| 蒙古国呼勒德地区正长岩锆石SHRIMP铀-铅年龄及其地质意义 |
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| 关键词:alkaline syenite zircon SHRIMP U-Pb dating Khuld REE mineralized district Indosinian Central-South Mongolia |
| 基金项目:国家科技支撑课题(编号: 2007BAB25B02) ; 地质调查项目(编号: 1212010911029) |
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| Zircon SHRIMP U-Pb Dating of the Alkaline Syenite Stock in the Khuld Rare Earth Element Mineralized District of Central-South Mongolia and Its Geological Implications |
| Located on the southern margin of the Siberian Platform, the Khuld district is one of the most important REE, gold and uranium mineralized districts in Central-South Mongolia. Mineralization occurs both in the Late Paleozoic volcano-sedimentary sequence and in the Paleozoic-Mesozoic intrusions. Among these intrusions, the Khuld alkaline syenite stock shows an intimate spatial relationship with the REE ore spots. It intruded into the Permian volcano-sedimentary rocks, and has an outcrop of 15 km2. The stock consists mainly of alkaline porphyritic syenite in the central phase and fine- to medium-grained alkaline syenite in the marginal phase. A fresh alkaline porphyritic syenite sample from the Khuld stock was selected for SHRIMP U-Pb age dating. The zircon grains separated from the fresh whole rock sample have given a weighted mean 206Pb/238U age of 214.3±2.5Ma, with a MSWD value of 0.52. Comparative studies indicate that the Khuld alkaline syenite stock and related REE ore spots are similar to REE-bearing Lugiin Gol nepheline syenite complex which also occurs in Central-South Mongolia. Both Khuld and Lugiin Gol REE-bearing alkaline syenite intrusions have ?Nd(t) values ranging from 1.22 to 2.26 with an average of 1.62. The Khuld stock is similar to Paleozoic and Mesozoic granitoid intrusions in petrology, geochemistry and isotopic geology, with positive ?Nd(t) values occurring within the Da Hinggan Ling-Mongolia orogenic belt. Based on the zircon SHRIMP U-Pb age data mentioned above, in combination with other geological evidence, it is suggested that the Khuld alkaline syenite stock and its related REE mineralized belt were formed within a re-working deep-rooted fault zone to the north of the collision zone of the North China continental massif and Siberian platform. The Khuld alkaline syenite stock, which was probably produced by Mesozoic Indosinian tectonic-magmatic activities, might have played an important role in the ore-forming process of the REE ore spots. The rock-forming materials of the Khuld alkaline syenite stock were derived from a mixed source comprising mantle- and crustal-related components. |
| YUN Fei,LIU Yi-fei,JIANG Si-hong,BAI Da-ming.2010.Zircon SHRIMP U-Pb Dating of the Alkaline Syenite Stock in the Khuld Rare Earth Element Mineralized District of Central-South Mongolia and Its Geological Implications[J].Acta Geoscientica Sinica,31(3):365-372. |
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