首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 640 毫秒
1.
Pavements of manganese nodules and crusts and outcrops of Miocene limestones were observed on the flanks and flat top of the Tenpo Seamount during three Shinkai 2000 dives. The pre‐Miocene volcano supplied nuclei of volcanic rocks and hydrothermal manganese deposits, and subsequent slow or no sedimentation promoted deposition of abundant hydrogenetic nodules and crusts, mainly on the upper flank of the seamount. Nodule pavements generally cover calcareous sand surface sediments, while crusts cover hard outcrops composed probably of volcanic rocks. The fields of crusts and nodules are sparsely distributed with each other on scales of meters to tens of meters. The on‐site observation suggests the deposits have encountered tectonic and/or mass movements that resulted in unusual occurrences of densely stacked nodules and occasionally the nodules resting directly on crusts or hard substrates. Mineralogical and chemical compositions reveal that for nodules and crusts the encrusting manganese layers of around 1 cm thickness are composed of hydrogenetic vernadite, and diagenetic influence is negligible.  相似文献   

2.
Ferromanganese crusts comparable with central Pacific occurrences with respect to thickness and extension have been discovered at the Tropic Seamount in the subtropical NE Atlantic. A comparison with typical hydrogenetic crusts from a central Pacific seamount revealed lower concentration of the Mn phase with Mn, Co, Ni, Zn, and Cu but a strongly increased terrigenous input of Fe, Pb, Al, and Si in the Atlantic crusts. Growth rates are increased compared with the Pacific crusts, and crust ages average at 10 My. The old phosphatized crust generation that started to grow about 20 My ago on the Pacific seamounts is not pronounced at the Tropic Seamount. The typical hydrographic and morphological parameters for hyrogenetic crust growth have also been found at the Tropic Seamount, which implies that the Tropic Seamount crusts have developed according to the hydrogenetic growth model. There are no indications of hydrothermal influence.  相似文献   

3.
Eighteen deep-sea ferromanganese crusts (Fe-Mn crusts) from 10 seamounts in the northeast Atlantic were studied. Samples were recovered from water depths of ～1,200 to ～4,600 m from seamounts near Madeira, the Canary and Azores islands, and one sample from the western Mediterranean Sea.

The mineralogical and chemical compositions of the samples indicate that the crusts are typical continental margin, hydrogenetic Fe-Mn crusts. The Fe-Mn crusts exhibit a Co + Cu + Ni maximum of 0.96 wt%. Platinum-group element contents analyzed for five samples showed Pt contents from 153 to 512 ppb.

The resource potential of Fe-Mn crusts within and adjacent to the Portuguese Exclusive Economic Zone (EEZ) is evaluated to be comparable to that of crusts in the central Pacific, indicating that these Atlantic deposits may be an important future resource.  相似文献   

4.
A sampling expedition has shown that largely hydrogenetic marine ferromanganese deposits occur in the Christmas Island region south of Java (~10°S), as small nodules on seamount slopes and abyssal plains (red clay), and as thick crusts on volcanic ridges and seamounts. Vernadite is dominant, with birnessite, jacobsite and todorokite common. Nodules were recovered in 25% of free-fall grab stations in water 4600-5900 m deep, and are not abundant where present. The nodules average 9.6% Fe, 19.7% Mn, 0.51% Ni, 0.49% Cu, and 0.12% Co. Crusts are common in water 1450-3700 m deep, with average deposition rates of 1-1.5 mm / m.y. The crusts average 13.9% Fe, 16.2% Mn, 0.35% Ni, 0.11% Cu, and 0.44% Co. Cobalt grades are higher (~0.8%) in shallower water ( < 2500 m), so future exploration should concentrate on depths of 500-1500 m near the oxygen minimum zone.  相似文献   

