【作者】 王建中；

【导师】 李建威；

【作者基本信息】 中国地质大学 ， 矿物学、岩石学、矿床学， 2007， 硕士

【摘要】 朝山金矿床位于铜陵矿集区中部狮子山矿田内，是长江中下游唯一的矽卡岩型独立金矿床。区域地层除缺失中、下泥盆统和下石炭统外，自志留系-第四系均有分布。主要地层为石炭系-三叠系海相沉积碳酸盐岩，其中赋矿地层主要为二叠-中三叠灰岩、硅质岩、页岩夹半深海-海陆交互相碎屑岩。区内岩浆活动强烈，广泛出露的晚中生代侵入岩类主要为一套中基性-中酸性侵入岩，主要岩石类型有辉石闪长岩、闪长岩、石英闪长岩、花岗闪长岩、花岗岩，但许多岩体实质上是中酸性岩和基性岩组成的复式岩体或杂岩体。前印支期棋盘格式的导岩、导矿基底断裂和燕山期浅部北东向“S”形盖层褶皱构造相复合，组成了铜陵地区“立体网络状”构造格架，控制着铜陵矿集区矿田和矿床的分布。区内矿产丰富，已探明矿产地上百处，主要矿种为Cu，Au，Mo，S，主要矿床类型为矽卡岩型、层控型，其次还有斑岩型及少量热液脉型，组成完整的岩浆热液矿床组合。绝大多数矿床的形成与晚中生代中酸性岩浆作用有关。朝山金矿床是铜陵矿集区典型的还原性矽卡岩金矿，规模不大，但品位高（6-38g／t，平均18.4g／t）。矿区内出露地层主要为三叠系中统南陵湖组（T₂n）和分水岭组（T₂f），岩性以灰岩、大理岩为主，夹少量泥岩或角岩条带。矿区内近EW向、近SN向、NNE向、NW向断裂构造及层间破碎带或层间断层发育，这些构造控制了矿床（体）的空间展布。矿区内侵入岩以花岗闪长岩和石英闪长岩为主，其次是辉石闪长岩和后期的脉岩。矿体主要赋存于三叠系下统南陵湖组与白芒山中基性杂岩体东接触带及其围岩的层间裂隙中。主矿体形态多呈透镜状、陡薄板状，严格受构造控制，构造叠加处矿体变厚。矿石矿物以磁黄铁矿黄铁矿、为主，其次为毒砂、黄铜矿、方铅矿、闪锌矿、黝铜矿和辉铋矿等，其中磁黄铁矿是矿床内含量最多和主要的载金矿物。脉石矿物为方解石、石英、绿泥石、石榴石等。围岩蚀变主要有矽卡岩化、钾长石化、黑云母化、交代石英岩化、碳酸盐化，局部见绿帘石化、阳起石化、绿泥石化、绢云母化。白芒山杂岩体以辉石闪长岩为主，其次为石英闪长岩。辉石闪长岩含大量角闪石和辉石巨晶和堆积晶以及辉石堆积岩，寄主岩具有准铝质、高钾钙碱性的地球化学特点。此外，白芒山辉石闪长岩富集大离子亲石元素（Rb、Ba、Th、Sr）和轻稀土LREE，亏损高场强元素（Nb、Ta、Ti）和HREE，无明显的Eu异常。Sr-Nd同位素组成较均一，具有较低的(⁸⁷Sr／⁸⁶Sr)_i值和较高的ε_Nd（t），分别为0.7065～0.7074和-7.78～-8.01。Ba／Th和Ba／La比值较高，分别为64.65-74.76和13.61-15.56，，但Rb／Sr比值和Sm／Nd比值低，分别为0.068-0.09和018-0.20。地球化学和同位素组成特征与长江中下游地区白垩纪玄武岩和基性侵入岩基本一致，表明白芒山岩体的初始岩浆可能来源于富集的岩石圈地幔（EMⅠ）。结合前人资料，可将白芒山岩体的成因总结为：富集的岩石圈地幔减压熔融形成高钾钙碱性玄武质岩浆，之后底侵到壳幔边界形成深位岩浆房。大量幔源岩浆的底侵导致下地壳物质的熔融及岩浆混合，形成壳幔混源型岩浆。这种岩浆在深位岩浆房及随后的上升侵位过程中与中下地壳之间发生了较明显的AFC过程，并在不同深度的结晶分异过程中形成角闪石、辉石巨晶／堆积晶和辉石堆积岩和辉长质包体。在整体伸展的构造背景下，经过复杂演变的中基性岩浆以“底辟”形式侵位，至大约2.5-3.2km的上地壳浅部就位，形成白芒山辉石闪长岩。白芒山辉石闪长岩中角闪石的Ar-Ar定年结果表明其侵位时代大致为142-138Ma；而磁黄铁矿的Re-Os定年说明朝山金矿床形成于141.7Ma左右。这反映成岩成矿时代基本一致，也进一步证明了白芒山辉石闪长岩与朝山金矿床的成因联系。矿石矿物和蚀变脉石矿物的O、C、S、Pb、H、Os、Si同位素分析结果表明成矿物质主要来自白芒山辉石闪长岩，成矿作用与燕山晚期的岩浆活动密切相关。成矿流体早期以岩浆水为主，，晚期则大气降水的加入增多。朝山金矿床是地层、构造和岩浆岩等多种地质因素和地质作用综合作用的结果。地层的虚脱部位和层间裂隙系统是成矿和赋矿的主要场所；白芒山岩体不仅为朝山金矿床提供直接的热动力，而且为成岩成矿提供了必要物质基础；而构造则是密切组合各成矿因素的关键，既是岩浆侵位和流体迁移的通道，又是有利的控岩控矿因素（接触带的内凹部分），控制着岩体和重要的矿床（体）的分布。近年的高精度同位素年代学研究结果(如SHRIMP锆石U-Pb、辉钼矿Re-Os、单矿物⁴⁰Ar／³⁹Ar等)表明，铜陵地区大规模的中酸性-中基性岩浆活动时代始于晚侏罗世末期，但集中在143-136Ma。同样，绝大多数矿床的成矿时代集中在145-135Ma，说明铜陵地区大规模成矿作用发生于早白垩世约8-10Ma的时间内，成矿作用与早白垩世岩浆作用密切相关。铜陵矿集区成岩成矿时代与鄂东南矿集区巨量岩浆活动与大规模成矿的时代（144-135Ma）几乎完全一致，也与长江中下游晚中生代第一阶段（145-133Ma）成岩成矿时代十分吻合。不同矿集区内岩浆活动与成矿作用近于同时发生的事实表明它们受统一的地球动力学背景和深部过程控制。长江中下游成矿带位于地幔的隆起带，地壳厚度比邻区一般要小2-3km，表明该区自晚中生代以来发生了明显的软流圈上涌和岩石圈伸展减薄。热的软流圈上涌必然引发岩石圈地幔的大规模熔融和伸展减薄，并沿几条超岩石圈断裂（如长江深断裂、常州-阳新断裂等）形成长江中下游凹陷带，这也是朝山金矿床和长江中下游晚中生代成矿作用发生的深部地球动力学背景：强烈的岩石圈伸展及玄武岩浆底侵为大规模岩浆活动及成矿作用提供了必要的热、物质和流体来源以及重要的构造。这种构造背景与晚中生代时期整个中国尔部地区处于总体伸展的地质事实一致，并可能与古太平洋板块向欧亚大陆的斜向俯冲有关。更多还原

【Abstract】 The Chaoshan gold skarn deposit is situated in the Shizishan ore field, the center ofTongling district Anhui province, which is the only one gold deposit of the well-known middleand lower Yangtze River. Regional strata host from the Silurian to the Quaternary exceptthe Devonian lower-medium series and the Carboniferous lower series. Thestratigraphy in this district is dominated by the Carboniferous-Triassicmarinecarbonate carbonate rock, in which Permian period-Triassic period limestone,silicalites, shales interbeding half deep sea-thalassianic terrestrialis alternate clasticrocks are main ore-beating strata. It is marked by widespread distribution of Late Mesozoicintrusive rocks are intermidiate -basic to intermediate-acid rocks, which are dominated bypyroxene diorite, quartz diorite, granodiorite and granite related with the most copper-golddeposits. However, many