Fractal characteristics of resource quantity of cobalt crusts and seamount topography, the West Pacific

This paper presents the fractal distribution of topography of seamounts from the West Pacific and the resource quantity of cobalt crust therein. The cobalt resource quantity has three to four variable fractal dimensions, corresponding to the distinct slopes and water depths of the seamount. The multiple fractal property of resource quantity may have resulted from various factors, such as types and components of cobalt crusts and ages of oceanic crusts hosting the seamounts. Individual seamounts display complex topography and quantity of cobalt crust, both in the same and different regions. Translated from Acta Sedimentologica Sinica, 2006, 24(5): 705–713 [译自: 沉积学报]     

钴结壳矿区圈定和资源评价的参数指标

大洋海山钴结壳集海洋资源和环境双重信息, 各国对它的调查研究方兴未艾.钴结壳资源勘查的最终目的是圈定钴结壳矿区和开发钴结壳资源.迄今为止, 国内外尚未就钴结壳矿区圈定和资源评价给出具体的参数指标, 基于我国近十年对西太平洋26座海山钴结壳资源调查, 结合太平洋环境资料, 在深入分析钴结壳厚度、丰度、品位、覆盖率、资源量、面积, 海山坡度和水深资料的基础上, 对13座重点海山进行了钴结壳矿区圈定、资源评价和钴结壳分布规律的系统研究, 进而提出圈定钴结壳矿区的八项重要参数指标: 钴结壳矿区的结壳厚度为≥3cm或≥4cm, 取决于海山具体地理位置; 水深为≤2500m或≤3000m;Co含量为≥0.50%或≥0.60%;丰度为≥60kg/m2或≥70kg/m2; 坡度为≤15°; 结壳覆盖率为≥30%;钴结壳矿区的申请面积为17000~20000km2, 矿区最终保留面积为5000~6000km2.钴结壳矿区8项参数指标的提出, 将有力地促进大洋钴结壳矿区圈定、资源量计算和资源评价工作, 为我国积极参与联合国海底管理局制定钴结壳资源开发利用规章制度提供量化参考指标.      

大洋富钴结壳资源调查与研究进展

富钴结壳是继多金属结核资源之后被发现的又一深海沉积固体矿产资源,在太平洋、大西洋和印度洋的海底均有分布。据估算,全球三大洋海山富钴结壳干结壳资源量为(1081.1661~2162.3322)×108t。世界各国对富钴结壳的调查始于20世纪80年代初,截至目前,已有日本、中国、俄罗斯和巴西等4个国家与国际海底管理局签订了富钴结壳勘探合同,而韩国的矿区申请也于2016年获得核准。富钴结壳按形态可分为板状结壳,砾状结壳和钴结核3种类型。富钴结壳内部结构构造在宏观上通常表现为三层构造,即底部亮煤层、中部疏松层和顶部较致密层;在微观下主要表现为柱状构造、叠层构造、斑块状构造、纹层状构造等多种类型。富钴结壳的矿物成分主要为自生的铁锰矿物,包括水羟锰矿、钡镁锰矿、羟铁矿、四方纤铁矿、六方纤铁矿、针铁矿等。富钴结壳富含Mn、Fe、Co、Ni、Cu、Pb、Zn等金属元素以及稀土元素和铂族元素,其中Co含量尤为显著。三大洋中,以太平洋富钴结壳的Co平均含量最高。富钴结壳的生长过程极其缓慢,平均仅几毫米每百万年。研究表明,西太平洋富钴结壳最早于始新世-早中新世开始生长。目前通常认为富钴结壳为水成成因,即Co、Fe、Mn等金属元素来源于海水。此外,有研究表明微生物在富钴结壳的形成过程中也起着非常重要的作用。富钴结壳的分布及特征受地形、水深、基岩类型、海水水文化学特征、经纬度等多种因素的影响,其主要分布于碳酸盐补偿深度以上、最低含氧带以下、水深800~2500 m的海山、岛屿斜坡和海底高地上,西、中太平洋海山区被认为是全球富钴结壳的最主要产出区。     

