研究生知识库

铁氧化物铜金(iron oxide copper-gold, 即IOCG)矿床是上世纪九十年代提出的一种矿床类型，该概念的提出一定程度上促进了世界上一系列同类矿床的发现，引起工业界和学术界的广泛关注。通过近三十年的研究，有关该类矿床的成矿时代、大地构造背景、成矿机制等取得了不少的重要进展。中国IOCG矿床的研究起步较晚，尽管通过不到十年的研究识别了中国一些地区Fe-Cu矿床具有IOCG矿化的特点，但目前为止，仅有扬子西缘康滇地区Fe-Cu矿床的研究程度最高，被确立为中国典型的IOCG成矿省而受国内外认可的程度相对较高。那么，中国其它地区是否还有IOCG矿床？在中国云南南部龙脖河至越南北部新泉地区，沿着哀牢山-红河剪切带分布了一系列Fe-Cu矿床，构成一条重要的Fe-Cu成矿带。已有线索显示它们可能具有类似于IOCG的矿化特点，且不少研究推测该成矿带很可能是扬子西缘康滇IOCG成矿省的一部分，被新生代哀牢山-红河剪切带错位至目前位置。然而，由于缺乏对该成矿带围岩时代、矿化特点及成矿机制等方面的详细研究，目前仍不清楚该带Fe-Cu矿床是否类似于IOCG矿床、是否是康滇IOCG成矿省的一部分。为此，本文描述和总结龙脖河-新泉Fe-Cu成矿带中典型矿床(龙脖河和新泉矿床)的地质和矿化特点，并通过对赋矿围岩及其侵入体进行锆石U-Pb年代学研究限定围岩时代及地层属性，以期全方位对比该成矿带与康滇IOCG成矿省。龙脖河和新泉矿床分别位于该成矿带的北西端和南东端，其赋矿围岩分别为龙脖河群和新泉群。龙脖河群由变质沉积岩和变火山岩组成，变质沉积岩包括片岩、片麻岩、麻粒岩、大理岩等。而新泉群则主要由变质沉积岩组成，包括石墨片岩、云母片岩、片麻岩等，局部可见大理岩及混合岩。龙脖河和新泉矿床具有类似的矿化特征，均包括成矿前的Na化蚀变、早期的Fe-REE矿化，以及稍晚的铜矿化。成矿前的Na化蚀变，其矿物组成主要为钠长石，可见少量浸染状的磁铁矿颗粒，蚀变强烈的地区可形成钠长岩。早期的Fe-REE矿化矿物组成主要为磁铁矿、褐帘石、角闪石、黑云母及部分磷灰石等；而铜矿化阶段主要矿物为黄铜矿、角闪石、黑云母、部分磁黄铁矿、绿泥石以及少量黄铁矿。此外，局部存在大理岩的地方，还发育有矽卡岩化形成少量矽卡岩矿物，主要包括石榴石和辉石。这些矿化特点与康滇IOCG成矿省的Fe-Cu矿床相似，也类似于世界上其它典型的IOCG矿床。锆石U-Pb年代学表明赋矿龙脖河群可以分为上、下龙脖河群两部分。上龙脖河群变质沉积岩形成时代为1000-750 Ma，下龙脖河群变火山岩形成时代为~1700 Ma。另一方面，赋矿新泉群最年轻碎屑锆石和侵入地层花岗岩的U-Pb年龄很好的约束其时代为870-830 Ma。碎屑锆石年龄柱状图显示，上龙脖河群碎屑锆石谱峰主要集中在2.9-2.7、2.3-2.2、1.9-1.7、1.5-1.3、1.2-1.05 Ga五个主要年龄谱峰和2.5-2.4 Ga一个次要年龄谱峰，而赋矿新泉群的碎屑锆石则集中在2.5-2.3、1.9-1.7、1.6-1.3、1.0-0.87 Ga四个主要年龄谱峰和1.2-1.05 Ga一个次要年龄谱峰。总体来讲，龙脖河-新泉Fe-Cu成矿带的赋矿围岩碎屑锆石谱峰能大致和康滇IOCG成矿省同时代的地层相对比，如昆阳群、会理群和延边群。而下龙脖河群~1700 Ma的变火山岩则与康滇IOCG成矿省大红山群和河口群~1700 Ma的变火山岩类似。本次研究结果显示龙脖河-新泉Fe-Cu成矿带很可能是康滇IOCG成矿省的一部分，后期被哀牢山-红河剪切带错位至目前位置。因此，该研究结果也指示在哀牢山-红河剪切带中可能具有重要的Fe-Cu找矿潜力。

Iron oxide copper-gold (IOCG) deposit is a proposed type of deposit in the 1990s, which extensively promoted the discovery of series similar deposits in the world. Research on IOCG deposit thus has widely attracted attention from industrial circles and academical communities. Much progress had been obtained through near 30 years of investigation, including the time of mineralization, tectonic setting, metallogenic mechanism etc. In China, investigations of IOCG deposit are rarely in past decades. Although researches on Fe-Cu deposits in some regions have unraveled some potential IOCG mineralizaton. So far, only Fe-Cu deposits in the Kangdian region of the western Yangtze Block have been highly studied. It was established as a typical IOCG metallogenic province and widely recognized by other researchers. So, are there IOCG deposits in other parts of China?A number of Fe-Cu deposits distribute along the Ailao Shan-Red River shear zone (ASRR) in South Yunnan, China and northern Vietnam, defining the potential important Longbohe-Sin Quyen Fe-Cu belt. Some clues suggested that these Fe-Cu deposits are likely similar to IOCG mineralization. Recent studies have inferred that this belt was tentatively considered to be initially part of the Kangdian IOCG province in southwestern Yangtze Block (SW China) before being southeastward displaced by the Cenozoic ASRR shear zone. However, such a model is still not confirmed convincingly due to poor understanding of the age of ore-hosting rocks, mineralization styles, ore genesis. Now it is not clear whether Fe-Cu deposits in the Longbohe-Sin Quyen Fe-Cu belt are similar to IOCG deposits, and whether the Longbohe-Sin Quyen Fe-Cu belt