Control of magmatic oxidation state in intracontinental porphyry mineralization: A case from Cu (Mo–Au) deposits in the Jinshajiang–Red River metallogenic belt, SW China

Cao

et al. 2018

Minerals

Two small-sized granitic plutons, outcropped in Xianghualing ore field, South Hunan (South China), have a close relationship with the super large-scale Sn-W polymetallic mineralization in this ore field. The Laiziling and Jianfengling plutons are composed of medium-to coarse-grained two-mica and coarse-grained biotite granites, respectively, and have zircon U-Pb ages of 156.4 ± 1.4 Ma and 165.2 ± 1.4 Ma, respectively. Both of the Laiziling and Jianfengling granites are characterized by extremely similar elemental and Lu-Hf isotopic compositions with high contents of SiO 2 , Al 2 O 3 , Na 2 O, K 2 O, high A/CNK ratios, negative ε Hf (t) values (ranging from −3.86 to −1.38 and from −5.44 to −3.71, respectively), and old T DMC ages (ranging from 1.30 to 1.47 Ga and from 1.32 to 1.56 Ga, respectively). These features indicate that they both belong to highly fractionated A-type granites, and were formed in an extensional setting and from the same magma chamber originated from the Paleoproterozoic metamorphic basement of South China with a certain amount of mantle-derived magma involved with temperatures of ca. 730 • C and low oxygen fugacity.

Section: Oxygen Fugacities and Fractional Crystallizationmentioning

confidence: 99%

Section: Oxygen Fugacities and Fractional Crystallizationmentioning

confidence: 99%

Geochronology, Petrology, and Genesis of Two Granitic Plutons of the Xianghualing Ore Field in South Hunan Province: Constraints from Zircon U–Pb Dating, Geochemistry, and Lu–Hf Isotopic Compositions

Cao

et al. 2018

Minerals

“…As a consequence of this strike-slip, lithospheric-scale extension has occurred, causing a set of secondary NNW-trending strike-slip faults and folds, and the emplacement of numerous alkali-rich intrusions along the Jinshajiang suture zone [31][32][33]. These intrusions form a 2000-km-long and 50-to 80-km-wide alkaline magmatic belt, and are associated with several important porphyry and skarn polymetallic (Cu, Au, Mo, Zn, Pb, and Ag) deposits [34,35] in the Jinshajiang-Ailaoshan metallogenic belt (Figure 1b) [7], from north to south: the Yulong Cu, the Beiya Au, the Machangqing Cu-Mo-Au, the Yao'an Au, the Habo Cu-Mo-Au, and the Tongchang Cu-Mo deposits.…”

Section: Geological Settingmentioning

confidence: 99%

“…Au solubility was investigated as a function of f O 2 in sulfur-saturated silicate melts [12], indicating Au solubility in sulfur-free silicate melt increases with increasing of f O 2 [48]. In addition, high f O 2 favors sulfur as sulfate dissolved in the evolved magmas and suppresses magmatic sulfide precipitation [4,7], which can cause sequestration of metals before they partition into the aqueous phase [10]. On the other hand, a high H 2 O content and a low pressure results in the Wandongshan parental magma reaching water saturation easier, because water solubility increases with increasing pressure [44], hence ensuring exsolution of aqueous volatile phases and the partitioning of Au between sulfides and silicate melt efficiently [12,49,50].…”

Section: Implications For Au Mineralizationmentioning

confidence: 99%

“…It's widely accepted that high water content (>4 wt %) [2,3] and a high oxidation state (>FMQ + 1.3-2) [4,5] of the magma are critical factors for the generation of Cu-Au mineralization. The solubility of Cu and Au in hydrous silicate melts was proven to be affected by the amount and proportion of dissolved sulfate and sulfide in S-bearing magma, whereas f O 2 controls the speciation of sulfur [5][6][7]. Under high f O 2 conditions, the majority of sulfur exists as SO 2 or SO 4 2− with very low concentrations of S 2− in a magma [6], which prevents saturation of immiscible Cu-and Au-sulfides during magmatic fractionation [4,6].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Self Cite

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.

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

Self Cite

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.