研究生知识库

华南陆块在中生代经历了强烈的构造-岩浆活动，产生了广泛分布的花岗岩，并形成了多期次、大规模的钨锡多金属矿床。美国地质调查局2019年统计数据显示中国的钨、锡储量分别占世界钨、锡储量的50%和20%，而前人统计结果显示华南地区钨、锡储量分别占中国探明储量的83%和63%，因此华南地区是研究钨、锡等成矿作用的理想基地。大量研究表明，华南中生代大规模钨、锡等有色金属成矿作用与该地区广泛而强烈的花岗质岩浆活动密切相关。湖南和江西省是华南陆块中生代爆发式成矿的重要地区，发育有大吉山、西华山、瑶岗仙、柿竹园、芙蓉等一大批超大型-大型钨、锡多金属矿床。近年来新发现的赣北大湖塘和朱溪钨铜矿突破了江西钨矿主要分布在赣南的传统认识。因此本文选取华南主要钨、锡矿产出地湘东南、赣南、赣北的含钨花岗岩、含锡花岗岩和含钨锡花岗岩作为研究对象，开展花岗岩的年代学、矿物学、岩石学对比研究，通过分析花岗岩体主、微量元素地球化学特征以及Sr-Nd-Hf同位素组成，并结合MAPGIS建立地球化学特征数据库，利用LA-ICPMS进行石英、锆石原位微量元素组成分析，主要得出如下结论：（1）揭示了湘赣地区钨、锡矿床和相关花岗岩的时空分布格局。尽管存在印支期和燕山晚期的成矿花岗岩，但湘、赣地区与钨锡成矿作用密切相关的花岗岩成岩时代主要集中于140Ma～165Ma的燕山早期。其中含钨锡花岗岩侵入年龄包括印支期（210 Ma～250 Ma）、燕山早期（140Ma～170Ma），含钨花岗岩侵入年龄跨度较大，从印支期到燕山晚期均有分布，而含锡花岗岩的年龄明显晚于含钨花岗岩，主要集中于燕山早、晚期。岩浆活动时间在空间上呈现东西分异的格局，其中赣北地区含钨花岗岩成岩时代主要为燕山早、晚期，湘东南、赣南地区含钨花岗岩多集中于燕山早期。印支期、燕山早期含锡花岗岩及含钨锡花岗岩主要分布在湘东南地区。锡成矿年龄主要集中于燕山早期的140Ma～160Ma之间，与成矿母岩侵入年龄基本一致，钨、锡矿成矿时代均可分为三期：印支期（215 Ma～233 Ma）、燕山早期（141Ma～162Ma）和燕山晚期（115 Ma ～140 Ma），印支期以钨矿化作用为主，燕山早期钨锡矿化并重，但显示出东部以钨为主、西部钨锡并重的格局，燕山晚期矿化以锡为主。成岩成矿时代具有一致性。（2）揭示了湘赣地区与钨、锡成矿相关花岗岩的矿物、元素-同位素组成特征和它们的主要差异及其成岩作用过程的异同。所有成矿花岗岩体主要造岩矿物为石英、钾长石、斜长石、黑云母、白云母，副矿物主要为磁铁矿、锡石、电气石、独居石、磷灰石、金红石、钛铁矿、锆石等，但锡矿相关花岗岩中多含黄玉。所有花岗岩具有高硅、富钾、碱性-钙碱性的特点，为准铝质-过铝质。含钨、含锡花岗岩Al2O3、MnO、CaO、MgO、TiO2、P2O5、Na2O+K2O、Fe2O3等含量与SiO2多呈明显负相关关系，表现出磷灰石、钛铁矿、钾长石、斜长石等分离结晶的特点。研究区含钨、含锡、含钨锡花岗岩的微量元素蛛网图和稀土元素球粒陨石标准化图解表明，三类花岗岩均富集Rb、U、Ta、Nd、Sm元素，亏损Ba、Nb、La、Sr、Zr、Ti元素。含锡花岗岩仅为右倾型，含钨花岗岩可分为两类，表现在微量元素特征上有一类更亏损Ba、La、Sr、Zr、Ti元素，Nb亏损程度相对较低，表现在稀土元素特征上可分为“海鸥型”和“右倾型”。研究区花岗岩分异演化程度，含钨花岗岩演化程度高于含锡花岗岩；含钨花岗岩在不同地区的演化程度，赣南地区>湘东南地区>赣北地区； 相对于右倾型稀土类型的花岗岩，“海鸥型”花岗岩的分异演化程度更高。研究区含锡花岗岩多分布在湘东南地区，Sr-Nd-Hf同位素数据表明含锡花岗岩有更多的幔源物质的加入。（3）揭示了湘赣地区与钨、锡成矿相关花岗岩的氧逸度特征和典型岩体中石英和锆石的微量元素组成特征。含锡、含钨花岗岩全岩Fe2O3/ FeO比值、锆石Ce4+/ Ce3+比值以及黑云母成分均表明含钨花岗岩比含锡花岗岩岩浆更具氧化性，暗示氧逸度可能是影响不同矿化类型的重要因素之一，而氧逸度的差异可能与物源有关。

South China Block is located in the southeastern Eurasian continent and close to the Western Pacific Ocean, which was formed by the integration of the Cathaysia and Yangtze blocks during the Neoproterozoic. W and Sn reserves in China account for about 50% and 20% of all the W and Sn reserves in the world (United States Geological Survey,2019), of which about 83% W and 63% Sn prosepected in China are found in the Nanling area of the South China Block, making the Nanling area to be an ideal place to study the W and Sn mineralizations. Numerous studies have revealed that the large-scale Mesozoic metallic mineralization in South China Block is associated with the granitic magmatism. Traditionally, W deposits in Jiangxi province are thought to distribute in South of Jiangxi province, but in recent years, with the discovery of Dahutang and Zhuxi tungsten-copper ore depositslocated in northern Jiangxi province, this area has become a new important tungsten mineralization zone. In this paper, W-, Sn- and W-Sn-bearing granites in Southeastern Hunan, northern Jiangxi and Southern Jiangxi are selected as studying objects.According to the published data, this paper summarizes the geochemicalcharacteristics of theseganites, including the diagenetic ages, mineralogy, major and trace element concentrations,Sr-Nd isotopic compositions and their relationship to metallic mineralization This thesis has set up a spatial database of geochemical