Geochemistry, geochronology and mineralisation potential of the granites in the Central Iberian Zone: The Jalama batholith

The Jalama batholith (Spain and Portugal) is one of the numerous granites of the Central Iberian Zone with Sn- and W-associated mineralisation. On the basis of petrographical and geochemical characterisation three types of granite have been distinguished: inhomogeneous granitoids, porphyrytic granites and leucogranites, all of these being peraluminous and subalkaline. All the granites correspond to S-type granites. The field data, the petrography and lack of geochemical affinity relationships of the leucogranites with the remaining granites indicate that their geneses correspond to an independent magma batch and superimposed fractional crystallisation process. The granitic units show subparallel REE patterns. There is a decrease in total REE and an increase in the negative Eu anomaly from the inhomogeneous granitoids to leucogranites. Some leucogranites show relatively low contents of Sn and W almost certainly due to segregation in the magma of a melt rich in water carrying Sn-W. These elements are concentrated in the water phase, which eventually gives rise to Sn-W-associated mineralisation.The ages obtained by means of a whole-rock Rb-Sr isochron for the granites mainly indicate an early intrusion of the inhomogeneous granitoids (319±10 Ma), followed in time by porphyrytic granites (279±9 Ma), which can be associated to the late-post-kinematic granites within the third Variscan deformation phase (D₃).Apart from the average Sn content, the variations of trace elements, principally Sr, Ba, Rb, Th and P, establish that the porphyritic granites and the inhomogeneous granitoids will be barren granites while the leucogranites and the subfacies at the margin of the porphyritic granites correspond to granites with mineralisation potential. It is precisely in these granites of the Jálama batholith that the Sn-W mineralisation is located, for which the criteria utilised has been demonstrated to be effective.     

Nb–Ta–(Ti–Sn) oxide mineral chemistry as tracer of rare-element granitic pegmatite fractionation in the Borborema Province,Northeastern Brazil

The Borborema Pegmatitic Province (BPP), northeastern Brazil, is historically important for tantalum mining and also famous for top-quality specimens of exotic Nb–Ta oxides and, more recently, for the production of gem quality, turquoise blue, ‘Paraíba Elbaite.’ With more than 750 registered mineralized rare-element granitic pegmatites, the BPP extends over an area of about 75 by 150 km in the eastern part of the Neoproterozoic Seridó Belt. The Late Cambrian pegmatites are mostly hosted by a sequence of Neoproterozoic cordierite–sillimanite biotite schists of the Seridó Formation and quartzites and metaconglomerates of the Equador Formation. The trace-element ratios in feldspar and micas allow to classify most pegmatites as belonging to the beryl–columbite phosphate subtype. Electron microprobe analyses (EMPA) of columbite, tapiolite, niobian–tantalian rutile, ixiolite and wodginite group minerals from 28 pegmatites in the BPP are used to evaluate the effectiveness of Nb–Ta oxide chemistry as a possible exploration tool, to trace the degree of pegmatite fractionation and to classify the pegmatites. The columbite group mineral composition allows to establish a compositional trend from manganoan ferrocolumbite to manganocolumbite and on to manganotantalite. This trend is typical of complex spodumene- and/or lepidolite-subtype pegmatites. It clearly contrasts with another trend, from ferrocolumbite through ferrotantalite to ferrowodginite and ferrotapiolite compositions, typical of pegmatites of the beryl–columbite phosphate subtype. Large scatter and anomalous trends in zoned crystals partially overlap and conceal the two main evolution patterns. This indicates that a large representative data set of heavy mineral concentrate samples, collected systematically along cross-sections, would be necessary to predict the metallogenetic potential of individual pegmatites. Other mineral species, e.g. garnets and/or tourmaline, with a more regular distribution than Nb–Ta oxides, would be more appropriate and less expensive for routine exploration purposes. The currently available Nb–Ta oxide chemistry data suggest the potential for highly fractionated Ta–Li–Cs pegmatites in the BPP, so far undiscovered, and encourages further, more detailed research.     

