Search

Shuangqishan and Xiaoban Au deposits: chromian sericite is related to gold mineralization and the product of the late stage of Late Jurassic (ca. 153–146 Ma) magmatism. [Display omitted] • 40Ar/39Ar ages of chromian sericite in Shuangqishan and Xiaoban gold deposits are (146.21 ± 1.59 Ma) and (149.28 ± 1.26 Ma) respectively. • The gold mineralization is related to the late stage of Late Jurassic (ca. 153–146 Ma) magmatism. • The granite porphyry, chromian sericite, and Cr elements anomaly are the significant gold ore-prospecting indicators. The shuangqishan and Xiaoban are the two largest gold deposits in the Dehua-Youxi-Yongtai (DYY) mineral concentrated area of central Fujian Province. They are located adjacent to each other and show similarities in geological background, metallogenic characteristics and mineral assemblage. The orebodies are hosted in the Caledonian alaskite and the metamorphic rock of Neoproterozoic Daling Formation. Gold mineralization is closely related to pyritization, silicification, and micatization, with native gold mostly occurring in the cracks of pyrite, which formed slightly later than pyrite. In this paper, geochronologic work has been conducted on the granite porphyry and chromian sericite related to gold mineralization in the two deposits to determine the age of mineralization and discuss the genesis of the deposits. The chromian sericite is a hydrothermal alteration product of granite porphyry, and is a main indicator of gold enrichment. The plateau 40Ar/39Ar isotopic dating of chromian sericite indicates the mineralization ages of the two deposits were 146.21 ± 1.59 Ma and 149.28 ± 1.26 Ma respectively, similar to the LA-ICP-MS zircon U-Pb age(149.0 ± 1.0 Ma) of granite porphyry in the mining district. The ages of the chromian sericite and granite porphyry point to a close link with a large-scale magmatism event at the late stage of Late Jurassic in central Fujian. Based on the geology, alteration, mineralization and chronology characteristics, the Shuangqishan and Xiaoban gold deposits can be classified as the magmatic hydrothermal type gold deposits. [ABSTRACT FROM AUTHOR]

The Dehua Au-polymetallic ore cluster, as one of the most important area in the Wuyi Au-Cu-Mo metallogenic belt, consists of many large to middle sized epithermal Au deposits and recently discovered porphyry Cu-Mo deposits. We first study the geochronology and geochemistry characteristics of the Cu-Mo mineralization-related Xianyang granite porphyry to constrain its petrogenesis, tectonic setting and metal endowment. LA-ICP-MS zircon U-Pb dating yield a precise age of 157.2 ± 0.8 Ma for the Xianyang granite porphyry, indicating that the granite porphyry was emplaced during the Late Jurassic. The Xianyang granite porphyry was suggested to be generated under continental arc setting, associated with subduction of the paleo-Pacific slab beneath the South China Block. The Xianyang granite porphyry belongs to the high-K calc-alkaline series, with SiO 2 of 71.16–72.02 wt% and K 2 O of 4.28–4.69 wt%. It shows light rare earth element-enriched distribution patterns with (La/Yb) N of = 9.74–13.93, enrichment in large ion lithophile elements, but depletion of high field strength elements, with negative Nb, Ta and Ti anomalies, suggesting an arc magma geochemical affinity. It has lower initial 87Sr/86Sr ratios of 0.7079–0.7086 and relatively higher ε Nd (t) and ε Hf (t) values of −8.03 to −7.69 and − 8.86 to −5.48, respectively, than those of basement rocks of the Cathaysia block, suggesting that it was most likely generated by partial melting of the regional ancient crustal materials, with the involvement of asthenosphere mantle-derived materials. The Xianyang granite porphyry has remarkably high zircon Ce4+/Ce3+ values of 119–404 (mean = 245) and Eu N /Eu N * values of 0.37–0.60 (mean = 0.51), indicating a high oxygen fugacity, which is favor of the formation of the Xianyang porphyry Cu-Mo mineralization. Combining with published research results for regional subvolcanic rocks-related epithermal Au deposits, the porphyry Cu-Mo deposits and epithermal Au deposits in the Dehua ore cluster share similar petrogenetic-metallogenic ages and magma sources in the continental arc setting during the Late Jurassic period. The identification of the coeval porphyry-epithermal Cu-Mo-Au metallogenic system in the Dehua ore cluster highlights the possibility of finding the hidden porphyry Cu-Mo orebodies beneath the discovered epithermal Au deposits. [Display omitted] • The Xianyang granite porphyry were formed during the Late Jurassic. • The Xianyang granite porphyry was generated under continental arc setting. • The Xianyang granite porphyry had high oxygen fugacity. • The porphyry-epithermal Cu-Mo-Au metallogenic system was proposed. [ABSTRACT FROM AUTHOR]