Fluid source and metal precipitation mechanism of sediment-hosted Chang'an orogenic gold deposit, SW China: Constraints from sulfide texture, trace element, S, Pb, and He-Ar isotopes and calcite C-O isotopes

Abstract

The source of fluids and mechanism of metal precipitation in sediment-hosted, disseminated orogenic gold deposits are ambiguous. Pyrite texture, trace element, S, Pb and HeAr isotope compositions of sulfides and CO isotope data of calcite from Chang'an orogenic gold deposit in the Ailaoshan orogenic belt, SW China, were studied to provide a new genetic model for the sediment-hosted orogenic gold deposit, and furthering knowledge of the source of fluids and their mechanism of metal precipitation. Orebodies at Chang'an are mainly hosted by Ordovician turbidite with minor in Oligocene syenite. Two stages of mineralization have been identified in the deposit: stage I disseminated quartz-arsenopyrite-pyrite, and stage II veined quartz-calcitepolymetallic sulfides. Five generations of pyrite have been identified in turbidite: preore syn-sedimentary pyrite, pyI-1 and pyI-2 in stage I, and pyII-1 and pyII-2 in stage II, and an unzoned pyrite population developed in syenite. PyI-1 commonly overgrows synsedimentary pyrite with irregular boundaries and contains arsenopyrite, galena, chalcopyrite and electrum inclusions along the boundaries. PyI-1 is overgrown by thin and inclusion-free pyI-2, and crosscut by pyII-1, which is rimmed by pyII-2. The syn-sedimentary pyrite is distributed parallel to the sedimentary bedding and contains As (620.8 ppm), Pb (61.6 ppm), Ni (59.8 ppm), Mo (54.4 ppm), Co (23.4 ppm), and Cu (13.0 ppm) with low Au content of 0.06 ppm. This pyrite has δ 34 S values of-18.1 to +30.4 ‰ and high radiogenic Pb isotope ratios (average 206 Pb/ 204 Pb, 207 Pb/ 204 Pb and 208 Pb/ 204 Pb of 19.05, 15.86 and 39.87, respectively). PyI-1 and coexisting arsenopyrite are enriched in invisible Au (up to 227.1 ppm and 353.3 ppm, respectively), This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Lithosphere architecture characterized by crust–mantle decoupling controls the formation of orogenic gold deposits

“…The lamprophyre dikes have narrow ranges of 206 Pb/ 204 Pb (18.50–18.59), 207 Pb/ 204 Pb (15.60–15.65) and 208 Pb/ 204 Pb (38.75–38.84), which overlap with those of gold-related sulfides in the Ailaoshan gold belt ( Supplementary Data ) [ 91 , 92 ]. The gold-rich rims of ore pyrites uniformly display a limited range of δ 34 S values around 0‰ [ 6 , 93 , 94 ], similar to those expected for a mantle source for the lamprophyre dikes that are spatially related to the gold deposits.…”

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.…”

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.…”