Geology and D‐O‐C Isotope Systematica of the Tieluping Silver Deposit, Henan, China: Implications for Ore Genesis

Abstract

Abstract The Tieluping silver deposit, which is sited along NE‐trending faults within the high‐grade metamorphic basement of the Xiong'er terrane, is part of an important Mesozoic orogenic‐type Ag‐Pb and Au belt recently discovered. Ore formation includes three stages: Early (E), Middle (M) and Late (L), which include quartz‐pyrite (E), polymetallic sulfides (M) and carbonates (L), respectively. The E‐stage fluids are characterized by δD=−90‰, δ13Cco2=2.0‰ and δ18O=9‰ at 373°C, and are deeply sourced; the L‐stage fluids, with δD=−70‰, δ13CCo2=−1.3‰ and δ18O=−2‰, are shallow‐sourced meteoric water; whereas the M‐stage fluids, with δD=−109‰, δ13CCo2=0.1‰ and δ18O=2‰, are a mix of deep‐sourced and shallow‐sourced fluids. Comparisons of the D‐O‐C isotopic systematics of the E‐stage ore‐forming fluids with the fluids derived from Mesozoic granites, Archean‐Paleoproterozoic metamorphic basement and Paleo‐Mesoproterozoic Xiong'er Group, show that these units cannot generate fluids with the measured isotopic composition (high δ18O and δ13C ratios and low δD ratios) characteristic of the ore‐forming fluids. This suggests that the E‐stage ore‐forming fluids originated from metamorphic devolatilization of a carbonate‐shale‐chert lithological association, locally rich in organic matter, which could correspond to the Meso‐Neoproterozoic Guandaokou and Luanchuan Groups, rather than to geologic units in the Xiong'er terrane, the lower crust and the mantle. This supports the view that the rocks of the Guandaokou and Luanchuan Groups south of the Machaoying fault might be the favorable sources. A tectonic model that combines collisional orogeny, metallogeny and hydrothermal fluid flow is proposed to explain the formation of the Tieluping silver deposit. During the Mesozoic collision between the South and North China paleocontinents, a crustal slab containing a lithological association consisting of carbonate‐shale‐chert, locally rich in organic matter (carbonaceous shale) was thrust northwards beneath the Xiong'er terrane along the Machaoying fault. Metamorphic devolatilization of this underthrust slab provided the ore‐forming fluids to develop the Au‐Ag‐(Pb‐Zn) ore belt, which includes the Tieluping silver deposit.