The origin of giant lode gold deposits of Mesozoic age in the North China craton (NCC) is enigmatic because high-grade metamorphic ancient crust would be highly depleted in gold. Instead, lithospheric mantle beneath the crust is the likely source of the gold, which may have been anomalously enriched by metasomatic processes. However, the role of gold enrichment and metasomatism in the lithospheric mantle remains unclear. Here, we present comprehensive data on gold and platinum group element contents of mantle xenoliths (n = 28) and basalts (n = 47) representing the temporal evolution of the eastern NCC. The results indicate that extensive mantle metasomatism and hydration introduced some gold (<1–2 ppb) but did not lead to a gold-enriched mantle. However, volatile-rich basalts formed mainly from the metasomatized lithospheric mantle display noticeably elevated gold contents as compared to those from the asthenosphere. Combined with the significant inheritance of mantle-derived volatiles in auriferous fluids of ore bodies, the new data reveal that the mechanism for the formation of the lode gold deposits was related to the volatile-rich components that accumulated during metasomatism and facilitated the release of gold during extensional craton destruction and mantle melting. Gold-bearing, hydrous magmas ascended rapidly along translithospheric fault zones and evolved auriferous fluids to form the giant deposits in the crust.
Desilicification elevates extraction of Re and platinum‐group elements (PGEs) from many geological reference materials (RMs), but the extent to which it affects less chalcophile elements has been investigated rarely. To further evaluate the effect of desilicification, mass fractions of elements with variable chalcophile affinities (In, Cd, Cu, Ag, S, Se, Te, Re and PGEs) in different RMs were obtained by isotope dilution and digestion procedures involving HF‐HNO3 in bombs versus HNO3‐HCl in Carius tubes. The results show that the extraction efficiencies of HF‐desilicification vary in different RMs and for different elements. HF‐desilicification led to a significant increase (30–70%) for In and Cd mass fractions in all analysed RMs, but it played a negligible role in other strongly chalcophile elements in many samples (e.g., UB‐N and WGB‐1). Noticeably, desilicification led to a 10–30% increase in the mass fractions of Cu, Ag, S, Se and Te in BHVO‐2 and BIR‐1a, but less so in BCR‐2. These results could be attributed mainly to the variable chalcophile affinities of elements and their relative budget in sulfides, alloys and silicates. Desilicification should thus be preferred to determine chalcophile elements for most samples, except in cases where they are negligibly hosted in silicates.
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