【作者】 张乐骏；

【导师】 周涛发；

【作者基本信息】 合肥工业大学 ， 矿物学岩石学矿床学， 2011， 博士

【摘要】 长江中下游成矿带位于扬子板块北缘，是我国最重要的陆内铜金铁多金属成矿带之一，庐枞（庐江~枞阳）盆地位于长江中下游成带中部的安徽省境内，是长江中下游成矿带的重要组成部分。作为断拗区典型代表的庐枞盆地的成岩成矿作用特色显著，矿床类型复杂多样。盆地中发育有白垩纪的四个旋回的钾玄岩系列岩石和多个侵入岩体。随着2006年庐枞盆地泥河大型铁矿床的发现，人们对庐枞盆地的找矿潜力进行了重新评价，并将其作为深部找矿的重要靶区之一，这使得成岩成矿时代、矿床成因、成矿规律及成矿系统之间的演化关系等工作亟待进行。因此，本文选择长江中下游成矿带中的庐枞盆地作为研究对象，在充分收集、整理前人研究成果的基础上，通过大量的野外地质调查和室内分析测试工作，综合运用多学科多方法，尤其是矿床学、蚀变岩石学、成岩成矿同位素地球化学、同位素年代学和流体包裹体地球化学及高精度微区微量分析等手段对对庐枞盆地的成岩成矿作用开展了系统的研究工作，获得的主要认识和进展如下：庐枞盆地的侵入岩可以分成两个阶段，其中包含了三种类型的岩石。早阶段的为二长、闪长岩类侵入体，主要分布在盆地的北部，形成时代为134Ma~130Ma，与龙门院旋回和砖桥旋回的火山活动有关。晚期的侵入岩包括正长岩和A型花岗岩，主要分布在盆地的南部，形成时代为129Ma~123Ma，与双庙旋回和浮山旋回的火山活动有关。本文对庐枞盆地内主要矿区内的侵入岩体进行LA-ICP-MS锆石U-Pb定年的结果显示，主要矿区内部侵入岩体的形成时代集中在134Ma~129Ma之间。其中泥河矿区的闪长玢岩、二长斑岩、粗安斑岩、正长岩、正长细晶岩，大岭闪长玢岩，小岭粗安斑岩，大鲍庄闪长玢岩，井边安山斑岩，杨山闪长玢岩以及岳山粗安斑岩属于早阶段的侵入岩，与龙门院旋回和砖桥旋回的火山岩浆活动密切相关。泥河矿区的正长斑岩和马口矿区的石英正长斑岩属于晚阶段的侵入岩，与双庙旋回和浮山旋回的火山岩浆活动有关。对比表明，庐枞盆地主要矿区内的侵入岩的形成时间明显晚于长江中下游成矿带中断隆区与成矿有关的高钾钙碱性侵入岩体的形成时间，但与该区的其它火山岩盆地中的侵入岩浆活动的时代几乎相同。庐枞盆地内的侵入岩是区域第二期（135Ma~127Ma）和第三期（126Ma~123Ma）岩浆作用的产物。岩石地球化学特征显示，庐枞盆地四个旋回的火山岩和两期三种类型侵入岩的岩浆具有同源性关系，其岩浆源区为成分接近EMI型富集地幔的交代地幔，交代地幔的形成与古板块的俯冲交代作用有关。岩浆演化经历了岩浆分异、分离结晶作用和同化混染作用，岩浆分异、分离结晶作用主要发生于岩浆房中，早期的龙门院旋回、砖桥旋回火山岩以及早期侵入岩的岩浆分异程度相对较低，而晚期的双庙旋回、浮山旋回火山岩和晚期侵入岩的岩浆分异程度较高，在岩浆演化、上升侵位（喷发）的过程中，发生了一定程度的陆壳同化混染作用。在早白垩世，庐枞盆地的大地构造背景发生了从挤压向拉张过渡的构造背景向典型拉张的构造背景转变，转换的时间约为130Ma。盆地中早阶段的火山侵入岩浆活动（龙门院旋回和砖桥旋回火山岩和早期二长、闪长岩）发生于挤压~拉张过渡的构造背景；而晚期火山侵入岩浆活动（双庙旋回和浮山旋回火山岩和晚期正长岩和晚期A型花岗岩）发生于典型的拉张构造背景。运用40Ar-39Ar定年方法对泥河铁矿床、龙桥铁矿床、马鞭山铁矿床、杨山铁矿床、马口铁矿床中的金云母以及井边铜金矿床内石英中流体包裹体进行分析测试得出，上述矿床的形成时代为134Ma~127Ma之间。在上述结果的基础上，我们还根据矿区内与成矿关系最为密切的岩浆岩的形成时代间接的约束约束了其它未进行精确定年矿床的形成时代，最终得到庐枞盆地内成矿作用演化的时间序列为：盘石岭铁矿床的形成时代最早，与砖桥旋回火山喷发活动的时间基本一致（134Ma），脉状铜矿床、热液铅锌矿床的形成时代约为133Ma~132Ma，其时代与砖桥旋回末期的次火山岩或二长岩类侵入体的形成时代基本一致；盆地中玢岩型铁矿床（包括罗河、泥河、杨山、龙桥、大岭、小岭和大鲍庄）的形成时代基本一致，均为130Ma左右，是在较短时间内集中“爆发式”形成的；矾山明矾石矿床形成时代与玢岩铁矿一致或略晚；形成时代最晚的是产于正长岩和A型花岗岩中的Fe-Cu-Au-U矿床，时代大约≤127Ma。本文对盆地中主要矿床的地质特征进行了详细的总结和描述，并对主要矿床的蚀变矿化期次进行了划分。在此基础上，我们运用电子探针（EPMA）和激光探针（LA-ICP-MS）对主要矿床中的矿石矿物和脉石矿物（黄铁矿、磁铁矿、辉石、石榴石、磷灰石和硬石膏）进行了元素组成分析。运用这些结果总结了不同矿物在不同成矿阶段和不同矿床中的元素富集规律，并与国内外研究成果进行了对比，初步探讨了元素富集变化规律对成矿流体演化和矿床成因的指示。例如，黄铁矿微量元素LA-ICP-MS面扫描图像显示，泥河铁矿床中形成于磁铁矿阶段的黄铁矿核富集Co，Ni，As和Se这一组元素，而形成于硫化物阶段的黄铁矿边除了含有上述元素之外，还富含Cu、Pb、Zn、Ag、Au和Tl等一些元素，指示了相应成矿阶段流体的性质。对磷灰石中微量元素研究结果表明，泥河铁矿床和马口铁矿床中的磷灰石与宁芜盆地陶村铁矿床中的磷灰石相似，而不同于Kiruna型矿床和IOCG型矿床中的磷灰石，这可能表明庐枞盆地中的铁矿床不属于Kiruna型矿床或IOCG型矿床。泥河铁矿床不同阶段的硬石膏具有不同的颜色，我们尝试性的运用LA-ICP-MS方法对其中的微量元素组成进行了研究，结果显示，Ba、Na、Y和REE的含量从紫色硬石膏（磁铁矿阶段）到红色硬石膏（硫化物阶段）再到白色硬石膏（石英-方解石-硫化物阶段）急剧降低。泥河铁矿床的蚀变岩石从空间上可以分为上部浅色蚀变带（晚期），中部深色蚀变带（中期）和下部浅色蚀变带（早期）。蚀变岩石学研究表明，早期矿化蚀变阶段主要形成下部浅色蚀变带，所伴随的物质组分变化有Fe、Ca、Mg从原岩中析出，而有大量的Na从溶液中进入岩石；中期形成矽卡岩的阶段有大量的Fe、Ca、Mg及少量Si的带入，并富含F、P、CO2等挥发分；中期矿化蚀变的末期主要形成矿床中部的绿泥石-绿帘石带，没有明显的组分带入带出现象，主要为挥发份H2O、CO2起作用，使早期无水硅酸盐矿物（辉石、石榴子石）转变为含水硅酸盐矿物（绿泥石、绿帘石）和方解石、菱铁矿等。