Abstract
In the eastern Hegenshan-Heihe suture zone (HHSZ) of NE China, Cu-Au hydrothermal mineralization at the newly discovered Hongyan deposit is associated with the Shanshenfu alkali-feldspar granite (SAFG). Zircon U-Pb dating showed that the inner phase and outer phase of the SAFG were formed at 298.8 ± 1.0 Ma and 298.5 ± 1.0 Ma, respectively. Whole rock geochemistry suggests that the SAFG can be classified as an A-type granite. Halfnium isotopes and trace elements in zircon suggest that the SAFG has high Ti-in-zircon crystallization temperature (721–990 °C), high magmatic oxygen fugacity and largely positive εHf(t) (from +6.0 to +9.9). We proposed that the SAFG was derived from crustal assimilation and fractional crystallization of juvenile crust metasomatized by subducting oceanic crust. The high oxygen fugacity of the SAFG suggests the chalcophile elements (e.g., Cu, Au) remained in the magma as opposed to the magma source. An arc-related juvenile source favors enrichment of Cu and Au in the resulting magma. Combined, these magmatic characteristics suggest Cu ± Au exploration potential for magmatic-hydrothermal mineralization related to the SAFG, and similar bodies along the HHSZ. The results obtained combined with regional geological background suggest that the Permian A-type granites and related mineralization along the HHSZ were formed in a post-collisional slab break-off process.
Highlights
Since the introduction of the A-type granite classification by Loiselle and Wones [1], rocks of this type have been studied extensively due to their important geodynamic significance, complicated petrogenesis and economic potential [2,3,4,5,6,7,8,9,10,11,12,13]
The oxidation state and petrogenesis of A-type granites has important geological significance, for regional tectonic evolution, and for understanding the metallogenic process related to A-type granites
Based upon geochronological and geochemical data from the Shanshenfu alkali-feldspar granite (SAFG), we suggest the following: (1) LA-ICP-MS U-Pb zircon dating shows the inner phase and outer phase of the SAFG were formed at 298.8 ± 1.0 Ma and 298.5 ± 1.0 Ma, respectively
Summary
Since the introduction of the A-type granite classification by Loiselle and Wones [1], rocks of this type have been studied extensively due to their important geodynamic significance, complicated petrogenesis and economic potential [2,3,4,5,6,7,8,9,10,11,12,13]. The oxidation state and petrogenesis of A-type granites has important geological significance, for regional tectonic evolution, and for understanding the metallogenic process related to A-type granites. Decoding this petrogenetic intricacy, inherent geodynamic background and the related metallogenic process requires the use of an integrated whole rock geochemical and zircon chemical approach. Zircon chemistry relates to crystallization temperature and oxygen fugacity (f o2 ) of magma [15,16,17,18], the composition of parental melts [19,20], source-rock type and crystallization environment [21,22,23]. The refractory nature and low elemental diffusion [24] mean that zircon chemistry remains unchanged through most geological processes, such as hydrothermal alteration, providing a powerful tool for documenting magmatic conditions (e.g., magma source and f o2 ) and the resulting behavior of elements such as Cu [25,26,27,28]
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