Biogenic origin of intergrown Mo-sulphide- and carbonaceous matter in Lower Cambrian black shales (Zunyi Formation, southern China)

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

“…Se was mostly enriched in the Ni-Mo-Se sulfide layer (average, 2081 ppm), similar to values of 1000-2000 ppm reported by Orberger et al (2007), the black shales (84.19 ppm) and K-bentonite (131.18 ppm). There was no obvious difference between carbonaceous cherts (28.86 ppm) and phosphorite (20.36 ppm).…”

“…However, the formation mechanism for the Ni-MoSe sulfide ore layer is still strongly debated, with its possible origins being sorption from normal seawater (e.g. Mao et al, 2002;Lehmann et al, 2003Lehmann et al, , 2007 or from seawater enriched in metals through hydrothermal fluid (Lott et al, 1999;Steiner et al, 2001;Coveney, 2003;Jiang et al, 2007;Orberger et al, 2007;Pasava et al, 2008).…”

“…The Ni-MoSe sulfide layer varies in thickness that can be as much as 30 cm, and consists largely of MoSC phase (a complex mixture of MoS 2 and carbonaceous matter nanocrystallites; Orberger et al, 2007), Ni-sulfides (such as vaesite, gersdorffite), pyrite, apatite, quartz, carbonate and clay minerals, i.e., illite (Fan, 1983;Kao et al, 2001). The Ni-Mo-Se sulfide layer commonly contains 2-4 wt.% Mo (the highest value be up to 7 wt.%), $2 wt.% Ni, 2000 ppm Se (Orberger et al, 2007) and 1 ppm of total PGE (in particularly, Os, 137 Â 10 À9 ; Pt, 424 Â 10 À9 and Pd, 411 Â 10 À9 , Mao et al, 2002). The sulfide layer was initially dated to Late Ediacaran and/or Early Cambrian based on arthropods and sponges (Steiner et al, 2001), consistent with Pb-Pb isochron ages of 531 ± 24 Ma (Jiang et al, 2006) and ReOs (541 ± 16 Ma;Mao et al, 2002;560 Ma;Horan et al, 1994).…”

“…The Se-enriched strata, located at the late Neoproterozoic/Cambrian boundary, host numerous rock types such as black shales, cherts, phosphorite and K-bentonite, and include an economically significant Ni-Mo-Se sulfide ore layer with up to 2000 ppm Se (Orberger et al, 2007). This study will lead to a better understanding of Se biogeochemical cycling, under specific redox environments, during this critical geological period.…”

Origin of iron oxide spherules in the banded iron formation of the Bababudan Group, Dharwar Craton, Southern India

“…The detection limit of N and C by NRA is about 100 ppm. The method, standards used for measurements and the data evaluation from the NRA and X-ray spectra are described in (Khodja et al, 2001;Daudin and Gallien, 2003;Orberger et al, 2007a;Orberger et al, 2007b;Pinti et al, 2007).…”