晚期矿化蚀变阶段主要形成上部浅色蚀变带，伴随有大量的Ca、Fe、S及Si的富集，形成硬石膏矿体及黄铁矿矿体。流体包裹体研究表明，从泥河铁矿床磁铁矿化阶段到硫化物阶段，温度逐渐降低，同时泥河铁矿床磁铁矿阶段的温度高于龙桥铁矿床。脉状铜金矿床的成矿流体显示了中等温度特征，矾山明矾石矿床的流体属于浅成低温热液系统。H、O同位素组成表明泥河铁矿床的成矿流体以岩浆水为主，但体现了流体在上升过程中与围岩发生了同位素交换反应，有地壳组分的加入；龙桥铁矿床的成矿流体来源于岩浆，但与地层水和大气降水发生了混合。脉状铜金矿床的成矿流体显示了以更多比例的大气水加入。龙桥铁矿床C同位素研究表明成矿晚期存在岩浆岩和沉积岩（东马鞍山组地层）的双交代作用。S同位素研究表明金属矿床的硫源主要为岩浆硫和含膏盐地层硫的混合。闪长玢岩是整个庐枞盆地中最为重要的成矿流体驱动器，成矿流体在闪长玢岩体的内部和向外运移过程中在不同的位置与围岩发生反应，与地下水发生混合，成矿流体物理化学性质随之改变，从而导致了成矿物质在不同的部位发生沉淀形成矿床。庐枞盆地的成矿流体系统与长江中下游多金属矿床成矿流体子系统中的“玢岩型铁矿”成矿流体系统相似。本文在上述研究成果基础上，对盆地中的主要矿床进行了成因分析，并与国内外相关、相似地区和矿床进行了详细对比，建立了陆内环境下庐枞盆地的成矿模式，认为庐枞盆地的成岩成矿作用是一个连续而且成因上相互联系的过程，是与早白垩世岩浆热液活动有关的一个完整成矿系统演化作用的产物。庐枞盆地的成岩成矿作用是长江中下游成矿带以致整个中国东部中生代构造-岩浆-成矿系统演化的有机组成部分，受中国东部中生代燕山期地球动力学背景的制约。早白垩世135Ma后，区域完全进入太平洋构造体制，太平洋板块斜向俯冲、岩石圈拆沉、软流圈上升和地幔隆起作用加剧，区域伸展作用加强，在135Ma-123Ma之间形成了一系列火山岩盆地及其中的铁、铜多金属矿床及非金属。更多还原

【Abstract】 The Luzong (Lujiang~Zongyang) volcanic basin is located in the central part of theMiddle-Lower Yangtze (Changjiang) River Valley metallogenic belt, the Northern margin of theYangtze block in Anhui Procvince, which is one of the most important polymetallic mineralizationbelt in east-central China. As a representative volcanic basin in the Middle-Lower Yangtze(Changjiang) River Valley metallogenic belt, the Luzong basin shows noticeable feature ofmineralization and magmatism and occured multiplicity deposits, which contains four shoshoniticvolcanic units and many intrusive rocks of cretaceous age. With the Nihe iron deposit wasdiscovered in2006, the evaluation of the mineralization ability of the Luzong basin has beenimproved. In order to clarify the diagenetic and metallogenic epoch, the ore genesis, metallogenicregularity and the relationship between the magmatism and the mineralization many comprehensiveresearch work needs to do. This paper taking the Luzong basin as the subject, based on thesummarise of previous studies, by the means of detailed geological investigation, sampling andmicroscope observation, combine with geochemistry, geochronology, fluid inclusion geochemistryand in-situ laser ablation trace elements analysis methods, aims to achieve a comprehensiveunderstanding of magmatism and mineralization.The intrusive rocks in the Luzong basin can be divided into two stages and three types. Theearly stage monzonite-diorite intrusions mainy distributed in the north part of the basin, ages from134Ma to130Ma, which have close relationship with Longmenyuan and Zhuanqiao cycle volcanicactivity. The late stage syenite and A-type granite intrusions distributed in the south part of the basin,ages from129Ma to123Ma, which have close relationship with Shuangmiao and Fushan cyclevolcanic activity. New LA-ICP-MS zircon U-Pb dating results of the intrusive and subvolcanic rocksfrom