TIME–SPACE DISTRIBUTIONS OF DIVERSE ORE DEPOSITS IN SOUTHERN ALTAIDS, NW CHINA AND ITS TECTONIC IMPLICATIONS

Trench-arc-backarc system is a classic geological feature, which can be observed in active orogens or preserved in fossil orogens. In such a tectonic setting, orogenic gold ore deposits are always close to the trench and located within a serious of regional faults; porphyry copper ore deposits are located at the arc and volcanogenic massive sulfide (VMS) deposits are located at the backarc basin (Groves et al., 1998). Because the different stress field between building the arc (compression) and forming the backarc basin (extension), the porphyry and VMS ore deposits cannot form synchronously (Sillitoe 1980), which is consistent what we observed at active arc-backarc system.

The Chinese Altai–East Junggar collage in the southern Altaids hosts three metallogenic belts, which are, from north to south: (1) a volcanogenic massive sulphide (VMS) Cu–Pb–Zn belt; (2) a belt of shear zone-related gold deposits; (3) a porphyry Cu–Au–Mo belt. The VMS deposits formed in two pulses (c. 405 Ma and c. 375 Ma) in the Chinese Altai arc (Wan et al., 2011). The porphyry deposits developed in three pulses in the East Junggar arc, the first two synchronous with the VMS mineralization, and the third at c. 310 Ma (Wan et al., 2014). The shear zone-related gold and iron deposits developed in the late Carboniferous to Permian at the contact between the Chinese Altai and East Junggar arcs (Wan et al., 2012). Time–space distributions of diverse ore deposits across the Altai–East Junggar collage indicate that the collage developed from two independent arcs, the Chinese Altai and the East Junggar. The VMS and porphyry deposits developed in the Chinese Altai and East Junggar arcs, respectively. The Chinese Altai arc is interpreted to be a Japanese-type arc, and the East Junggar arc a Mariana-type arc. During the latest Palaeozoic, the two arcs were juxtaposed by the Erqis Fault, when many shear zone-related lode gold deposits were emplaced. These metallogenic distributions were a likely response to spatially localized mechanisms of crust growth and to the tectonic evolution of the Altai–East Junggar collage, and they are consistent with interpretation of the Altaids as a multiple subduction–accretion collage.