Distribution and Classification of Cobalt-Rich Crust

INTRODUTIONThe sea- floor metallic mineral resources are classified asmany types such as multi- m etallic nodules,metallic oozes,massive sulfide deposits and iron- manganese crusts.Before1980 s,China did not made any researches into metallic oozeand massive sulfide deposits;but China started to study m ul-ti- metallic nodules in the early1980 s,15 - 2 0 years later thanthe developed industry countries did.However,in the shortten years,we have caught up with the developed countries,and our…     

New data on the structure of the Vitoria-Trindade seamount chain (western Brazil basin,South Atlantic)

In 2008, during cruise 24 of the R/V Akademik Vavilov, much of our research work was focused on the central segment (Jaseur and Davis seamounts, Dogaressa Bank) of the Vitoria-Trindade seamount chain (west of the Brazil basin) extending along 20.5° S. Work was conducted to survey the upper part of the sedimentary cover and to perform subbottom profiling. The samples dredged on the seamount slopes are represented by volcanites and Fe-Mn crusts.     

Distance-gradient-based variogram and Kriging to evaluate cobalt-rich crust deposits on seamounts

The spatial distribution of cobalt-rich crust thicknesses on seamounts is partly controlled by water depth and slope gradients. Conventional distance–direction-based variogram have not effectively expressed the spatial self-correlation or anisotropy of the thicknesses of cobalt-rich crusts. To estimate resources in cobalt-rich crusts on seamounts using geostatistics, we constructed a new variogram model to adapt to the spatial distribution of the thicknesses of the cobalt-rich crusts. In this model, we defined the data related to cobalt-rich crusts on seamounts as three-dimensional surface random variables, presented an experimental variogram process based on the distance–gradient or distance–“relative water depth,” and provided a theoretical variogram model that follows this process. This method was demonstrated by the spatial estimation of the thicknesses of cobalt-rich crusts on a seamount, and the results indicated that the new variogram model reflects the spatial self-correlation of the thicknesses of cobalt-rich crusts well. Substituted into the Kriging equation, the new variogram model successfully estimated the spatial thickness distribution of these cobalt-rich crusts.     

太平洋海山钴结壳资源量估算

为合理地估算出太平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以及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, 创造性地按海山不同高度、不同洋壳年龄赋予不同结壳厚度, 进而首次计算出太平洋海山干结壳资源量为(507.06~1 014.11)×108 t, 锰为(111.15~222.29)×108 t, 钴为(3.04~6.08)×108 t, 镍为(2.23~4.46)×108 t, 铜为(0.66~1.32)×108 t, 结壳分布面积为2 062 862 km2.通过Co通量与结壳Co沉积量、结壳厚度的相关分析表明, 赋予不同洋壳年龄段的结壳厚度是理论厚度的6.10%~12.20%, 这与Ku et al.得出"结壳生长时间只占其整个生命史4%"的认识非常相近, 说明所赋结壳厚度基本合理, 得出的结壳资源量基本正确.为整个大洋海盆内海山钴结壳资源量的估算提供了新方法.      

Growth of the Afanasy Nikitin seamount and its relationship with the 85°E Ridge,northeastern Indian Ocean

The Afanasy Nikitin seamount (ANS) is a major structural feature (400 km-long and 150 km-wide) in the Central Indian Basin, situated at the southern end of the so-called 85°E Ridge. Combined analyses of new multibeam bathymetric, seismic reflection and geochronological data together with previously described magnetic data provide new insights into the growth of the ANS through time, and its relationship with the 85°E Ridge. The ANS comprises a main plateau, rising 1200 m above the surrounding ocean floor (4800 m), and secondary elevated seamount highs, two of which (lie at 1600 and 2050 m water depths) have the morphology of a guyot, suggesting that they were formed above or close to sea-level. An unbroken sequence of spreading anomalies 34 through 32n.1 identified over the ANS reveal that the main plateau of the ANS was formed at 80–73 Ma, at around the same time as that of the underlying oceanic crust. The ⁴⁰Ar/³⁹Ar dates for two basalt samples dredged from the seamount highs are consistent, within error, at 67 Ma. These results, together with published results of late Cretaceous to early Cenozoic Indian Ocean plate reconstructions, indicate that the Conrad Rise hotspot emplaced both the main plateau of the ANS and Conrad Rise (including the Marion Dufresne, Ob and Lena seamounts) at 80–73 Ma, close to the India–Antarctica Ridge system. Subsequently, the seamount highs were formed by late-stage volcanism c. 6–13 Myr after the main constructional phase of the seamount plateau. Flexural analysis indicates that the main plateau and seamount highs of the ANS are consistent with Airy-type isostatic compensation, which suggest emplacement of the entire seamount in a near spreading-center setting. This is contrary to the flexural compensation of the 85°E Ridge further north, which is interpreted as being emplaced in an intraplate setting, i.e., 25–35 Myr later than the underlying oceanic crust. Therefore, we suggest that the ANS and the 85°E Ridge appear to be unrelated as they were formed by different mantle sources, and that the proximity of the southern end of the 85°E Ridge to the ANS is coincidental.     

