• Paterson, David
• Schmid, Susanne
• Coveney, Ray
• Le Vaillant, Margaux
• Fan, Haifeng
• Wen, Hanjie

Abstract

Shale-hosted Ni-Cu-PGE sulfide occurrences can be associated with large amounts of Mo, Zn, Mn, V and U and represent economic resources. In recent years, metalliferous black shales have proven to represent a valuable resource for Ni (Talvivaara mine in Finland) and other base metals (Red Dog and Howards Pass Pb-Zn deposits, USA and Canada). In South China, during the Early Cambrian, a thin accumulation of phosphorite, Ni, Mo, Au, Ag, Se, Cr, V, Zn, U and PGEs occurred in shallow water environments, on the Yangtze platform. This narrow mineralised layer, within 10 m of the Proterozoic-Cambrian boundary, crops out for up to 2000 kilometers. This thin ore horizon is particularly enriched in organic matter (OM) (> 10 % TOC), in Mo-Ni-Re-Os-Se-As-Hg-Sb (> 1000*continental crust) and Ag-Au-Pt-Pd (> 100*continental crust) (Xu et al., 2013). This is one of the most enigmatic examples of a sediment-hosted base and precious metal deposit showing an association of ore-grade metals with OM. Of all known deposits, the Ni-Mo sulfide beds of the Devonian Nick prospect in the Selwyn Basin, Canadian Yukan, present the strongest similarities with the South China black shales (Coveney and Nansheng, 1991). The bed thickness varies between 5 and 15 cm, it is associated with a significant unconformity at the edge of the basin and contains abundant Ni (7.8 % Ni), Mo (0.4 %) and PGE (up to 1050 ppb). The Nick prospect shows a less complex mineralogy than the Niutitang shales, but they both display clastic textures and abundant vaesite. The Nick prospect also preserves plant material, suggesting an input of terrestrial material. Although a SEDEX mineralisation has been suggested for the Nick deposit (Hulbert et al., 1992), very few studies have focused on the detailed associations and origin of the metals. XFM combined with the Maia detector (384 detector array) was performed on the Australian Synchrotron XFM beamline (Paterson et al., 2011) to investigate the fine-scale distribution of metals in these rare mineralised horizons. The high-definition images obtained with the Maia detector allow the detection of metal segregation on a wide range of spatial scales (Ryan et al., 2016). For the first time, detailed mineral structures and spatial associations with OM were investigated in the South China shales and the Nick prospect to gain further understanding of metal deposition in these complex organic-rich sedimentary systems, based on a comparison of two distinct localities.

Topics

• Deposition
• impedance spectroscopy
• mineral
• laser emission spectroscopy
• positron annihilation lifetime spectroscopy
• Photoacoustic spectroscopy
• texture