Sulfur Content and Isotopic Ratio of Cambro‐Ordovician Carbonate Rocks from South Korea: A Possible Source for Mesozoic Magmatic‐hydrothermal Ore Sulfur

<jats:p><jats:bold>Abstract: </jats:bold> Carbonate rocks of Cambrian (18 samples) and lower‐middle Ordovician (11 samples) ages from South Korea were analyzed for sulfur contents of structurally substituted sulfate (SSS) and sulfides and their δ<jats:sup>34</jats:sup>S values. The δ<jats:sup>34</jats:sup>S values of SSS ranging from +25.9 to +45.2 permil, are averaged as +33.6 and +33.5 permil for the Cambrian and Ordovician rocks, respectively, which indicate high δ<jats:sup>34</jats:sup>S values of the Cambro‐Ordovician seawater. The SSS contents in the carbonate rocks are low being 2.9 to 17.3 ppm S (averaged as 7.0 ppm S). Sulfide sulfur, on the contrary, is much abundant containing 3 to 1,880 ppm S and the δ<jats:sup>34</jats:sup>S values range widely between –17.6 and +31.1 permil. Sulfide sulfur of the studied rocks excluding impure carbonates has an average content of 187 ppm S and δ<jats:sup>34</jats:sup>S value of +12.8 permil (n=24). The estimated δ<jats:sup>34</jats:sup>S (sulfate–sulfide) values, which range from 13.8 to 25.4 permil in general with a few exceptions from 36.5 up to 52.3 permil for some impure carbonates, may provide evidence for the persistent oceanic anoxia with its temporary recovery during the Cambro‐Ordovician time.</jats:p><jats:p>The SSS and sulfide sulfurs have often higher δ<jats:sup>34</jats:sup>S values than the Mesozoic‐Cenozoic ore sulfur (Ishihara et al., 2000). Since carbonate rocks are very reactive with circulating hydrothermal ore solution, high δ<jats:sup>34</jats:sup>S values of the Korean ore deposits might be caused to some extent by <jats:sup>34</jats:sup>S enrichment from the host carbonates, resulting in the low SSS contents observed.</jats:p>