Geology and Cu mineralization in the Jiangbian deposit of the Yangla polymetallic orefield, SW China: In situ trace element constraints and s-pb sulfide isotopic compositions

Abstract

The Jiangbian deposit is an important component of the Yangla Cu–polymetallic orefield in the central area of the Jinsahjiang suture zone (JSZ), Sanjiang region, southwestern China, comprising 0.53 Mt Cu, 0.70 t Au, and 39 t Ag at 0.94 %, 0.13 g/t, and 14.28 g/t, respectively. The layered and veined Cu orebodies within the contact or fracture zone between the Triassic granitoid plutons (granodiorite) and Devonian wall rocks (meta-quartz arenite, sandy slate and marble). Three ore stages: Pre-ore (andradite and diopside), syn-ore (sulfides, quartz, and calcite), and supergene have been preliminarily identified in the Jiangbian Cu mineralization. In this study, in-situ trace element and S-Pb isotopic compositions of ore-related sulfides were systematically determined and used to precisely constrain metals source, ore genesis and ore-forming processes. Trace elemental geochemistry of sulfides from the Jiangbian deposit indicate that various trace elements are predominantly present in sulfides as solid solutions and nano-inclusions, with less micro-inclusions.

The calculated ore deposition temperature mainly ranged from 281 to 371 ℃ (avg. 319 ℃) based on the trace element geochemistry of sulfides, suggesting that the Cu ore-related sulfides formed at medium–high temperature conditions. Arsenopyrite, pyrite, chalcopyrite, and sphalerite from the Jiangbian deposit show uniform δ³⁴S values ranging from –7.29 to + 3.18 ‰ (avg. –2.18 ‰; n = 40) and highly similar to the sulfides (δ³⁴S ≈ 0 ± 3.0 ‰) from the Linong and Lunong Cu deposits, a typical magmatic-derived S. The in-situ Pb isotopes of galena exhibited narrow ranges (²⁰⁶Pb/²⁰⁴Pb = 18.305–18.317, ²⁰⁷Pb/²⁰⁴Pb = 15.675–15.682, and ²⁰⁸Pb/²⁰⁴Pb = 38.626–38.647; n = 10) and highly similar to that of typical skarn Cu-Pb-Zn ores from Linong-Luong Cu deposit, indicating that the metals originated from a mixed source of upper-lower crustal materials. Considering the new elemental and S-Pb isotopic data of these sulfides combined with the Cu orebodies are spatially and genetically related to Triassic granodiorite and skarn, we preliminarily propose that the Jiangbian deposit is a typical intrusion-related skarn Cu deposit. Studying the genesis of the Jianbian deposit provides a better understanding of the Cu mineralization potential of the Yangla Cu–polymetallic orefield.