CAJ | 학술논문

中蒙边境及邻区铀矿床产出环境、地质特征、形成作用和找矿标志
중몽변경급린구유광상산출배경、지질특정、형성작용화조광표지
Geological setting, features, origin and exploration criteria of uranium deposits occurring within the China-Mongolia border region and its neighboring areas

万方数据

中国地质中國地質 중국지질
CHINESE GEOLOGY
2014年 4期 1037-1058 ,共22页

聂凤军%李强峰%王佳新%蒋喆%张晓康%吴科锐%丁成武%曹毅

섭봉군%리강봉%왕가신%장철%장효강%오과예%정성무%조의

火山岩型铀矿床%砂岩型铀矿床%叠加成矿作用%前侏罗系变质岩体%时空分布规律%中蒙边境地区火山巖型鈾礦床%砂巖型鈾礦床%疊加成礦作用%前侏囉繫變質巖體%時空分佈規律%中矇邊境地區
화산암형유광상%사암형유광상%첩가성광작용%전주라계변질암체%시공분포규률%중몽변경지구
volcanic type uranium deposit%sandstone type uranium deposit%rejuvenation%Pre- Jurassic metamorphic terrane%spatial-temporal distribution%China-Mongolia border region

中蒙边境及邻区位于西伯利亚板块、塔里木板块和华北克拉通的结合部位，是全球范围内重要的铀多金属成矿带之一。受多期次构造岩浆活动影响，该区前侏罗纪变质岩块体和中新生代火山-沉积岩分布广泛，深大断裂纵横交错，各类铀矿床（矿化区）星罗棋布。根据围岩类型，结构构造及成矿过程可将该区铀矿床划分为6种类型：（1）火山岩型；（2）砂岩型；（3）岩脉型；（4）褐煤型；（5）交代岩型；（6）磷灰盐型。其中火山岩型和砂岩型铀矿床具有重要经济意义。 　　区域矿产地质研究表明，中蒙边境产出的大部分铀矿床（矿化区）与前侏罗纪变质岩块体具有密切时空分布关系。前侏罗纪变质块体可划分为2部分：（1）前寒武纪高级变质岩；（2）古生代中、低级变质岩。铀的亲石元素特性致使其在壳-幔物质发生分异时富集于地壳的硅铝层。鉴于在地壳长期演化历史中，古老变质岩已具备有较高的铀含量，那么它们在显生宙构造-岩浆活动中就为铀的富集成矿提供有利的物质条件。显生宙构造运动的形式除了断裂活化外，也包括陆相沉积盆地的上隆和下陷。铀在地壳硅铝层中的富集是通过2种方式实现的：（1）陆壳的深熔和岩浆的分异作用；（2）富铀岩体（层）的风化剥蚀和再沉积活动。研究结果表明，铀的富集过程十分缓慢，其中火山岩型铀矿床的形成作用就是长英质岩浆活动的组成部分。 　　火山型铀矿床主要出现在中蒙边境最东端蒙古国境内，它们是中蒙古-额尔古纳地块伸展构造环境（裂陷槽为大量高钾长英质火山岩所充填）中构造-岩浆作用及相关流体活动的产物。长英质火山杂岩体内产出的若干处大型铀矿床（区）和铅-锌-银-铀矿床即是很好的佐证。一般来讲，具有强烈分异特点的富碱性火山岩及相关铀矿床大都在侏罗纪-白垩纪构造-岩浆作用对前侏罗纪岩体（层）发生强烈叠加改造部位产出，其形成作用可能与晚侏罗世-早白垩世构造-岩浆活动有关。同位素年代学（铀矿床铀-铅同位素测年）研究结果表明，铀矿体的形成时间为153~136 Ma，该时间段与其所在的多尔诺德组安山-玄武岩和流纹岩的形成时间基本一致，同时，与俄罗斯远东地区斯特尔特苏维卡（Streltsovsk）超大型铀矿床的形成时代（136~134 Ma）相吻合。矿区范围内富钾流纹岩铀含量较高（300×10-6左右），暗示了这套火山岩可能为铀矿床的矿源层。另外，流纹岩中熔融包裹体铀含量（14~25）×10-6进一步印证了上述推论的可靠性。与富钾长英质岩浆作用有关的热液活动对早期含铀岩体（层）的叠加改造可导致铀的进一步富集，进而形成大规模和高品位铀矿体。大量黄铁矿、方铅矿、闪锌矿和白铁矿等硫化物的存在暗示了成矿作用是在还原条件下形成的。大多数砂岩型铀矿床分布在中新生代断陷盆地内，这些盆地一般为各类沉积岩（物）所充填，其中河流相、三角洲相和浅海沉积相（物）为铀矿床的容矿围岩。在所有上述沉积岩（物）中，辫状河流相沉积岩（物）是最重要的含矿层位。砂岩型铀矿床大都是断陷和凹陷带构造运动最后阶段构造-沉积联合作用的产物。盆地周缘前侏罗纪富铀岩体（层）的风化剥蚀，为砂岩型铀矿床的形成提供了丰富的物质来源。早期构造运动（176~156 Ma）为古潜水面氧化提供了有利条件并且形成了低品位铀矿化区。在晚白垩世（96 Ma）到渐新世（35 Ma）时期，古陆块体抬升与沉降活动期间为氧化作用的发生创造了有利条件，并且为主要砂岩型铀矿床的形成奠定了基础。 　　中蒙边境火山型和砂岩型铀矿床独特的地质、地球化学特征受到国内外地质学家的广泛关注。对于这些矿床的地质环境，地质和地球化学特征以及其容矿围岩的系统研究将极大地提高人们对于铀矿床成矿作用的理解。与此同时，对这些铀矿床的成因类型和勘查标志的研究也将在中蒙边境及其邻区开展隐伏铀矿床的综合评价中发挥重要作用。
중몽변경급린구위우서백리아판괴、탑리목판괴화화북극랍통적결합부위，시전구범위내중요적유다금속성광대지일。수다기차구조암장활동영향，해구전주라기변질암괴체화중신생대화산-침적암분포엄범，심대단렬종횡교착，각류유광상（광화구）성라기포。근거위암류형，결구구조급성광과정가장해구유광상화분위6충류형：（1）화산암형；（2）사암형；（3）암맥형；（4）갈매형；（5）교대암형；（6）린회염형。기중화산암형화사암형유광상구유중요경제의의。 　　구역광산지질연구표명，중몽변경산출적대부분유광상（광화구）여전주라기변질암괴체구유밀절시공분포관계。전주라기변질괴체가화분위2부분：（1）전한무기고급변질암；（2）고생대중、저급변질암。유적친석원소특성치사기재각-만물질발생분이시부집우지각적규려층。감우재지각장기연화역사중，고로변질암이구비유교고적유함량，나요타문재현생주구조-암장활동중취위유적부집성광제공유리적물질조건。현생주구조운동적형식제료단렬활화외，야포괄륙상침적분지적상륭화하함。유재지각규려층중적부집시통과2충방식실현적：（1）륙각적심용화암장적분이작용；（2）부유암체（층）적풍화박식화재침적활동。연구결과표명，유적부집과정십분완만，기중화산암형유광상적형성작용취시장영질암장활동적조성부분。 　　화산형유광상주요출현재중몽변경최동단몽고국경내，타문시중몽고-액이고납지괴신전구조배경（렬함조위대량고갑장영질화산암소충전）중구조-암장작용급상관류체활동적산물。장영질화산잡암체내산출적약간처대형유광상（구）화연-자-은-유광상즉시흔호적좌증。일반래강，구유강렬분이특점적부감성화산암급상관유광상대도재주라기-백성기구조-암장작용대전주라기암체（층）발생강렬첩가개조부위산출，기형성작용가능여만주라세-조백성세구조-암장활동유관。동위소년대학（유광상유-연동위소측년）연구결과표명，유광체적형성시간위153~136 Ma，해시간단여기소재적다이낙덕조안산-현무암화류문암적형성시간기본일치，동시，여아라사원동지구사특이특소유잡（Streltsovsk）초대형유광상적형성시대（136~134 Ma）상문합。