U–Pb Age and Hf–Nd–Sr Isotopic Systematics of Vein Rocks of the Volkovsky Massif, Middle Urals, Russia

Аннотация

This paper reports chemical, geochronological, and Hf–Nd–Sr isotopic-geochemical data on granite, leucogabbro, and microgabbro porphyrite vein bodies in the gabbro of the Volkovsky massif. It was proved that the vein granite and leucogabbro are genetically related to the leucogabbro–anorthosite–plagiogranite (anorthosite–granite) series of the Urals Platinum Belt. The granite was dated by U-Pb laser ablation inductively coupled plasma mass spectrometric method at 409.0 ± 2.3 Ma. The rock has ⁸⁷Sr/⁸⁶Sr_{(409 Ма)} = 0.70358, high ε_{Nd(409 Ма)} = 6.4–6.5, and ε_{Hf(409 Ма)} ≥ 10.8. Similar values of ⁸⁷Sr/⁸⁶Sr_{(409 Ма)} = 0.70370 and ε_{Nd(409 Ма)} = 5.9 were obtained for the vein leucogabbro. The isotopic-geochemical data are consistent with existing concept of the formation of the leucogabbro–anorthosite–plagiogranite (anorthosite–granite) series through partial melting of the olivine gabbro. The measured ¹⁴³Nd/¹⁴⁴Nd = 0.512939 value obtained for the microgabbro porphyrite reflects their more radiogenic composition and likely a mantle source. The granite, associated leucogabbro, and microgabbro porphyrite were emplaced at the final magmatic stage in the massif evolution. This event marks the upper age boundary of the Au–Pd mineralization related to the gabbroic rocks. The vein rocks lack any signs of the mineralization. However, it is highly probable that they were sources of energy and fluid for reworking of the earlier olivine gabbro and redeposition of ore components in this rock.