Geological and geochemical characteristics and ore-bearing potential of alkali-rich gabbro in Huaqiao, southern Qinling area

The ore-bearing rock of the Huaqiao titanomagnetite deposit in southern Qinling area is alkali-rich gabbro, and its ore-bearing petrofacies is mainly biotite-pyroxenolite composed of titaniferous augite and biotite. The ore-bearing gabbro belongs to typical agpaitic alkaline rock, in which Na2O>K2O, Na2O/K2O is 2.55~5.23, alkalinity ratio(AR) is 1.24~1.29, MgO is 5.32%~6.74%, TiO2 is 3.82%~5.84%, Al2O3 is 13.27%~15.06%, and m/f=0.37~0.56, belonging to ferruginous rock. It occurred in an intraplate environment, as judged by the FeO-MgO-Al2O3 graphical method. The Huaqiao alkali-rich gabbro is also characterized by a relatively high total REE content and a marked enrichment of LREE as well as weak Eu anomaly. The titanomagnetite ores in Huaqiao are enriched in Fe, Ti and MgO, but its SiO2 is unsaturated. In the magnetite, TiO2 is 0.415%~23.69%, FeO is 69.7%~96.18%, and Cr2O3 is 0.062%~0.761%. All these characteristics show that the Huaqiao titanomagnetite deposit resulted from magmatic segregation and mineralization of the low-degree partial fusing product of mantle source material on the northern edge of the Yangtze block in the early Paleozoic period.