Low-rhenium molybdenite by metamorphism in northern Sweden: Recognition, genesis, and global implications

Re–Os dating of molybdenite is an accurate means to date intrusions and intrusion-related ore deposits using the model age or isochron approach. But, molybdenite has a new niche in the greenschist- to granulite-facies metamorphic environment. Re–Os ages for metamorphic molybdenite may be used to construct regional metamorphic histories. Age significance and accuracy are established by analyzing multiple molybdenite separates extracted from single, petrographically-characterized molybdenite occurrences. In this study, twelve geologically distinct molybdenite-bearing samples from two small Mo districts in northern Sweden trace a 150 m.y. Paleoproterozoic Svecofennian metamorphic history from 1900 to 1750 Ma. These data reveal a little-known, widespread and protracted, Late Svecofennian anatexis in northern Sweden.The Kåtaberget Mo–(Cu, F) deposit is located in the Moskosel granite batholith north of the economically-renown Skellefte district. Four different molybdenite samples from outcrop at Kåtaberget indicate an intrusion age of 1895 ± 6 Ma with the formation of later pegmatite–aplite at 1875 ± 6 Ma. The Allebuoda (Björntjärn) and Munka Mo–(W) deposits in the Rappen district are represented by three outcrop and five drill core samples of molybdenite-bearing aplite–pegmatite–granite. These two deposits were previously described as intrusion-related Climax-type Mo mineralization. Re–Os ages for molybdenites from these deposits range from 1865 to 1750 Ma and, significantly, Re concentrations are markedly low, extending to the sub-ppm level. Age agreement within the deposits is conspicuously lacking, whereas, with one exception, age agreement within any single sample (geologic occurrence), as established by analysis of additional molybdenite separates, is very good. These data, together with fundamental geologic observations discussed in this paper, suggest that Mo–(W) mineralization in northern Sweden is not intrusion-related, but the local product of episodic melting of Archean–Paleoproterozoic supracrustal gneisses related to the Svecofennian orogeny. Petrographic traverses across the boundary between widespread, foliation-parallel units of aplitic to pegmatitic pink granite and hosting biotite gneiss directly capture the process of ore formation. Dehydration breakdown of zircon-rich biotite aligned with the foliation in the gneiss is accompanied by formation of new pristine, post-deformational biotite plus sulfides, oxides, hydrothermal zircon and fluorite, all associated with microcline-dominant leucosomes.This process has profound implication for the traditional leucogranite, intrusion-related genesis attributed to the broad classification of Mo–W–Sn–base and precious metal mineralization (e.g., South Mountain Batholith, Nova Scotia; Okiep, Namaqualand, South Africa; Mactung, Yukon; Pogo–Liese, Tintina, Alaska; Carajás and Goiás–Rio Tocantins, Brazil; New England Batholith, NSW, Australia; Bergslagen, Sweden; Nevoria, Western Australia; Alpeinerscharte, Austria; Erzgebirge, Germany; Sardinia–Corsica Batholith). In addition to biotite, metallogenic contributions (e.g., Mo, W, Sn, U, Bi, Cu, Pb, Zn, Fe, Ni, Co, Au, Ag, Te, As, Sb, REE) in various combinations may also be controlled by breakdown of amphibole. In effect, the trace element composition of dehydrating or recrystallizing components in a gneissic rock essentially defines the local and district metallogenic suite. In the absence of focusing structures (e.g., shear zones, sheeted vein development), this process will generally form small and disconnected subeconomic deposits with erratic and unpredictable grades. Low Re content in associated molybdenite is a key indicator for a subeconomic origin by local melting of biotite gneiss (Mo–W) or muscovite schist (Sn–W).     

中国大陆科学钻100～850 m深度岩心的贵金属地球化学

本文对CCSD超深钻中首次获得的铂族元素及金、银的地球化学特点进行了分析和研究,结果表明各类样品的铂族元素含量均偏低,100～850 m深度平均Ir小于0.1×10-9,Os小于0.3×10-9,Pd小于0.5×10-9,Pt小于0.4×10-9,Rh小于0.1×10-9,Ru小于0.4×10-9,只有个别橄榄岩样品的铂族元素含量接近于地壳丰度,但远远低于超基性岩的一般含量.这种极低的铂族元素含量,属于"负异常",表明在变质作用过程中铂族元素发生了活化转移.榴辉岩和橄榄岩的铂族元素含量都偏低,但其球粒陨石标准化配分明显具有明显不同的特点,利用铂族元素仍然可以帮助对变质岩进行分类或恢复原岩.前人在蒋庄超基性岩岩体的人工重砂中发现有铂族矿物,其中包括有铱铂矿.可见,铂族元素是可以活化转移的,其活化转移的原因还需要探讨,是在结晶分异过程中转移的、还是在折返过程中活化的、或者是在造山运动结束之后由于其他原因而造成的,尚需要深入研究.     

