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 ±99 Ma ( 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 breakup of the Columbia supercontinent at about 1. 7Ga.%迤纳厂矿床是康滇地区典型的铁-铜-稀土矿床之一.因为其特殊的矿物组合(磁铁矿与黄铜矿共生)以及富含稀土矿物,这类矿床一直是矿床学家研究的热点.然而由于其围岩遭受不同程度的变质和蚀变作用,这类矿床的成矿时代与矿床成因一直存在争议.本文通过对迤纳厂组中层状凝灰岩和火山角砾岩所含锆石进行LA-ICP-MS U-Pb定年来揭示迤纳厂组的最大沉积年龄.大多数锆石具有明显的震荡环带和较高的Th/U比值(＞0.4)表明它们均是岩浆锆石,近200粒碎屑锆石的207 pb/206 Pb年龄大致可以分为四组:1.75 ～ 1.88Ga,1.90 ～2.00Ga,2.02～2.20Ga和2.30 ～2.40Ga,且最老年龄在3.0Ga左右,而最年轻年龄在1750Ma左右.这一定年结果反映了迤纳厂组的沉积上限大约为1.7Ga,并且在康滇地区可能还有更老的基底存在.通过对矿石矿物黄铜矿的Re-Os同位素定年测试,直接限定了矿床的成矿时代.6个黄铜矿样品的Re-Os同位素等时线年龄为1690±99Ma(MSWD =9.0),模式年龄的加权平均值为1685±37Ma(MSWD=3.0),表明该矿床形成于距今约1.7Ga.另外,主要类型矿石具显著的正铕异常和轻稀土富集的特点,与现代海底热液极其相似.年代学研究显示矿床的形成时代和地层的沉积时代大致相同,而REE揭示的流体特征反映其成矿作用与海底热液活动有关.这些结果暗示了该矿床为海底火山喷发-同生沉积形成.近来的较多研究证实,康滇地区存在1.7Ga左右较大范围的岩浆活动和较多同期铁-铜矿床,表明该期岩浆活动可能是制约该区铁-铜矿床形成的关键因素,且岩浆活动可能与约1.7Ga的Columbia超大陆的裂解事件有关.
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