Thallium: a sensitive indicator of rock/seawater interaction and of sulfur saturation of silicate melts

Radiochemical neutron activation analysis for Tl in a number of young pillow basalts, hydrothermally altered basalts and associated hydrothermal and hydrogenous Mn crusts from the Mid-Atlantic Ridge and adjacent regions of the North Atlantic indicate that Tl is a sensitive indicator of both S saturation of silicate melts and of rock/seawater interactions. Rb-Cs-K-Tl trend lines for fresh MAR basalts (whose melts remained saturated with S during silicate fractionation) are distinctly different to Hawaiian basalts whose melts lost S during or prior to eruption, but were saturated with S at an earlier stage. Varying degrees of Tl enrichment are found in the hydrogenous Mn nodules (91,000 ppb), hydrothermal Mn crusts (2300–32,000 ppb), palagonitized glass (300–2700 ppb), hydrothermally altered basalts (1140–4560 ppb), and even slightly altered pillow interiors (11–45 ppb) relative to the fresh glasses (6–12 ppb). This enrichment has taken place due to incorporation of Tl into secondary silicate phases along with the alkalis and also due to co-precipitation of Tl with ferromanganese oxides and hydroxides. Thallium enrichment in the hydrothermal products is interpreted as being due to cooling and oxidation of hydrothermal fluids as these approached the sea floor. Haloes of Tl-enriched country rock may occur around sulfide deposits in which seawater has acted as the ore fluid.     

Composition and distribution of REE in ferromanganese crusts of the Belyaevsky and Medvedev seamounts in the Sea of Japan

This paper presents the results of the integrated study of ferromanganese crusts from the Belyaevsky (Central Basin) and Medvedev (Honshu Basin) seamounts from the Sea of Japan. The study of the mineral composition using powder diffraction and optical and electron microscopy showed that the crusts are made up of todorokite, birnessite, and pyrolusite minerals typical of hydrothermal ferromanganese deposits of the World Ocean. The composition of the ferromanganese crusts from the Sea of Japan was determined by ICP-MS and ICP-OES. The contents of Mn, Fe, Co, Cu, Ni, and other major and trace elements indicate the hydrothermal genesis of the crusts. The obtained data on the composition of ferromanganese crusts of the Sea of Japan, as well as their comparison with different types of deposits of the World Ocean, suggest the endogenic genesis of the studied crusts. However, the REE and Y distribution patterns testify to a significant admixture of hydrogenic matter, which participated in the growth of ferromanganese crusts from the Belyaevsky and Medvedev seamounts.     

Hydrothermal Fe-Si-Mn oxide deposits from the Central and South Valu Fa Ridge, Lau Basin

A series of samples from the Hine Hina hydrothermal field (HHF) and the Mariner hydrothermal field (MHF) in the Central and Southern Valu Fa Ridge (VFR), Lau Basin were examined to explain the source origin and formation of the hydrothermal Fe-Si-Mn oxide deposits. The mineralogy was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy, and energy-dispersive spectroscopy (EDS). For the Fe-Mn oxide crusts in the HHF, varying amounts of volcanic fragments and some seawater contributions were recognized, along with higher concentrations of Mn, Al, Co, Ni, Zn, Sr, Mo, elevated ∑REE and negative Ce anomalies. In contrast, the Si-rich oxide samples of the MHF were enriched in Cu, Pb and Ba, indicative of proximity to a hydrothermal jet. Moreover, conductive cooling of hydrothermal fluid evoked the Si-rich deposit formation in the MHF. The Sr, Nd and Pb isotope data provided further constraints regarding the source and formation of the Fe-Si-Mn deposits in the VFR by showing that the samples of the HHF are a mixture of three components, namely, hydrothermal fluid, seawater and volcanic materials, whereas the samples of the MHF were dominated by hydrothermal fluids. The seawater had a minor influence on the Nd isotope data, and the Pb isotope data exhibited a close association with the substrate rock and preformed volcaniclastic layers in this area. The occurrence of relatively high Mn/Fe ratios in the hydrothermal deposits of this area may be a good indicator of the propagating activities of the VFR over geological time.     

