Timing of hydrothermal activity associated with the Douzhashan uranium-bearing granite and its significance for uranium mineralization in northeastern Guangxi, China

The Miaoershan uranium(U)ore field in northeastern Guangxi is one of the important granite-related U deposits in south China and is closely related to the Douzhashan U-bearing granite.The Douzhashan granite contains primary U-rich accessory minerals,including monazite(UO2=0.98-1.75 wt%)and xenotime(UO2=1.48-6.14 wt%).Primary monazite and xenotime yield chemical ages of 231±28 Ma and 230±38 Ma by electron microprobe analysis and U-Pb isotopic ages of 220±6 Ma and 211±7 Ma by laser ablation-inductively coupled-mass spectrometry respectively.These ages demonstrate that the Douzhashan granite formed during the period of Indosinian magmatic activity.Back scattered electron imaging shows that monazite and xenotime are commonly altered to assemblages of low-U synchisite and apatite,which was associated with loss of U to hydrothermal fluids.U-Th-Pb analyses of secondary apatite yielded a chemical age of 136±17 Ma,which corresponds to the timing of Cretaceous-Tertiary crustal extension in south China.We suggest that the heat and CO2required for mineralization was the result of Yanshanian crustal extension,and that this triggered the breakdown of U-rich accessory minerals in the Douzhashan U-bearing granite.Uranium remobilization from the Douzhashan granite provided materials for mineralization within the granite and/or surrounding country rocks.Therefore,a combination of Indosinian compression and Yanshanian extensional overprint produced the hydrothermal U deposits associated with the Douzhashan granite.     

含锡锌铁矿的矿物学性及其综合利用新技术

研究含锡锌复杂铁精矿的矿物学特性,并开发含锡锌铁精矿球团预氧化-弱还原焙烧新技术。研究结果表明：铁精矿中的主要载铁矿物为磁铁矿,主要含锡矿物为锡石,主要含锌矿物包括闪锌矿和铁闪锌矿,其中闪锌矿占绝大部分;以单体锡石形式存在的锡占54.78％,而磁铁矿颗粒中的锡占41.31％;磁铁矿中的锡绝大部分为锡石的微细粒包体;88.95％的锌存在于硫化矿中,闪锌矿多以单体粒状或以不规则状与磁铁矿及其他矿物构成连生体;在w(C)/w(Fe)为0.2,焙烧温度为1075℃,时间为50min时,球团矿抗压强度为2 380N/个,Sn和Zn的挥发率分别为71.86％和56.28％,残余Sn和Zn含量均小于0.08％。     

与碳酸岩-碱性杂岩体相关的内生稀土矿床成矿作用研究进展

综述与碳酸岩?碱性杂岩体相关的内生稀土矿床的基本特征和成矿作用研究进展。根据矿化特征, 该类矿床大体可以分为原生岩浆型和热液型, 前者稀土矿物是从碳酸岩岩浆中直接结晶出来, 矿化主要产于碳酸岩岩体中; 后者稀土矿物通常与方解石、萤石、重晶石、石英等矿物共生形成脉体, 穿插于碳酸岩杂岩体及围岩中, 或作为裂隙或空洞充填物, 或呈细粒多晶集合体叠加在碳酸岩中早期形成的矿物之上。以往的研究对于稀土富集成矿的主要机制是碳酸岩和硅酸岩岩浆的液态不混溶作用或碳酸岩岩浆中碳酸盐矿物的分离结晶作用, 还是岩浆期后热液蚀变或不混溶的碳酸岩质流体的萃取作用, 存在很大的争议; 同时,与稀土成矿相关的碳酸盐体系选择性地富集轻稀土, 该类矿床中很少见到重稀土矿物, 亦是有待解决的问题。因此, 加强稀土元素在富挥发份的碳酸岩熔体和碱性硅酸岩熔体或流体之间, 以及碳酸盐矿物及共沉淀相与碳酸岩熔体之间分配行为的高温高压实验研究, 将是揭示该类稀土矿床成因的关键。     

Significance of native arsenic in the Baogutu gold deposit, western Junggar, Xinjiang, NW China