the the main mineral deposits shows the age range from134Ma to129Ma. The magmatic rocksin the Nihe district (include diorite porphyry, monzonite porphyry, trachyandesite porphyry, syeniteand aplite), the diorite porphyry in the Daling deposits, the trachyandesite porphyry in the Xiaolingdeposits, diorite porphyry in the Dabaozhuang deposit, andesitic porphyry in the Jingbian deposit,diorite porphyry in Yangshan deposits and trachyandesite porphyry in the Yueshan deposit arebelong to the early stage magmatism, the syenite porphyry in Nihe deposit and the quzrtz syeniteporphyry in Makou deposit belongs to the late stage magmatism. Compare with tthe magmaticactivity in the Middle-Lower Yangtze River Valley metallogenic belt, the intrusions in the mainmineral deposit in the Luzong basin were the product of the second(135Ma~127Ma) and thirdperiod(126Ma~123Ma) magmatic activity and obviously later than high-k calc-alkaline intrusionsrelated to skarn-porphyry Cu-Au deposits in uplift areas in the Middle-Lower Yangtze River Valleymetallogenic belt.The geochemical features of the four groups volcanic rocks and two stage intrusive rockssuggest that the volcanic rocks and intrusions might be derived from a same source, themetasomatic mantle closing to the enriched mantle I (EMI). The form of the source might berelated to the subduction of the paleo-plate. The evolution of the magma was controlled by thecrystal fractionation mainly and influenced by the crust materials partially in the high-level magmachamber. The Shuangmiao group and Fushan group volcanic rocks and the late stage intrusive rockshows a higher degree crystal fractionation and much more influenced by the crust contaminationthan the Longmenyuan and Zhuanqiao group volcanic rocks and the early stage intrusive rocks. TheThe tectonic setting of Luzong basin existed a change from the transition of compressional to extensional regime to the extensional regime in Early Cretaceous, and the time was about130Ma. The magmatic rocks of Longmenyuan and Zhuanqiao stage formed in the transitional setting fromcompressional to extensional regime, and those of the Shuangmiao and Fushan groups formed inthe extensional regime.The40Ar-39Ar dating of phlogopite from Nihe, Longqiao, Mabianshan, Yangshan, Makou andfluid inclusions in quartz from Jingbian deposit shows the mineralization age of these deposit rangefrom133Ma to127Ma. Combine with the age of the magmatic rocks which closely related to themineralization, which can indirect constrain the mineralization ages, of other mineral deposits wecan summarize the time sequence of the mineralization in the Luzong basin as following: thePanshiling iron deposit formed earliest, the age consistent with