Ore Geology Reviews | 2019
Evolution of the carbonatite Mo-HREE deposits in the Lesser Qinling Orogen: Insights from in situ geochemical investigation of calcite and sulfate
Abstract
Abstract The Early Mesozoic Huanglongpu and Huangshui’an carbonatites in the Lesser Qinling Orogen are unique as they are associated with economic molybdenite mineralization and relatively enriched in heavy rare earth elements (HREE) compared to typical carbonatites. The carbonatites are composed of dominant calcite, quartz, sulfate (barite-celestite series), K-feldspar, and minor sulfides (molybdenite, galena, pyrite, sphalerite), rare earth minerals (monazite-(Ce), bastnasite-(Ce), parisite-(Ce), parisite-(Y), aeschynite-(Ce) and allanite-(Ce)), Nb oxides and silicates. The Lesser Qinling carbonatites formed in three mineralization stages, i.e., an early quartz-K-feldspar stage (I), a middle sulfide-rare earth mineral stage (II), and a late sulfate-biotite stage (III). The δ13C (−4.78 to −6.93‰) and δ18O (7.10 to 9.48‰) for calcite from the Lesser Qinling carbonatites generally plot within the primary carbonatite field. Bulk rock trace element compositions display strong enrichments of U, Pb, Mo and HREE compared to typical carbonatites. In situ Sr isotopic compositions of calcite overlap that of sulfate for both Huanglongpu and Huangshui’an carbonatites. Huangshui’an calcite and sulfate are characterized by 87Sr/86Sr ratios of 0.70579–0.70640, which are slightly enriched compared to those (0.70498–0.70582) for Hunglongpu calcite and sulfate. Calcite from the Lesser Qinling carbonatites display variable chondrite normalized REE patterns, with the (La/Yb)CN ratios (0.30–12.9) and REE abundances (323–3840\u202fppm) decreasing from early to late stages. In addition, calcite with HREE enrichments of 69.2–386\u202fppm is the dominant mineral that controls the HREE budget of these carbonatites. Sulfate shows an extremely light REE (LREE) enriched pattern [(La/Yb)CN\u202f>\u202f5677] with REE contents ranging from 706 to 4027\u202fppm. Combined with other trace element abundances (e.g., Pb) within calcite, the variable REE contents can be explained by distinct mineralization at different evolution stages. The late stage HREE enrichment within calcite can be explained by intense sulfate mineralization.