on the southern margin of the North China
the Yan-Liao molybdenum belt on the northern margin, and with more than
5million metric tons of explored Mo metal reserves, the East Qinling
Molybdenum Belt (EQMB) is the largest molybdenum producing region in
China. Molybdenum deposits in the EQMB include porphyry Cu-Mo, porphyry
Mo, skarn Mo-W, and carbonatite deposits.
The five known major monometallic high-fluorine porphyry Mo deposits in
the EQMB – Jinduicheng, Shijiawan, Leimengou, Yuchiling, and Donggou –
bear a striking similarity in mineralization, hydrothermal alteration,
and igneous geochemistry. Mineralization of four of the deposits is
associated with a small granite porphyry stock, and the Yuchiling
deposit is related to a composite granitoid batholith. Porphyries
related to mineralization share broad likenesses in major elemental
features (SiO2- and Al2O3-rich, MgO-
and CaO-poor, TiO2 depletion,
A/CNK > 1.1, (Na2O+K2O)
7.5, (K2O/Na2O) > 1) and high LREE/HREE
The East Qinling Molybdenum Belt shows systematic variation along its
axis. Published molybdenite Re-Os ages indicate mineralization
progressed from west to east: Jinduicheng (138.3 ± 0.8 Ma),
Shijiawan (138.0 ± 8 Ma), Leimengou (132.4 ± 1.9 Ma),
Yuchiling (131.2 ± 1.4 Ma), and Donggou (116.0 ± 1.7 Ma).
Re content of molybdenite and alkali-lime index decrease gradually, and
Eu anomaly systematically increases eastward.
Prior researchers suggested that the five deposits formed at different
times with different magmatic source regions (upper mantle, lower
crust, and upper crust). Alternatively, we propose the systematic
differences in geochemistry, mineralization age, REE pattern, and
isotopic characteristics, may have resulted from magmas of similar
primary source region that experienced progressively greater degrees of
crustal interaction and fractionation during ascent, as post-orogenic
extension of the Qinling Mountains progressed eastward.