5.
We propose a geochemical parameter, “metal flux” in evaluating hydrogenetic Co-rich ferromanganese crust deposits in the Pacific seamount area, that is based on physical, chemical, and geological characterization of the integrated growth piles of crusts. We calculated the metal flux for fifteen sites from different depths ranging between 900-6000m from different seamounts. The secular and areal variations of metal flux indicate a strong geological controls, and also can be a reliable tool for estimating an economic potential of the crusts. The Co flux decreases with increasing water depth, followed by almost constant flux of Ni and Mn. The Al and Fe fluxes vary with regions, indicating higher values in the western regions near the island arc probably related to a supply from the Asian continents. The results imply that Co, a redox sensitive metal element, is controlled by redox conditions of seawater, while Fe and Al are by terrigenous input. The metal flux reflects global and regional conditions and controls the compositional diversity of metals, thus consequently, the parameter can be a reliable powerful tool to estimate or single out more potential areas.  相似文献   

6.
Marine hydrogenetically precipitated ferromanganese crusts are widespread in the Pacific Ocean. They occur as pavements coating volcanic or sedimentary hard-rock substrates, mainly on the slopes of seamounts, plateaus and hills in ocean basins and continental margins. We studied three ferromanganese crusts from one dredge haul from the Rivera Plate (western margin of Mexico), which are up to 15 mm thick and grow directly on a substrate of pillow basalt fragments. They consist of laminated, botryoidal, porous aggregates mostly of Fe and Mn oxyhydroxides and up to 10% silicates. XRD analysis showed the predominance of poorly crystallized mineral phases in the crusts that include Mn-feroxyhyte and vernadite, and an authigenic smectite-like clay. Detrital minerals probably derive from granodiorites of the eastern wall of the neighboring Middle America Trench. Scattered barite grains occur on the crust surface and suggest plume fall-out derived from hydrothermal vents, although a possible pelagic source cannot be dismissed. Ratios between major (Fe, Mn, Si) and trace (Co, Ni, Cu) elements reveal that such crusts are predominantly hydrogenetic in origin, although they show a hydrothermal influence that increases in the outer layers. Iron contents range from 16.2 to 25.2 wt.%, and manganese from 3.4 to 14.5 wt.%. The Fe/Mn ratio ranges from 1.6 to 7.0. The SiO2/Al2O3 ratio ranges from 4.3 to 6.6, indicating the presence of biogenic silica (radiolarians). The concentrations of copper (up to 383 ppm) and cobalt (up to 534 ppm) are significantly below those of the typical hydrogenetic crusts, whereas Ni (up to 1320 ppm) is about the same or slightly lower. REE normalized profiles and ΣREE values (486 to 732 ppm) match those reported for hydrogenetic crusts, but suggest a hydrothermal contribution for the later crust layers. The inferred crust growth rates using the Co-chronometer (44 and 229 mm/Myr) are higher than those reported for pure hydrogenetic crusts (mostly 1 to 6 mm/Myr), thus indicating an increasing hydrothermal influence. The highest growth rate (229 mm/Myr, corresponding to the outer crust layers) suggests a regional hydrothermal input of iron and manganese to seawater. The intensification of regional submarine hydrothermal activity began about 13,000 yr ago, and may be related to the tectonic activity in the complex junction of the Rivera, Cocos, Pacific and North America plates.  相似文献   

