Origin of the Eocene porphyries and mafic microgranular enclaves from the Beiya porphyry Au polymetallic deposit, western Yunnan, China: Implications for magma mixing/mingling and mineralization

et al. 2018

Minerals

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The Beiya Au deposit is the largest Cenozoic Au deposit in the Jinshajiang-Ailaoshan porphyry metallogenic belt. Numerous studies document that high water content and fO2 are vital factors for the generation of Au mineralization. In this belt, only the Wandongshan and Hongnitang districts are considered to be of economic importance, while the other districts, such as Bailiancun, are barren. So in order to reveal the importance of water content and oxidation state for Beiya porphyry-style Au mineralization, the amphiboles and zircons compositions are used to evaluate the physicochemical conditions (e.g., pressure, temperature, fO2, and water content) of the Wandongshan ore-fertile porphyries and Bailiancun ore-barren porphyries observed in the Beiya Au deposit. The results show that the water content of the Wandongshan parent magma (≤4.11 ± 0.4 wt %) are slightly higher than those of the parent magma at Bailiancun (≤3.91 ± 0.4 wt %), while the emplacement pressure of the Wandongshan parent magma (31.5–68.6 MPa) is much lower than that of the parent magma at Bailiancun (142.3–192.8 MPa), indicating that the Wandongshan magma reached water saturation earlier. In addition, the Wandongshan porphyries crystallized from more oxidized magma (average of ΔFMQ = +3.5) with an average temperature of 778 °C compared to the Bailiancun porphyries (average of ΔFMQ = +1.5) with a mean magmatic temperature of 770 °C. The Ce4+/Ce3+ ratio of zircon in the Wandongshan ore-related intrusions (average Ce4+/Ce3+ of 62.00) is much higher than that of the Bailiancun barren porphyries (average Ce4+/Ce3+of 23.15), which further confirmed Wandongshan ore-related magma is more oxidized than the Bailiancun barren magma. Therefore, melts that are more enriched in water and with a high oxidation state will be more fertile to form an economic porphyry-style Au system.

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Implications For Au Mineralizationmentioning

confidence: 99%

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Importance of Magmatic Water Content and Oxidation State for Porphyry-Style Au Mineralization: An Example from the Giant Beiya Au Deposit, SW China

Bao

et al. 2018

Minerals

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“…Potassic magmatic suites are widely exposed in the general vicinity of Jinshajiang-Ailaoshan Suture (Figure 1). Previous studies mainly focused on the northwestern margin of the Yangtze Craton in central Jinshajiang-Ailaoshan Suture Ding, Hou, & Zhang, 2016;He et al, 2016;Hu et al, 2004;Liang et al, 2006; in the Jinshajiang-Ailaoshan suture and its vicinity (Deng, Wang, Li, & Santosh, 2014, Li, 2014. The magmatic belt extends 50 km westward to the hinterland of Simao terrane and 150 km eastward to the Yangtze Craton (Figure 1; Zeng, Mo, & Yu, 2002;Guo et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Petrogenesis of the Cenozoic Lianhuashan pluton (SW China): Constrained by zircon U–Pb geochronology, Lu–Hf isotope, and geochemistry

