Technogenic hydrogeochemical anomalies of tungsten deposits in Kykylbey ore region

Peculiarities of the tungsten deposits drainage flow chemical composition formation, the development of which was ceased almost 40 years ago, have been considered. Migration peculiarities of ore components have been covered, and forms of their migration have been calculated. Inertial characteristics of the surface flow contamination are shown.     

New Olivine Reference Material for In Situ Microanalysis

A new olivine reference material – MongOL Sh11‐2 – for in situ analysis has been prepared from the central portion of a large (20 × 20 × 10 cm) mantle peridotite xenolith from a ~ 0.5 My old basaltic breccia at Shavaryn‐Tsaram, Tariat region, central Mongolia. The xenolith is a fertile mantle lherzolite with minimal signs of alteration. Approximately 10 g of 0.5–2 mm gem quality olivine fragments were separated under binocular microscope and analysed by EPMA, LA‐ICP‐MS, SIMS and bulk analytical methods (ID‐ICP‐MS for Mg and Fe, XRF, ICP‐MS) for major, minor and trace elements at six institutions world‐wide. The results show that the olivine fragments are sufficiently homogeneous with respect to major (Mg, Fe, Si), minor and trace elements. Significant inhomogeneity was revealed only for phosphorus (homogeneity index of 12.4), whereas Li, Na, Al, Sc, Ti and Cr show minor inhomogeneity (homogeneity index of 1–2). The presence of some mineral and fluid‐melt micro‐inclusions may be responsible for the inconsistency in mass fractions obtained by in situ and bulk analytical methods for Al, Cu, Sr, Zr, Ga, Dy and Ho. Here we report reference and information values for twenty‐seven major, minor and trace elements.     

西北冰洋冰筏碎屑指示的MIS 5以来冰盖和洋流的演化历史

通过西北冰洋楚科奇边缘地区4个柱状沉积物组成的岩芯断面,分析MIS 5以来粗颗粒（>250 μm）冰筏碎屑（IRD）的岩矿组成,确定西北冰洋不同时期IRD的来源和搬运模式,进而重建MIS 5以来欧亚冰盖和北美冰盖的消长以及北冰洋海盆中表层洋流的演化历史。研究结果显示MIS 5.5和MIS 5.1期间,波弗特环流的影响范围大于MIS 1期,而在MIS 5.4~5.2期间,波弗特环流的影响范围小于现代;MIS 4期间,岩芯中发现了大量来源于欧亚冰盖或东西伯利亚海冰盖的冰川浊积物,冰盖可能扩张到了楚科奇边缘地区南部;在同一时期,在楚科奇边缘地区南部的岩芯中IRD几乎全部为铁锰结核,可能受到了欧亚冰盖或东西伯利亚海冰盖的影响,但铁锰结核与欧亚冰盖的关系仍需进一步研究;MIS 3期间,波弗特环流的影响范围和强度略弱于现代;在末次冰盛期,研究区受到以劳伦冰盖为主要来源的冰川浊积物输入;在末次冰消期,研究区发生了一次来源于北美劳伦冰盖的冰融水排泄事件;在MIS 1期,西北冰洋主要受到波弗特环流的控制,将来源于加拿大北极富含碎屑碳酸岩的IRD带入北冰洋海盆。

     

峨眉火成岩省内带岩浆硫化物含矿岩体橄榄石的成因意义

峨眉火成岩省内带出露数十个含Ni-Cu-铂族元素(PGE)硫化物矿床(或矿化)的镁铁质-超镁铁质侵入岩体.根据铂族元素(PGE)含量的不同,这些岩浆硫化物矿床可分为Ni-Cu型(如力马河和清水河)、Ni-Cu-PGE型(如清矿山和黄草坪)和PGE型(如金宝山和杨合武).不同类型含矿岩体的橄榄石电子探针分析表明,除了清矿山岩体少数几个橄榄石晶体属于镁橄榄石外(Fo90.1～Fo93.1),其余均为贵橄榄石(Fo76.8～Fo89.6).不同矿化类型的岩体的橄榄石成分差异明显.Ni-Cu型硫化物含矿岩体的橄榄石Fo为77～87,Ni含量变化范围为(976～2176)×10-6.Ni-Cu-PGE型硫化物含矿岩体的橄榄石Fo为80～86,Ni含量范围为(1024～2543)×10-6.PGE型硫化物含矿岩体的橄榄石Fo为78～84,Ni含量在(776～1755)×10-6之间变化.清矿山Ni-Cu-PGE型硫化物含矿岩体橄榄石具有高Fo(最高达93.1)和CaO含量(0.245%～1.14%)、以及非常低的Ni(266×10-6)的特征,可能是同化混染作用的结果.利用力马河岩体最高Fo含量的橄榄石成分计算表明,母岩...     