7.
全球三大洋海山钴结壳资源量估算   总被引：8，自引：0，他引：8  
钴结壳具有Co、Ni、Cu和Mn及其他金属的潜在矿产资源和储存在结壳层中古环境信息的双重意义。与深海多金属结核和热液硫化物矿床相比,具有较高Co、Ni和Pt含量的海山钴结壳有可能成为商业勘探的潜在目标。为合理地估算出全球三大洋海山钴结壳资源量,基于我国西太平洋海山钴结壳拖网采样调查资料和对太平洋海山钴结壳资源分布规律和钴结壳矿区圈定参数指标的深入研究,按海山不同高度、不同洋壳年龄赋予不同结壳厚度,进而计算出全球三大洋海山钴结壳分布面积为3 039 452.14km2和干结壳资源量为(1 081.166 1~2 162.332 2)×108 t。太平洋海山钴结壳分布面积为2 123 087.12km2和干结壳资源量为(513.244~1 026.488)×108 t,大西洋海山钴结壳分布面积为512 509.74km2和干结壳资源量为(116.503 2~233.006 4)×108 t,印度洋海山钴结壳分布面积为403 855.28km2和干结壳资源量为(81.484 9~162.969 8)×108 t。三大洋海山钴结壳的Mn、Co、Ni和Cu金属量分别为(138.848 0~277.696 0)×108 t,(3.967 6~7.935 2)×108 t、(2.793 6~5.587 2)×108 t和(0.825 1~1.650 2)×108 t。根据钴结壳的Co含量、Co通量和厚度相关分析,所赋予的钴结壳厚度占理论推测厚度的6.10%~12.20%,这与Ku等得出"钴结壳生长时间约占其整个生命史4%"的认识非常相近。三大洋海山钴结壳实测厚度与赋值厚度对比分析表明,太平洋海山钴结壳赋值厚度平均值为1.87cm,实测厚度平均值为1.77cm,相对误差为5.35%,大西洋和印度洋相对误差分别为18.18%和23.23%。研究数据表明按海山高度和洋壳年龄所赋的钴结壳厚度基本合理,估算出的钴结壳资源量基本可靠。本文首次估算出三大洋海山钴结壳资源量,为整个海盆和三大洋海山钴结壳资源量估算提供了新方法。  相似文献   

8.
过渡金属元素Cu、Co、Ni在铁锰结核(壳)中富集的控制因素   总被引：7，自引：0，他引：7  
在不同生成环境下生成的铁锰结核(壳)吸收不同的过渡金属元素。在成岩作用形成的铁锰结核中,Cu、Ni主要以锰相形式存在,而Co则以铁相的形式存在;在水成作用形成的铁锰结核(壳)中Cu、Co、Ni均以锰相的形式存在。这些过渡金属元素在成岩作用形成的结核中的存在与铁锰结核(壳)中锰矿物和铁的氧化物、氢氧化物的晶体化学特征密切相关,而在水成作用形成的铁锰结核(壳)中的富集与锰矿物和铁的氧化物、氢氧化物的晶体化。学特征关系不大。同时铁锰结核(壳)中锰矿物和铁的氧化物、氢氧化物又严格地受结核(壳)的生成环境的制约,因此,过渡金属元素Cu、Co、Ni在铁锰结核(壳)中的富集在一定程度上受结核(壳)生成环境的控制。  相似文献   

9.
This is the first article to describe mineralization of midplate submarine rift zones and hydrothermal manganese oxide mineralization of midplate volcanic edifices. Hydrothermal Mn oxides were recovered from submarine extensions of two Hawaiian rift zones, along Haleakala and Puna Ridges. These Mn oxides form two types of deposits, metallic stratiform layers in volcaniclastic rocks and cement for clastic rocks; both deposit types are composed of todorokite and bimessite. Thin Fe‐Mn crusts that coat some rocks formed by a combination of hydrogenetic and hydrothermal processes and are composed of δ‐MnO2. The stratiform layers have high Mn contents (mean 40%) and a large fractionation between Mn and Fe (Fe/Mn = 0.04). Unlike most other hydrothermal Mn oxide deposits, those from Hawaiian rift zones are enriched in the trace metals Zn, Co, Ba, Mo, Sr, V, and especially Ni (mean 0.16%). Metals are derived from three sources: mafic and ultramafic rocks leached by circulating hydrothermal fluids, clastic material (in Mn‐cemented sandstone), and seawater that mixed with the hydrothermal fluids. Mineralization on Haleakala Ridge occurred sometime during the past 200 to 400 ka, when the summit was at a water depth of more than 1,000 m. Hydrothermal circulation was probably driven by heat produced by intrusion of dikces, magma reservoirs, and flow of magma through axial and lateral conduits. The supply of seawater to ridge interiors must be extensive because of their high porosity and permeability. Precipitation of Mn oxide below the seafloor is indicated by its occurrence as cement, growth textures that show mineralizing fluids were introduced from below, and pervasive replacement of original matrix of clastic rocks.  相似文献   