the Zhuanqiao formation volcanicrocks(~134Ma); the vein-type Cu-Au deposits and the Yueshan Pb-Zn deposit formed in133Ma~132Ma, which consistent with the ages of the subvolcanic rocks or monzonite intrusions ofZhuanqiao formation; the porphyry iron deposits(include Luohe, Nihe, Yangshan, Longqiao, Daling,Xiaoling and Dabaozhuang) are “booming” formed in a short interval, around130Ma; the age of theFanshan alunite deposit might be consistent with or slightly younger than the porphyry iron deposits;the last mineralization event is the Fe-Cu-Au-U mineralization occurs in the late stage syenit and theA-type granite, the age approximately≤127Ma.We present the geologic characteristics and subdivided the alteration and the mineralizationstages of the main deposits in the Luzong basin. Detailed mineral chemistry studies on the main oreminerals and gangue minerals (pyrite, magnetite, pyroxene, garnet, apatite and anhydrite) have beendone by means of EPMA and LA-ICP-MSanalyses. These data are used as an indicator of the natureof the hydrothermal fluids involved in the formation of deposits. For instance, the trace elementsLA-ICP-MS map of the pyrite core from magnetite stage of Nihe deposit enriched in Co, Ni, As, andSe. While pyrite rim from sulphide stage is enriched in Cu, Pb, Zn, Ag, Au, Tl and so on. Thegeochemical composition of apatite from the Nihe, Makou and Taocun iron deposit are much similarwhereas shows some differents from the Kiruna type deposit and IOCG deposits, which mightindicate that the iron deposits in the Luzong basin is not belongs to the Kiruna type deposits and theIOCG type deposit. The anhydrite fromdifferent stage of the Nihe iron deposit display different color.The Ba, Na, Y and REE are drasticly decrease from pink color anhydrite(magnetite stage), redcolor anhydrite(sulphide stage) to white color anhydrite(quartz-calcite-sulphide vein stage).The alteration in the Nihe iron deposit can be divided into upper leucocratic alteration zone(late stage), middle Melanocratic alteration zone(middle stage), lower leucocratic alterationzone(early stage). The alteration geochemistry study results shows that the early alteration stageresult in the Fe、Ca、Mg add to the solution and the Na add to the wall rock, the skarn alteration ofmiddle stage addition Fe、Ca、Mg and minor Si, with a volume of volatile (F、P and CO2). There isno obvious component addition or loss in the middle alteration stage. However, the volatile (H2Oand CO2) making the anhydrous silicate minerals (pyroxene and garnet) into the hydrous silicateminerals (chlorite and epidote) and calcite, siderite. A large number of Ca、Fe、S and Si enrichment inthe late stage, and formed the anhydrite ore bodies and