Hegen Ouyang

Early Cretaceous magmatism and ore mineralization in Northeast China: examples from Taolaituo Mo and Aobaotu Pb–Zn deposits

The recently discovered Taolaituo porphyry Mo deposit and Aobaotu hydrothermal vein Pb–Zn deposit are both located in the Great Xing’an Range, Northeast China. Here we present new zircon U–Pb ages, whole-rock geochemical and Pb isotopic data, and molybdenite Re–Os ages for these two deposits. The Mo mineralization in the Taolaituo area occurred in quartz porphyry, which yields zircon U–Pb ages ranging from 138.5 ± 0.8 to 139.1 ± 0.5 Ma. Fine-grained granite representing pre-mineralization magmatic activity was formed at 145.2 ± 0.5 Ma. Molybdenite Re–Os dating indicates that Mo mineralization occurred at 133.8 ± 1.2 Ma. In the Aobaotu deposit, the ore-related granodioritic porphyry has a zircon U–Pb age of 140.0 ± 0.4 Ma. These geochronological data indicate that these magmatic and hydrothermal activities occurred during the Early Cretaceous. The mineralogical and geochemical features of the Taolaituo and Aobaotu granitoids suggest they can be classified as A1-type within-plate anorogenic granites and I-type granites, respectively. The Pb isotopic compositions suggest a mixed crust–mantle origin of the granitoids in these two deposits. The Taolaituo granitoids were formed by the partial melting of lower crust and crust–mantle interaction, with subsequent fractionation of apatite, feldspar, Ti-bearing phases and allanite or monazite. In contrast, the Aobaotu granites were derived primarily from lithospheric mantle that had been transformed or affected by the addition of subduction-related components. Combined with the regional geology, tectonic evolution and available age data from the literature, our results suggest that the Early Cretaceous (140–100 Ma) was likely to be the most important peak period for metallogenic mineralization in Northeast China. The Taolaituo and Aobaotu deposits formed under an extensional environment at an active continental margin in response to subduction of the Palaeo-Pacific oceanic plate.

The Nature and Timing of Ore Formation in the Budunhua Copper Deposit, Southern Great Xing'an Range

0.5 Mt) deposit, is located in the northeastern TianshanTuquan copper-polymetallic metallogenic belt of the southern Great Xing’an Range. The deposit consists of the Kongqueshan ore block in the north and in the Jinjiling ore block in the south, with the Budunhua composite stock occurring at the boundary between the blocks. Several previous geological and geochemical studies have attempted to characterize the mineralization in this deposit, most of which were published in Chinese (e.g., Jin and Pang, 1983; Shen and Fu, 1999; Liu, 2001; Xiao, 2008; Feng, 2010; Wu et al., 2012). Some of the previous studies suggest that this deposit might be related to late Mesozoic magmatic-hydrothermal activity (Jin and Pang, 1983; Wu et al., 2012), although detailed deposit characterization and evaluation of mineralization style, especially for the Jinjiling ore block (e.g., Jin and Pang, 1983; Shen and Fu, 1999), have not yet been well constrained. For example, Jin and Pang (1983) suggested that Budunhua is a hydrothermal vein-type deposit, whereas Shen and Fu (1999) and Liu (2001) proposed that the mineralization in the Jinjiling ore block is of porphyrytype. The appropriate classification of this deposit is critical to the prospecting and evaluation of the Budunhua area, as well as for the northeastern Tianshan-Tuquan copper-polymetallic metallogenic belt. This paper draws on new detailed field investigations, geochronology and fluid inclusions from the Budunhua deposit to address the following aspects: 1) the genesis and mineralization processes that formed the Budunhua deposit, and 2) the genetic link between the Budunhua copper deposit and other copper deposits in the northeastern Tianshan-Tuquan copper-polymetallic metallogenic belt, such as the Naoniushan, Chentaitun and Lianhuashan deposits. The results from our study sheds light on the division of the metallogenic systems in the northeastern Tianshan-Tuquan copper belt and offer guidelines for expanding the size of pre-existing deposits or future prospecting of new mineral deposits in this area. The Budunhua copper deposit is located in the southern Great Xing’an Range where the stockwork ore bodies are mainly hosted in the Lower Permian Dashizhai Formation. The mineralization occurs in two blocks the Jinjiling and Kongqueshan – and both are characterized by four main stages: arsenopyrite pyrite (molybdenite)quartz, chalcopyrite pyrrhotite quartz, galena sphalerite chalcopyrite quartz and calcite fluorite quartz. Wallrock alteration, which is related to mineralization, is dominated by silicification, sericitization, and chloritization. Fluid inclusion studies show that the ore fluids from Cu stages in both the blocks are broadly identical with trapping temperatures of 280 to 400°C for the Kongqueshan, and 300 to 420°C for the Jinjiling. Estimated trapping pressures for the Kongqueshan is 15.0 to 26.6 MPa and for the Jinjiling is 14.9 to 29.4 MPa, corresponding to entrapment depth of 1.5 to 2.7 km and 1.5 to 2.9 km below the paleowater table, respectively. Zircon grains from the tonalite porphyry in the deposit yielded a weighted Pb/U mean age of 152 ± 0.7 Ma, OUYANG Hegen, XU Xinli, MAO Jingwen, SU Huiming, M. SANTOSH, ZHOU Zhenhua and LI Chao, 2014. Geology, fluid inclusions, and U-Pb and Re-Os geochronology study of Budunhua copper deposit, southern Great Xing’an Range. Acta Geologica Sinica (English Edition), 88(supp. 2): 29-30.