Search

Conventional geochemical methods are not suitable for or ineffective in geochemical mapping for concealed deposits hidden bellow the thick cover of transported overburden or thick sequence of post-ore sedimentary or vocanic rocks. Recently, leaching of mobile forms of metals in overburden (MOMEO) has been developed and widely tested in geochemical mapping by using wide-spaced sampling in diverse concealed terrains. The case histories of pilot study show that large-scale geochemical patterns consistent with or favorable for large metallogenic belts can be delineated using wide-spaced MOMEO geochemical mapping in concealed terrains in different settings. The sequence of cover does not mask the mineralization indications. The methods have potential in strategic exploration for giant ore deposits in concealed terrains in the future.

The synergic strengthening of multiple phases is an essential way to achieve high-performance Mg alloys. Herein, Mg-Gd-Zn alloy containing four phases was prepared by rapid solidification (RS) ribbons and spark plasma sintering (SPS). The microstructure of the alloy consisted of &alpha, Mg, nanosized &beta, 1 phase particles, lamellar long period stacking ordered (LPSO) phase, and &beta, &prime, phase precipitates. The microstructural evolution was also investigated. The results show that the metastable &beta, 1 phase was formed in the as-cast solidification through rapid solidification, because both Zn atoms and the short holding-time at molten liquid facilitated the formation of the &beta, 1 phase. The &beta, 1 phase grew from 35.6 to 154 nm during the sintering process. Meanwhile, the fine lamellar LPSO phase was simultaneously formed after the Zn-Gd clusters were generated from the supersaturated solid solution, and the width of the LPSO phase was only in the range of 2&ndash, 30 nm. The third strengthening phase, the metastable &beta, phase, was obtained by aging treatment. The results of hardness testing implied that the hardness of the alloy containing the aforementioned three nanosized strengthening phases significantly improved about 47% to 126 HV compared with that of the as-cast ingot.

The resources and environmental problems are the two most fundamental issues facing all nations in the world. Everything in and on the Earth – minerals, animals and plants – is made from one, or generally some combination of, chemical elements, which are scientifically listed in the periodic table. Thus it is important to understand the present abundance and spatial distribution of all the elements across the Earth's surface. Such kinds of data can only be obtained at present and for the foreseeable future by on-earth geochemical mapping at all scales. The 30-year efforts made by Chinese geochemists in carrying out multi-element, multi-media, multi-scale geochemical mapping projects to delineate 39–76 element distribution at home and abroad culminated in a successful case of high-quality geochemical data acquirement. The new idea for a four-level plan for global geochemical mapping was advanced to obtain global data in the foreseeable future and the collection of updated geochemical information. Such information needs to be easily accessible not only by the science community, but also by industry, agriculture, governments, and even individuals, by all who would make an effort to promote sustainable living on our planet. The concept of a Digital Element Earth (DEE) fulfills the aims.