광구범위내부갑류문암유함량교고（300×10-6좌우），암시료저투화산암가능위유광상적광원층。령외，류문암중용융포과체유함량（14~25）×10-6진일보인증료상술추론적가고성。여부갑장영질암장작용유관적열액활동대조기함유암체（층）적첩가개조가도치유적진일보부집，진이형성대규모화고품위유광체。대량황철광、방연광、섬자광화백철광등류화물적존재암시료성광작용시재환원조건하형성적。대다수사암형유광상분포재중신생대단함분지내，저사분지일반위각류침적암（물）소충전，기중하류상、삼각주상화천해침적상（물）위유광상적용광위암。재소유상술침적암（물）중，변상하류상침적암（물）시최중요적함광층위。사암형유광상대도시단함화요함대구조운동최후계단구조-침적연합작용적산물。분지주연전주라기부유암체（층）적풍화박식，위사암형유광상적형성제공료봉부적물질래원。조기구조운동（176~156 Ma）위고잠수면양화제공료유리조건병차형성료저품위유광화구。재만백성세（96 Ma）도점신세（35 Ma）시기，고륙괴체태승여침강활동기간위양화작용적발생창조료유리조건，병차위주요사암형유광상적형성전정료기출。 　　중몽변경화산형화사암형유광상독특적지질、지구화학특정수도국내외지질학가적엄범관주。대우저사광상적지질배경，지질화지구화학특정이급기용광위암적계통연구장겁대지제고인문대우유광상성광작용적리해。여차동시，대저사유광상적성인류형화감사표지적연구야장재중몽변경급기린구개전은복유광상적종합평개중발휘중요작용。
The Sino-Mongolia border region and its neighboring areas are located at the convergence zone of the Siberian platform, Tarim plate and North China craton, and is one of the most important uranium metallogenic provinces in the world. Deep-seated faults, pre-Jurassic metamorphic terrane and various types of uranium deposits (mineralized areas) are well developed in the region due to the multiphase tectonic-magmatic events. These uranium deposits can be classified into six types in term of their host rocks, geometry and ore-forming processes: (1) volcanic type; (2) sandstone type; (3) vein type; (4) lignite type; (5) metasomatitic type; (6) phosphorite type, among which the first two types of uranium deposits bear the most important economic significance. Regional metallogenic studies show that most of the uranium deposits (or mineralized areas) occurring within the Sino-Mongolian border region are closely spatially associated with pre-Jurassic metamorphic terrane consisting of two parts: (1) Precambrian high-grade metamorphic rocks; (2) Paleozoic lightly metamorphic rocks. Since uranium is a lithophile element, it is more easily enriched in the acidic sialic section of the crust during the differentiation of mantle matter. Because these old formations had already been enriched in uranium through the long geological evolution, they might have provided the precondition for economic enrichment of uranium in the Phanerozoic tectonic movements when downfaulted or downwarped continental basins occurred with terrestrial dominated sediments. Where the uranium-enriched geological bodies existing in one region are eroded, all of them can serve as the source for the sandstone-type deposits. The early tectonic event occurring around 176 to 125Ma provided suitable conditions for the oxidization of the groundwater table and the formation of low-grade uranium mineralization area. In the Phanerozoic tectonic-activated regions, the economic enrichment of uranium usually occurred in intensive rejuvenated places of the pre-Jurassic metamorphic terrane. The gradual enrichment of uranium in the sialic crust is mainly achieved through two differential processes:granitization and sedimentary differentiation. However, this combined process is very slow and takes a long time. The ore-forming processes of volcanic type uranium deposits may be an integrated part of the uranium-bearing granitization. For the volcanic type