10.
A total of 843 samples of Pacific Ocean polymetallic nodules (PNs) from five survey areas have been studied (metals analyzed: Mn, Fe, Ni, Cu, Co, Zn, Pb). The statistical analysis included the following techniques: factor R analysis, quick cluster Q analysis into 50 preclasses, various hierarchical cluster Q analyses (HCAs) using the preclasses (application of different HCAs to an identical set of data and of an identical HCA to two different subsets of the data), comparison of the HCA. The PNs of the survey areas can be grouped into five geochemical types (I‐V). The genesis of the PNs was interpreted as early diagenetic, hydrogenetic, and mixed (early diagenetic/hydrogenetic and hydrogenetic/hydrothermal. In addition, some further conclusions regarding the applicability of various HCA techniques depending on the structure of the data set have been drawn.  相似文献   

11.
Abstract

Hydrothermal iron‐rich crusts have been recovered from a number of hot spot volcanos including Crough Seamount, Pitcairn Volcanos 2 and 1, Cyana Seamount, Teahitia, Moua Pihaa, and Macdonald Seamount in the S. W. Pacific. Mineralogically, the crusts consists of ferrihydrite with traces of the weathering products of volcanic ash (feldspar, nontronite, pyroxene, and serpentinite). The iron oxyhydroxide phase has a mean particle size of 3–4 nm indicating rapid deposition. Electron microprobe studies have revealed the presence of filamentous iron‐silica deposits within the crusts reflecting the possible bacterial oxidation of iron from the hydrothermal fluids. The crusts display wide variability in composition both between individual sampling stations and between seamounts. Endmember analysis shows that the compositional data can be resolved into three endmembers: a Fe‐rich endmember, a light and heavy rare earth element endmember, and a Ba (barite)‐rich endmember. The Fe‐rich endmember appears to contain very low concentrations of most trace elements. For bulk samples, the composition of the iron‐rich crusts reflects dilution of the iron oxyhydroxide phase by volcanic ash and, to a lesser extent, a hydrogenous component. This is illustrated by the wide variability in SiO2 (11.1–71.3%) and Mn (0.01–1.21%) contents of the crusts. For iron‐rich crusts containing greater than 40% Fe, the Pitcairn crusts display lower contents of Pb, Ba, Mo, U, Th, As, and rare earth elements (REE) and lower cerium anomalies than those from Teahitia. REE profiles of crusts from each of the hot spot volcanoes are characterized by small negative cerium anomalies but pronounced positive europium anomalies. The low average La/Fe ratios of the crusts from the various seamounts (47–572 X 10‐6) and positive Eu anomalies of the crusts suggest rapid deposition of the iron oxyhydroxide near the hydrothermal vent. The high Fe/Mn ratio of vent fluids at hot spot volcanoes (8.5–5.6) may account for the formation of these iron‐rich crusts. The present data indicate that there may be differences in the nature of the iron‐rich crusts based on the depth of occurrence. This influences the temperature of the venting hydrothermal fluids and the possibility of occurrence of submarine phreatomagmatic eruptions.  相似文献   

12.
Deep Seabed Mining: Past Failures and Future Prospects   总被引：8，自引：0，他引：8  
The first attempt to exploit deep-sea manganese nodules ended in failure as a result of the collapse of world metal prices, the onerous provisions imposed by the U.N. Convention on the Law of the Sea (UNCLOS), and the overoptimistic assumptions about the viability of nodule mining. Attention then focused on Co-rich manganese crusts from seamounts. Since the mid-1980s, a number of new players have committed themselves to long-term programs to establish the viability of mining deep-sea manganese nodules. These programs require heavy subsidy by the host governments. Au-rich submarine hydrothermal deposits located at convergent plate margins are now emerging as a more promising prospect for mining than deep-sea manganese deposits.  相似文献   

13.
The first attempt to exploit deep-sea manganese nodules ended in failure as a result of the collapse of world metal prices, the onerous provisions imposed by the U.N. Convention on the Law of the Sea (UNCLOS), and the overoptimistic assumptions about the viability of nodule mining. Attention then focused on Co-rich manganese crusts from seamounts. Since the mid-1980s, a number of new players have committed themselves to long-term programs to establish the viability of mining deep-sea manganese nodules. These programs require heavy subsidy by the host governments. Au-rich submarine hydrothermal deposits located at convergent plate margins are now emerging as a more promising prospect for mining than deep-sea manganese deposits.  相似文献   

