【作者】 杨振军；

【导师】 刘继顺；

【作者基本信息】 中南大学 ， 矿产普查与勘探， 2011， 博士

【摘要】 桂北四堡地区出露有江南最古老的元古代地层四堡群,分布大量的变镁铁质火山-沉积岩、镁铁质-超镁铁质侵入岩、中酸性侵入岩,是桂北岩浆型Cu-Ni-PGE成矿带、Sn、Cu、Pb、Zn、Sb、W、U/ Au成矿带的重要组成部分和中国南方极具潜力多金属找矿远景区之一.本文在详细研究区域成矿地质背景及其演化及全面收集研究区内矿床(点)的地质、物探、化探、勘探、开采资料的基础上,以区域成矿学、岩浆成矿理论为指导,以构造-岩浆-成矿作用为主线,对区域内四堡群地层、镁铁质-超镁铁质侵入岩、中酸性岩体、典型矿床-清明山铜镍硫化物矿床和Sn, Cu、Pb、Zn等矿化(床)进行深入剖析和系统研究,取得以下主要成果和认识：(1)桂北四堡地区处于扬子地台东南缘,中元古代早期,处于华南洋与扬子古陆的过渡环境,华南洋与扬子陆块洋-陆碰撞诱发了弧后盆地的形成,接受了大量具有浊积岩沉积特征的半深海-深海相碎屑沉积(四堡群)；俯冲的大洋板片部分熔融、底辟和上侵形成镁铁质火山喷发；中元古代晚期至新元古代初期,沉积盆地裂谷化进一步演化,火山-沉积加厚,镁铁质岩浆活动主要表现为岩浆的侵入；伴随着镁铁质岩浆分异演化、混染和部分地壳重熔形成了花岗闪长岩；新元古代中晚期,随着板块汇聚运动,弧后盆地裂谷化运动结束,褶皱造山及深部岩浆热侵蚀、陆壳物质大量重熔形成了大规模的黑云母花岗岩。(2)四堡群为一套具有浊积岩沉积特征的深海-半深海浅变质碎屑沉积岩系夹中-基性熔岩、科马提岩、火山碎屑岩,富集Mn、Cu、Ni、Co、Cr、V, Pb、Zn等亲铁元素；丹洲群为陆相-浅海相-半深海相砾岩、砂岩、粉砂岩、碳酸盐岩建造,富集Zn、Ba等酸性元素。在四堡群中广泛分布有Cu、Ni、Co、PGE系列矿床(化),Sn、Cu、Pb、Zn、Sb、W、U、Au等矿床(化)。(3)镁铁质火山岩、镁铁质-超镁铁质侵入岩在空间上相伴分布,岩石地球化学特征相同,富集MgO、贫K2O、TiO2,属拉斑玄武岩系列；富集Rb、Ba, Cr, Th,亏损Nb、Ta、P等,富集轻稀土,稀土配分模式右倾、弱或无明显的Eu负异常。Th/Nb比值远高于MORB和OIB岩的Th/Nb比值,也高于扬子地块上地壳Th/Nb比值；Nb/Ta、Nb/U比值均远低于正常洋脊玄武岩和球粒陨石值；具有高87Sr/86Sr比值(>0.7033)、低143Nd/144Nd<0.5130和eNd(t)<0的特点。地质地球化学特征表明,两者的岩浆源区为位于弧后陆缘区域部分熔融地幔(EM1),两者是同源岩浆不同阶段形成的产物。(4)中酸性岩体花岗闪长岩与黑云母花岗岩均为过铝质岩石,微量元素均富集K、Rb、Th,亏损Ti,dEu强亏损,稀士配分模式平坦；花岗闪长岩属混合源型花岗岩,而黑云母花岗岩属重熔型花岗岩。(5)四堡群及其火山岩形成于中元古代,四堡群下部沉积岩时代约1190～1800Ma、火山岩时代约1190～1734Ma；丹洲群的形成于新元古代早期(822～890Ma)；镁铁质-超镁铁质侵入岩形成于中元古代晚期-新元古代初(982～1088Ma)；花岗闪长岩形成时代820～1064Ma,形成时间晚于镁铁质-超镁铁质侵入岩；黑云母花岗岩形成于820～898Ma；清明山铜镍矿床形成时代为1087±56 Ma。(6)清明山铜镍矿含矿岩体,呈镁铁质-超镁铁质侵入岩墙(岩脉)产出,分异较好,从岩体底部向顶部岩性可以划分为辉石岩-辉长辉绿岩-闪长岩等岩相。地球化学特征是：ω(SiO2)为42.68～45.84%,ω(Al2O3)为6.62～10.58%,ω(MgO)为17.87～25.12%,ω(TiO2)为0.33～0.52%,ω(K2O)为0.05～1.19%；微量元素特征富集大离子半径元素Rb等,亏损高场强元素Ta、Nb等；稀土特征SREE含量平均为40.95-63.7×10-6, SLREE/SHREE为1.82～1.93,LaN/YbN为2.92～3.29,dEu值为0.56～1.13；轻稀土相对弱富集,重稀土亏损,没有或弱Eu异常。以上特征表明,清明山地区的镁铁质岩浆及含矿岩体表现出了弧岩浆地球化学特征,壳源物质混染明显,岩性略偏酸性。(7)清明山铜镍矿体产于岩体底部,严格地受辉石岩相控制。含矿岩体呈东西走向,倾向南,倾角28°～52°,厚20～250m,长1.0～3.5 Km。目前控制的含矿岩体从地表往下,逐渐变大,对应的铜镍矿体变富。清明山矿床分南北两个矿区,南部清明山铜镍矿体,控制长1500m以上,延深达500m,厚0.81-3.78m,镍品位0.31%～0.49%,铜品位0.14%～0.27%,伴生钻0.008%～0.016%；北部马漕山铜镍矿体,控制长大于500 m,延深250m,厚0.8～3.5m,矿床平均镍品位0.20%～0.30%,铜品位0.10%～0.30%。主要矿石类型有浸染状矿石、斑杂状矿石、块状矿石和脉状矿石四种类型；主要金属矿物有磁黄铁矿、镍黄铁矿、黄铜矿等。铜镍矿石的d34s为-0.5%0～+3.60%0,镁铁质岩体的d34S为6.3‰～+24.9‰；矿床地质地球化学特征与Duluth铜镍矿床比较接近,与甘肃金川铜镍矿床差异较大,这与所处大地构造位置不同有关。(8)清明山岩浆型铜镍矿的形成主要受制于岩浆熔离作用,次为结晶分异作用。引起清明山镁铁质岩浆硫饱和而致熔离作用发生的因素,主要为同化混染四堡群文通组富硫的变火山-沉积岩及似层状黄铁矿型铜铅锌矿化,次为温度快速下降和结晶分异。(9)清明山矿区存在两个主要的成矿系列：Cu、Ni、Co、PGE系列形成于弧后盆地裂谷化阶段(地壳拆沉、减薄和幔源岩浆侵入),形成于中元古代晚期-新元古代早期,为镁铁质岩浆熔离形成,分布在镁铁质-超镁铁质岩体的底部；Sn、Cu、Pb、Zn、Sb、W、U、Au成矿系列形成于弧后盆地褶皱造山阶段(地壳增厚、重熔和花岗岩化),形成于新元古代中晚期,与黑云母花岗岩侵入有关。成矿主要受制于三大因素,①四堡群变火山-沉积岩系富含成矿元素,为成矿奠定了良好的物质基础和丰富的硫源环境。②板块运动、构造演化导致了地幔的部分熔融和镁铁质-超镁铁质岩的侵入；弧后裂谷盆回返、褶皱造山与镁铁质岩浆热侵蚀促使了陆壳物质的大规模重熔和黑云母花岗岩侵入；板块构造演化决定了成矿有关岩体的形成,是成矿的主导因素,是动因。