Selenium and its importance to the study of ore genesis: the theoretical basis and its application to volcanic-hosted massive sulfide deposits using pixeprobe analysis

Selenium speciation in Lower Cambrian Se-enriched strata in South China and its geological implications

“…up to 2500 ppm) occur in high-temperature mineral assemblages in the middle of the deposit (Auclair et al, 1987). High Se contents in pyrite (200 ppm) in volcanic-hosted Cu-rich massive sulfide deposits also were reported by Huston et al (1995). This indicates that hydrothermal fluid can provide a large amount of Se(-II) associated with sulfides/selenides.…”

“…Similar to Se, the S content is highest in the Ni-Mo-Se sulfide layer (21.3%), and the other samples contain equivalent S content (0.1-1.5%). The ratios of Se/S from all samples (0.6-46.5 Â 10 À3 ) are several orders of magnitude higher than that of seawater (10 À7 ) (Measures and Burton, 1980) and apt to that of hydrothermal fluid (1.5 Â 10 À4 ) (Huston et al, 1995). The C org content varied from 3.3% to 20.2% for black shales (average 11.5%), 3.4-8.9% for carbonaceous cherts (average, 6.7%), 9.2-11.6% for the Ni-Mo-Se sulfide layer, 0.1% for K-bentonite and 1.0% for phosphorite.…”

Extreme enrichment of selenium in the Apliki Cyprus-type VMS deposit, Troodos, Cyprus

“…Modelling by Huston et al (1995) argues that Se incorporation is enhanced at low temperatures (Figure 3). At temperatures <200 ˚C Se incorporation in pyrite is controlled by redox and pH whereas at temperatures >200 ˚C Se incorporation is controlled by fluid H 2 Se/H 2 S ratio and temperature (Huston et al, 1995). In hydrothermal fluids above 200 ˚C H 2 Se/H 2 S are the dominant species and thus approximate to Se/S ratios (Huston et al, 1995).…”

“…Trace elements may be classified into three categories based on their behaviour during incorporation into pyrite (Huston et al, 1995). Group (i) occur as inclusions (Cu, Zn, Pb, Ba, Bi, Ag and Sb), group (ii) in non-stoichiometric substitution (As, Tl, Au and Mo) and group (iii) as a stoichiometric substitution for S (Se and Te) or Fe (Co and Ni) (Huston et al, 1995).…”

“…Trace elements may be classified into three categories based on their behaviour during incorporation into pyrite (Huston et al, 1995). Group (i) occur as inclusions (Cu, Zn, Pb, Ba, Bi, Ag and Sb), group (ii) in non-stoichiometric substitution (As, Tl, Au and Mo) and group (iii) as a stoichiometric substitution for S (Se and Te) or Fe (Co and Ni) (Huston et al, 1995). Huston et al, (1995) state that both Te and Se are incorporated via stoichiometric substitution with S ions; this however seems unlikely for Te given its larger ionic radius (2.42 Å) compared with S (2.14 Å) (e.g.…”