Provenance, tectonic setting and mineralization significance in the Linxi Formation, eastern Inner Mongolia, NE China

摘要

y The strata of the Linxi Formation (LXF) occupy an extensive area of eastern Inner Mongolia, NE China and have close spatial and genetic relationships with important Mesozoic Sn-Cu-Pb-Zn-Ag veins and porphyry polymetallic deposits (ores). The rock types of the LXF include sandstone, siltstone and shale. Major and trace element (including rare earth element) data for rocks from the LXF in the Hanmiao area indicate that these rocks have a greywacke protolith derived from intermediate to acidic arc igneous rocks and were deposited during intensive tectonic activity. Laser ablation inductively coupled plasma mass spectrometry U-Pb dating of detrital zircons from sandstones in the LXF yields ages of 985 +/- 10 to 242 +/- 2 Ma. The youngest population of ages shows a peak at c. 258 Ma, suggesting that the main period of deposition of the LXF was in the late Permian. These ages, together with the youngest zircon age (c. 242 Ma), suggest that the deposition of the LXF mainly occurred during the late Permian and extended to the early Triassic. According to the results of the analysis of 44 sandstone and siltstone samples, ore elements (e.g. W, Sn, Ag and Mo) are significantly enriched in the LXF in this region. Combined with the fact that increasing numbers of polymetallic deposits have been discovered within the LXF strata in the southern Great Xing'an Range, we conclude that the strata of the LXF may be the source bed of the ore and there is potential for ore prospecting in the polymetallic deposits of the LXF in the Great Xing'an Range.