Jinla Pb-Zn-Ag poly-metallic ore field across China and Myanma, is tectonically located in the south segment of the Mengtong–Gengma–Ximeng passive continental margin of Proterozoic era-Palaeozoic era, and the eastern margin of the Baoshan–Shantai Massif. Mineralization related granitoids within the ore field include Laochang amphibole admellite, Menglinshan biotite admellite and Nanla K-feldspar granite-porphyry. This paper systematically presents the characteristics of the above granites on their major elements, REE and trace elements (including ore-forming elements) and their isotopic ages determined by zircon SHRIMP dating. The intrinsic connection and genesis of the granites, and the relationships between granites and Pb-Zn-Ag mineralization are discussed. It comes to the conclusions as follows: (1) Among the three types of granites in Jinla ore field, the U-Pb zircon ages for both Laochang porphyraceous amphibole admellite and Menglinshan porphyraceous biotite admellite are (45.41±1) Ma, and Nanla K-feldspar granite porphyry, with a zircon U-Pb age of (43.41±0.78) Ma, formed at the late stage of a syn-collisional mineralization process of Himalayan orogenesis. The magma may have been resulted from partial melting in the crust due to crust and mantle interaction and therefore, is dominated by crustal source materials mixed with some mantle components. Laochang porphyraceous amphibole admellite and Menglinshan porphyraceous biotite admellite contrain significant amount of mantle source materials, whereas Nanla K-feldspar granite porphyry is dominated by crustal materials mixed with minor mantle component. (2) Major and trace elements (including REE and some trace elements (Zr/Hf, Nb/Ta, Rb/Sr, Rb/Ba, K/Rb, (Rb/Yb)N, Sr*, K* and Zr*) suggest that the granitic intrusions in the research area may have formed in locally extensional tectonic environment. Laochang porphyraceous amphibole admellite and Menglinshan porphyraceous biotite admellite may have formed at deep crust during the early stage of magma differentiation. Nanla K-feldspar granite porphyry, on the other hand, may have formed at shallow crust during the late stage of magma differentiation. These three granite intrusions are the products of various stages of magma differentiation during magmatic-tectonic evolution process. (3) Our study on the ore-forming elements in these intrusions suggests that in comparison with granites in China, although Laochang porphyraceous amphibole admellite and Menglinshan porphyraceous biotite admellites are relatively rich in some ore-forming minerals, Nanla K-feldspar granite porphyry has the highest ore-forming potential because, comparing with the other two intrusions, it not only contains more ore-forming minerals, such as W, Cu, Bi, Sb, Mo, Sn, Ag, Pb, Au, etc., the granite is also much richer in F, B, As and other mineralizing elements.

Over 3 million samples were collected from southern China at a density of 1–2 stream sediment samples per square kilometre as part of the Regional Geochemistry National Reconnaissance (RGNR) programme of China initiated in the late 1970s. Approximately 5244 composite samples of stream sediments from twelve provinces of southern China were prepared from the original RGNR samples collected from a territory with an area of 2300000 km2 at a density of one composite sample per 1:50000 map sheet (about 400 km2). Seventy-six elements were determined by the geoanalysis laboratory of Henan Province (platinum-group elements) and by the Institute of Geophysical and Geochemical Exploration (IGGE) laboratory for the remainder. Internal quality and external quality control methods were applied to ensure that the analytical data were comparable. Statistics were used to derive the mean and background values and indicate the average concentrations of the seventy-six elements. Comparisons were made against the mean values obtained from stream sediments, floodplain sediments, overall sediments and overall soils of the entire territory of China. The concentrations of Hg, Cd, rare earth elements and 24 other elements were higher than their background for the whole of China. In contrast, the concentration of Na2O, CaO, Ba and Sr were lower in the stream sediments in southern China than their whole China background. Plus de 3 millions d'echantillons de sediments fluviaux ont ete preleves dans le sud de la Chine avec une densite de 1 a 2 echantillons par kilometre carre dans le cadre du programme de Reconnaissance Nationale de la Geochimie Regionale (RNGR) que la Chine a lance a la fin des annees 1970. Environ 5244 echantillons composites de sediments fluviaux provenant de douze provinces du sud de la Chine ont ete prepares a partir des echantillons originaux du programme RNGR recueillis sur un territoire d'une superficie totale de 2 300 000 km2 avec une densite d'un echantillon composite par feuille de carte au 1:50 000 (environ 400 km2). Soixante-six elements ont ete determines par le laboratoire de Geoanalyses de la province du Henan (elements du groupe du platine) et par l'Institut d'exploration geophysique et geochimique (IGGE, reste des elements). Les methodes de controle de qualite interne et externe ont ete appliquees pour s'assurer que les donnees analytiques etaient comparables. Des methodes statistiques ont ete utilisees pour calculer les valeurs moyennes et du niveau de fond et indiquer les concentrations moyennes des soixante-seize elements. Les comparaisons ont ete faites par rapport aux valeurs moyennes obtenues pour les sediments fluviaux, les sediments de plaine inondable, les sediments et sols globaux du territoire de la Chine dans son entier. Les concentrations de Hg, Cd, des terres rares et de vingt-quatre autres elements sont plus elevees que leur niveau de fond pour l'ensemble de la Chine. En revanche, les concentrations de Na2O, CaO, Ba et Sr sont plus faibles dans les sediments des cours d'eau du sud de la Chine que leur niveau de fond au niveau de l'ensemble de la Chine.