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Granitic magmatism associated with gold mineralization: evidence from the Baizhangzi gold deposit, in the northern North China Craton

Published online by Cambridge University Press:  21 June 2023

Zhi-xiong Zhao
Affiliation:
School of Earth Science and Resources, China University of Geosciences, Beijing, China Ulanqab Key Laboratory of Geospatial Big Data Application and Environmental Monitoring, Jining Normal University, Ulanqab, China
Wei-jun Xu
Affiliation:
School of Earth Science and Resources, China University of Geosciences, Beijing, China Rixing Mining Co. Limited of Lingyuan, Liaoning, China
Guo-chen Dong*
Affiliation:
School of Earth Science and Resources, China University of Geosciences, Beijing, China
M Santosh
Affiliation:
School of Earth Science and Resources, China University of Geosciences, Beijing, China Department of Earth Science, University of Adelaide, Adelaide, Australia
Hong-bin Li
Affiliation:
School of Earth Science and Resources, China University of Geosciences, Beijing, China
Ze-guang Chang
Affiliation:
School of Earth Science and Resources, China University of Geosciences, Beijing, China
*
Corresponding author: Guo-chen Dong; Email: donggc@cugb.edu.cn
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Abstract

The relationship between magmatism and gold mineralization has been a topic of interest in understanding the formation of ore deposits. The Baizhangzi gold deposit, located in the northern margin of the North China Craton, is hosted by the Baizhangzi granite (BZG) and provides a case to evaluate the relation between granite and gold mineralization in Late Triassic. In this study, we present petrography, bulk geochemistry, zircon U-Pb isotope and trace elements data, as well as major elements of biotite and plagioclase for the BZG to evaluate the petrogenesis and link with gold mineralization. The BZG comprises biotite monzogranite, biotite-bearing monzogranite and monzogranite (BZGs). Zircon U-Pb geochronology shows that all the granitoids of BZGs were coeval with a formation age of 232 Ma. The granitoids, with high SiO2, Al2O3 and Sr, while low Y and Yb, show adakitic affinity. They are enriched in LILFs (e.g., Rb, Ba, Th, U and Sr) and LREEs, while depletion in HFSEs (e.g., Nb, Ta, P and Ti). The geochemical and mineral chemical data suggest that the granitoids have experienced the fractional crystallization of biotite + plagioclase + K- feldspar + apatite. Crystallization temperature is estimated as ca. 700°C, and pressure is between 0.71 kbar and 1.60 kbar. The monzogranite shows higher values of logfO2, △FMQ and △NNO than the biotite-bearing monzogranite, ranging from −19.76 to −11.71, −4.93 to +3.67 and −5.48 to +3.11, respectively. The fractional crystallization, together with high fO2, K-metasomatism and low evolution degree, provided favourable conditions for gold mineralization.

Information

Type
Original Article
Copyright
© The Author(s), 2023. Published by Cambridge University Press
Figure 0

Figure 1. (a) Tectonic map of the North China Craton (Jiang et al.2013), CAOB – Central Asian Orogenic Belt, SLS – Solonker suture, QDOB – Qinling-Dabie Orogenic Belt. (b) Sketch geological map of the LX district showing the distribution of gold deposits and igneous rocks with ages (modified from Xiong et al.2017; Zhang et al.2020). (c) Sketch map of BZG at the 30m level with photos of contact relationship. Intrusive rocks: BJ – Baijiadian, DS – Dushan, DSZ – Dashizhuzi, GJ – Gaojiadian, GSZ – Gushanzi, HK – Hekanzi, JG – Jinbaogou, JJ – Jiajiashan, LW – Luowenyu, MJ – Maojiagou, NX – Niuxinshan, QS – Qingshankou, SJ – Sanjia, TZ – Tangzhangzi, XY – Xiaoyingzi, YE – Yu’erya, YZ-Yangzhangzi, ZJ-Zhaojiazhuang.

Figure 1

Figure 2. Photographs of BZGs. (a) and (b) Biotite Monzogranite. (c) Sericitization. (d) Biotite-bearing monzogranite. (e) and (f) Monzogranite. (g) Silicification (quartz metasomatic K- feldspar). (h) Potassium (K- feldspar metasomatic plagioclase). Ser – sericite; Bi – biotite; Kf – K- feldspar; Pl – plagioclase; Q – quartz.

Figure 2

Figure 3. U–Pb concordia diagrams with cathodoluminescence (CL) images of representative zircons analysed and zircon chondrite-normalized REE patterns from the BZGs. (a) and (b) Biotite-bearing monzogranite (sample No. 0-8). (c) and (d) Monzogranite (sample No. -30-7). Chondrite values are from Sun and McDonough (1989).

Figure 3

Figure 4. Classification diagrams of samples from the BZGs. (a) QAP diagram (Le Maitre, 2002). (b) An-Ab-Or diagram (Barker & Millard, 1979). (c) (Na2O +K2O-CaO) vs. SiO2 (Frost et al.2001). (d) A/NK vs. A/CNK diagram (Manilar & Piccoli, 1989).

Figure 4

Figure 5. Chondrite-normalized rare earth element (REE) patterns (a, c, and e) and primitive-mantle-normalized trace element spider diagrams (b, d, and f) are shown. Chondrite values and primitive-mantle values are from Sun and McDonough (1989).

Figure 5

Figure 6. Ternary plots of plagioclase compositions (after Smith, 1974), and the right is a 5× magnification of the projection area of the left.

Figure 6

Figure 7. Correlation diagram of plagioclase compositions.

Figure 7

Figure 8. Genesis (a, after Nachit et al.2005) and classification (b, after Foster, 1960) diagram of biotite.

Figure 8

Figure 9. Variation of ω(SiO2) % vs. ω(TiO2) %, ω(Al2O3) %, ω(FeOT) %, ω(CaO) %, ω(P2O5) %, ω(MgO) %.

Figure 9

Figure 10. Diagrams of (a) TiO2 (wt%) versus Nb/Ta ratios, (b) P2O5 (wt%) versus REE (ppm) (after Wang et al.2017), (c) Sr (ppm) versus Rb (ppm), (d) Sr (ppm) versus Ba (ppm), (e) Eu (ppm) versus Rb/Ba ratios and (F) Ba (ppm) versus Rb/Sr ratios, showing the fractional crystallization of different minerals. See Supplementary Table S7 for the partition of those minerals. Symbols are: Mt = magnetite; Sp = spinel; Hb = hornblende; Pl = plagioclase; Kf = K- feldspar; BI = biotite; Ap = apatite.

Figure 10

Figure 11. (a) Variation of Sr/Y vs. Y. Fields for adakites and island arcs are from Defant and Drummond (1990). (b)Variation of (La/Yb)N vs. YbN. Data are normalized (N) to C1 (chondrite) values of Sun & McDonough (1989). Fields for adakites and island arc magma are from Martin (1999).

Figure 11

Figure 12. Fe2+-Fe3+-Mg2+ ternary diagram (after Wones, 1989) of the biotite from the BZGs.

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