③Cu、Ni、Co、PGE系列成矿直接来自镁铁质岩浆的熔离分异和岩体中成矿元素的富集；而Sn、Cu、Pb、Zn、Sb、W、U、Au成矿与黑云母花岗岩的定位、分异和岩浆期后热液循环有关,因此岩体自身的高度分异演化是成矿的关健。在此基础上,建立了清明山铜镍矿床的成矿模式。(10)清明山铜镍硫化物矿床控矿因素有：弧后盆地大地构造背景,四堡深源断裂旁侧次级构造-清明山复式褶皱,岩体岩相专属性,岩体底部与围岩接触的岩性界面,四堡群文通组变火山-沉积岩系。总结的找矿标志有：区域性深大断裂旁侧次级褶皱、分异较好的超镁铁质岩体、辉石岩相、矿化蚀变、铁帽及氧化矿露头、综合性物探和化探异常。(11)综合地质、地球物理、地球化学和矿床地质资料,预测清明山铜镍矿区具有大型以上铜镍硫化矿的找矿前景,中小型与花岗岩有关的锡铜多金属找矿前景。重点找矿方向是：探索清明山矿区深部隐伏的大规模镁铁质-超镁铁质岩体及大型岩床底部与侵入通道内的块状铜镍硫化物矿体。提出了清明山矿床3个找矿靶区：清明山矿区东南部Ⅱ号物探异常预测区,马漕山矿区东部Ⅲ号物探异常预测区,清明山矿区Ⅰ号物探异常西部预测区。通过研究和总结玄武岩与镁铁质侵入岩的地质、地球化学特征、两者相互关系、镁铁质岩浆成因环境和源区性质、铜镍硫化物矿床的地质和地球化学特征、矿床的形成机制、成矿规律等,阐述了铜镍矿体与玄武岩和镁铁质侵入岩成因联系、铜镍矿床地质特征,建立了铜镍硫化物矿床的成矿和及找矿模式,总结出了地质、地球物理和地球化学找矿标志,肯定了研究区的找矿前景。更多还原

【Abstract】 Sipu group is the oldest Proterozoic stratum which exposed in Sibao region in north Guangxi, China, have large quantity of mafic volcanic rocks, mafic intrusive rocks, intermediate-acid intrusive rocks,is the important component of Cu-Ni-PGE and Sn, Cu, Pn, Zn, Sb, W, U, Au metallogenic belts in northern Guangxi province, and also one of the great potential polymetallic prospective zones in Southern China. This paper is based on the detailed research on regional geological background and its evolution, the comprehensive geological, geophysical, geochemical, survey and mining data of deposits(mineral points) in the research area. According to the guidance of regional metallogeny and volcanic mineralization theory, and to the main line of structure-magmatism-metallogenesis, it’s the first time for us to do in-depth analysis and system research on typical deposit-Qingmingshan copper-nickel sulfide deposit, representative mafic intrusive rocks, mafic volcanic rocks, and Sn-Cu-Pb-Zn etc. deposits compatibly. We achieve the following main results and understanding:(1) Sibao region located in southeast margin of the Yangtze platform in tectonic setting, the early Mesoproterozoic, the happening tectonic movement, which ancient Huana oceanic crust nose down below the Yangtze platform, induced the forming of the basin behind island-arc, received a large number of hemipelagic sea-deep sea clastic deposition (Sibao Group); magmatic diapir and intruding which partial melting of subducted oceanic crust formed large-scale polycyclic mafic volcanic rocks; in the period of late Mesoproterozoic to early Neoproterozoic, accompanied by the further evolution of rift basins and volcanic-sedimentary thickening, mafic magmatism mainly changed as magmatic intrusion; in the same time, the differentiation and evolution of mafic magma, crustal contamination and partial melting formed a granodiorite; the late Neoproterozoic, with the plate convergence movement, the Movement of arc