Sulfur content and isotopic ratio of Cambro-Ordovician carbonate rocks from South Korea: A possible source for mesozoic magmatic-hydrothermal ore sulfur

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 delta(34)S values. The delta(34)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 delta(34)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 delta(34)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 delta(34)S value of +12.8 permil (n=24). The estimated Deltadelta(34)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. The SSS and sulfide sulfurs have often higher delta(34)S values than the Mesozoic-Cenozoic ore sulfur (Ishihara et al., 2000). Since carbonate rocks are very reactive with circulating hydrothermal ore solution, high delta(34)S values of the Korean ore deposits might be caused to some extent by S-34 enrichment from the host carbonates, resulting in the low SSS contents observed.