Zircon U-Pb and Chalcopyrite Re-Os Geochronology, REE Geochemistry of the Yinachang Fe-Cu-REE Deposit in Yunnan Province and Its Geological Significance
详细信息
- 责任者：Ye Xiantao (State Key Laboratory of Ore Deposit Geochemistry ; Institute of Geochemistry ; Chinese Academy of Sciences ; Guiyang 550002 ; China) ; Zhu Weiguang
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(4)
- 关键词：铁矿 ; iron ores ; 铜矿 ; copper ores ; 稀土矿床 ; rare earth deposit ; 铀—铅计时 ; U-Pb dating ; 铼—锇计时 ; Re-Os dating ; 云南 ; Yunnan Province
- 页码：p.1167-1186
- 图表：illus., 3 tables, 66 refs.
- 分类号：1001
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
The Yinachang Fe-Cu-REE ore deposit is hosted in the Paleoproterozoic Yinachang Formation of the Lower Kunyang Group in the Kangdian iron-copper metallogenic province, SW China. The main minerals in the Yinachang ore bodies consist of chalcopyrite, magnetite, quartz and calcite. As the host rocks of the deposit had experienced intensively alternation and metamorphism, the age and origin of the Yinachang deposit are still a matter of hot debate. U-Pb ages of detrital zircons from the volcanic tuff and breccia in the Yinachang Formation have been used to identify the provenance and evaluate the age of the Yinachang Formation of the Lower Kunyang Group. Most analyzed zircon grains show oscillatory zoning and have high Th/U ratios (>0.4), suggesting that they were mainly derived from igneous rocks. A total amounts of about 200 detrital zircons exhibit U-Pb age populations at 1.75～1.88Ga, 1.90～2.00Ga, 2.02～2.20Ga and 2.30～2.40Ga, with the oldest 207Pb/206Pb age of ～3.0Ga and the youngest age of ca. 1750Ma. The dating results provide a maximum deposition age of ca. 1.7Ga for the Yinachang Formation, and suggest the possible existence of older basement. Rhenium-osmium dating for six chalcopyrite samples from the Yinachang Fe-Cu-REE deposit was conducted to constrain the timing of sulfide mineralization. Direct Re-Os dating for chalcopyrite of ore minerals yields an isochron age of 1690±99Ma (MSWD=9.0) and a weighted mean of 1685±37Ma (MSWD=3.0), respectively, indicating the main ore-forming age of about 1.7Ga. In addition, the major ore types exhibit significantly positive Eu anomaly and LREE enrichment, similar to those of modern submarine hydrothermal fluids. The above dating results reveal that the ore-forming age of the deposit is nearly contemporaneous with the deposition timing of the Yinachang Formation, and the characteristics of fluid deduced from REE indicate that the ore formation was related to submarine hydrothermal fluids activity. It is therefore suggested that the Yinachang Fe-Cu-REE deposit is a volcanic exhalation-hydrothermal sedimentary deposit. Several recent studies showed the occurrence of relatively widespread magmatism at ca. 1.7Ga and large numbers of synchronous Fe-Cu deposits, suggesting that the magmatism is probably the crucial factor for the formation of deposits in this region. Furthermore, the Fe-Cu deposits in the Kangdian region may be related to the break-up of the Columbia supercontinent at about 1.7Ga.