is likely considered as a part of the Kangdian IOCG province. In this paper, we described and summarized the geology and mineralization styles of the typical deposits (the Longbohe and Sin Quyen deposits) in the Longbohe-Sin Quyen belt, and obtained new zircon U-Pb ages of the ore-hosting rocks and intruding granites to constrain the age of hosting rocks, in order to comprehensively compare with those of the Kangdian Fe-Cu province. The Longbohe and Sin Quyen deposits, which are located in northwestern section (south Yunnan, China) and southeastern section (northern Vietnam) of the belt, hosted in the Longbohe and Sin Quyen Groups, respectively. The Longbohe Group consists of meta-sedimentary and meta-volcanic rocks, and meta-sedimentary rocks include schist, gneiss, granulite and marble. However, the Sin Quyen Group is only composed of meta-sedimentary rocks, including graphite-schist, mica schist and gneiss, minor marble and migmatite. Both the Longbohe and Sin Quyen deposits have similar mineralization sequences of pre-ore Na alteration, early Fe-REE and late Cu mineralization. Pre-ore Na alteration consists of albite and minor disseminated magnetite, and albitite can be formed in strong altered areas. Early Fe-REE mineralization is mainly composed of magnetite, allanite, amphibole, biotite with local apatite, but late Cu mineralization mainly comprises chalcopyrite, amphibole, and biotite with local pyrrhotite, chlorite and minor pyrite. Besides, skarnization occurred where marble locally existed, which formed some skarn minerals, including garnet and pyroxene. The characters of these two Fe-Cu deposits are similar to those of Fe-Cu deposits in the Kangdian IOCG province, and also similar to other typical IOCG deposit in the world.Our new zircon U-Pb dating results suggest that the ore-hosting rocks from the Longbohe Group can be devided into upper and lower parts, which was formed at 1000-750 Ma (sedimentary) and ~1700 Ma (volcanic). On the other hand, the minimum age of detrital zircon and the age of intruding granites tightly constrain the depositional age of ore-hosting rocks from the Sin Quyen Group as 870-830 Ma. Age histogram reveal that detrital zircon grains from the upper Longbohe Group have dominantly age groups clustering at 2.9-2.7, 2.3-2.2, 1.9-1.7, 1.5-1.3, 1.2-1.05 and subsidiary 2.5-2.4 Ga. The ore-hosting rocks from the Sin Quyen Group that cluster at 2.5-2.3, 1.9-1.7, 1.6-1.3, 1.0-0.87 and subsidiary 1.2-1.05 Ga. In total, the age spectrums of detrital zircon are roughly comparable with those of the synchronous strata in the Kangdian IOCG province, such as the Kunyang, Huili and Yanbian Groups. It is important to note that the older, ~1700 Ma meta-volcanic rock of the lower Longbohe Group is also comparable with those of ~1700 Ma meta-volcanic rocks of the Dahongshan and Hekou Groups in the Kangdian IOCG province. These new results support that the Longbohe-Sin Quyen Fe-Cu belt is likely considered as a part of the Kangdian IOCG metallogenic province before being displaced by the ASRR shear zone. The new findings thus have important implications for regional metallogeny, implying that the ASRR shear zone is likely potential target for future Fe-Cu mineralization.