Native arsenic together with comb quartz and stibnite is found in the Baogutu gold deposit, western Junggar (Xinjiang), NW China. It is anhedral with various grain size (<0.001 to 2 mm), and contains 98 wt% to 98.7 wt% As. Micro-granular electrum, the main auriferous mineral in the Baogutu gold deposit, is commonly enclosed in or closely accompanied by native arsenic. Three ore-forming paragenetic stages could be identified. Native arsenic mainly formed at stage II which is also the major stage for gold deposition. Mineral assemblage formed at this stage is native arsenic-stibnite-electrum-arseno- pyrite-miargyrite-freibergite-pyrrhotite-pyrite. Based on native arsenic and its coexisting minerals, the temperature (230 to 170℃), oxygen fugacity (logfO₂ = −42―−56.5) and sulfur fugacity (logf S₂ = −13.3― −16.6) of stage II are estimated. From stage I to stage II, the temperature, sulfur fugacity and S²⁻ con-centration of hydrothermal fluid decrease obviously, whereas the As concentration increases. Coexis-tence with native arsenic of electrum and its contents of 0.5 wt%―1.3 wt% As suggest that As is im-portant to transport Au when S²⁻ concentration decrease in hydrothermal fluid. Crystallization of native arsenic induced the deposition of electrum and consequently the formation of the Baogutu gold deposit.     

An experimental study of tin partition between melt and aqueous fluid in F/Cl-coexisting magma

In order to investigate the formation mechanism of tin ores associated with F-bearing granite, an ex-perimental study of tin partition between F-bearing granitic melt and coexisting HCl-bearing aqueous fluid was conducted at 850℃ and 100MPa with fo2 approaching NNO. Geochemical behavior of tin was traced by changes in starting solid materials with different alumina saturation index ASI, in F content and in starting fluids of various HCl concentrations. The results show that DSn increases with ASI of melt and peraluminous melt is favorable for tin partition into aqueous fluid in the F/Cl-coexisting sys-tem. Aqueous fluid of higher HCl concentrations is advantageous for enrichment of tin. Furthermore, chlorine contents in glass run products correlate positively with F and Cl contents in the magma. In the F/Cl-coexisting system, granitic melts with high F contents (> ~1 wt%) could extract and enrich tin in the melt which can serve as a reservoir for the formation of tin ores. However, the partition coefficient of tin would increase significantly when F contents in the melt were below 1 wt%. Therefore, the de-crease of F contents is favorable to the partition of tin into aqueous fluid with high HCl contents, thus promoting deposition of hydrothermal tin ores.     

苗儿山北段深冲铀矿地质特征及成因探讨

深冲矿区位于苗儿山铀矿富集区,是花岗岩型铀矿产地.本文从地质背景、矿床地质特征、矿石矿物组成、围岩蚀变、包裹体特征、铅同位素组成、氢氧同位素组成等入手,系统阐明深冲矿区铀矿地质、地球化学特征.初步认为该矿床类型为碎裂蚀变花岗岩型,铀成矿物质来源具有壳幔源混合特点,是低温低盐度岩浆热液成因铀矿床.     

一种特殊类型的夕卡岩—镁铝夕卡岩的矿物特征

在研究我国河北省邯邢铁矿的过程中,发现了一种矿物组成比较特殊的夕卡岩。其组成矿物主要有富铝透辉石、绿脆云母、尖晶石、钙镁橄榄石、钙铝榴石、富铝角闪石、硅硫磷灰石、及蓝色方解石等。与我国常见的钙夕卡岩及镁夕卡岩有明显不同。它作为一个早期独立的阶段分布在各矿区,因其组成的矿物中富含镁、铝,故名“镁铝夕卡岩”。其后期的热液蚀变产生了众多的罕见矿物如雪硅钙石、碳硅钙石、吉水硅钙石、硅灰石膏等及大量沸石类矿物,但无石英,酷似基性火山岩的蚀变产物。矿物学研究表明,这种夕卡岩形成于一种富镁、铝而SiO_2不饱和的地球化学环境和高温低XCO_2的条件。     

四川巴塘县夏塞银多金属矿床特征

夏塞银矿位于川西义敦岛弧造山带燕山晚期绒依措花岗岩体外接触带浅变质岩中,是一个超大型的中低温热液脉型银多金属矿床.通过对该矿床的地质、矿石矿物、流体包裹体与同位素地球化学等进行系统的研究表明,矿体产出严格受断层破碎带控制,矿体主要为脉状、透镜状和浸染状;容矿岩石为上三叠统图姆沟组的浅变质砂岩、粉砂岩和板岩;金属矿物主要有方铅矿、闪锌矿、黄铜矿、黄铁矿、银矿物和硫盐矿物等,脉石矿物为石英、方解石、绢云母、绿泥石等;成矿作用可划分为三期四个阶段;成矿物质来源于围岩和花岗岩,矿床为燕山晚期-喜马拉雅期岩浆期后成矿流体浅成中低温热液充填交代矿床.     