Wang

et al. 2019

Geological Journal

Potassic magmatic rocks provide significant insights in understanding of mantle composition, evolution, and interaction with crust. Potassic magmatism along the Jinshajiang-Ailaoshan Paleo-Tethyan suture has drawn much attention. Whereas igneous intrusion in the Simao terrane, west to Jinshajiang-Ailaoshan potassic magmatic belt has rarely been investigated. Hence, we present zircon U-Pb ages and Lu-Hf isotope and whole-rock geochemistry for the Lianhuashan pluton. Zircon U-Pb dating from monzonite and quartz monzonite porphyry yield ages of 33.6 ± 0.2 and 33.5 ± 0.3 Ma, respectively. Monzonites are characterized by high K 2 O (4.93-5.16%) and K 2 O/Na 2 O (1.46-1.71), high Y (22.90-23.80 ppm), and Yb (1.87-2.21 ppm), relatively enrichment of light rare earth element (LREE). Zircons from monzonites show ε Hf (t) values ranging from −1.1 to +0.6 and crustal model ages (T DM C ) between 1.04 and 1.15 Ga. These geochemical features suggest that parent magmas of the rocks originated from a metasomatized lithospheric mantle. Quartz monzonite porphyries are characterized by high Sr (836.00-1,529.00 ppm), Sr/Y (70.85-99.93) and La/Yb (32.31-49.83), low Y (11.80-15.60 ppm), and Yb (0.95-1.30 ppm), enrichment in LREE and depletion in heavy rare earth elements (HREE).Quartz monzonite porphyries have higher Mg # , MgO, Ni, and Cr contents than the lower crust-derived adakite-like rocks. It is suggested that they were derived by variable degree of mixing between lower-crustal melts and mafic magmas. Based on petrology and geochemistry features, the following evolution process are concluded.During the Neoproterozoic, metasomatic-enriched mantle magma resulted from the bisubduction of oceanic plate; meanwhile, the crust thickened, and juvenile lower crust formed. During late Eocene, hot asthenosphere upwelled and K-rich mafic magmas resulted from the decompression of delamination, followed by magmatism emplacing, crystallizing, and the forming of the Lianhuashan pluton. KEYWORDS Lianhuashan potassic pluton, magmatism model, metasomatized lithospheric mantle, the Sanjiang Orogen ). However, few detailed investigations have been carried out on the Lianhuashan pluton in the Simao terrane, which restricts understanding of the deep crust-mantle interaction, the genesis, and dynamic processes of potassic magmatic rocks in the Jinshajiang-Ailaoshan Suture. The Lianhuashan pluton is part of the Jinshajiang-Ailaoshan potassic magmatic belt and a representative pluton developed in the Lanping basins. Despite of few geological and geochemical researches on the Lianhuashan pluton since the 2000s (Dong et al., 2005;Liu et al., 2017), the magma source, evolution, and the tectonic setting are still obscure. This is partly due to the lack of precise geochemical data and integrated studies. In this paper, we present zircon LA-ICP-MS U-Pb age, Lu-Hf isotope, and whole-rock geochemistry for the Lianhuashan pluton with a view to (1) constrain the crystallization age, (2) reveal the magma source and magma evolution, and (3) construct a geodynamic ...

Geochronology and geochemistry of the Tongjige granodiorites in the Jinshajiang suture zone, SW China: Constraints on petrogenesis and tectonic evolution of the Palaeo‐Tethys Ocean

Zhang

et al. 2020

Geological Journal

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The Jinshajiang suture zone (JSZ) is one of the most significant tectonic zones in the eastern Tethys area. A large number of plutons are regarded as the result of tectono‐magmatic activities associated with the evolution of the Palaeo‐Tethys Ocean. The Tongjige pluton in the central part of JSZ can indicate the magmatism and its geodynamic evolution. The Tongjige pluton (225.6 Ma) consists mainly of granodiorite with abundant coeval mafic microgranular enclaves (MMEs) (226.1 Ma). The host granodiorite is calc‐alkaline and typical I‐type, with SiO2 contents ranging from 65.75 to 66.91 wt%. The MMEs have relatively high MgO (4.00–4.07 wt%) and Fe2O3T (9.27–9.40 wt%) abundances and low SiO2 (53.59–53.87 wt%). Both MMEs and host granodiorites are characterized by the enrichment of light rare earth elements and depletion of heavy rare earth elements. They are also negative in Eu and enriched in Th and U, which are consistent with the trace element characteristics of typical island‐arc magmatite. The zircon Hf(t) values (−3.48 to −0.31) are negative, with the model ages of 1.3–1.2 Ga. These petrographic and geochemical characteristics indicated that the Tongjige pluton was derived from the melting of an ancient lower crust and underwent the process of mafic‐felsic magmatic mixing in the post‐collision background. The Triassic granitoids in the JSZ show a temporal–spatial relationship with the subduction zone, which constrain the evolution of the Palaeo‐Tethys Ocean. The mixing mechanism of the Tongjige pluton is associated with the break‐off of a subducted slab, which triggered subsequent upwelling of asthenosphere beneath accreted arc fragments and induced underplate of lithospheric mantle‐derived magmas and mixed with the lower crust‐derived felsic magma. In general, the Late Triassic pluton recorded significant crustal growth and continental development, marking the final stage of subduction‐related magmatism in the JSZ region, after which the region entered into a stage of post‐collision evolution.