uranium deposits occurring in the easternmost segment of the Sino-Mongolian border, they were formed during the time of tectonic extension when a number of troughs that were filled with high K-felsic vocanics were formed within the Central Mongol-Argun terrain. Several large-sized Pb-Zn-Ag-U deposits have been identified in the felsic volcanic complexes. Both uranium and fractionated peralkaline magma were produced by the intensive rejuvenation of the pre-Jurassic metamorphic terrane. The formation processes of the sandstone type uranium deposits might have been genetically related to Late Jurassic to Early Cretaceous igneous activities. Geochronological studies (U-Pb isotopes on uranium ores) demonstrate that the uranium ores formed around 153 to 136 Ma. That time of the uranium ore formation coincides with the formation age of andesitic basalt and rhyolite of the Dornod Formation. Late Jurassic to Early Cretaceous ages are practically equivalent to the formation time of uranium deposits in the Streltsosk caldera in Russia (136-134 Ma). The high K rhyolite is clearly enriched in uranium (about 30 × 10-6), making it the probable uranium source. The high U content of the melt inclusions (U, 14 × 10-6-25 × 10-6) from the rhyolite provides the further evidence for the hypothesis mentioned above. The Early formed uranium mineralized zones were intensively overprinted by the hydrothermal events associated with the emplacement of the high K-felsic magma. Widespread pyrite, galena, sphalerite and marcasite suggest formation from metastable sulfur species, which are powerful reductants. Most of the sandstone type uranium deposits occur in the Meso-Cenozoic rift basins filled with various sediments. The uranium-bearing layers formed by amalgamation of braided channels deposited in a fluvial, terrestrial delta and offshore environment. All these sandstone uranium deposits were formed at the last stage of phaneroic tectonic movement when downfaulted or downwarped continental basins occurred with terrestrial dominated sediments. The Early tectonic event (176-156 Ma) provided suitable condition for the paleo-phreatic oxidation and led to the formation of low-grade uranium mineralized zones. During the period of Late Cretaceous (96 Ma) to Oligocene (35 Ma), the uplifting erosion and sedimentation resulted in suitable condition for the inter-layers oxidation and led to the formation of major sandstone type uranium deposits. Geological and geochemical features of both volcanic type uranium deposit and sandstone type uranium deposit have attracted much attention among geologists both in China and abroad. The integrated analyseis of the geological setting, geological and geochemical features of these deposits and their related wall rocks will greatly upgrade the understanding of the ore-forming processes of the uranium deposits. Meanwhile, the genetic model and mineral exploration criteria of these uranium deposits can also be used during the comprehensive evaluation of the concealed uranium deposits in the China-Mongolia border region and its neighboring areas.