Petrological characteristics of granitic rocks related to the world large molybdenum deposits are studied. The granitoids are evaluated by Fe2O3+TiO2-FeO+MnO-MgO diagrams, and found to all plot to the magnetite-series field. They are all high silica and high-K series, but not A-type, except for the Climax-type porphyries and some others in the Colorado mineral belt. By-product molybdenum contained in porphyry copper deposits, lower grade but huge tonnage, occurs with calc-alkaline I-type magnetite-series granodiorite and monzogranite.Felsic intrusive rocks of the Climax mine are A-type and are exceptionally high in trace elements such as F and Rb, which are generally enriched with W and Sn-related granitoids that originated in crustal source rocks. The by-product molybdenites in porphyry copper deposits appear to originate in adakitic granodiorite or monzogranite, having deep origins with the subducted slab or thickened juvenile mafic lower crust. Therefore, there is no single magma type but the magnetite series, which concentrates a large volume of molybdenum in the ore deposits.

Located in the central part of Altay pegmatite province, Northwestern China, the Kelumute-Jideke pegmatite field (KJPF) provides a natural lab to study the regional zonation of pegmatite and longevity of pegmatitic magmatism. Rare-metal pegmatites in the KJPF are interpreted to be genetically related to the emplacement of the Jideke two-mica granite, which is described as the parental pluton by previous studies (eg. Lv et al., 2012). Except for the Kelumute Li-Be-Nb-Ta pegmatite located inside the Jideke two-mica granite, other pegmatites with different types of mineralization distributed outward the parental pluton are as following: Azubai, Xiaojideke and Dajideke muscovite-Be, Qunkuer Be-Nb-Ta, Jiamukai LiNb-Ta and Kukalagai Li-Be-Nb-Ta pegmatite, corresponding to the regional zonation of pegmatite groups (Černý, 1991).Kelumute and Kukalagai are the only two large-scale rare metal deposits in the KJPF. The Kelumute No.112 pegmatite is 1200 m in length, varying in thickness from 3.81 m (east) to 7.31 m (west), and is 200 m deep; its rare metal reserve is the second largest after the most famous Koktokay No. 3 pegmatite in the Altay pegmatite province. The main part of No. 112 pegmatite occurs EWtrending, which is controlled by faults of same direction. Five internal zones have been identified by mineral assemblages and textures, including quartz-microclinealbite zone, blocky quartz-albite-microcline zone, quartzalbite-spodumene zone, albite-quartz-muscovite zone and saccharoidal albite zone. The Kukalagai No. 650 pegmatite dips westward with an angle of 60° to 78°, which is controlled by N-S trending foliation of biotitequartz schist. With a length of 1230 m and an average thickness of 9.88 m, the only internal zone in No. 650 pegmatite is quartz-spodumene-albite zone, with lepidolite aggregates and medium-coarse garnet grains developed locally. It iss worth mentioning that evidence of replacement (eg. saccharoidal albite and blocky quartzmuscovite) and reconstruction on the earlier pegmatite (nests of spodumene and massive albite in quartzspodumene-albite pegmatite) were identified during field observation in both No. 112 and No. 650 pegmatite. Zircon U-Pb DatingTo reveal the timing of pegmatitic magmatism, a study of LA-ICP-MS zircon U-Pb dating is conducted on the Kelumute and Kukalagai pegmatites. Zircons in this study are opaque and anhedral, indicating that these magmatic zircons have experienced different degrees of hydrothermal alteration. However, due to the high closure temperature, homogeneous, clear and less porous zircons or domains of these zircon grains still yield concordant ages with geological significance. Three weighted mean 206 Pb/ 238 U ages are observed in one sample from quartzalbite-spodumene zone of the Kelumute No. 112 pegmatite, which are 237 ± 5 Ma (n=1), 196.9 ± 4.5 Ma (n=8) and 156.6 ± 3.9 Ma (n=8). Similarly, one sample from quartz-spodumene-albite zone of the Kukalagai No. 650 pegmatite shows two weighted mean 206 Pb/ 238 U ages: 233.8 ± 2.5 Ma (n=9) and 204.4 ± 4.1 Ma (n=7).