New chronological evidence for Yanshanian diagenetic mineralization in China's Altay orogenic belt

Granitoids and related pegmatitic rare-metal deposits are widespread in China's Altay region, they used to be considered as Hercynian rocks and mineral deposits. Reported here are the 40Ar-39Ar ages of potassium-rich minerals (muscovite and microcline) in the Koktokay pegmatitic rare-metal orefield and whole-rock as well as quartz fluid-inclusion Rb-Sr isochron ages of granite and ores in the Shangkelan pegmatite rare-metal orefield. The ages indicate that there are Yanshanian Diagenetic Mineralization events happening in China's Altay orogenic belt and that formation of the famous Koktokay No.3 pegmatitic rare-metal deposit endured about 30 Ma of magmatic crystallization differentiation.     

小佟家堡子金矿床微量稀土元素特征

为进一步探讨小佟家堡子金矿床成矿物质来源及印支-燕山期岩浆活动对其成矿作用的影响,对该矿床岩矿石进行微量稀土元素的测试和特征分析.微量稀土元素特征显示,与矿体相比,盖县组片岩、大石桥组大理岩显示出相似的微量元素变化趋势以及稀土配分模式,印支期花岗岩仅在P,Zr,Hf等微量元素上出现较大反差,吕梁期-燕山期岩浆岩体在稀土配分模式上只有Er明显亏损,反映金成矿与地层和岩浆岩关系密切;稀土元素特征显示成矿热液为富Cl^-的还原性流体,成矿物质来源和成矿流体来源具有复杂性,吕梁期和燕山期花岗岩与盖县组片岩和大石桥组大理岩均为该矿体的形成提供了成矿物质,且深部成矿物质也参与成矿,矿床类型为岩浆热液叠加型金矿床.     

Paleoproterozoic reworking of ancient crust in the Cathaysia Block, South China: Evidence from zircon trace elements, U-Pb and Lu-Hf isotopes

A combined study of zircon LA-ICP-MS U-Pb dating, trace elements and Hf isotope was carried out for gneissic granite from the Sanzhishu area in Jingning, SW Zhejiang Province. Nearly all the zircons separated from the granite exhibited oscillatory zoning and high Th/U ratios (>0.1). The REE profile showed a pronounced positive Ce anomaly, negative Eu anomaly and an enrichment of HREE, which are typical characteristics of magmatic zircon. Thirteen concordant or nearly concordant analytical data yielded a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 1860±13 Ma (MSWD=0.084), representing the formation age of the granite. The magmatic zircons had negative εHf(t) values of −15.6 to −10.0 and two-stage Hf model ages of 3.1 to 3.4 Ga, indicating that the granites were formed by reworking of ancient crust. The major- and trace-element data indicate that the gneissic granites are metaluminous high-K calc-alkaline rocks and exhibit the same geochemical characteristics as aluminous A-type granites, implying the emplacement of the granite in a post-orogenic extensional tectonic setting. We conclude that the Paleoproterozoic crustal reworking event in the Cathaysia Block of South China marked the transition from assembly to break-up of the Columbia supercontinent. Supported by National Natural Science Foundation of China (Grant No. 40873004), Special Funds for National Scientific Research of Commonweal Industries, the Ministry of Land and Resources of China (Grant No. 2008110015), Opening Foundation of State Key Laboratory of Continental Dynamics, Northwest University (Grant No. 06LCD12) and the Project of Land and Resources Bureau of Zhejiang Province (Grant No. 2004005)     

New chronological evidence for Yanshanian diagenetic mineralization in China’s Altay orogenic belt

