金川铜镍矿床隐伏富铜矿体成因研究及其深部找矿意义

金川矿床赋存于富橄榄石超镁铁质岩中,是目前世界第三大在采铜镍硫化物矿床.经过多年开采,如何在深、边部找到新的替代资源问题显得越来越重要.通过对金川矿床富铜隐伏矿体的矿体特征、矿石特征和矿石特殊地球化学特性等方面进行分析研究,特别是从空间立体对其矿化规律进行总结,并与其附近Ⅱ1#主矿体进行对比,指出该类型矿体既有岩浆熔离作用的特点,又有后期改造作用的特征,其形成经历了三个阶段:富含Cu、PGE岩浆深部熔离-脉动贯入、构造活化富集和后期热液叠加.同时探讨了来源于地幔深部的高镁玄武质岩浆,在深部岩浆房和阶段岩浆房熔离分异过程中,富镍岩浆和矿浆之间存在富铜岩浆.此外,Pb同位素表明,该隐伏富铜矿体形成时间为8亿年左右,早于块状特富矿;Pb、S同位素表明,该矿体主要来源于地幔,但曾被少量地壳物质混入.最后指出铜镍硫化矿床的成因是复杂多样的,在金川矿床深边部寻找新型矿体,尤其是富铜矿体的前景很大,而F_6断层可能是富铜隐伏矿体岩浆通道和Ⅱ1#主矿体岩浆的深部侵位通道之一.     

南天山阔克萨勒岭地区晚古生代玄武岩地球化学特征、成因及意义

齐齐哈尔纳克玄武岩与哈拉布拉克玄武岩出露于南天山阔克萨勒岭区,两组玄武岩均属碱性玄武岩系列,样品富集大离子亲石元素和高场强元素,轻重稀土分馏明显,（La／Yb）N=5．4～7．0,Ce／Y=18．04～24．52,Eu／Eu^＊=0．96～1．13,无负Eu异常,总体特征与洋岛型玄武岩（OIB）的特点类似。Mg^#与高场强元素Ni,Sr,Cr,V与Nb／La值无相关性,Ti^＊（1．02～1．7）与Nb^＊（1．77～2．14）表明以单斜辉石为主的分离结晶是岩浆演化的主要趋势,与岩相学观察一致。将Zr／Nb,La／Nb,Ba／Nb,Ba／Th等比值与OIB端元及主要化学库不相容元素比值进行对比,发现源区类似EMI和EMII。Zr／Nb=7．4～8．38,Ce/Yb=16．11～24．52,高（La／Yb）N和（Gd／Yb）N值表明岩浆是含石榴子石相橄榄岩与尖晶石相橄榄岩富集过渡地幔源区低部分熔融的产物。对玄武岩稀土元素运用分离结晶部分熔融过程（CL／CO=（1-F）^（1/Do-1／DO）反演计算,模拟结果表明齐齐哈尔纳克玄武岩经1．57％～3．27％部分熔融形成,地慢源区Gt：Sp=5：95;哈拉布拉克玄武岩经4．09％部分熔融形成,地幔源区Gt：Sp=25：75。模拟结果表明南天山洋深部地幔可能并不是均一的。结合玄武岩年代（晚泥盆系-石炭系）、南天山中部库勒湖蛇绿混杂带的硅质岩、黑英山阿尔腾卡什组硅质岩中大量中泥盆-早石炭世放射虫化石、与玄武岩共生的蛇绿岩富大离子亲石元素,亏损Nb、富集Ce和P等边缘海岛弧特点及出露弧后盆地中沉积碳酸盐岩,表明玄武岩产于弧后盆地,弧后洋盆在晚泥盆世消减并最终于早石炭世末期闭合。     

Magnetic studies of magma-supply and sea-floor metamorphism: Troodos ophiolite dikes