intrusives characteristic complexes composing of the intermediate-acidrocks and the basic rocks. Preindo Chinese epoch basement faults and Yanshanian NE directionsigmoid cover drape folds compound and constitute "solid network" structure trellis controllingthe distribution of the ore fields and ore deposits. There are more than one hundred mineraloccureences including Cu, Au, Mo, S etc. The intact deposit compages are dominated by skarndeposits and stratabound deposits are the dominant type of mineralization, although porphyrydeposits and hydrothermal lode deposits are also developed.The Chaoshan deposit, small scale, is typical reduced gold skam deposit with high oregrade from 6 t 38 g/t Au, average of 18.4 g/t. Triassic Nanlinghu and Fenshuiling Formationlimestone, mables interbeding minor mudstone or chert bandings are import wall rock or andhost of skarn and stratabound mineralization. The utmost important ore deposits/bodiescontrolling structures are almost east-west, south-north, north -north west folds and interbeddedfracture zone and interbedded faults. The ordinate intrusives are granitic diorite and diorite, theminor are proxene dioriteand the later dike rocks. Ore bodies lie in the east contract between theBaimangshan intermidiate-basic complex and the Nanlinghu limestone and its interbeddedcrannies, Main ones controlled by the strutures are commonly lenticular and podiform in shapeand thicken at the congruence of the structures. Ore minerals are pyrrhotite, arsenopyrite andpyrite, with minor amounts of chalcopyrite, galena, sphalerite, tetrahedrite and bismuthinite etc, in chich pyrrhotite is the most Au-bearing mineral. Gangue minerals are calcite, quartz, chlorite andgart etc. Wall alteration develop skarnlization, k-felspathic alteration, biotite, alterated quartzite,carbonate and in place occur epidote, actinolite, chlorite and sericite etc.Baimangshan complex hosting abundant hornblende and proxene accumulatingcrystal xenolits is dominated by pyroxene diorite with minor quartz diorite belonging tothe pre-aluminum, high potassium calc-alkaline rock. Besides,i t is enriched in large ionlithosphere elements （Rb, Ba, K, Sr） and LREE, but strongly depleted in high field strengthelements （Nb, Ta, Ti）. All samples have high Sr, Ba/Th和Ba/La, they are 1007-1100, 64.65-74.76 and 13.61-15.56 respectively, on the contrary, they have low Rb/Sr ratio （0.068-0.09） andSm/Nd ratio（0.18-0.20）. Rock has high and even Sr-Nd composition (⁸⁷Sr/⁸⁶Sr)_i=0.7065-0.7074,(¹⁴³Nd/¹⁴⁴Nd)_i=0.5121, and the calculatedε_Na（t）=-7.78--8.01. The geochemistric and isotopiccharacteristics are indistinguishable from the cretaceous basalt and basic rocks origining from theenriched geosphere mantle in from the middle and lower reaches of Yangtze River. All thatmentioned above indicates that primary magma of the Baimangshan complex maybe source fromthe enriched geosphere mantle （EMⅠ）. The enriched Lithosphere mantle partialy melted as thetemperature descended, and formed the high potassium（K） calc-alkaline basaltic magma, and thenunderplated and melt the lower crust and came into being the crust-mantle admixing（Ⅰ） magma.These magma represented distinct AFC action with the middle-lower crust during the upliftingprocess resulting in the hornblende and proxene crystal xenolits accumulated at the differentdepth. Under the extending constrcture