Geology, geochronology and geochemistry of the Gaogangshan Mo deposit: A newly discovered Permo-Triassic collision-type Mo mineralization in the Lesser Xing'an Range, NE China

Abstract

The newly discovered medium-sized Gaogangshan porphyry Mo deposit is located in the northern Lesser Xing'an Range (LXR) of NE China. The mineralized rocks consist of granitic rocks and were intruded into gneissic granodiorite. In this paper, we present new U-Pb ages and Hf isotopic data from zircons, Re-Os and H-O-S-Pb isotopic data from sulfides and quartz, and whole-rock geochemistry data for the granitic rocks related to Mo mineralization. The granitic rocks are mainly S-type granites with uniform SiO2 content of 68.5–77.5wt%. Most are typically peraluminous with K2O>Na2O and low MgO contents. They are enriched in light rare-earth elements relative to heavy rare-earth elements, with negative Eu anomalies, and are enriched in Th, U and large ion lithophile elements (e.g., K and Rb), and depleted in high field strength elements (e.g., Nb, Ta, P and Ti). Extensive fractional crystallization played a vital role in concentrating Mo in the host granite, and can explain the Mo- rather than Cu-mineralization in the Gaogangshan deposit. The εHf (t) values (−1.2 to +3.7) and two-stage Hf model ages (TDM2=1208–1295Ma) for zircon suggest that the mineralized granitic rocks may come mainly from melting of metasedimentary rocks, with contribution of the lower crust originated from the Mesoproterozoic depleted mantle. The δ18OH2O of quartz values vary from −1.3‰ to 2.9‰, and the δD values range from −111‰ to −75‰, indicating that the ore-forming fluids were a mixture of magmatic and meteoric water. The δ34S values of pyrite range from 3.6‰ to 4.6‰. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of pyrite are in the ranges of 18.733–19.370, 15.587–15.622 and 38.410–38.571, respectively. Both the S and Pb isotopic compositions indicate that the ore materials were mainly derived from magmas under collisional tectonic setting. LA-ICP-MS U-Pb dates of zircon in granitic porphyry yielded a weighted average age of 259.9±2.0Ma, corresponding to the Late Permian collision of the Jiamusi-Mongolia block and the northeastern part of the Sino-Korean Plate. Re-Os dating of molybdenum ore gave a weighted average age of 250.2±1.4Ma and an isochron age of 247±6Ma, which slightly postdate the emplacement of the granite and coincide with the transition from collisional to post-collisional tectonism in the region. Considering that the Gaogangshan deposit is a newly discovered Permo-Triassic collision-type porphyry molybdenum deposit in the Lesser Xing'an Range metallogenic belt, it has a great significance for the understanding of regional tectonic evolution and ore prospecting.