Petrogenesis of the Xingluokeng W-bearing granitic stock, western Fujian Province, SE China and its genetic link to W mineralization.

[Display omitted] • The granitic stock in the Xingluokeng W deposit was intruded at ca. 152 Ma. • Petrographic variations within the stock are ascribed to co-magmatic evolution via fractionation. • The granites show I-type affinity, mainly derived from Paleoproterozoic meta -igneous rocks. • Fractionation crystal and fluid-rock interaction have contributed to the W mineralization of the Xingluokeng deposit. The Xingluokeng deposit is the largest tungsten deposit discovered in the Wuyi metallogenic belt, with 30.43 Mt WO 3 reserves averaging at 0.23%. The main orebody mainly occurs in an altered granitic stock, comprising veinlet-disseminated and vein-type scheelite and wolframite mineralization. A comprehensive study of field investigations with whole-rock and in-situ geochemical and isotopic compositions was conducted on different intrusive phases of the Xingluokeng ore-bearing granitic stock, aiming to constrain the petrogenesis and its genetic link to W mineralization. The Xingluokeng stock is mainly composed of the porphyritic biotite granite (G1) as the upper part of the stock, intruded by the medium- to fine-grained biotite granite (G2) in the deep. Petrographic observations suggest that the stock experienced intense fractional crystallization as well as assimilation of country rocks close to stock margins. Zircon U − Pb geochronology and trace element analyses indicate that G1 and G2 were emplaced coevally at ~152 Ma at a relatively lower oxygen fugacity condition (Ce4+/Ce3+ = 44 ± 18 for G1, and 104 ± 41 for G2). Ti-in-zircon thermometer and AlT-in-biotite geobarometer reveal average crystallization temperature and depth at 762 ℃−740 ℃ and 7.3–7.0 km, respectively. Geochemically, obvious negative correlation between SiO 2 and P 2 O 5 and low A/CNK values (mostly < 1.1) indicate that they belong to the weakly peraluminous I-type granite, rather than S-type granite as proposed previously. Whole-rock geochemical compositions from G1 to G2 display systematic variations, with a general decrease in major oxides (such as Al 2 O 3 , TiO 2 , FeOT, MgO, CaO) and Zr/Hf ratio, but a gradual increase in DI value, Rb/Sr ratio and δEu with increasing SiO 2 , suggesting fractional crystallization is the major factor that controls the compositional variations between G1 and G2. They have consistent initial 87Sr/86Sr ratios of 0.71170 to 0.71477 and ε Nd (t) values of −12.5 to −10.8, as well as zircon ε Hf (t) values of −17.4 to −9.2 with Paleoproterozoic Nd − Hf model ages (1783–2081 Ma), suggesting a mixed crustal source of about 88% Paleoproterozoic meta -basaltic rocks and about 22% Paleoproterozoic gneissic granites, with minor assimilation of country rocks. These results favor that the Xingluokeng granites were formed by co-magmatic evolution via K-feldspar-dominated fractionation. High degrees of fractional crystallization have immensely enriched W in reduced magma, then intensive fluid-rock interaction liberated Ca from the G1 to form the scheelite and some Fe might come from the country rocks (biotite hornfels) to precipitate the wolframite. [ABSTRACT FROM AUTHOR]