Mineral Assemblages, Fluid Inclusions, Pyrite Trace Elements, and S-O Isotopes of Gold Ores From the Cenozoic Daping Deposit, Sw China: Implications for the Genesis of Complex Orogenic Lode Gold Systems

Abstract

The Cenozoic Daping orogenic gold deposit, on the southeastern margin of the Tibetan Plateau, China, contains four lode types that contain a total of 55 t gold. Pyrite-chalcopyrite–dominated (VA) and galena-dominated polymetallic sulfide veins (VB) hosted by Neoproterozoic diorite are associated with quartz-sericite-chlorite ± epidote (± barite in VB veins) alteration. Pyrite-dominated (VC) and pyrite-pyrrhotite–dominated veins (VD) hosted by Silurian dolostone (intercalated with carbon-bearing argillaceous limestone in VD veins) are related to ankerite-siderite-quartz ± sericite alteration. All have free gold spatially and temporally associated with pyrite, chalcopyrite, galena, pyrrhotite, or quartz. Most VA and VB veins are controlled by steeply SW-dipping ductile-brittle shear zones with jigsaw wall-rock breccias in VB veins, whereas gently SW-dipping faults host VC and VD veins. There are some significant differences between different veins: (1) there were more acidic mineralization conditions for VA and VB veins relative to VC and VD veins, and more oxidized conditions for VB veins relative to other veins; (2) pyrite is rich in Co-Ni in VA and VB veins, compared to enrichment in As-Au for VC and VD veins; (3) sulfide δ34S values of 3.2 to 11.8‰ (median 8.2‰) for VA, VC, and VD veins contrast with −4.6 to +0.9‰ (median 0‰) for VB veins. The contrasting mineral parageneses, pH values, and pyrite geochemistry can be attributed to fluid-rock interaction as evidenced by replacements of amphibole by sericite in diorite and dolomite by ankerite and siderite in dolostone. The lower (~8‰) VB sulfide δ34S values and interpreted fluid oxidation relative to other veins, together with the presence of breccias and barite, can be explained by phase separation due to flash vaporization triggered by extreme hydrofracturing. The consistent NW-trending vein sets, similar median S-O isotope ratios of original ore fluids, and lack of multistage overlap of gold mineralization and alteration zones support a single-source fluid for gold mineralization at Daping. This study is diagnostic rather than just indicative in that it systematically and quantitatively portrays the mineralization diversity in an orogenic gold system formed by a single-source fluid regulated by the external fluid-rock interactions and internal hydrofracturing.

The Formation of the Jiaodong Gold Province

“…Gold mineralization is a process associated with structural deformation, fluid flow, fluid-rock reaction, and related changes in physico-chemical conditions of oreforming fluids (e.g., Sibson et al, 1988;Cox, 1995;Sibson, 1996;Sausse et al, 2001;Williams-Jones et al, 2009;Weatherley and Henley, 2013;Peterson and Mavrogenes, 2014;Yang et al, 2021Yang et al, , 2022. Many studies have demonstrated that structure-fluid feedback produces and/or destroys permeability by mineral dissolution and/or precipitation with mass and volume changes (Fig.…”

“…Mineralization styles mainly occur as thick quartz veins, quartz-vein arrays, and replacement and disseminated ores, which are mostly hosted in the greenschist-facies sedimentary or mafic rocks. The Au of orogenic gold deposits precipitate from the low-salinity H 2 O-CO 2 (CH 4 , N 2 ) fluid through the sulfidation during fluid-rock interaction or fluid phase separation during hydrofracturing (Li et al, 2019a(Li et al, , b, 2022Yang et al, 2022), and the host structures mainly include anticlines, fault jogs or fault intersections (Fig. 12b; Groves et al, 1998Groves et al, , 2005Groves et al, , 2018Goldfarb and Groves, 2015;Wang et al, 2020bWang et al, , 2021.…”

Enhancing Geological Understanding and Identifying Gold Anomalies in the Ailaoshan Orogen

“…1). The host rocks for these Au deposits are Triassic sandstone and slate for Xiaoshuijing, Carboniferous to Triassic ophiolitic mé lange for Zhenyuan and Jinchang, Permian dolostone for Tongchang, and Neoproterozoic diorite for Daping, Ordovician turbudite for Chang'an (Li et al, 2019(Li et al, , 2023Wang et al, 2020;Yang et al, 2021bYang et al, , 2023. More geological characteristics for each deposit can be found in Table 1.…”

“…The Ailaoshan Orogen (ALS), located in the southeastern Tibet Plateau with a complex geological background, is one of the rare Cenozoic orogenic gold (Au) belts globally (Goldfarb et al, 2001;Wang et al, 2020), with reserves of about 200 t Au (Yang et al, 2023). This study focuses on the orogen and applies Scb, FA, C-A model, and lineament density analysis across the entire region and separate subzones distinguished on their geological background, Scb, or ore cluster fields, such as the Zhenyuan-Jinchang and Daping-Chang'an for contrast.…”

Geology and Geochemistry of K‐feldspar Veins in Lamprophyre at the Zhenyuan Gold Deposit, Yunnan, Southwest China: Implications for Gold Mineralization

“…Abundant Cenozoic lamprophyres and hydrothermal gold deposits are widely distributed in the Ailaoshan tectonic belt, SW China. Previous studies focused on the alteration, ore mineralogy, and ore fluid compositions of these hydrothermal gold deposits (Deng et al, 2015b;Zhang et al, 2019;Wang Y et al, 2020;Yang et al, 2023), and considered that these gold deposits have intimately temporal and spatial relationships with lamprophyres (Chen et al, 2014;Wang Q et al, 2020). Sulfides-bearing K-feldspar veins, which connect lamprophyres and hydrothermal gold deposits, have not been reported in the Ailaoshan tectonic belt.…”