg sulfate and borate minerals.