Dikes of the eastern Troodos ophiolite of Cyprus intruded at slow ocean-spreading axes with dips ranging up to 15° from vertical and with bimodal strikes (now NE–SW and N–S due to post-88 Ma sinistral microplate rotation). Varied dike orientations may represent local stress fields during dike-crack propagation but do not influence the spatial-distributions or orientation-distributions of dikes' magnetic fabrics, nor of their palaeomagnetic signals. Anisotropy of magnetic susceptibility (AMS) integrates mineral orientation-distributions from each of 1289 specimens sampled from dikes at 356 sites over 400 km² in the eastern Troodos ophiolite of Cyprus. In 90% of dikes, AMS fabrics define a foliation (k_MAX–k_INT) parallel to dike walls and a lineation (k_MAX) that varies regionally and systematically. Magma-flow alignment of accessory magnetite controls the AMS with a subordinate contribution from the mafic silicate matrix that is reduced in anisotropy by sea-floor metamorphism. Titanomagnetite has less influence on anisotropy. Occasionally, intermediate and minimum susceptibility axes are switched so as to be incompatible with the kinematically reasonable flow plane but maximum susceptibility (k_MAX) still defines the magmatic flow axis. Such blended subfabrics of kinematically compatible mafic-silicate and misaligned multidomain magnetite subfabrics; are rare. Areas of steep magma flow (k_MAX plunge ≥ 70°) and of shallow magma-flow alternate in a systematic and gradual spatial pattern. Foci of steep flow were spaced 4 km parallel to the spreading axes and 6 km perpendicular to the spreading axes. Ridge-parallel separation of steep flow suggest the spacing of magma-feeders to the dikes whereas ridge-perpendicular spacing of 6 km at a spreading rate of 50 mm/a implies the magma sources may have been active for 240 Ka. The magma feeders feeding dikes may have been ≤ 2 km in diameter. Stable paleomagnetic vectors, in some cases verified by reversal tests, are retained by magnetite and titanomagnetite. In all specimens, the stable components were isolated by three cycles of low-temperature demagnetization (LTD) followed by ≥ 10 steps of incremental thermal demagnetization (TD). 47% of primary A-components [338.2 /+ 57.2 n = 207, α₉₅ = 3.9; mean T_UB = 397 ± 8 °C] are overprinted by a B-component [341.4 /+ 63.5, n = 96, α₉₅ = 8.7; mean T_UB = 182 ± 11 °C]. A- and B-components are ubiquitous and shared equally by the N–S and NE–SW striking dikes. A-component unblocking temperatures (T_UB) are zoned subparallel to the fossil spreading axis. Their spatial pattern is consistent with chemical remagnetization at some certain off-axis distance determined by sea-floor spreading. A-components indicate less microplate rotation and more northerly palaeolatitudes that are consistent with metamorphic remagnetization after some spreading from the ridge-axis. Thus, their magnetizations are younger than those of the overlying volcanic sequence for which ChRMs are commonly reported as 274 /+ 33 (88 Ma).     

北祁连西段古元古代大陆裂谷火山岩性质的确定

北祁连西段古元古代火山岩是大陆裂谷火山作用的产物,具典型的“双峰式”特征。岩石地球化学研究表明,斜长角闪岩和石英阳起石岩派生于上地幔,属大陆拉斑玄武岩—安山岩,而石英黑云母岩则来源于地壳。其源岩浆在上升过程中受到了陆壳成分的混染,有较多的陆壳成分的卷入,它们的形成是地幔热柱和陆壳共同作用的结果。     

Tephra glass chemistry provides storage and discharge details of five magma reservoirs which fed the 75 ka Youngest Toba Tuff eruption,northern Sumatra

The Youngest Toba Tuff contains five distinct glass populations, identified from Ba, Sr and Y compositions, termed PI (lowest Ba) – PV (highest Ba), representing five compositionally distinct pre-eruptive magma batches that fed the eruption. The PI–PV compositions display systematic changes, with higher FeO, CaO, MgO, TiO₂ and lower incompatible element concentrations in the low-SiO₂ PIV/PV, than the high-SiO₂ PI–PIII compositions. Glass shard abundances indicate PIV and PV were the least voluminous magma batches, and PI and PIII the most voluminous. Pressure estimates using rhyolite-MELTS indicate PV magma equilibrated at ~6 km, and PI magma at ~3.8 km. Glass population proportions in distal tephra and proximal (caldera-wall) material describe an eruption which commenced by emptying the deepest PIV and PV reservoirs, this being preferentially deposited in a narrow band across southern India (possibly due to jet-stream and/or plinian eruption transport), and as abundant pumice clasts in the lowermost proximal ignimbrites. Later, shallower magma reservoirs erupted, with PI being the most abundant as the eruption ended, sourcing the majority of distal ash from co-ignimbrite clouds (PI- and PIII-dominant), where associated ignimbrites isolated earlier (PIV- and PV-rich) deposits. This study shows how analysis of tephra glass compositional data can yield pre-eruption magma volume estimates, and enable aspects of magma storage conditions and eruption dynamics to be described.     