setting, the evolved intermediate-basaltic magma ascendand formed the Baimangshan proxene diorite at the 2.5-3.2 Km under the earth’s surface due tocooling.The Ar-Ar dating of hornblende from the Baimangshan proxene diorite indicate thatmagma intruded at the 142-138 Ma approximately, otherwise, the Re-Os dating of pyrrhotite showthat the Chaoshan gold deposit formed at the 141.7Ma. It suggests that magmasim is consistentwith the mineralization and also prove the genesic intimate relationship between the Baimangshanproxene diorite and Chaoshan gold deposit.The H-O-C-S-Si-Pb-Os isotope composition of the ore minerals and Gangue mineralsindicates that the metallogeny matter derive from the Baimangshan proxene diorite, and also showthat the metallogeny of the Chaoshan gold skarn deposit is related with the later Yanshanianmagmatism intimately. The ore-bearing fluid is dominated by the magmatic water in the early, butatmosphere water increases in the later stage. Deposit is the result from the compositiveinteractions between strata, structure and magma-thermal liquid system. The collapse sections andinterbedded crannies of strata are the favorable sites for metallogeny.The Baimangshan complexprovides matter and heat energy. And that, structures assemble all kinds of metallogeny factors,they are the channels for magma emplacement and fluid transfer, and are also important factorcontrolling the rock and ore deposit （ore bodies）.Recent high precise isotope chronology studies （such as Zircon SHRIMP U-Pb, Re-Os ofmolybdenite, Ar-Ar of single mineral） reveal that this district developed extensiveintermidiate-basic to intermediate-acid magma at the 143-136 Ma of the end of the later Jurassic. Meanwhile, The most deposits have been well constrained 145-135 Ma and themetallogeny of this district focus on eight-eleven Ma interval, the coherence indicates that themetallgeny is related with the cretaceous magmatism intimately.The magmatism and mineralization ages of Tongling are not only almost coherent with themetallogeny ages （144-135Ma） of Southeastern Hubei province, and also are inosculate with thefirst large scale mineralization stage （145-133 Ma） of the Middle and lowerreches of Yangtze River.The coeval magmatism and mineralization recognized in distinct regions of the Mid-LowerYangtze River indicate that they had the same geodynamic setting.The middle and lower reaches Yangtze River Metallogenic Belt is coincident with at theYangtze River rift, where the crust is 2-3km thinner than its surroundings. This indicates thatsignificant asthenosphere upwelling and lithospheric thinning since the later Mesozoic. This riftalong several lithospheric fault （such as Yangtze River deep fault, Changzhou-Yangxin fault）wasformed by upwelling of hot asthenosphere and partial melting of lithosphere. Large-scalelithospheric extension and magma underplating of the Early Cretaceous time could have been thegeodynamic setting of Chaoshan gold deposit and the middle and lower reaches Yangtze RiverMetallogenic Belt. It provide vast heat, matter, fluids and important structures and is responsiblefor the voluminous magrnatism and large-scale mineralization. The setting is coincident with thefact that the whole east of China has been extending since the later Mesozoic, and it is mayberelated with the ancient Pacific Ocean Plate dived to Eurasia obliquely.更多还原