黄金珠宝首饰市场状况与四川宝石资源开发

介绍了黄金珠宝首饰的一些基本观念和近年来黄金珠宝市场的发展状况，指出１９９４年纯金饰品消费将会稳定增长，而且仍占主流，珠宝首饰市场会出现消费量增长，竞争日渐激烈，并由大中城市向中小城市扩展的趋势。就四川宝玉石普查找矿和开发利用提出了见解。     

曹蕴键和《曹南地震灾变记》

曹蕴键（1882—1970）,字铁如,原籍山东定陶县,寄居菏泽。清末与民国时期历任知县、秘书、文书等职。1952年6月,被聘为中央文史研究馆馆员。《曹南地震灾变记》详述了他在1937年菏泽大地震时的亲身经历、震后的应急自救措施,以及所见所闻。菏泽大震发生于抗日战争爆发后,战火已烧到河北南部、山东、江苏沿海地区,政府和民间均无力救灾,有关震情与灾情的资料严重缺失。《曹记》则可稍作弥补,堪称珍贵史料。

     

中国铂族元素矿床类型和地质特征

根据成矿地质环境、容矿岩石类型、元素共生组合、矿床地质特征和成矿作用性质，将我国的铂族元素矿床划分为岩浆型、热液弄才外生型三大类型和九个亚类，而赋存于基性超基性岩体中的铜镍型铂族元素矿床是我国最重要的铂族元素矿床。     

我国与火山作用有关的宝玉石资源研究

本文将我国已发现的与火山作用有关的宝石资源划分为5种类型,① 幔源成矿类型;② 壳幔成矿类型;③ 火山作用直接成矿类型;④ 火山期后热液成矿类型;⑤ 相关类型。讨论了各种成矿类型的宝石资源的地质学及宝石学特征,介绍了它们开发的情况和对地方经济的意义。通过归纳对比,认为我国目前对与火山作用有关的宝玉石资源形成机理及找矿勘探方面的研究工作是薄弱的。     

MPV-3显微光度计在宝石学中的应用

简述ＭＰＶ－３显微光度计的特点,阐述了有色宝石颜色评价的理论基础和方法,以四川平武无色绿柱石,山东昌乐蓝宝石的颜色评价和改色实验效果评价以及不同成因的天然红工 光性研究为例,论述了ＭＰＶ３显微光度计在宝石颜色评价、改色效果判定、红宝石定名和品种鉴别等方面的应用。     

湖南宝,玉石资源及其开发浅议

湖南出产宝石历史悠久，长期以来远销海内外，菊花石工艺享誉全球，曾多次在国际博览会上获奖。还有较丰富的海蓝宝石、祖母绿、水晶等十几种宝石、玉石、彩石资源。其地质成因类型主要有砂矿型、沉积型、伟昌岩型、火山岩型，气成－热液型、沉积变质和接触变质型。     

Fluid Inclusion and Stable Isotope Studies at Don Sixto,a Precious Metal Low Sulfidation Deposit in Mendoza Province,Argentina

The Don Sixto mining area in Mendoza province, central‐western Argentina, contains an epithermal low sulfidation Au–Ag deposit. It is a small deposit (～4 km²), with a gold resource of 36 t. In Don Sixto, ore minerals are disseminated in the hydrothermal quartz veins and hydrothermally altered volcanic‐pyroclastic rock units of Permian–Triassic age. On the basis of the texture, ore mineral paragenesis and cross cutting relationship of gangue minerals, seven stages of mineralization were recognized and described. The first six stages are characterized by quartz veins with minor amounts of base metal minerals and the last stage is represented by fluorite veins with minimal quantities of base metal minerals; the precious metal mineralization is mainly related to the fourth stage. The hydrothermal veins exhibit mainly massive, crustiform and comb infilling textures; the presence of bladed quartz replacement textures and quartz veins with adularia crystals are indicative of boiling processes in the system. Fluid inclusion and complementary stable isotope studies were performed in quartz, fluorite, and pyrite samples from the vein systems. The microthermometric data were obtained from primary, biphasic (liquid‐vapor) fluid inclusion assemblages in quartz and fluorite. The maximum values for salinity and homogenization temperature (T_h) came from the stage IV where quartz with petrographic evidence of boiling has average values of 4.96 wt% NaCl_equiv. and 286.9°C respectively. The lower values are related to the last stage of mineralization, where the fluid inclusions in fluorite have average salinities of 1.05 wt% NaCl_equiv. and average homogenization temperatures of 173.1°C. The oxygen and sulfur isotopic fractionation was analyzed in quartz and pyrite. The calculated isotopic fractionation for oxygen in the hydrothermal fluid is in the range of δ¹⁸O_H2O = ?6.92 up to ?3.08‰, which indicates dominance of a meteoric source for the water, while sulfur reaches δ³⁴S_H2S = 1.09‰, which could be reflecting a possible magmatic, or even a mixed source.     

现代微区测试技术在确定宝玉石产地来源中的应用及其研究进展

宝玉石产地来源的研究是近几年地质学、宝石学和考古学界的热门话题之一。一方面,不同产地来源的宝玉石可能具有不同的品质特征及经济价值,其研究有助于珠宝首饰价值的判断,为各国海关执法提供技术支持;另一方面,古代宝玉石产地的确定对了解古代宝玉石的开采与古代科技的发展水平及不同区域的文化交流均具有重要意义。在总结前人研究成果的基础上,结合现代微区测试技术的最新研究成果,从微量元素、包裹体以及同位素分析等方面探讨总结了微区测试技术在确定宝玉石产地来源研究中的应用。当前的研究结果显示,不同的技术方法对确定宝玉石的产地来源均有一定的意义,但宝玉石产地来源的最终确定往往需要依赖更大范围和更深入地对宝石矿床的地球化学进行多技术手段的交叉分析。显然,确定各种不同类型宝玉石产地来源的标型特征及建立相关重要宝石产地的地球化学数据库,是最终解决宝玉石产地来源鉴定问题的关键。