| 论犬陆地壳断裂拗陷带中的华南型块状硫化物矿床 |
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| 引用本文：.1986.On The South China Type Massive Sulfide Ore Deposits Formed In Marine Fault Depression Troughs On The Continental Crust[J].Mineral Deposits,5(2):1~13 |
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| On The South China Type Massive Sulfide Ore Deposits Formed In Marine Fault Depression Troughs On The Continental Crust |
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| Abstract:There exist, among the post-Caledonian uplifts in South China, several Hercynian-Indosinian marine fault depression troughs developed on the mature continental crust by tensional forces. In Devonian or Carboniferous sequences of these belts, there occur a number of stratiform ore deposits, such as Chenmenshan, Wushan, Dongxiang and Yongping in Jiangxi Province, Mashan, Dongguashan, Xingqiao, Tongguanshan in Anhui Province, and Dajiangping, Xiniu and Dabaoshan in Guangdong Province. These deposits were formerly considered by many authors as typical post-magmatic hydrothermal products. Detailed field and laboratory investigations reveal that they are actually massive sulfide deposits related to upper Paleozoic submarine volcanism. Metals in the ore layers of these deposits often exhibit stratigraphical zonations which, from the bottom upwards, show a general sequence of Fe(S)-Cu-(Cu,W)-Pb, Zn-Mn, Fe(W), and the paragenetic sequence of ore-forming minerals indicate a progressive transformation from lower to higher temperature assemblages during the post-depositional metamorphism. Metals and sulfur in these deposits came from different sources: The high concentration of As in the ores and the Co/Ni ratios of pyrite higher than l suggest their affiliation with submarine volcanism and thermal springs and exhalations. The concordance of the single-stage model ages of the least radiogenic lead isotopes with the geological ages of the, ore-bearing strata implies the mantle origin of some of the metal, whereas the high content of radiogenic lead isotopes reveals that a considerable amount of the metal was derived from the upper crust. The wide range of S/Se ratios and δ34S values show that, in addition to the deep sources, the reduction of sea-water sulfates also contributed much to the sulfur in the ores, and the biogenic processes may also be postulated in some of the deposits. In spite of the similarity in tectonic settings to the Sullivan type deposits defined by Sawkins (1976), the deposits varieties and are associated with better in South China contain much more metal dated marine volcanic rocks than those of the Sullivan type, therefore, it would be more proper to take the South China type deposits as the representatives of the massive sulfide deposits developed on continental crust. The South China type massive sulfide deposits have a series of distinctive features in comparison with the Cyprus and Kuroko types. The trough sediments are usually predominated by great thickness of terrigenous clastics and carbonate rocks, and ore layers frequently occur in the transitional horizons from clastics to carbonates, Volcanism in these belts is relatively weak. Only thin layers of dacitic, rhyolitic and basaltic lavas and volcanoclastic rocks are found in certain places within the ore-containing sequences. Andesitic rocks are of little sigaificance. Apart from Cu, Pb, Zn Au and Ag, the associated metals from these deposits also include tungsten and tm which are characteristic of the continental crust. The ores usually contain relatively high content of radiogenic lead isotopes. The alterations of the underlying rocks, mainly silicification, sericitization and kaolinization, reflect the geochemical characteristics of the continental crust in which silicon and potassium were enriched. Moreover, because of the formation of multistage granites in the weak zones of the continental crust, these deposits were often transformed and superimposed by hydrothermal solutions from Mesozoic granitic rocks, especially those of the syntactic type, resulting in the coexistence of massive sulfide deposits with ores of skarn and porphyry types in one district. |
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