Comparative Study of Magmatism in East Pacific Rise Versus Nearby Seamounts: Constraints on Magma Supply and Thermal Structure Beneath Mid‐ocean Ridge

Major elements of 2202 basalts from the East Pacific Rise (EPR) and 888 basalts from near-EPR seamounts are used to investigate their differences in magma crystallization pressures and mantle melting conditions. Crystallization pressure calculation from basalts with 5.0wt%相似文献   

An integrated method for the quantitative evaluation of mineral resources of cobalt-rich crusts on seamounts

Cobalt-rich crusts on seamounts potentially have the economic value of multiple metals. In the field of exploration, it is important to perform quantitative evaluations of mineral resources and delineate promising areas in survey regions for future mining. Accordingly, this study, based on prior knowledge, develops an integrated method to quantitatively evaluate mineral resources of cobalt-rich crusts on seamounts and gives an application example to demonstrate this method. The method includes four steps: first, defining units with certain areas and shapes on the target seamount (a 20 km² square block in the application example) and estimating characteristic values of the cobalt-rich crust for each unit with known geological survey data using a space interpolation method such as Kriging; second, presenting several model algorithms, i.e. Regional Coverage of Crusts, Suitable Slope Percentage for Mining and Fitting Area on Slopes, to extract the corresponding regional metallogenic factors for each unit by inputting regional surveying data (such as bathymetry data) into these models; third, considering both the features and regional metallogenic factors of cobalt-rich crusts in each unit to estimate their distribution of mineral resources on the entire seamount; and last, according to the distribution of the mineral resources and international social and economic requirements (such as the regulations of the International Seabed Authority), delineating a promising area for future mining.     

利用多波束回波强度进行中太平洋潜鱼海山底质分类

中、西太平洋海山区是富钴结壳的重要富集区,钙质远洋沉积、碳酸盐岩沉积及重力作用引起的滑塌沉积是海山山顶和斜坡的主要沉积类型,它们的空间分布规律对于富钴结壳的分布至关重要.在国内首次利用EM122多波束回波强度资料对中太平洋潜鱼海山进行了底质类型研究,对回波强度资料进行处理和统计分类,并与浅地层剖面和地质取样结果对比,分析得出了4种底质类型,即富钴结壳、钙质远洋沉积、碳酸盐岩基底及碎屑流沉积.这几种底质类型具有不同的回波强度特征,其中富钴结壳区表现为均一的回波强度高值特征;钙质远洋沉积区表现为均一的回波强度低值特征,二者回波强度值相差约20 dB.结果显示潜鱼海山山顶仅局部发育钙质远洋沉积,大部分为碳酸盐岩基底出露区,山顶边缘及侧翼山脊处为主要的富钴结壳分布区.此外,该海山存在3处较大规模的重力滑塌沉积区,主要为碎屑流沉积.      

