| 扬子板块北缘马元铅锌矿地球化学特征及成矿机制探讨 |
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| 关键词:sulfur isotope strontium isotope REE metallogenic mechanism Mayuan Pb-Zn deposit |
| 基金项目:中国地质调查局项目(编号: 1212011121117) |
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| Geochemical Characteristics and Metallogenic Mechanism of the Mayuan Pb-Zn Deposit on the Northern Margin of Yangtze Plate |
| The Mayuan stratabound Pb-Zn deposit in Nanzheng of Shaanxi Province is located on the northern margin of the Yangtze Plate, and the orebodies are stratiform and hosted in breciated dolostone of the Sinian Dengying Formation. The ore minerals are mainly sphalerite and galena, and the gangue minerals comprise dolomite, barite, and small amounts of quartz, fluorite and calcite. This study mainly focused on the strontium, sulfur isotopes and the rare earth elements of the major ore and gangue minerals for the purpose of investigating the metallogenic mechanism. The 87Sr/86Sr ratios of the early precipitation product dolomite and the fluid inclusions of sphalerite range from 0.71111 to 0.71241, suggesting that Sr was derived from the crust, that is, ore-forming fluid had flowed through the basement and the Paleozoic clastic rocks which had a high 87Sr/86Sr ratios. Besides, the two 87Sr/86Sr ratios (0.70918 and 0.70971) of the late precipitation product barite imply that strontium mainly came from seawater with the addition of a small amount of crust materials. The rare earth elements of the early product of dolomite, sphalerite and galena are characterized by obvious Eu anomaly of the hot brine, while the late barites by the negative Ce anomaly of the sea water. The δ34S values show that heavy sulfur is abundant (δ34S>12‰), and that the sulfur might have been derived from marine sulfate. The formation mechanism of the reduced sulfur was the thermochemical sulfate reduction, and the organic matter, such as methane, might have acted as a reductant. The δ34S values of sphalerite, galena and barite are all concentrated in a narrow range and, what is more, the sulfur isotope fractionation has reached equilibrium, which might imply that the reduced sulfur, metal cations and the sulfate ions might have been transported by the same fluid. The mineral precipitation of the Mayuan Pb-Zn deposit resulted probably from the mixing of the seawater (or meteoric water) and the hot brine which circulated in the basin and was enriched in radioactive strontium and metal elements. The fluid related to the early dolomite, sphalerite and galena precipitation was mainly associated with the hot brine, whereas the fluid related to late barite precipitation was relatively enriched in seawater (or atmospheric water). |
| LIU Shu-wen,LI Rong-xi,LIU Yun-hua,ZENG Rong.2016.Geochemical Characteristics and Metallogenic Mechanism of the Mayuan Pb-Zn Deposit on the Northern Margin of Yangtze Plate[J].Acta Geoscientica Sinica,37(1):101-110. |
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