Granitoids and related pegmatitic rare-metal deposits are widespread in China’s Altay region, they used to be considered as Hercynian rocks and mineral deposits. Reported here are the⁴⁰Ar-³⁹Ar ages of potassium-rich minerals (muscovite and microcline) in the Koktokay pegmatitic rare-metal orefield and whole-rock as well as quartz fluid-inclusion Rb-Sr isochron ages of granite and ores in the Shangkelan pegmatite rare-metal orefield. The ages indicate that there are Yanshanian Diagenetic Mineralization events happening in China’s Altay orogenic belt and that formation of the famous Koktokay No.3 pegmatitic rare-metal deposit endured about 30 Ma of magmatic crystallization differentiation.     

个旧岩体内铜多金属矿床围岩蚀变特征与成矿研究

云南个旧锡矿东矿区西部塘子凹凹陷带岩体内部新发现的铜多金属矿床,是深部找矿的新类型。矿床围岩蚀变类型较多,蚀变分带未见明显对称性,可能与热液的多期次性有关。矿床与围岩蚀变关系密切,尤其是钾长石化,可做为找矿标志。通过分析围岩蚀变特征及其与成矿的关系,总结出矿床形成的一些特点。     

云南个旧陡岩勘查区Sn多金属矿化信息提取与评价

个旧矿区被南北向个旧断裂分为东、西2个矿区。东区是已知矿床的集中区,随着东区"危机矿山"问题的日益凸显,西区的地质研究工作和资源潜力评价已成为矿山深部和外围找矿的热点。西区陡岩地区具有良好的成矿地质条件,是近年来个旧西区地质找矿工作的重点。采用因子分析(FA)-多重分形法(S-A)对1∶1万原生岩石化探数据中17种元素进行分析,获取锡多金属矿致异常信息,再通过变差函数分析异常控制因素,结合本次1∶1万野外地质填图成果,获得如下认识:①F1因子代表Cd-Hg-Pb-Zn元素组合,是中低温热液型多金属矿化的反应;F3代表Sn、Mo元素组合,反映的是岩体及热液的相关信息;F5包括Sn、Sr,Sr是碳酸盐岩的常见元素,反映Sn元素部分来源于个旧组灰岩和法郎组炭质、泥质灰岩。②勘查区东南部异常晕展布特征为串珠状分布且异常浓集中心恰好都位于岩性分段面,推测该区存在隐伏岩体。③该区的断裂控矿性不明显,Sn元素异常展布的空间结构性主要由南西向的地层和该区的隐伏岩体控制。     

赣东北大鄣山花岗岩的地质特征、形成时代及其旅游地学意义

为了研究赣东北大鄣山花岗岩的成岩时代及成岩背景,通过LA-ICP-MS锆石U-Pb方法对大鄣山二长花岗岩的形成时代进行了测定,大鄣山二长花岗岩形成于135.0±2.6 Ma B.P.,为早白垩世。花岗岩的主要矿物为钾长石、斜长石、石英等浅色矿物,暗色矿物稀少,有利于抵抗风化侵蚀,保持岩石的完整性。岩石形成于以伸展为主导的构造背景下,张性的节理和断裂更为发育。风化侵蚀作用只能沿节理和断裂逐渐进行,容易形成尖峰、峡谷、断壁悬崖等花岗岩地貌景观。岩石结构和矿物组成是花岗岩地貌景观形成的物质基础;节理和断裂是花岗岩地貌景观的造型控制因素;成岩之后的构造抬升是花岗岩成为景观的必备条件;气候条件、水文条件等也在景观形成过程中扮演着不可或缺的角色。     

富宁基性岩区尾硐铜镍硫化物矿床矿化特征及矿床成因探讨

通过对尾硐铜镍硫化物矿床矿区地质特征、矿体分布特征、矿床矿化特征和S同位素分析,认为该矿区内各岩相带呈渐变过渡关系,为同期侵入岩体,存在深部岩浆熔离作用。橄榄苏长辉长岩和辉长苏长岩是矿区内主要赋矿岩体。S同位素分析显示其主要为幔源原生硫;但也可能有硫通过地壳混染作用加入。含矿岩浆深部熔离和岩体侵位后的岩浆分异结晶是导致金属硫化物富集成矿的主要过程。岩浆期后热液的叠加改造作用对部分地段的成矿物质富集有重要贡献。     

