Paleoproterozoic basement beneath the southern Jiangxi Province: Evidence from U-Pb ages and Lu-Hf isotopes in zircons from the Doushui lamprophyre

This paper presents geochemical analyses of a lamprophyre intruding the Caledonian Doushui granite body in Shangyou County, southern Jiangxi Province. U-Pb dating and Hf-isotope analyses are espe-cially carried out for zircons from it. Petrological and geochemical features show that the lamprophyre belongs to a high-K, weakly alkaline pyroxene-biotite lamprophyre. It is characterized by high Mg# (0.74), Ni (253 μg/g) and Cr (893 μg/g) contents, and also enriched in incompatible elements, such as REE, Rb, Sr...     

大同煤田煌斑岩在地震和测井资料上的响应特征

通过对大同煤田煌斑岩侵入类型及其在煤田测井和地震资料的响应特征的分析研究,提出了利用大同煤田煌斑岩侵入煤层的物性特征来划定其影响范围的方法,为今后煤田的资源评价和可采起到一定的指导作用,也具有一定的现实意义。     

SHRIMP U-Pb zircon dating for lamprophyre from Liaodong Peninsula： Constraints on the initial time of Mesozoic lithosphere thinning beneath eastern China

It is undebated fact that the lithospheric mantle beneath eastern China was considerably thinned during the Mesozoic time. However, it has no adequate evidence for the exact timing when the lithosphere thinning started. The Liaodong Peninsula is located in the eastern segment of the North China Craton and is one of the important domains to explore the event of lithosphere thinning. SHRIMP U-Pb zircon dating and geochemical study were carried out for the lamprophyre dike swarm that intruded into the magnesite ore-beds in the Dashiqiao Formation of Paleoproterozoic Liaohe Group at the Huaziyu magnesite ore district, Liaodong Peninsula. The results indicate that these lamprophyre dikes were intruded in late Jurassic （155±4 Ma） and show some geochemical characteristics of potassic magmas. It is now accepted that the lithosphere thinning took place in the late Mesozoic, and the peak thinning stage occurred in early Cretaceous （130-120 Ma）. Considering the potassic mafic magmatism marking the onset of the lithospheric thinning, we therefore suggest that the studied late Jurassic potassic lamprophyre dike swarm could imply that the late Jurassic is the time that lithosphere thinning started.     

XW铀矿床成矿机理

本文探讨了成矿热液中水、铀和∑CO_2的来源,铀迁移沉淀的微观机理,以及矿岩时差的实质等问题。研究表明,由晚期花岗岩浆分异出的初始热液,是一种贫铀贫∑CO_2的热液。成矿热液中的铀主要是在煌斑岩浆贯入并为原来的贫∑CO_2热液提供了大量∑CO_2之后,从已固结的花岗岩中浸取而来。由于形成铀含量较高的成矿热液,有赖于因煌斑岩贯入所发生的加气作用,故铀矿床的形成不是紧接着花岗岩成岩之后,而是在煌斑岩贯入之后。     

The Sr, Nd isotopic composition of lamprophyres in Laowangzhai gold orefield, Yunnan Province

Lamprophyres are widely spread over the Laowangzhai gold orefield in northern Mt. Ailao structure zone, Yunnan Province. Lamprophyres in the orefield are temporally and spatially related to gold mineralization. Lamprophyres in the orefield have anomalous Sr and Nd isotopic compositions, e.g. the 87Sr/ 86Sr ratios (0.706 665-0.707 960, the 87Sr/ 86Sr ratio of sample YLW-44 is 0.709 041) are higher than the modern value of the original mantle (0.704 5), the 143Nd/ 144Nd ratios (0.512 463-0.512 551) are lower than the modern value of the original mantle (0.512 638), and the calculated values ε Sr>0 (28.1-63.7) and ε Nd<0 (-1.34--3.07). The results of investigation indicate that lamprophyres in the Laowangzhai gold orefield with anomalous Sr and Nd isotopic compositions would not be produced as a result of contamination of the primary magma with the isotopic features of MORB by the crust materials high 87Sr/ 86Sr ratios and low 143Nd/ 144Nd ratios in the processes of rising or in the magma chamber, but the result of metasomatism of source mantle.     

金刚石原生矿普查方法述评

总结当代找矿经验,以地质观察研究为基础,以重砂法为主要手段,辅以物化探和大样选矿直接寻找金刚石的综合方法,基本是切实可行的。     

中基性脉岩对金矿成矿的贡献──以小秦岭金矿区为例

文章以小秦岭金矿区为例，研究了中基性脉岩与金矿床成因的关系。研究表明，中基性脉岩的产出反映了区域性地壳拉张构造环境，此环境有利于构成富矿化剂的热液体系。只有当富矿化剂的热液体系在时间和空间上与金等成矿元素的矿源层（体）配合得当，才可能在适宜的地质地球化学条件下形成相应的矿床。即中基性脉岩对金成矿的制约关系主要在于矿化剂而非金源。     

Ultra-violet laser probe measurement of ^40Ar／^39Ar age profile in phlogopite

Ultra-Violet Laser Ablation Microprobe (UVLAMP) extraction technique enables the direct investigation of Ar-Ar age prorde in crystals, and yields more information on rates and durations of geological process than conventional single time snapshots. Phlogopite flakes from lamprophyre at Pishan dyke in western Kunlun were dated by using an UV laser (λ= 213 nm) microprobe with spot analyses. The results show good agreement with those from the conventional ^40Ar/^39Ar step heating experiments. This indicates that the Ar isotopes are distributed homogenously in the phlogopite and the UVLAMP can be a powerful tool in the study of thermal history.