Nature and origin of the Vani manganese deposit, Milos, Greece: an overview     

A. Liakopoulos  G. P. Glasby  C. T. Papavassiliou  J. Boulegue 《Ore Geology Reviews》2001,18(3-4)

The Vani manganese deposit is located in the rugged NW sector of Milos Island. It occurs within the Vani volcano-sedimentary basin, which is underlain by dacitic domes and flows of Upper Pliocene age (3.5–2.0 Ma). The end of the emplacement of the dacites was marked by the collapse of the magma chamber, which resulted in a huge pyroclastic episode and the deposition of a thick layer of pyroclastic material within a shallow submarine basin. This pyroclastic material subsequently compacted to form the volcaniclastic sandstone, which became the host for the manganese ore beds which were about 4 m thick in the two sections studied. Hydrothermal fluids penetrated these sandstone horizons via fractures and fissures to produce the manganese deposit. The permeable nature of the sandstone facilitated the retention of the hydrothermal fluids within these layers. This permitted the fluids to cool slowly and deposit the manganese oxides almost quantitatively. Formation of the hydrothermal manganese deposit took place fairly rapidly over a period of several tens of thousands of years at most. Strong tectonic activity resulted in rapid uplift of the area which elevated the deposit above sea level.Two generations of manganese oxides have been identified within this deposit; the first generation consists of pyrolusite and ramsdellite; the second generation of oxides of the isostructural series cryptomelane–hollandite–coronadite plus hydrohetaerolite characterized by high contents of K, Ba, Pb and Zn, respectively. This sequence is the result of a two-stage process of formation of the manganese-oxide minerals in which a second high-salinity hydrothermal fluid enriched in Ba, Pb and Zn as a result of the dissolution of sulphide minerals remineralized the original manganese-oxide assemblage. It is this two-stage process of formation, which was mainly responsible for the unique characteristics of this deposit. Although formed in a submarine setting, the deposit shows marked differences in mineralogy and composition from known submarine hydrothermal manganese deposits and is most analogous to the epithermal vein deposits of the southwestern United States.  相似文献   

Emplacement of xenolith nodules in the Kaupulehu lava flow,Hualalai Volcano,Hawaii     

J. E. Guest  P. D. Spudis  R. Greeley  G. J. Taylor  S. M. Baloga 《Bulletin of Volcanology》1995,57(3):179-184

The basaltic Kaupulehu 1800–1801 lava flow of Hualalai Volcano, Hawaii contains abundant ultramafix xenoliths. Many of these xenoliths occur as bedded layers of semi-rounded nodules, each thinly coated with a veneer (typically 1 mm thick) of lava. The nodule beds are analogous to cobble deposits of fluvial sedimentary systems. Although several mechanisms have been proposed for the formation of the nodule beds, it was found that, at more than one locality, the nodule beds are overbank levee deposits. The geological occurrence of the nodules, certain diagnostic aspects of the flow morphology and consideration of the inferred emplacement process indicate that the Kaupulehu flow had an exceptionally low viscosity on eruption and that the flow of the lava stream was extremely rapid, with flow velocities of at least 10 m s^-1 (more than 40 km h^-1). This flow is the youngest on Hualalai Volcano and future eruptions of a similar type would pose considerable hazard to life as well as property.  相似文献   

川北高燕锰矿的锰质岩类型和生物成矿作用   总被引：2，自引：0，他引：2  

赵东旭 《岩石学报》1994,10(2):171-183

川北高燕陡山沱组锰矿的锰质岩有四种主要类型：由富藻层和碎屑层组成的叠层石锰质岩，由藻屑，鲕屑组成的藻屑锰质岩和由锰质内碎屑与各种基质组成的内碎屑锰质岩。根据矿层中赋存的大量藻类遗体及其与矿石的密切共生关系来看．生物特别是藻类参与了锰矿的成矿作用。  相似文献   

湘潭锰矿的酸性水污染及其防治对策     

傅丰海 《湖南地质》1993,12(4):268-271,267

湘潭锰矿酸性水的形成,与含矿岩系富含黄铁矿的黑色页岩密切有关。本文揭示了它的形成条件和影响因素及其对工农业生产的危害。作者根据当地酸性水的来源与分布。提出了一些防治措施,并对石灰中和法原理及其应用效果作了介绍。  相似文献   

类质同象的研究方法及意义     

隋延辉  梁一鸿  戚长谋 《世界地质》2004,23(4):326-331

结合研究史作者论述了元素类质同象、间隙原子和固溶体概念的异同。指出类质同象元素的3个属性：同生性、共生性和同晶体化学位。提出元素统计式均匀分布为鉴别类质同象状态的理论准则,例举电子探针、矿物物性鉴别“杂质”属性的可行性,指出电子探针方法为最佳选择。论述了类质同象的重要地学意义：岩浆演化的指示剂和地质温压计。提出类质同象副成分作为找矿地球化学标志的新思路。元素不同存在状态的查定在矿产资源评价中具有重要意义。  相似文献   

Microbial ecology and geochemistry of soils containing iron pans     

C.?R.?AndersonEmail author  I.?M.?Turnbull  M.?R.?Rosen 《Environmental Geology》2003,45(2):209-220