塔里木巴楚小海子正长岩杂岩体的岩石成因探讨

巴楚小海子正长岩杂岩体是二叠纪塔里木大火成岩省的重要组成部分.SIMS锆石U-Pb定年显示其形成于279.7±2.0Ma,与本区辉绿岩脉和石英正长斑岩岩脉近于同时侵位.根据矿物学特征,小海子正长岩体可分为铁橄榄石正长岩和角闪正长岩两类.前者主要由碱性长石、铁橄榄石、单斜辉石、角闪石和少量石英、斜长石组成,后者主要由碱性长石、角闪石、黑云母和少量的石英、斜长石组成.小海子正长岩体为铁质、碱性系列,轻稀土相对富集,重稀土亏损,具有明显的Eu正异常,无Nb、Ta负异常,相对低的(87Sr/86Sr);(0.7033 ～0.7038)和正的εNd(t)值(+3.1～+3.8),暗示它们来自亏损的地幔源区,没有地壳物质的加入.主微量和同位素地球化学分析,暗示巴楚小海子正长岩的母岩浆为碱性的幔源玄武质岩浆经橄榄石、单斜辉石分离结晶后的残余熔体,并且含有堆晶的碱性长石.这种含有碱性长石堆晶的熔体,在相对还原的条件下结晶,形成铁橄榄石正长岩;在相对氧化的条件下结晶,并经过不同程度斜长石的分离结晶形成角闪正长岩.     

峨眉山高钛玄武岩中主要的赋钛矿物——榍石的产状、特征及成因

峨眉山玄武岩中钛以什么矿物形式存在一直以来很少有学者提及。本文通过镜下观察、全岩化学分析、X-衍射、能谱、扫描电镜、电子探针、阴极发光对川西南部周公山-汉王场地区钻井岩心中峨眉山玄武岩进行了详细的分析,讨论了其主要赋钛矿物及成因。(1)SiO₂含量46.4%~48.3%和TiO₂>3%显示区内峨眉山玄武岩属于高钛峨眉山玄武岩系列。但多个层段榍石含量>5%,而极少见磁铁矿、钛铁矿;(2)榍石主要以隐晶质的云雾状、雪花状、芝麻点状、枝状等形态分布于微晶长石之间和溶孔、溶洞边缘及裂缝中,少量呈显晶质粒状分布于微晶长石、绿泥石之间。(3)电子探针分析显示:所有含钛矿物中,钛铁矿中TiO₂含量最高,为39.069%,榍石中TiO₂次之,TiO₂含量为17.143%~38.648%,磁铁矿中TiO₂含量最高为12.293%,平均在5%~10%左右,其他矿物基本上都少于1%。(4)扫描电镜及其能谱分析显示:榍石中的Ti含量(2.49%~24.97%)明显高于含钛磁铁矿(2.68%~9.21%)、含钛赤铁矿(3.64%)中Ti含量,与钛铁矿(19.51%)含量相当。分析结果认为:峨眉山玄武岩中大量出现的隐晶榍石可能是岩浆后期产物或期后蚀变的产物。在峨眉山玄武岩中首次鉴别出的大量隐晶质榍石是高钛峨眉山玄武岩中最主要的赋钛矿物。隐晶榍石在玄武岩中的含量是区分"高钛"和"低钛"玄武岩的主要标志之一。     

骑田岭花岗岩体的岩浆混合成因:寄主岩及其暗色闪长质包体的锆石U-Pb年龄和Hf同位素证据

燕山期骑田岭花岗岩体的仰天湖单元中花岗岩以发育暗色闪长质微细粒包体为特征.这些包体大小不等,呈被打散的片云状或次圆状,颜色较寄主岩深,粒度较细.在错石内部结构的CL图像特征研究基础上,用LA-ICP-MS和MC-ICP-MS测定了锆石U-Pb年龄及Hf同位素组成,探讨了寄主二长花岗岩、暗色闪长质微细粒包体的锆石U-Pb...     

甘肃北山成矿作用研究与展望——兼及与古亚洲成矿域对比

甘肃北山成矿带处于我国古亚洲成矿域的中段,工作程度较低,但从近年来取得的进展说明,该带矿产资源潜力、经济意义和前景不亚于古亚洲域的东部和西部,因此,应加强对该带的认识和采取更有利的找矿措施。该带在中、晚元古代及古生代成矿作用的基础上又叠加了中生代强烈的成矿作用,特别是酸性和富碱岩浆活动及有关矿化十分活跃。本文从区域成矿...     

广西姑婆山里松岩体及暗色包体的副矿物研究:含锡矿物特征与岩浆混合的矿物指示

南岭中段以花山一姑婆山为起点,发育一条南西-北东向的燕山早期富钨锡A型花岗岩带,其中姑婆山岩体以其富含暗色微粒包体( MME)而闻名.为寻找岩浆混合的矿物学证据并探索基性岩浆与钨锡富集的关系,我们使用电子探针对姑婆山岩体花岗岩和暗色包体中的副矿物进行了系统的成分分析和对比.研究首次确认了暗色包体的铁镁矿物解理中含有岩浆...