分形理论在云南个旧锡矿遥感信息定量化分析中的应用

应用分形理论和方法对个旧锡矿遥感信息进行了定量化研究。结果显示,在格子边长为1．4～4．5km的标度范围内,其遥感蚀变和断裂构造进入的总格子数的对数与格子边长的对数均具有很好的线性相关性,表明在研究标度范围内,各子区遥感线性与蚀变信息具有良好的统计自相似性和分形特征。在此基础上,以19号区和26号区为例,分析并进一步探讨了遥感信息分形特征的成矿意义。     

武夷山地区钨锡铜金银成矿区带找矿评价

武夷山地区是一个有色、贵金属、稀有、稀土矿床的重要找矿远景区。通过对该区地质背景、成矿地质条件、矿床富集规律的分析归纳,指出该区以政和-大埔深大断裂为界,其外带（沿海）中生代火山岩大面积出露,内带则常呈一些孤立的火山断陷盆地分布,矿床与火山-侵入岩浆热液作用有密切的成因联系,中生代不同的火山-次火山活动旋回,对该区成矿作用、成矿系列有重要控制作用。     

广西北香铅锌锡矿区成矿地质及地球化学找矿前景评价

文章从区域成矿背景、地层、构造等几方面探讨了矿床的成矿地质条件,指出NW向同沉积断裂对矿床的空间分布、产状等起主要控制作用,其次一级NW向断裂则是矿床的主要赋存构造,矿床的形成受地层岩性和构造双重控制。通过化探次生晕异常评价,圈定出北香一下大莫和莫四一南华两个呈NW-SE走向的综合矿化异常带。认为北香一下大莫异常带的走向延伸部位以及莫四一南华异常带的深部应具有一定的找矿潜力。     

湖南金船塘矿区矽卡岩矿物及Sn元素在绿帘石中的分布特征

金船塘矿区位于千里山花岗岩岩体西侧, 与东侧柿竹园矿区均是湖南柿竹园特大型W-Sn-Mo-Bi矿床目前正在开采的重要矿区.该矿区块状矽卡岩的矿物特点是: 石榴子石以钙铝石榴子石为主, 辉石存在透辉石-钙铁辉石连续系列, 长石以钙长石大量产出为特点, 硅灰石出现了不常见的锰铁硅灰石; 绿帘石中普遍含Sn, SnO₂含量0.2%~2%.根据绿帘石中Sn元素的详细测定和计算, 查明Sn元素在绿帘石中含量与在矿物中位置具幂律函数关系, 计算的分形维为1.93, 从矿物微观的尺度确认Sn等成矿元素在运移和分布上具分形时-空结构, 从而证实自组织的临界状态是柿竹园特大型多金属矿床动力学的基本特点.      

浙江省常山县八面山矿区萤石及钨、锡多金属成矿地质特征

八面山萤石、钨锡多金属矿床赋存于中、上寒武统碳酸盐岩地层内,沿燕山期侵入的岩前二长花岗岩体环状分布。成矿具有多阶段、多类型特征,主要有矽卡岩型萤石、锡多金属矿床、蚀变花岗岩型锡矿床(或矿化体)、高温热液石英脉型钨锡多金属矿床、中低温热液交代(伴充填)萤石矿床等。其中以似层状、透镜状和陡倾斜脉状产出的萤石矿床规模最大,是近几年浙江省新发现的萤石矿床类型,对今后本区域进一步开展勘查找矿具有重要指导意义。     