characteristics of the studiedarea by MapGIS software. A combined study of zircon U-Pb ages and trace element compostion of zircon and quartz has been carried out for the typical granites. From the above studies, the following conclusions have been obtained:(1) The geochronological data of W-, Sn- and W-Sn-bearing granites and the related deposits demonstrate that these plutons were emplaced at 140 to165 Ma, the early period of Yanshanian. W-bearing granites intruded during Indosinian and Yanshanian, while Sn-bearing granites intruded in Yanshanian. W-Sn-bearing granites intruded in Indosinian and early Yanshanian.The regional feature of the magmatic intrusions and mineralization of the granites indicates that, Sn-bearing granites in northern Jiangxi and southern Jiangxi \Southeastern Hunan is intruded in late yanshanian and early yanshanian respectively, meanwhile the ore-forming age in northern Jiangxi, southern Jiangxi and Southeastern Hunan is late yanshanian, late yanshanian and indosinian\early yanshanian; the rock-forming age of W-bearing granites in northern Jiangxi, southern Jiangxi\ Southeastern Hunan belongs to middle late yanshanian and indosinian\middle yanshanian separately, and the ore-forming age in northern Jiangxi, southern Jiangxi\Southeastern Hunan is middle yanshanian and indosinian\middle yanshanian; while the rock-forming and ore-forming age of W-Sn-bearing granites is indosinian\middle yanshanian in all three regions.(2) Geological facts show that the main minerals of pluton are quartz, potassium feldspar, plagioclase, biotite and mica, accessory minerals consist of magnetite, cassiterite, tourmaline, monazite, apatite, rutile, illite and zircon, and W-Sn-bearing granites are rich in topaz.Major element characteristics show that the SiO2 contents of W- and Sn-bearing granites have an obvious negative correlation with Al2O3、MnO、CaO、MgO、TiO2、P2O5、Na2O+K2O and Fe2O3 respectively , accompanied with fractional crystallization of Apatite, ilmenite, potassium feldspar and plagioclase.Trace element primitive mantle normalized spidergram and REE chondrite normalized diagram show that W-, Sn- and W-Sn-bearing granites are characterized by Rb, U, Ta, Nd, Sm enrichment, and Ba, La, Sr, Zr, Ti depletion. Sn-bearing granites is right type, while W-bearing granites can be devided into two types, trace element characteristics show Ba, La, Sr, Zr, Ti are strongly depleted, Nb is weaker depleted, REE pattern are displayed as right type and seagull form. The degrees of fractionationshow the following trend: W-bearing granites > Sn-bearing granites; degree fractionation of W-bearing granites in different regions: southern Jiangxi > Southeastern Hunan > northern Jiangxi；granites with seagull form have higher degree fractionation than granites with right type. (3) The oxide content data of elements of biotite by EPMA, Ce4+/ Ce3+ and Fe2O3/ FeO ratios indicate that W-bearing granites have a higher antioxidant rating than Sn-bearing granites. Oxygen fugacity may be the important factors to form W mineralization or Sn mineralization. The difference of oxygen fugacit maybe related to source of material foming granites.