Soils in New Zealand, and elsewhere, often contain substantial zones of ferro-manganese concretions and pans (laterally continuous layers) that can affect soil quality and management. Soils containing concretions and pans from Southland, New Zealand, were investigated to determine links between microbial ecology and geochemistry. Three soil profiles were sampled at 100-mm intervals to a depth of 1 m and then assayed for nine different populations of bacteria using selective media. Geochemical analysis was performed on the soils at the same intervals, and on shallow groundwater from nearby wells. The largest concentrations of iron (Fe) and manganese (Mn) coincide with concretions. Nitrogen (N) and carbon (C) are not correlated with Fe and Mn but may be depleted due to bacterial metabolism. Fe and Mn concentrations in groundwater are low, suggesting that the source of these elements in the concretions and pans is in situ weathering rather than groundwater. Numbers of iron oxidising organisms increase where concretions and pans are encountered, but manganese-oxidising organisms decrease. Heterotrophic, sulphur-oxidising, and anaerobic populations have relatively consistent numbers at all depths within the profiles. Fifty organisms were selected for phylogenetic characterisation, of which only Pseudomonas sp. is known to have significant interactions with Fe and Mn. These results suggest a link between concretion development and iron-oxidising microbial populations.  相似文献   

Altered carbon cycling and trace-metal enrichment during the late Valanginian and early Hauterivian   总被引：1，自引：0，他引：1  

Oliver Kuhn  Helmut Weissert  Karl B. F?llmi  Susanne Hennig 《Eclogae Geologicae Helvetiae》2005,98(3):333-344

  相似文献   

Enzyme leach anomalies associated with deep Mississippi Valley-type zinc ore bodies at the Elmwood Mine, Tennessee   总被引：1，自引：0，他引：1  

James R. Yeager  J. Robert Clark  Wallace Mitchell  Roy Renshaw 《Journal of Geochemical Exploration》1998,61(1-3)

Deeply buried Mississippi Valley-type deposits that have been or are currently being mined in North America were initially discovered by drilling. Conventional geochemical methods are ineffective for detecting these ‘blind' deposits when they occur deep within sequences of stable-platform carbonates and shales. The ‘enzyme' leach is a selective analytical technique for determining trace elements associated with amorphous Mn oxide coatings in soils. In many areas of the world, the enzyme leach method is useful for detecting low-level geochemical anomalies in soils, which are associated with blind mineral deposits. Enzyme leach analysis of soils, collected at the Elmwood Mine, Tennessee, revealed high-contrast anomalies over ore bodies 370 m below the surface. In areas where the soils are in chemical equilibrium, ‘combination' anomalies occur over Zn ore bodies. These are characterized by asymmetrical halogen halos which occur around a halogen ‘central low'. Commodity metals (Zn and Pb) and trace elements associated with the ore (Cd, Ba, and Mn) form apical anomalies, which occur over the ore bodies and within the halogen halo. Under most circumstances, agricultural practices do not affect enzyme leach results. However, agricultural activity in central Tennessee appears to have altered the proportion of amorphous Mn oxides in the soils in some locations. Where the MnO₂-form equilibrium of the soil has been disturbed, enzyme leach data are erratic. In the one instance where this was encountered, ratioing the data to Mn reveals anomalies which bracket the blind ore bodies.  相似文献   

A Preliminary Study on the Preparation of Four Pacific Ocean Polymetallic Nodule and Sediment Reference Materials: GSPN-2, GSPN-3, GSMS-2 and GSMS-3   总被引：6，自引：0，他引：6  

Yimin Wang  Daihong Luo  Yushu Gao  Haowei Song  Jiaxi Li  Weiyue Chen  Yunye Teng  Shiguang Zhou 《Geostandards and Geoanalytical Research》1998,22(2):247-254

The research project for the preparation of two polymetallic nodule (GSPN-2, GSPN-3) and two marine sediment (GSMS-2, GSMS-3) reference materials was completed in 1996. The samples were collected from the Eastern and Central Pacific Ocean and prepared to less than 74 μm fine powder. The homogeneity of the materials was tested by X-ray fluorescence spectrometry. The relative standard deviations (RSD %) of measurements of selected elements in samples taken from thirty bottles selected at random were less than 0.5%. Thirty four laboratories worldwide participated in the collaborative analysis programme. The number of elements or constituents analysed was seventy nine for nodules and eighty one for sediments. Among those, sixty three elements were certified in each sample. The sum of major elements or components is 99.7% for GSPN-2, 99.5% for GSPN-3, 99.8% for GSMS-2 and 99.8% for GSMS-3.  相似文献   

答《关于深海锰结核中“纳米级超微生物化石”的思考和建议》一文   总被引：2，自引：0，他引：2  

林承毅  边立曾 《高校地质学报》1997,3(2):236-240

本文详细讨论了东太平洋深海锰矿结核中新发现的中华微放线菌和太平洋螺球孢菌究竟是不是超微结构，首先，它们是笔者根据形态，结构和元素成分作为超微生物化石进行鉴定的，其次，透射电子显微镜中可以清楚地区分出完整的微生物结构，包括菌丝，孢子，孢囊和菌落等，它们之间的尺寸比例也是适当的，此外，透射电子显微像还揭示，深海锰质叠层石的纹层就是这些超微生物韵律性生长的结果，与滨海叠层中的纹层十分相似，笔者认为，已知微生物的最小尺寸不能作为否定新发现的超微生物化石的依据。本文还讨论了超微生物化石的术语问题。  相似文献