阿克提什坎金矿床稀土元素研究

系统地研究了新疆阿尔泰诺尔特地区阿克提什坎金矿床的稀土元素组成特征及热液中稀土元素的配分模型 ,并应用 Grant等位线方法讨论了热液蚀变作用过程中稀土元素的行为。认为在热液蚀变作用过程中 ,稀土元素保持惰性 ,成矿热液与岩浆热液有关 ,赋矿围岩及矿区花岗岩提供了成矿物质。     

Geochronolosic constraints on masmatic intrusions and mineralization of the Zhunuo porphyry copper deposit in Gansdese, Tibet

In situ zircon U-Pb ages for the recently discovered Zhunuo porphyry copper deposit in the western part of the Gangdese metallogenic belt in Tibet were determined by sensitive high-resolution ion microprobe （SHRIMP）. The ages can be divided into two separate groups, reflecting more than four major tectono-magmatic events in the area. The 62.5±2.5 Ma age of inherited zircons may be related to the volcanic eruption of the Linzizong Group formed shortly after the India-Asia continental collision. The 50.1±3.6 Ma age most likely corresponds to the time of underplating of mantle-derived mafic magma in Gangdese. The 15.6±0.6 Ma age obtained from magmatic zircons is interpreted as the age of crystallization of the Zhunuo ore-forming porphyry. Finally, a molybdenite Re-Os isochron age of 13.72±0.62 Ma is consistent with another zircon U-Pb age of 13.3±0.2 Ma, representing the time of copper mineralization. These ages, in combination with available literature data, indicate that magmatic crystallization and copper mineralization in the Gangdese metallogenic belt became gradually younger westward, and further suggest that the Zhunuo porphyry copper deposit was formed in the same tectonic stage as other porphyry copper deposits in the eastern and central Gangdese belt. This conclusion provides critical information for future exploration of porphyry copper deposits in western Gangdese.     

川口矿田屋背冲矿区钨矿地质特征及成因探讨

屋背冲矿区位于衡阳盆地东缘川口矿田东北部,通过对本区钨矿的地质背景、时空分布特征及成矿物理化学特征的阐述,探讨屋背冲钨矿成因机理.初步认为区内存在花岗岩型和石英脉型两类钨矿,成矿物质主要来源于花岗岩浆岩,花岗岩型钨矿是岩浆期后热液（气成高温热液）交代、活化富集成矿,以规模大,品位低特点,石英脉型钨矿含矿热液充填断裂构造沉淀富集成矿,以规模小,品位富为特点.花岗岩型找矿潜力大,为下一步主要勘查目标.矿区南西延伸段是寻找隐伏大矿体的有利部位.     

REE composition in scheelite and scheelite Sm-Nd dating for the Xuebaoding W-Sn-Be deposit in Sichuan

The scheelite with large size and euhedral shape from Xuebaoding, Sichuan Province is an ideal min- eral to study REE patterns and Sm-Nd dating of non-gold deposits. The scheelite has diameters of 1― 10 cm and colors of pale beige to deep orange. Most of these scheelites occur in association with beryl, cassiterite and muscovite. The rare earth elements indicate that scheelite samples from Xuebaoding W-Sn-Be deposits contain high concentrations of rare earth elements with total ΣREE Y contents in the range of 369―1725 μg·g?1 and nearly all of these scheelite samples are enriched in LREE and depleted in HREE and have negative Eu anomalies. The REE patterns of the scheelites are similar to those of A-type granite with obvious tetrad effect, similar to that of type II scheelites. Based on reported fluid inclusion studies, the mineralizing-fluid of the Xuebaoding W-Sn-Be deposit indicates low Na activity. The REE patterns of the scheelite are probably controlled by partition coefficient in hydrothermal fluid. In the 147Sm/144Nd-143Nd/144Nd diagram, the scheelites show a linear array corresponding to an isochron age of 182.0±9.2 Ma (MSWD = 0.52). The Sm-Nd age represents the formation age of the scheelite and can indicate that the W, Sn and Be mineralization at Xuebaoding took place in the Early Yanshanian. The Sm-Nd dating result is important for the study of the multi-metal resources in western Sichuan Province.