14.
Regional variation of Mn, Fe, Co, Ni and Cu in ferromanganese oxides (nodules and crusts) in the central south Pacific is related to primary productivity, oxygen minimum layer, and calcium carbonate compensation depth. The largely latitudinal influence of these environmental parameters on nodule and crust composition reflects their predominantly latitudinal variation. Primary productivity is the principal regional environmental control, influencing diagenetic enrichment of these elements in nodules through its effect, mediated by the CCD, on supply and concentration of labile organic matter vs. carbonate remains to the sediments. It influences hydrogenetic enrichment of these elements in nodules and crusts through its effect, mediated by the oxygen minimum layer (mainly in the case of crusts), on their export from surface waters.The elements’ varying susceptibility to being scavenged or organically bound influences the contrasting composition of diagenetic vs. hydrogenetic ferromanganese oxides, which is further influenced by depth. Hydrogenesis is the fundamental process governing nodule and crust formation, superimposed on which is diagenesis under specific circumstances; both are subject to intermittent interruption, diminution and augmentation by changes in environmental parameters. Application of regionally operative environmental controls locally explains local compositional variations and helps refine exploration criteria for economically viable nodules and crusts.  相似文献   

15.
Six manganese crusts, 13 manganese nodules, and 16 sediments were analyzed by instrumental neutron activation analysis. Data were generated on selected major and minor elements but geochemical evaluations are based only on Fe, Sc, U, Th, and the rare earth elements (REE). Manganese crusts and manganese nodules have comparable trivalent REE contents and show a shale‐like distribution pattern. Both crusts and nodules are characterized by a positive Ce anomaly but the anomaly is higher in nodules. REE contents in manganese nodules show a linear dependence on the Fe content, and it is concluded that these elements are incorporated in the Fe‐rich (δ‐MnO2) phase. In the crusts, the REE correlate with Sc and are therefore assumed to be associated with the clay minerals. Uranium contents are significantly higher in the crusts than in nodules whereas Th is slightly higher in the nodules. There is a clear positive correlation between U and Th in nodules but there are too few data to make a similar conclusion for crusts. Compositional data suggest a division of the sediments into two groups. The carbonate sediments have much lower REE contents and a more pronounced negative Ce anomaly than the clays, while both show a lithogenous component as indicated by a slight negative Eu anomaly.  相似文献   

16.
Abstract

The morphological features associated with Co-rich manganese deposits, the size variations of nodules, and the occurrence of different substrates have been analyzed, to evaluate the influence of various seabed slope angles on the distribution of these features. The coverage and size of the crusts depend on their surface morphology and seabed topography, resulting in cobble-type, lineated, or step-like outcrops. Small nodules (1–4 cm in diameter) dominate all seabed slopes, with a few locations having nodules ranging from 1 to 8 or 1 to 10 cm. Sediments invariably occur as substrates for nodules and as cover for crusts, their coverage being inversely proportional to that of the nodules and crust outcrops.

Steeper seafloor areas have large crust outcrops exposed with no or few nodules and sediments associated with them. The intermediate slopes have a combination of nodules, sediments, and crusts in various proportions, depending on topography and gradient. Large-scale nodule occurrences, followed by sediment fields and crust outcrops on seabed slopes of < 3°, 3–7°, and > 15°, respectively, represent typical morphological distribution zones of the Co-rich manganese deposits on a seamount in the central Pacific Ocean. A transition zone between nodule-dominated fields and large crust outcrops occurs for slopes from 7° to 15°. This detailed study on distribution of Co-rich deposits gives a better understanding for purposes of their exploitation.  相似文献   

