Extreme enrichment of arsenic and antimony during alteration of serpentinized peridotites to form listvenite-like dolomite-quartz rocks and Ni-Cr-rich jasper and quartzites in the Highland Border Complex of Scotland

Alteration of serpentinized peridotites of the Highland Border Complex in Scotland took place in two steps. Listvenite-like dolomite-quartz rocks formed by addition of CaO, Sr and CO2 at constant MgO and SiO2 involving a mass increase of c. 140%. Stage two involved the dissolution of dolomite, evinced by the abundant pores and rhombohedral grains of quartz, to form Cr- and Ni-rich jasper and quartzites. Formation of the jasper-quartzites involves a mass reduction of c. 80%. The listvenite-like and jasper-quartzite rocks show enrichment in the fluid-mobile elements Ba, Sr, Cs, As and Sb. The As is present in the Aluminium-Phosphate-Sulfate group of minerals formed during alteration of Cr-spinel. Cr-spinel also alters to porous hematite and ferrihydrite with patches containing up to 5.5 wt% As2O3. Enrichment of As, related to alteration of chromite, is previously unknown from natural rocks, but strongly resembles efficient methods used for remediation of this toxic element. Formation of quartzite and jasper from peridotite and their common presence as pebbles in the Devonian Old Red conglomerates, the Highland Border Complex and Devonian basins in the Scandinavian Caledonides highlight their importance and potential for provenance and tectonostratigraphic correlations.

Automated summary

Alteration of serpentinized peridotites in Scotland occurred in two steps, forming dolomite-quartz rocks and then jasper-quartzites. These rocks are enriched in certain elements, such as barium, strontium, and arsenic, during the alteration process. The formation of these rocks is important for studying their provenance and tectonic characteristics.