Bastnäsite 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
Jia‐Ying Feng, Li Tang, Bo-Chang Yang, M. Santosh, Shouting Zhang, Bo Xu, Sung Won Kim, Yuan‐Ming Sheng
Abstract
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 bastnäsite 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 δ34S values of the various pyrite types range between −9.6‰ and −3.5‰, and the obviously negative values resulted from sulfur isotope fractionation between sulfide and sulfate minerals. The total δ34S value calculated from co-genetic galena and barite is −0.11‰, 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 bastnäsite 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.