Bastnasite U-Th-Pb age, sulfur isotope and trace elements of the Huangshui'an deposit: Implications for carbonatite-hosted Mo-Pb-REE mineralization in the Qinling Orogenic Belt, China

The Huangshui'an deposit is hosted in carbonatite dykes and located in the southern margin of the North China Craton which forms part of the Qinling Orogenic Belt. The genesis of Mo-Pb-REE mineralization associated with carbonatitic magmatism and hydrothermal activity remain poorly understood. Here we present results from field investigation, petrography, in situ sulfur isotope and trace elements of pyrite, and bastnasite U-Th-Pb age with a view to understand the age and genesis of the Huangshui'an deposit. Three types of pyrite are identified in the Huangshui'an deposit as follows: (i) Py1a is composed of irregular pyrite in stage Ia carbonatite dykes; (ii) the euhedral Py1b coexists with sphalerite and galena in the margin of stage Ia carbonatite dykes; and (iii) Py2 occurs as irregular and anhedral grains in the fluorite + quartz veins. The highly variable Co (Py1a = 0.032-3230 ppm; Py1b = 0.053-779 ppm; Py2 = 0.98-164 ppm) and Ni values (Py1a = 2.1-418 ppm; Py1b = 0.78-28.8 ppm; Py2 = 8.6-373 ppm) indicate heterogeneous material sources. The delta S-34 values of the various pyrite types range between - 9.6 parts per thousand and -3.5 parts per thousand, and the obviously negative values resulted from sulfur isotope fractionation between sulfide and sulfate minerals. The total delta S-34 value calculated from co-genetic galena and barite is -0.11 parts per thousand, in combination with previous Sr-Nd-Pb-He-Ar isotopes, indicate a material source dominantly from enriched mantle (EMI) with an additional contribution through partial melting of the thickened lower crust. In situ bastnasite U-Th-Pb dating results yield mean ages of 211.7 +/- 3.1 Ma and 209.6 +/- 2.1 Ma, representing the timing of Mo-Pb-REE mineralization in the Huangshui'an deposit. The Late Triassic carbonatite magmatism and associated mineralization were controlled by the fertile source from the enriched mantle and the thickened lower crust, and the post-collisional extension setting facilitated the partial melting and fast propagation of carbonatite magma from the mantle to shallow crustal level.

Automated summary

This study provides insights into the age and genesis of the Huangshui'an deposit through field investigation and experimental analysis. Results reveal heterogeneous material sources for the deposit and suggest that Late Triassic carbonatite magmatism and mineralization were controlled by the enriched mantle and thickened lower crust, facilitated by a post-collisional extension setting.