The cretaceous dynamics of the pacific plate and stages of magmatic activity in Northeastern Asia

The dynamics of the Pacific Plate is recorded in the systematic variation of location and the ⁴⁰Ar-³⁹Ar age of seamounts in the western Pacific from 120 to 65 Ma ago. The seamounts are grouped into three linear zones as long as 5000 km. The seamounts become younger in the southeastern direction along the strike of these zones. Correlation between age and location of seamounts allows division of the history of their formation into three stages. The rate of seamount growth was relatively low (2–4 cm/yr) during the first and the third stages within the intervals of 120–90 and 85–65 Ma, whereas during the second stage (90–85 Ma), the seamounts were growing very fast (80–100 cm/yr). In the midst of this stage, at ～87 Ma ago, the magmatic activity increased abruptly. The dynamics of seamount building is in good agreement with (1) pulses in the development of the Ontong Java, Manihiki, and Caribbean-Colombian oceanic plateaus; (2) the age of spreading acceleration in the mid-Cretaceous; and (3) the short period when the Izanagi Plate ceased to exist and the Kula Plate was formed. The variation of the seamounts’ age and location is in consistence with the hypothesis of diffuse extension of the Pacific Plate in the course of its motion with formation of impaired zones of decompression melting. The direction of extension (325°–340° NW) calculated from the strike of seamount zones is consistent with the path of the Pacific Plate (330° NW) in the Late Cretaceous. The immense perioceanic volcanic belts were formed at that time along the margin of the Asian continent. The Okhotsk-Chukchi Peninsula Belt extends at a right angle to the compression vector. Three stages of this belt’s evolution are synchronous with the stages of seamount formation in the Pacific Plate. The delay in the origination of the East Sikhote-Alin Volcanic Belt and its different orientation were caused by counterclockwise rotation of the vector of convergence of oceanic and continental plates in the mid-Cretaceous. At the same time, i.e., 95–85 Ma ago, the volcanic activity embraced the entire continental margin and the tin granites were emplaced everywhere in eastern Asia. This short episode (90 ± 5 Ma) corresponds to the mid-Cretaceous maximum of compression of the continental margin, and its age fits a culmination in extension of the Pacific Plate well.     

麦哲伦戈沃罗夫盖特平顶海山钴结壳资源评价

为能科学、快速量化地圈定出大洋海山钴结壳优质矿区,笔者基于国际海底管理局提出的矿区选取模型,利用我国西太平洋海山钴结壳资源调查的公开的拖网采样资料,综合钴结壳的分布规律和证据权法所得海山钴结壳资源预测后验概率图,将西太平洋麦哲伦海山区戈沃罗夫盖特平顶海山圈定为钴结壳资源前景较好的远景区,并采用人机交互式的矿区圈定方法圈定出符合国际海底管理局规章要求的7个群组共100个钴结壳矿块。据此估算出戈沃罗夫盖特平顶海山湿结壳资源量为69 487.6×10⁴ t;圈定的100个矿块主要分布在2 000~3 000 m斜坡上,湿结壳资源量为14 092×10⁴ t,干结壳资源量为9 789.35×10⁴ t;锰金属量为1 961.3×10⁴ t,铜金属量为10.17×10⁴ t,钴金属量为54.06×10⁴ t,镍金属量为34.87×10⁴ t。这些数据表明,戈沃罗夫盖特平顶海山规模较大,钴结壳资源前景潜力大,可作为钴结壳深入调查和矿区申请备选海山。     

Calcareous Nannofossils and Molecular Fossils in Cobalt-rich Crusts and their Response to the P/E Global Event

A biostratigraphic study on calcareous nannofossils from the CM3D06 Co-rich ferromanganese crust from the Magellan seamounts in the northwestern Pacific enabled estimation of depositional age.The bio-imprinting of calcareous nannofossils and other fossil species suggests six age ranges for the nannofossils: late Cretaceous,late Paleocene,(early,middle,late) Eocene,middle Miocene,late Pliocene,and Pleistocene.Gas chromatography(GC) and gas chromatography-mass spectrometry(GC-MS) were used to test the Co-rich crusts,and a variety of molecular fossils were detected,such as chloroform bituminous "A",n-alkane,isoprenoid and sterol.Peak carbon and molecular indices(such as ΣC23 /ΣC24 +,CPI,Pr/Ph,Pr/nC17,Ph/nC18 and δ13C) indicate that the parent organic matter is dominated by marine phytoplankton and thallogen whereas there is little input of terrestrial organic matter.Researches on calcareous nannofossils,molecular fossils and molecular organic geochemistry data reveal that the Paleocene/Eocene(P/E) global event is recorded in the cobaltrich crusts from the northwestern Pacific Ocean.A succession of biomes can be observed near the 85 mm boundary(about 55 Ma),i.e.,the disappearance of the late Cretaceous Watznaueria barnesae and Zigodicus spiralis,and Broisonia parka microbiotas above the P/E boundary,and the bloom of Coccolithus formosus,Discoaster multiradiatus,Discoaster mohleri and Discoaster sp.below the boundary.Typical parameters of molecular fossils,such as saturated hydrocarbon components and carbon-number maxima,Pr/Ph,Pr/C17,Ph/C18,distribution types of sterols,Ts/Tm ratios and bacterial hopane,also exhibit dramatic changes near the P/E boundary.These integrated results illustrate that the biome succession of calcareous nannofossils,relative content of molecular fossils and molecular indices in the cobalt-rich crusts near the 85 mm boundary faithfully record the P/E global event.     

