Late Pleistocene and early Holocene ecological response of Lake El Trébol (Patagonia, Argentina) to environmental changes

Stratigraphy of Lake El Trébol (41°S 71°W, 758 m a.s.l.) described from an 11 m long sediment core provided a continuous record of patecenvironmental changes occurred during the last 14,000 years in southern South America east of the Andes. Located in an ecotonal area within a strong humidity gradient, this lake offers a unique opportunity to develop paleolimnological studies. Using a geochemical approach that includes elemental analysis, bulk organic matter, major nutrients and pigments combined with chironomids and pollen analysis, three zones were identified in the sedimentary record of this take. The oldest one (between 680 and 1,100 cm) corresponds to the late Glacial period. During that time, clayish laminated sediments were formed in a proglacial environment. Low organic matter, biogenic silica and nitrogen contents and the absence of pigments, pollen and chironomids characterise this period. At the end of this period, ca. 14,000 yr BP, a sharp increase in phosphorus concentrations predates major changes in limnological parameters. The transition zone (between 560 and 680 cm) is related to major changes in the drainage system that started soon after ca. 14,000 yr BP and continued to ca. 10,500 yr BP. The chemical composition of the sediments was affected by an increase in physical weathering mechanisms almost coincident with the increase in the regional volcanic activity that produced suspended volcanic detritus. The increase of mainly coarser detritical components may indicate a reorganisation of the fluvial system by that time. Simultaneously, an increase in the productivity of the lake accompanied by a gradual replacement of open vegetation with Nothofagus, Poaceae and Ericaceae, by Nothofagusforest, was observed. In the last zone (between 0 and 560 cm) the productivity of Lake El Trébol achieves maximum values. The trends in geochemical and biological indicators observed at Lake El Trébol can be up to some extent, correlated to those registered in Lake Mascardi. The results support earlier paleoctimatic scenarios from southern South America.     

华北西缘太原组火山事件沉积的发现及太原组地层对比

摘要：作者主要依据镜下岩矿特征,辅以岩石的野外产状与分布特点,并参考ＲＥＥ配分模式特征,首次发现华北西缘太原组存在３个火山事件层。根据火山事件沉积并结合最大海侵事件层对华北西缘太原组进行了区域对比．     

金龙山-丘岭卡林型锑金矿床稀土元素地球化学

金龙山—丘岭卡林型Sb—Au矿床的形成受沉积建造和岩相、剪切变形构造、后生成矿作用3种因素的控制,矿床属沉积—改造成因类型。根据REE含量、组成和特征参数,即REE、Ce/Y、(La/Sm)N、(La/Yb)N、δEu、δCe,探讨了该矿床的稀土元素地球化学及它与金龙山—丘岭矿床形成和演化的关系。     

秦岭煎茶岭金矿床含金富砷黄铁矿增生环带研究

在秦岭剪茶岭金矿床中发现了含金富砷黄铁矿增生环带。其产状,结构构造和成分特征共同显示了,金成矿主期金与砷有密切的地球化学相关性,在富砷增生环带发育时,金与砷共沉淀并可能在其中发育了不可见金。这种环带包含有重要的成矿作用信息,至少在矿区范围内可用于判别是否有主期矿化发育。     

生物地球化学方法与金矿找矿--以新疆西准噶尔安齐成矿断裂带为例

以新疆西准噶尔安齐成矿断裂带的生物地球化学测量工作为例,详细研究了生物地球化学找金法的样品选取,采集和分析过程及其影响因素,并对生物地球化学方法的实际找金效果进行了分析。实验表明,在干旱,半干旱地区,野薤、等是金的敏感载体植物,它们可以带来地下７０ｍ深处的地球化学信息,利用这些信息生物,可以有效地指导找矿。     

LA-ICP-MS in situ analyses of the pyrites in Dongyang gold deposit,Southeast China: Implications to the gold mineralization

The Dongyang gold deposit is a newly discovered epithermal deposit in Fujian Province, Southeast China, along the Circum-Pacific metallogenic belt. Herewith, the authors present mineralogical, scanning electron microscope, and laser ablation inductively coupled clasma mass spectrometry analysis to reveal the relations between Au and Te, As, S, Fe, etc., and discuss the gold precipitation process. The pyrites in this deposit are Fe-deficient, and are enriched in Te and As. The authors infer that As was mainly in form of As-complexes, and Te-Au-Ag inclusions/solid solution also exsits in the Py I. Along with the depletion of Te and As, they were less active chemically in the Py II, and Au may be incorporated into As-rich and Fe-deficient surface sites by chemisorption onto As-rich growth surfaces. Because of the incorporation of new fluid, Te and As became the most active chemically in the Py III, which was the main elements precipitation stage, and As dominantly substituted for S in the lattice of pyrite, due to the more reducing condition. The authors propose Au was in form of invisible gold, and the incorporation of gold can be considered as post-pyrite event, while the Au-bearing minerals were result of post incorporation of gold in arsenian pyrite.     

中国首例铁氧化物-铜-金-铀-稀土型矿床的厘定及其成矿演化

通过对拉拉矿床物共生组合、矿物生成顺序、矿石特征的研究，发现其矿石物以磁铁矿为主，铁和铜的硫化物次之，并含有大量稀土矿物和自然金。拉拉矿床至少经历了两期成矿作用：早期为区域变质成矿作用，晚期为热液成矿作用。早期形成Fe-REE-P矿化，晚期为Cu-Mo-Au-Co-(U)矿化。根据这些特征，首次指出该矿床属于铁氧化物-铜-金-铀-稀土型矿床，而不是以往所称的块状硫化物型铜矿。     

冰期与间冰期在第四纪地层与岩性上的作用

论述了冰期与间冰期的气候变化与海平面升降的关系以及冰期与间冰期的古地貌，全面系统地阐述了上海地面沉降之后的地质环境，并提出了控制地面沉降的５条建议。     

原子吸收分光光度法快速测定红土镍矿中镍

试样经烘干处理后,利用酸溶法或碱融法制备稳定的分析溶液,然后利用原子吸收分光光度计于波长232.0nm处,随同标准曲线测量镍含量,此方法简单、快捷,所选分析线干扰小、灵敏度高,稳定性和准确度均满足要求。     

湘西北黑色岩系中的镍钼矿床及其贵金属矿化特征

湖南西北部下寒武统黑色岩系蕴藏着丰富的镍钼钒多金属矿床及其伴生的Au,Ag,Pt,Pd等贵金属矿化。它是我国新类型的镍钼矿床及贵金属矿化极具找矿潜力的地区。富含有机质和黄铁矿的黑色岩系既是镍钼矿的富集层,也是贵金属矿化的主要富集层。矿床的成矿作用是伴随热水的加入而开始,热水沉积与正常沉积交替期是成矿的高峰期,至正常沉积期结束。生物及生物地球化学作用在黑色岩系的成岩成矿过程中起了重要作用。矿床以同生沉积为主,兼有热水性质沉积特点。其成因应归属于生物地球化学沉积矿床范畴。