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This study reports the high-precision silver (Ag) isotopic compositions of the dominant Ag-bearing mineral (galena) in the representative Zhaxikang polymetallic deposit, which experienced a complex ore-forming process that can be divided into two episodes composed of six stages (first episode: Pb–Zn mineralization, stages 1 and 2; second episode: Sb mineralization, stages 3 to 6). The objective of this case study is to investigate the Ag isotopic fractionation mechanisms in a hydrothermal ore-forming system and explore the potential application of Ag isotopes. The earlier-generated stage 2 galena (0.17–6.07‰) has higher δ109AgNIST 978 Ag values with a significantly broader range in comparison to the subsequent stage 3 galena (–3.65 to 2.27‰). The δ109AgNIST 978 Ag values of galena also decrease from deep to shallow along with the trend of orebody V. These temporally and spatially decreasing trends indicate that the second episode of ore-forming fluid overprinted the first episode of mineralization along with the trend of orebodies from deep to shallow within the Zhaxikang orefield. A simple triple-phase separation model captures the temporal and spatial patterning of the data resulting from Ag isotopic fractionation, which is most likely related to the solid–liquid-vapor dynamics of the ore-forming fluid. According to approximate theoretical calculations, there is still great prospecting potential for Ag at depth within the Zhaxikang orefield. In summary, the Ag isotopes have the potential to trace phase changes, monitor ore-forming fluid evolution, constrain ore formation processes, and provide insights into ore exploration. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Mazhala Au-Sb deposit in South Tibet was constrained at ca. 35 Ma. • Mazhala apatite belongs to fluorapatite having F contents of 2–4%. • Mazhala apatite is rich in MREE but depleted in LREE- and HREE. • Mazhala apatite have δ18O values in the range of 16-19‰. • The Mazhala Au-Sb deposit was mainly precipitated from metamorphic water. Due to lack of suitable datable minerals, timing of the Mazhala Au-Sb deposit in South Tibet remains unresolved. Also, previous geochemical studies suggest an ambiguous conclusion on the source of ore-forming fluid, with diverse viewpoints of magmatic water, mixed magmatic–meteoric water or mixed metamorphic-meteoric water, respectively. In this study, hydrothermal apatite U-Pb dating constrains the Mazhala Au-Sb deposits to have formed at ca. 35 Ma, consistent with the timing of Eocene leucogranite intrusions in South Tibet. The Mazhala Au-Sb mineralization occurred during the main collision stage to late collision stage in Eocene to Oligocene, and predates the Cuonadong Sn mineralization in South Tibet which occurred during the crustal extension stage in Miocene. An EPMA analysis shows the apatite belongs to fluorapatite that have F contents in the dominant range of 2–4%. The Mazhala apatite displays an overall MREE enrichment and LREE- and HREE depletion distribution pattern with positive Eu anomalies, and have δ18O values dominantly in the range of 16-19‰ with a mean δ18O‰ value of 17.74 ± 0.15‰ (2σ), which suggest a relatively homogenous chemical composition for the ore forming fluids with a relatively stable temperature regime. In combination with previous temperature estimates, the ore forming fluids are inferred to have a dominant δ18O fluid value of 13-16‰, which overlap with metamorphic water. The combined age and geochemical data suggest Eocene leucogranite intrusion induced metamorphic fluid circulation within Paleozoic-Mesozoic metamorphic sedimentary rocks around the study area, which prompted precipitation of fluorapatite together with Au-Sb bearing pyrite and arsenopyrite in the Mazhala Au-Sb deposit. This study puts an emphasis on the contribution of metamorphic water as the dominant ore-forming fluid origin in the Mazhala Au-Sb deposit. In contrast, the close spatial and temporal association of the Cuonadong Sn polymetallic mineralization with the Miocene leucogranite intrusion-induced hydrothermal activity in the Cuonadong dome demonstrates that their genetic links, as was also evidenced by C-H-O-S-Pb isotope data that point to a dominant contritution of Miocene leucogranite to ore-forming fluid and materials for the Cuonadong Sn polymetallic ore deposits. As such, from a perspective of ore-forming model in South Tibet it be seen that during the main collision stage to late collision stage ore-forming fluid and materials were mainly derived from metamorphic water, whereas during the crustal extension stage, ore-forming fluid and materials were dominantly sourced from magmatic water. [ABSTRACT FROM AUTHOR]

The article focuses on a research paper on the geological study of Chalapu Goldfield in South Tibet, China. Topics discussed include the nature and source of ore-forming fluids of the gold deposit, gold and sulphide mineralization and the analysis of fluid inclusions suggesting high carbon dioxide content.

• Pyrite hosting visible gold is low in Au and As. • Gold-bearing pyrite was subject to brittle rather than ductile deformation. • Visible gold in pyrite did not result from remobilization of lattice gold. • Visible gold in pyrite was introduced by evolved ore fluids after host pyrite. Pyrite (FeS 2) is one of the most common hosts for gold (Au) in different types of gold deposits, including visible and invisible gold. For visible gold in pyrite, it remains unclear whether it resulted from remobilization of invisible gold in the gold-hosting pyrite or from external input. This paper reports a case study from the Zhaoxian gold deposit, which is the deep extension of the well-known Jiaojia gold deposit, in the Jiaodong gold province. The texture and composition of Au-bearing pyrite from the Zhaoxian deposit were studied with petrographic, Electron Back-Scattered Diffraction (EBSD) mapping, and Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) methods. Four types of pyrite (Py-1 to Py-4), corresponding to four generations of veins, i.e., the pre-ore V1, syn -ore V2 and V3, and post-ore V4, were distinguished. Py-2 is volumetrically the most abundant among the four, and is the main host of visible gold. LA-ICP-MS analyses of pyrite indicate that gold contents in most analysis points are below the detection limit, with measured Au contents ranging from 0.02 to 0.17 ppm (median 0.09 ppm) in Py-1, and 0.03 to 2.45 ppm (median 0.07 ppm) in Py-2. EBSD analyses indicate that pyrite (Py-2) display brittle deformation features including microstructures, lattice dislocation, and grain boundary displacement. Visible gold in Py-2 occurs in micro-fractures, cavities, and grain boundaries. The generally low contents of Au in pyrite, including Py-2, and the brittle deformation features, suggest that the visible gold grains did not result from remobilization of invisible gold from pyrite. Rather, the majority of gold was introduced by fluids after the formation of the gold-hosting pyrite. These fluids were derived from the same sources as those precipitating the gold-hosting pyrite, but were more evolved and enriched in Au. Circulation of these auriferous ore-forming fluids in microfractures of pyrite and interstitial space resulted in precipitation of visible gold. [ABSTRACT FROM AUTHOR]