basin rift over, folds and deep magmatic orogenic thermal erosion, melting of continental crust formed a large number of massive biotite granite. (2) Sipu group are hemipelagic sea-deep sea clastic deposition with characteristics of turbidite, which consist of sandstone, arkose lithic sandstone, mudstone, and mafic volcanic rocks, which the feature of the composition of petrochemistry is rich in pro-iron elements, shch as Mn, Cu, Ni, Co, Cr, V, Pb, Zn. Danzhou group are transition facies-marine facies deposition, which consist of conglomerate, sandstone lithic sandstone and carbonatite. Which is enrichment in Zn, Ba and other acidic elements. There are widely distribution of Cu-Ni-PGE series of deposits, Sn, Cu, Pn, Zn, Sb, W, U, Au series of deposits in Sipu groups.(3) Mafic Intrusive rocks and volcanic rocks interdepended and associated with each other in spatial and temporal distribution, many characteristic of which include chemical composition, the feature and pattern of trace elements and rare earth elements, and the tectonic discrimination result are same, such as which is poor in TiO2 and K2O, rich in MgO, belong to tholeiite series; Trace Elements richen in large ionic radius elements Rb, Cr, Ba and Th, poor in Sr, depleted in high field strength elements Ta, Nb, P and Ti. Light rare earth slightly enriched, HREE loss, weak or no dEu aberrant, lean right in REE distribution pattern; Th/Nb ratio both are much higher than MORB and OIB rocks, Th/Nb ratio, and also higher than Th/Nb ratio of Yangtze block in the region; Nb/Ta and Nb/U ratio all much lower than normal ridge basalt and chondrite values; have the feature of higher 87Sr/86Sr ratio(> 0.7033), lower 143Nd/144Nd (<0.5130) and negative eNd(t)(<0), what mentioned above indicate that magam originated from partly melted mantle(EMI) and mixed by crust materials in continental margin near island arc, belong to the same source magma and formed in dissimilar time.(4) Diorite granites and biotite granites both are enriched on aluminum in the composition of petrochemistry, and trace elements enrichen in K, Rb and Th, loss of Ti, LREE enrichment, dEu significant losses, lean right in REE distribution pattern; Diorite granite is a mixed-source-type granite, and biotite granite is a remelting-type granite.(5) Sipu group formed in early-middle Proterozoic, about 1190-1800 Ma; Danzhou group formed in the 822-890 Ma; Proterozoic volcanic rocks formed in the mid-late Proterozoic, about 1090-1734Ma; mafic intrusive rocks formed in roughly late, about 982-1088 Ma, diorite granite formation age is about 820-1064 Ma, biotite granite formed in the 820-898 Ma. Qingmingshan Cu-Ni deposit formation age is about 1087±56Ma.