Crustal origin for coupled 'ultra-depleted' and 'plagioclase' signatures in MORB olivine-hosted melt inclusions: evidence from the Siqueiros Transform Fault,East Pacific Rise

Geochemical data from melt inclusions in olivine phenocrysts in a picritic basalt from the Siqueiros Transform Fault on the northern East Pacific Rise provide insights into the petrogenesis of mid-ocean ridge basalts (MORB). The fresh lava contains ~10% of olivine phenocrysts (Fo_89.3-91.2) and rare, small (<1 mm) plagioclase phenocrysts with subhedral to irregular shapes with a range of compositions (An_80-90, An_57-63). Melt inclusions in olivine phenocrysts are glassy, generally rounded in shape and vary in size from a few to ~200 µm. Although most of the inclusions have compositions that are generally consistent with being representative of parental melts for the pillow-rim glasses, several inclusions are clearly different. One inclusion, which contains a euhedral grain of high-Al, low-Ti spinel, has a composition unlike any melt inclusions previously described from primitive phenocrysts in MORB. It has a very high Al₂O₃ (~20 wt%), very low TiO₂ (~0.04 wt%) and Na₂O (~1 wt%) contents, and a very high CaO/Na₂O value (~14). The glass inclusion is strongly depleted in all incompatible elements (La =0.052 ppm; Yb =0.34; La/Sm(n) ~0.27), but it has large positive Sr and Eu anomalies (Sr/Sr* ~30; Eu/Eu* ~3) and a negative Zr anomaly. It also has low S (0.015 wt%) and relatively high Cl (180 ppm). We suggest that this unusual composition is a consequence of olivine trapping plagioclase in a hot, strongly plagioclase-undersaturated magma and subsequent reaction between plagioclase and the host olivine producing melt and residual spinel. Two other melt inclusions in a different olivine phenocryst have compositions that are generally intermediate between 'normal' inclusions and the aluminous inclusion, but have even higher CaO and Sr contents. They are also depleted in incompatible elements, but to a lesser degree than the aluminous inclusion, and have smaller Sr and Eu anomalies. Similar inclusions have also been described in high-Fo olivine phenocrysts from Iceland and northern Mid-Atlantic Ridge. We suggest that the compositions of these inclusions represent assimilation of gabbroic material into the hot primitive magma. The localised nature of this assimilation is consistent with it occurring within a crystal mush zone where the porosity is high as primitive magmas pass through earlier formed gabbroic 'cumulates'. In such an environment the contaminants are expected to have quite diverse compositions. Although the interaction of primitive melts with gabbroic material may not affect the compositions of erupted MORB melts on a large scale, this process may be important in some MORB suites and should be accounted for in petrogenetic models. Another important implication is that the observed variability in melt inclusion compositions in primitive MORB phenocrysts need not always to reflect processes occurring in the mantle. In particular, inferences on fractional melting processes based on geochemistry of ultra-depleted melt inclusions may not always be valid.     

Subcritical dynamo and hysteresis in a Babcock-Leighton type kinematic dynamo model

In the Sun and Sun-like stars,it is believed that cycles of the large-scale magnetic field are produced due to the existence of differential rotation and helici...     

The impact of glaciation, river-discharge and sea-level change on Late Quaternary environments in the southwestern Kara Sea

Sedimentary records from the southwestern Kara Sea were investigated to better understand the extent of the last glaciation on the Eurasian Arctic shelf, sea-level change, and history of the Ob' and Yenisey river discharge. Sediment-core and seismic-reflection data indicate that the Quaternary depositional sequence in the southwestern Kara Sea consists of glacial, glaciomarine, and marine sedimentary units. Glaciogenic sediments in the deep Novaya Zemlya Trough are presumably related to the Last Glacial Maximum (LGM), whereas further east they may represent an earlier glaciation. Thus, it is inferred that the southeastern margin of the LGM Barents-Kara ice sheet was contained in the southwestern Kara Sea east of the Novaya Zemlya Trough. Changes in mineralogical, foraminiferal, and stable-isotopic composition of sediment cores indicate that riverine discharge strongly influenced sedimentary and biotic environments in the study area during the Late Weichselian and early Holocene until ca. 9 ka, consistent with lowered sea levels. Subsequent proxy records reflect minor changes in the Holocene hydrographic regime, generally characterized by reduced riverine inputs.