pyrite ore bodies.Fluid inclusion study shows the temperature and the pressure of the mineralization stageore-forming fluids decrease from magnetite stage of the Nihe deposits, magnetite stage of theLongqiao deposit, to the sulfide stage of the Nihe deposits. The vein-type Cu-Au deposits showsmiddle level temperature ore-forming fluids, the ore-forming fluids of the alunite deposit belongs tothe epithermal system. The hydrogen and oxygen isotope composition analyses results indicate thatthe ore-forming fluids of the Nihe iron deposit were predominated by magmatic thermal fluid, theascending ore-forming fluids reacted with the wall rock, and the crust materials were entered ore-forming fluids. The ore-forming fluids of Longqiao iron deposit derived from the magma and mixed with the stratum and meteoric water. The vein-type Cu-Au deposits shows the meteoric waterdominated ore forming fluids. The C isotope study of Longqiao deposit shows the carbon in thefluids of the later mineralization stages is a mixed source from both of the magmatic andsedimentary rocks (the Dongma’anshan Formation). Sulfur isotopic compositions show that thesulfur in the deposit was derived from a mixture of magmatic hydrothermal fluids andcarbonate-evaporite host rocks. The diorite porphyry is an important engine of the ore-forming fluidsin the Luzong basin, with flowing of the ore-forming fluids in different environment, interact withwall rock and mixed with the meteoric water, the changes of principal physicochemical conditions ofore-forming fluids cause different types mineralization occurred in different place. The ore-formingfluids was corresponding to the porphyry iron mineralization system of the Middle and LowerYangtze River Polymetallogenic mineralization system.Based on the above comprehensive study results, and compareing with the mineralizationsystem around the world systemic, we discussed the genesis of the main deposits, and propose ametallogenic model of the Luzong basin. This model shows the polymetallic mineralization andmagmatic activity in the Luzong basin is a continuous process, different magmatic rocks anddifferent mineral deposits are the products of the magmatic-hydrothermal system in differentevolution stages. The petrogenetic and metallogenetic of Luzong basin is one part of the Mesozoictectonic-magmatic-metallogenic event controlled by the geodynamic setting of eastern China in theYanshanian period. Widespread volcanic basins and Fe, Cu polymetallic mineralization formedduring135Ma to123Ma in early Cretaceous, in the extensional tectonic setting, whichcorresponding to the subduction of the pacific plate, lithospheric de delamination and asthenosphericupwelling in eastern China.更多还原