Petrogenesis of the Quanzigou porphyry Mo deposit at the northern margin of the North China Craton: Constrains from geochronology, geochemistry, and Sr–Nd–Hf isotopes characteristics
Introduction
The Jining Region (Inner Mongolia, China) is located at the northern margin of the North China Craton (northern NCC), notably within the eastern segment of the Central Asian Orogenic Belt (CAOB). The northern NCC is one of the most important Mo ore districts in China, containing at least 30 Mo (Mo-bearing) deposits with most of them relating to continental collision orogenies, including syn- to post-collision tectonism (Chen et al., 2017). So far, many Mo deposits have been discovered already in the middle and eastern parts of the northern margin of the NCC. However, the Jining Region, belonging to the western part, was still at a nearly “Greenfield” level of exploration until the early 2000s, when the discovery of the world-class Caosiyao porphyry-type Mo deposit with a Mo reserve of 1.78 Mt (average Mo 0.075%) and the Dasuji porphyry-type Mo deposit with a Mo reserve of 0.15 Mt (average Mo 0.135%) has made the region the focus for Mo deposit exploration (Nie et al., 2013).
Located between Paleo-Asian and Paleo-Pacific tectonic domains, the Jining Region has the mineralization potential during Indosinian (Triassic) and Yanshanian (i.e., Jurassic-Cretaceous). The Dasuji deposit was associated with the emplacement of a Triassic granite porphyry intrusion (Zhang et al., 2009, Zhang et al., 2019; Wu et al., 2014, Wu et al., 2018; Wu, 2015; Chen et al., 2018, Chen et al., 2019a, Chen et al., 2019b). The world-class Caosiyao deposit was recently dated at 130–150 Ma (molybdenite Re–Os method), relating to the Late Jurassic to Early Cretaceous granite porphyry intrusions (Nie et al., 2013; Wu et al., 2016, Wu et al., 2017; Wang et al., 2017; Zhou et al., 2019).
The Quanzigou Mo deposit is one of the newly discovered Mo deposits in the Jining Region. It was discovered and subject to further exploration in 2009 by the Inner Mongolia Nonferrous Geological Exploration Bureau (IMNGEB). Zhang et al. (2018) have reported a new molybdenite Re–Os age of 161.7 ± 3.1 Ma (n = 5, MSWD = 1.4) for the Quanzigou deposit, suggesting that it is the first early Yanshanian (i.e., early Jurassic) Mo deposit found in the western portion of the northern NCC. The origin of the magmatism and the related Mo mineralization in the Quanzigou deposit have not been adequately established. It is of vital importance to study the Quanzigou deposit to better understand the tectonic evolution of the northern NCC and to assist in the development of methods for exploration for similar deposits and mineral systems in the region. In this study, the petrology, geochemistry, geochronology and isotope systematics of the mineralization-related granites in the Quanzigou deposit are used to constrain the ages of Mo mineralization and to interpret the genesis and magma evolution of the Quanzigou Mo deposit.
Section snippets
Regional geology
The NCC is surrounded by the Qinling–Dabie Orogen to the south and east, and bounded on its northern and western sides by the late Paleozoic to the late Mesozoic Mongolian–Great Hinggan and the early Paleozoic Qilianshan orogens, respectively (Zhao et al., 2001). Two major blocks of the Eastern (Yanliao) and the Western (Ordos and Yinshan) are separated by the Central Orogenic Belt (Trans-North China Orogen), which was formed during the collision between the Eastern and Western Blocks at ca.
Granite major and trace element analyses
Eleven representative and fresh samples, including seven granite porphyry and four porphyritic biotite granite samples, were collected from the Quanzigou deposit district for major and trace elemental and Sr–Nd isotopic analyses (Fig. 3). Major elements were determined by an Axios X-ray fluorescence spectrometer. Trace elements, including rare earth elements (REEs), were obtained using a Thermo X-Series2 ICP-MS. Major and trace element analyses with precision being better than 5% relative error
Granite major and trace elements
The major and trace element contents of granite porphyry and porphyritic biotite granites are listed in Table 1. All samples with the loss on ignition (LOI) < 1 wt% are relatively fresh and unaltered.
These granitic samples have similar geochemical characteristics. All samples fall into the high-K calc-alkaline field in the plot of SiO2 versus K2O (Fig. 5a) and they exhibit peraluminous characteristics in the A/NK (molar Al2O3/Na2O + K2O) versus A/CNK (molar Al2O3/CaO + Na2O + K2O) diagram (Fig.
Magmatic and mineralization ages
As mentioned above, the Jining Region, located between the Paleo-Asian and Paleo-Pacific tectonic domains, was subject to several generations of mineralization during the Indosinian and Yanshanian. Zhang et al. (2009), Wu et al. (2014), Chen et al. (2018) and Zhang et al. (2019) reported weighted mean molybdenite Re–Os ages of 223.1 ± 1.6 Ma (2σ; n = 4), 223.9 ± 1.4 Ma (2σ; n = 5), 224.3 ± 1.5 Ma (2σ; n = 5) and 218.9 ± 1.6 Ma (2σ; n = 5) for the Dasuji Mo deposit. Nie et al. (2013), Wang et
Conclusions
- (1)
The molybdenite Re–Os isotopic analytic results indicate that the Mo mineralization of the Quanzigou deposit occurred at 170.8 ± 2.0 Ma, which is coeval with the mineralization-related porphyritic biotite granites and the granite porphyry dykes.
- (2)
The mineralization-related granites exhibit relative high-fO2 values, which is favorable for Mo mineralization and is consistent with the mineralization-related granites in other porphyry type Cu/Mo deposits.
- (3)
The whole-rock εNd(t), zircon εHf(t), and high-
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This research has been jointly supported by National Key Research and Development Program of China (2016YFC0600501), National Natural Science Foundation of China (41702075), a Chinese Geological Survey project (DD20190459), and Fundamental Research Funds for the Central Universities (2652018132). We appreciate the editors and three anonymous reviewers for constructive comments and suggestions.
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