Mercury isotope fractionation during ore retorting in the Almaden mining dilstrict, Spain

Almaden, Spain, is the world's largest mercury (Hg) mining district, which has produced over 250,000 metric tons of Hg representing about 30% of the historical Hg produced worldwide. The objective of this study was to measure Hg isotopic compositions of cinnabar ore, mine waste calcine (retorted ore), elemental Hg (Hg-(L)(0)), and elemental Hg gas (Hg-(g)(0)), to evaluate potential Hg isotopic fractionation. Almaden cinnabar ore delta Hg-202 varied from -0.92 to 0.15 parts per thousand (mean of -0.56 parts per thousand, sigma - 0.35 parts per thousand, n - 7), whereas calcine was isotopically heavier and delta Hg-202 ranged from -0.03 parts per thousand to 1.01 parts per thousand (mean of 0.43 parts per thousand, sigma = 0.44 parts per thousand, n = 8). The average delta Hg-202 enrichment of 0.99 parts per thousand between cinnabar ore and calcines generated during ore retorting indicated Hg isotopic mass dependent fractionation (MDF). Mass independent fractionation (MIF) was not observed in any of the samples in this study. Laboratory retorting experiments of cinnabar alsowere carried out to evaluate Hg isotopic fractionation of products generated during retorting such as calcine, Hg-(L)(0), and Hg-(g)(0). Calcine and Hg-(L)(0) generated during these retorting experiments showed an enrichment in delta Hg-202 of as much as 1.90 parts per thousand and 0.67 parts per thousand, respectively, compared to the original cinnabar ore. The delta Hg-202 for Hg-(g)(0) generated during the retorting experiments was asmuch as 1.16 parts per thousand isotopically lighter compared to cinnabar, thus, when cinnabar ore was roasted, the resultant calcines formed were isotopically heavier, whereas the Hg-(g)(0) generated was isotopically lighter in Hg isotopes. Published by Elsevier B.V.