论兴蒙造山带叠生成矿作用——以锡林浩特和额尔古纳地块为例

兴蒙造山带前寒武纪变质岩中间地块分布广泛,其中锡林浩特和额尔古纳地块以出露范围广泛、岩性组合复杂、后期改造明显和找矿潜力巨大而为人们所关注。找矿勘查结果表明,锡林浩特和额尔古纳地块及邻区铜、铁、铅-锌和银矿床(点)星罗棋布,并且以含有大量锡、钨和钼为特征。这些矿床独特的成矿元素组合(如铜-锡、铁-锡、铜-锡-铅-锌-银、铜-银-锡和铁-钨-钼)及其与前寒武纪变质岩块体和显生宙花岗岩密切时空分布关系均表明,它们很可能是深源岩浆再造和古陆块体活化相互联动(叠生)作用的产物。所谓的叠生作用主要指地壳浅部构造形迹活化和地壳深部物质再造,前者为成岩(矿)物质的就位提供了空间条件,后者为岩(矿)体的形成的奠定了物质基础。钕和铪同位素数据表明,前寒武纪变质岩块体和显生宙含锡、钨和钼花岗岩分别具有完全不同的εNd(t)值和εHf(t)值,成岩(矿)物质分别属于壳源和幔源,其中后者对前者的叠加改造是导致铜-锡、铁-锡和铜-银-锡等多元素矿床形成的关键因素。叠生成矿作用概念的提出不仅很好地解释了兴蒙造山带含锡、钨和钼多金属矿床的成因,而且为寻找隐伏金属矿床指明了方向。     

西藏玛雄郎铅锌矿区那舵松多矿段黑云母~(40)Ar-~(39)Ar年代学及硫、铅同位素地球化学

玛雄郎矿区那舵松多矿段以铅、锌成矿为主,伴有强烈的钨、锡矿化异常,是冈底斯成矿带上为数不多的具钨、锡找矿潜力的矿区之一。为确定该矿床成矿时代,对与成矿流体活动具有成因联系的蚀变围岩中的黑云母进行了40Ar-39Ar年龄测试。黑云母的坪年龄和等时线年龄分别为69.57±0.72 Ma和69.3±1.6 Ma,在误差范围内二者基本一致,限定了矿床成矿时代为晚白垩世晚期。为查明矿床成矿物质来源,对矿石硫化物S、Pb同位素组成特征进行了测试分析。金属硫化物δ34S值变化范围为-1.6‰~1.9‰,硫主要源自与成矿有关的岩浆岩;Pb同位素组成特征表明,成矿金属物质主要源自上地壳念青唐古拉结晶基底物质。矿床成矿时代和成矿物质来源的初步研究,对于区域上同种类型矿床的找矿工作具有重要意义。     

南岭地区成钨、成锡花岗岩组合的几个判别标志

南岭地区钨锡多金属成矿作用和区内中酸性-酸性花岗岩有着密切的成因联系。利用已发表的和野外收集的地质资料,本文尝试对区内成钨锡花岗岩组合(包括与钨锡矿相关的含钨锡花岗岩和成钨锡花岗岩)进行宏观地质判别。判别过程采用循序渐进的方式,首先将成钨锡花岗岩组合与不成矿花岗岩相区别,然后将含锡花岗岩和含钨花岗岩互相区别开来。相对于不成矿花岗岩,成钨锡花岗岩组合通常具有W、Sn、F、B化探组合异常、多期多阶段演化特点、适度的构造叠加(即存在明显的热液活动)等共同特点,且三者缺一不可。不成矿花岗岩一般具有W、Sn、F、B化探组合为背景值,岩性单一,少见晚期岩株、岩脉(演化不充分)及蚀变的特征。在野外地质工作中,含锡花岗岩一般为花岗闪长岩-二长花岗岩-二云母花岗岩岩性组合。基性端元以普遍发育暗色微粒包体、常见角闪石、含较多的黑云母为鉴别特征。酸性端元中可以含有少量白云母。而含钨花岗岩以黑云母二长花岗岩-二云母花岗岩-白云母花岗岩岩性组合为主,常见含B矿物电气石,基性端元少见或不见角闪石、含较少的黑云母,仅见变质岩、围岩捕掳体和黑云母团块,酸性端元白云母含量较高等组合特征可以与含锡花岗岩相区别。