Elemental and multiple isotopic evidences of enriched lithospheric mantle origin of the Xiadian gold deposit in the Jiaodong Peninsula, East China

Abstract

The Jiaodong Peninsula is the largest gold concentration district in China and the third largest one in the world. It covers no >0.2% of China's total landmass yet accounts for 30% of the total national gold reserves with total proved resources near 5000 t Au. One wonders where all this gold comes from. Here we present detailed whole-rock element and Sr-Nd-Pb isotope, quartz H-O isotope and pyrite He-Ar isotope geochemical data for the Xiadian gold deposit, a large Jiaojia-type gold deposit in the Jiaodong district, which furnishes new constrains on the sources of ore-forming fluids and metals. The results indicate that the ore and alterated rock have much higher HREE (e.g. Yb and Y), HFSE (e.g. Nb, Ta, Zr and Hf) and transition elements (e.g. Sc, Ti, V, Cr, Co and Ni) than the host granites but similar to the lithospheric mantle-derived lamprophyres, suggesting an enriched lithospheric mantle origin. The H-O isotopes (δDV-SMOW = −93.9‰ to −102.3‰, δ18OH2O = −0.2‰ to 1.6‰) of fluid inclusions in quartzs collected from auriferous pyrite–sericite–quartz altered rocks are distinctly different from either primary magmatic water and metamorphic water or meteoric water in the Jiaodong district but similar to the local enriched mantle-derived fluids. The He-Ar isotopes [3He/4/He = 0.58 × 10−6 to 1.90 × 10−6 (0.42–1.36 Ra), 40Ar/36Ar = 725–1358] of fluid inclusions in pyrites collected from auriferous pyrite–sericite–quartz altered rocks are also similar to the local enriched mantle-derived fluids. The ore and alterated rock have distinct Nd-Pb isotopic compositions either from the host Linglong granites or from the asthenosphere-derived mafic dikes but similar to the lithospheric mantle-derived mafic dikes. Their Sr isotopic compositions show a mix trend between the lithospheric mantle-derived mafic dikes and Neoarchaean basement. All the elemental and multiple isotopic features support a metallogenic model that the ore-forming fluids and metals were derived from the local previously enriched lithospheric mantle, and such deeply sourced fluids may have interacted with Neoarchaean basement along their flow path and mixed with a little meteoric water when they arrived high levels in the crust.