中太平洋海山富钴结壳主要成壳元素特征

通过大洋一号船DY105--12 /14 航次采集的结壳样品,对中太平洋CL、CM2、CM3、CX、CQ、 CA、CB 海山结壳的主要成壳元素Mn、Fe、Co、Ni、Cu 的含量进行了测试统计,并与邻区的麦哲伦海山、马绍尔群岛、夏威夷群岛和莱恩群岛进行了对比,中太平洋各海山以及不同区域海山结壳的主成分之间存在一些差异,这主要与各海山结壳的物质来源、成壳环境和成壳时代的差异有关。不同形态类型的结壳主成分具有一定的差别,其主要原因可能是生长机制和形成环境不同造成的。     

Role of Hydrology in the Formation of Co-rich Mn Crusts from the Equatorial N Pacific,Equatorial S Indian Ocean and the NE Atlantic Ocean

Co-rich Mn crusts from four different locations of the world ocean have been studied to understand the role of dissolved oxygen of the ambient seawater in the formation of Co-rich Mn crusts. WOCE (World Ocean Circulation Experiment) oxygen profiles of modern seawater in the Equatorial North Pacific Ocean, Equatorial South Indian Ocean and the North East Atlantic Ocean have been evaluated with respect to the occurrence of Co-rich Mn crusts at depths ranging from 1500 to 3200 m. The oxygen content at these depths varied from ∼90–240 µmol/kg. The oxygen minimum zone (OMZ), with oxygen contents in the range ∼45–100 µmol/kg, is located in the depth range 800–900 m in these regions. The age of the ocean crust on which seamounts formed is in the range 80.3–180 Ma. Profiles of the oxygen contents of seawater with depth in the oceans are shown to be extremely useful in establishing the optimum conditions for the formation of Co-rich Mn crusts. The use of WOCE oxygen profiles to study geochemical processes in the oceans is highly recommended.     

A Study on the Forming Conditions of Basalts in Seamounts of the South China Sea

Volcanic rocks in seamounts of the South China Sea consist mainly of alkali basalt, tholeiitic basalt, trachyandesitic pumice, dacite, etc. Inclusions in the minerals of the volcanic rocks are mainly amorphous melt inclusions, which reflects that the volcanic rocks are characterized by submarine eruption and rapid cooling on the seafloor. Furthermore, fluid-melt inclusions have been discovered for the first time in alkali basalts and mantle-derived xenoliths. indicating a process of differentiation between magma and fluid in the course of mantle partial melting. Alkali basalts and inclusions may have been formed in this nonhomogeneous system. Rock-forming temperatures of four seamounts were estimated as follows: the Zhongnan seamount alkali basalt 1155 ∼ 1185 °C; the Xianbei seamount alkali basalt 960 ∼ 1200 °C; tholeiitic basalt 1040 ∼ 1230 °C; the Daimao seamount tholeiitic basalt 1245 ∼ 1280 °C; and the Jianfeng seamount trachyandestic pumice 880 ∼ 1140 °C. Equilibrium pressures of alkali basalts in the Zhongnan and Xianbei seamounts are 13.57 and 8.8 × 10⁸ Pa, respectively. Pyroxene equilibrium temperatures of mantle xenoliths from the Xianbei seamount were estimated at 1073 ∼ 1121 °C, and pressures at (15.58 ∼ 22.47)×10⁸Pa, suggesting a deep-source (e.g. the asthenosphere) for the alkali basalts. This project was financially supported by the National Natural Science Foundation of China and Guangzhou Marine Geology Survey.     

