Constraints of lead isotopes on regional metallogeny of sediment-hosted sulfide deposits in the Langshan-Zhaertai ore belt, northern China

摘要

The Langshan-Zhaertai ore belt in northern China includes a dozen sediment-hosted Zn-Pb-Cu deposits, which are traditionally considered to have been formed during sedimentary exhalative (SEDEX) activities in different subbasins in the same Proterozoic marginal rift system. However, this assumption has never been systematically tested. Herein, we re-evaluate the regional metallogeny by the analysis and comparison of Pb isotope data obtained in this study and published in literatures. The Pb isotope signatures of several representative deposits from this ore belt are heterogeneous and do not lie along similar secondary or anomalous lead evolution lines, suggesting that these deposits belong to different metallogenic systems. The Pb isotope ratios of the bulk of the sulfide ores in south ore belt are characterized by unradiogenic isotope compositions and Proterozoic Pb-Pb model ages, whereas the various types of sulfides from the Huogeqi deposit in north ore belt show a very radiogenic lead signature ((206)pb/Pb-204 > 17.000), which is broadly consistent with common lead of associated Indosinian magmatic rocks, indicating an magmatic-hydrothermal origin. The Dongshengmiao and Tanyaokou massive-type ore sulfides have similar and exceedingly unradiogenic isotope compositions grouped around 15.200 ((206)pb/Pb-204) Their vein-type sulfides show scattered Pb isotope signatures that fall along a well-cor- related linear trend towards the right of the massive-sulfide array, indicating some modification during metamorphism. The similarity of lead isotope compositions of the Jiashengpan vein-type sulfides to the common lead of Hercynian igneous rocks indicates that the proximal source of the ore metals in its epigenetic hydrothermal system was Hercynian igneous activity.