(6) Qingmingshan’s mafic intrusive rocks contained copper-nickel sulfide occurred in the form of dike, with integrated magmatic differentiation, from bottom to top of the mafic intrusive rocks lithology may divided into pyroxenite-gabbro-diabase-diorite etc.; The chemical feature of mafic-ultramafic intrusive rocksω(Si02) is 42.68～45.84%,ω(Al2O3) is 6.62～10.58%, co(MgO) is 17.87～25.12%,ω(TiO2) is 0.33～0.52%,ω(K20) is 0.05～1.19%. Trace elements rich in large ionic radius elements Rb, Depleted in high field strength elements Ta and Nb; REE rare earth elements feature SREE content is 40.95～63.7×10-6, SLREE/SHREE is 1.82～1.93, LaN/YbN is 2.92～3.2, dEu is 0.56～1.13; light rare earth is relatively slightly enriched, HREE loss, weak or no dEu aberrant, what mentioned above indicate that Qingmingshan’s mafic intrusive rocks have arc-magma geochemical characteristics.(7) Qingmingshan copper-nickel sulfide deposits distributed the bottom of mafic-ultramafic intrusive rocks, controlled by pyroxenite lithofacies. Ore body is east-west direction, bedding output, tendency south, dip angle is 28°～52°, thickness is 20～250 m, length is 1.0～3.5 Km. From the surface to down, ore-bearing rock currently controlled by drills etc. gradually become larger in aspects of thickness, and corresponding to become rich on grade of copper-nickel ore. Qingmingshan copper-nickel sulfide deposit is divided into north and south mining area. In south mining area Qingmingshan copper-nickel sulfide orebody extend more than 1500m, thickness is 0.81～3.78m, Ni grade 0.31%～0.49%, Cu grade 0.14%～0.27%, Co 0.008%～0.016%; In north mining area Macaoshan copper-nickel orebody’s surface is mostly covered by quaternary landform. Ore controlled extend more than 500 m, thickness is 0.8～3.5m, Ni grade 0.20%～0.30%, Cu grade 0.10%～0.30%. There are four mainly types of ores:disseminated ore, taxiticstructure ore, massive ore and ore vein; most of the metal minerals are pyrrhotite, pentlandite, chalcopyrite, and so on. In Copper-nickel ore d34S is-0.5%o～+3.60%o, in mafic rock d34S is 6.3%o-+24.9%o. Compareing and analyzing with the geological and geochemical on Duluth Complex Cu-Ni deposits, show that Qingmingshan copper-nickel sulfide deposit is similar to Duluth Complex on mentioned above all, have many dfferent characters contrasting with Jingchuan Cu-Ni deposits; all these are arosed by different about tectonic settint.(8) The formation of Cu-Ni sulfide deposits on mafic intrusive rocks in Qingmingshan area are controlled by magmatic immiscibility, then crystallization differentiation, the central factor begeting magmatic immiscibility and saturation of S are magmatic mixed by sulfur-rich volcanic-sedimentary rocks, then rapid decline in magmatic temperature and fractional crystallization.