17.
Forty‐four sediment samples and 23 Mn crusts and Mn nodules have been analyzed for several elements in order to characterize their geochemical nature. Most of the Mn crusts and Mn nodules are of hydrogenous origin, although one crust (U375) from the flanks of the Rarotonga volcano is thought to be of hydrothermal origin. δ‐MnO2 is the principal Mn mineral in the crusts, whereas todorokite and birnessite occur in addition to δ‐MnO2 in the nodules. The sediments can be divided into carbonates, with calcite as the dominant phase, and deep‐sea clay, consisting mainly of illite and smectite.  相似文献   

18.
Abstract

Vast reserves of marine minerals are known to occur within the Mexican Exclusive Economic Zone. These reserves include: (1) heavy mineral placers rich in titanium and iron along the coast of San Antonio del Mar, Baja California and the southern States of Oaxaca and Guerrero; (2) phosphorites, which represent the only source for superphosphate fertilizers along the Pacific coast off the Baja California peninsula and the Gulf of Tehuantepec; and (3) manganese oxide deposits in nodule and crusts located adjacent to the Clarion-Clipperton Zone and containing high concentrations of Cu + Ni + Co (up to 1.9%), which are essential for the steel and super-alloy industries. Few but important efforts toward surveying these deposits have been carried out by Mexican and international researchers. Relevant data generated by these investigations are reviewed here and put together in a single document. Adequate knowledge of Mexican mineral resources is essential for the development of management strategies when offshore mining starts during this century. Thus, the review discusses the economics inherent to ocean mining in Mexico, setting baselines for future exploration and development activities in the Mexican Exclusive Economic Zone.  相似文献   

19.
Abstract

Considerable effort has been expended in studying the Izu–Bonin Arc over the past 15 years. In particular, 43 dives of the Shinkai 2000 have been undertaken there to discover and evaluate the extent of submarine hydrothermal activity and mineralization. Most effort has been focused on Myojin Knoll (23 dives), Suiyo Seamount (6 dives), and Kaikata Caldera (10 dives).

The Izu–Bonin Arc is divided in two by the Sofugan Tectonic Line. Eight submarine caldera are located north of this line but only one is south of it. The physiography of the northern sector of the arc is quite different from that of the southern sector. Volcanic rocks from the northern sector are more acidic than those from the southern sector.

Evidence for submarine hydrothermal mineralization has been observed at four seamounts along the Izu–Bonin Arc (Myojin Knoll, Myojinsho, Suiyo Seamount, and Kaikata Caldera), and submarine hydrothermal activity is evident at another three seamounts along the arc (Kurose Hole, Mokuyo Seamount, and Doyo Seamount).

The most extensive submarine hydrothermal mineral deposit so far located on the Izu–Bonin Arc is the Sunrise deposit at Myojin Knoll. This deposit, at least 400 m in diameter and 30 m high, is associated with black smoker venting, inactive sulfide chimneys, massive sulfides, hydrothermal Mn crusts, and a hydrothermal vent fauna. The maximum recorded temperature of the hydrothermal vents there was 278°C. Some of the sulfide chimneys contained as much as 49 μg/g Au and 3,400 μg/g Ag. The sunrise deposit is one of the largest submarine volcanic massive sulfide deposits so far discovered in midocean ridge, backarc, or arc settings and has an estimated mass of 9 × 106 t. This deposit may be of the Kuroko-type. The discovery of the Sunrise deposit in 1997 gives hope that other, similarly large, sulfide deposits may be found in other caldera along the Izu–Bonin Arc.

The geological variability along the arc, the high seismicity, the occurrence of active volcanism and submarine hydrothermal venting, and a proven submarine hydrothermal mineral potential coupled with the proximity of the region to Japan suggest that the Izu–Bonin Arc could profitably serve as a natural laboratory for the long-term monitoring of the seafloor.  相似文献   

20.
Oceanic, non-hydrothermal ferromanganese crusts and nodules are variably enriched in Mn, Fe, Co, Cu, Ni and Zn. Comparison of the content of these elements in crusts and nodules with the level of primary productivity in the South Pacific Ocean suggests that primary-producer-mediated complexation of several of these elements by organic ligands in solution may contribute to explaining a pattern of distinctive associations observed between compositional variations for these elements in these deposits and variations in the level of primary productivity.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号