西太平洋海山玄武岩的岩石学特征及与上覆富钴结壳的关系

通过对西太平洋海山玄武岩和玄武质火山角砾岩的岩石学特征及其气孔充填物成分变化的研究,讨论了海山玄武岩与上覆富钴结壳的关系。富钴结壳的基岩火山岩主要为碱性玄武岩和玄武质火山角砾岩。碱性玄武岩中气孔充填物为S型和C型,S型和C型气孔充填物不共存在同一个气孔中。S型气孔充填物的物质成分富Si、Fe、K、Mg、Al,Co含量一般为0.17%~0.46%,其成分与碱性玄武岩的组成类似,其物质来源可能与碱性玄武岩有关。C型气孔充填物为O、Ca、C及少量Si、Al、Mg、Fe、K等元素,C型气孔充填物可能与海水中物质的沉积有关。由Si、Al、Fe、Mg、K等元素变化曲线反映出的S型气孔充填物沉积过程与富钴结壳早期的沉积过程具有相似的趋势,说明富钴结壳早期沉积物的物质来源可能与碱性玄武岩有关,富钴结壳物质来源可能是碱性玄武岩和海水共同作用的结果。     

Continuous growth of hydrogenetic ferromanganese crusts since 17 Myr ago on Takuyo-Daigo Seamount,NW Pacific,at water depths of 800–5500 m

Ferromanganese crusts cover all outcrops on Takuyo-Daigo seamount traversed during remotely operated underwater vehicle (ROV) dives, except in places covered by foraminifera sand. Takuyo-Daigo is a Cretaceous seamount located in the northwest Pacific Ocean. Geological and bathymetric mapping provide the framework for this study. Chemical and mineralogical analyses of the hydrogenetic ferromanganese crusts show temporal and spatial variations typical of those found in previous studies. Outcrops from 800 to 5500 m water depths are covered with ferromanganese crusts up to 105 mm thick. Beryllium isotope dating shows that the crusts have apparently been growing continuously at all water depths, even through the modern oxygen minimum zone (OMZ), contrary to some earlier models for deposition. Growth rates vary from 2.3 to 3.5 mm/Myr, with Fe or Mn fluxes of 0.07–0.11 g/cm²/Myr since the early-middle Miocene. Co/Mn ratios decrease with water depth while Fe/Mn and other metallic elements increase or show no change, based on the analysis of the uppermost crust surface. This is probably because Co is the most abundant redox-sensitive element derived from seawater that occurs in crusts.     

大洋磷酸盐化作用对富钴结壳元素富集的影响

中国首次对与大洋富钴结壳密切相关的磷酸盐化作用进行了研究。对取自西太平洋麦哲伦海山区一厚度为 10cm的富钴结壳样品 ,自顶至底以 5mm间距采取了 2 0个分层样品进行了成矿元素和稀土元素分析。结果表明 ,未被磷酸盐化的新结壳和磷酸盐化的老结壳间主要成矿元素的含量相差显著。老结壳中Fe、Mn、Si、Al、Zn、Mg、Co、Ni、Cu元素亏损 ,亏损次序为Co >Ni>Mg >Al>Mn >Si>Cu >Zn >Fe;而Ca、P、Sr、Ba、Pb元素含量增加 ,富集次序为P >Ca >Ba >Pb >Sr。研究认为 ,结壳中磷酸盐化作用的强弱制约着富钴结壳成矿元素含量的变化 ,磷酸盐化作用是造成老结壳中主要成矿元素Co、Ni等贫化流失的根本原因。研究还表明 ,磷酸盐化作用对富钴结壳的稀土元素丰度也产生一定影响 ,使老结壳的稀土总量和Ce含量高于新结壳 ,但未显著改变其稀土配分模式和分馏特征。研究证实 ,老结壳的Y正异常与磷酸盐化作用无关。磷酸盐化作用的研究为富钴结壳矿产资源的评价和综合利用提供了有用信息。