(9) There are two series of deposits in Qingmingshan area, Cu-Ni-PGE series formed in stage of the nosing down of ocean crust and rift valley forming of deposition-basin, formed in period between Mesoproterozoic Era and Newproterozoic Era, fomed by liquid immiscibility and differentiation from melting mafic intrusive rocks, distributed in mafic-ultra mafic rocks bottom. Sn, Cu, Pb, Zn, Sb, W, U, Au mineralization series formed in stage of deposition-basin folding, orogeny and granitizing, formed in middle-late phase of Newproterozoic Era, related to location, evolution and hydrothermal circulation of biotite granite in genesis, distributed in the peaks and fault near granite. Analyse on the cause of ore-forming of the two metallogenic series, show that abundant component of metallogenic series in Sipu group stratum is basic, the evolution on plate tectonics and tectonics is main dynamic cause, the mafic-ultramafic rock formation, segregation, differentiation and positioning, evolution and hydrothermal circulation of biotite granite is the key. On this basis, established the Qingmingshan’s metallogenic model of copper-nickel deposits in genesis.(10) The major controlled ore-forming factors are:the tectonic setting-sea basin behind island arc, secondary structures-fold near Sipu fault (Qingmingshan double folds), lithofacies of ultramafic intrusive rocks, lithologic interface between intrusive rocks and country rocks, metamorphosed volcanic-sedimentary rocks in Sipu group. The direct and effective clues summarized for prespecting are secondary structures-fold near regional deeper and bigger fault, the bette-differentiation ultramafic rock, pyroxenite lithofacies, mineralized outcrops, integrated geophysical and geochemical anomalies.(11) Comprehensive geological, geophysical, geochemical and geological data deposits, indicated that there is better and bigger potential for prospecting on big-type copper-nickel sulfide deposits, middle-small type granite-related tin-polymetallic deposits. The major direction of prospecting are:to explore the the large-scale massive copper-nickel sulfide ore bodies distributed in bedrock and channel of mafic-ultramafic intrusive rocks. All analysis mentioned above suggest 3 prospecting target in Qingmingshan area:No.Ⅱgeophysical anomaly forecast district near southeastern Qingmingsahn mining area, No.Ⅲgeophysical anomaly forecast district near eastern Macaoshan mining area, and No.Ⅰgeophysical anomaly forecast district near western Qingmingsahn mining area.更多还原