Mineralogy of morphogenetic types of ferromanganese deposits in the world ocean

The mineralogy and structural features of the main types of ferromanganese deposits—nodules, micronodules, Co-bearing crusts, crustlike nodules, and low-temperature hydrothermal manganese crusts and ferruginous ochers—are considered. The correlation between their mineral composition and structure is shown. The proposed classification of mineral types is based on characteristic assemblages of Fe and Mn minerals.     

Rare Earth Elements Composition and Constraint on the Genesis of the Polymetallic Crusts and Nodules in the South China Sea

The rare earth elements(REE) composition of the polymetallic crusts and nodules obtained from the South China Sea(SCS) were analyzed through inductively coupled plasma mass spectrometry.Results revealed great differences in the REE abundances(∑REE) of the SCS polymetallic crusts and nodules; the crusts show the highest ∑REE, whereas the nodules exhibit the lowest ∑REE. The similarity in their NASC-normalized patterns, the enriched light REE(LREE), the markedly positive Ce anomaly(δCe), and the non-or weakly positive Eu anomaly(δEu), suggest that the polymetallic crusts and nodules are of hydrogenetic origin. Moreover, the REE contents and their relevant parameters are quite different among the various layers of the crusts and nodules, which probably results from the different marginal sea environments and mineral assemblages of the samples. The growth profiles of the SCS polymetallic crusts and nodules reveal the tendency ∑REE and δCe to slightly increase from the outer to the inner layers, suggesting that the growth environments of these samples changed smoothly from an oxidizing to a relatively reducing environment; in addition, the crust ST1 may have experienced a regressive event(sea-level change) during its growth, although the REE composition of the seawater remained relatively stable. On the basis of the regional ∑REE distribution in the SCS crusts and nodules,the samples collected near the northern margin were influenced by terrigenous material more strongly compared with the other samples, and the REE contents are relatively low. Therefore, the special geotectonic environment is a significant factor influencing the abundance of elements, including REE and other trace elements. Compared with the oceanic seamount crusts and deep-sea nodules from other oceans,the SCS polymetallic crusts and nodules exhibit special REE compositions and shale-normalized patterns, implying that the samples are of marginal sea-type Fe-Mn sedimentary deposits, which are strongly affected by the epicontinental environment, and that they grew in a more oxidative seawater environment. This analysis indicates that the oxidized seawater environment and the special nano property of their Fe-Mn minerals enrich the REE adsorption.     

Geochemistry and genesis of Fe-Mn mineralization in island arcs in the west Pacific Ocean

This paper presents materials on the chemical and mineralogical composition of Fe-Mn mineralization in island arcs (Kurile, Nampo, Mariana, New Britain, New Hebrides, and Kermadec) in the western part of the Pacific Ocean. The mineralization was proved to be of hydrothermal and/or hydrogenic genesis. The former is produced by hydrothermal Fe and Mn oxi-hydroxides that cement volcanic-terrigenous material in sediments. Some Fe oxi-hydroxides can be derived via the halmyrolysis of volcaniclastic material. Crusts of this stage are characterized by fairly low concentrations of trace and rare elements, and their REE composition is inherited from the volcanic-terrigenous material. The minerals of the Mn oxi-hydroxides are todorokite and “Ca-birnessite.” The Mn/Fe ratio increases away from the discharge sites of the hydrothermal solutions. The hydrogenic Fe-Mn crusts are characterized by high concentrations of trace and minor elements of both the Mn group (Co, Ni, Tl, and Mo) and the Fe group (REE, Y, and Th). The hydrogenic crusts consist of Fe-vernadite and Mn-feroxyhyte. Some of the hydrothermal crusts originally had a hydrothermal genesis. The first data were obtained on crust B30-72-10 from the Macauley Seamount in the Kermadec island arc, which contained anomalously high concentrations of Co (2587 ppm) and other Mn-related trace elements in the absence of hydrogeneous Fe oxi-hydroxides.     

东秦岭二郎坪群硅质岩热水沉积地球化学特征及其地质意义

二郎坪群硅质岩成因研究对二郎坪群的构造背景和铜多金属矿床成因的确定具有重要意义。通过对二郎坪群中三种硅质岩的地质特征和岩石地球化学分析，认为二郎坪群硅质岩是典型的热水沉积硅质岩。常量元素地球化学特征值（N(Al)/N（Al+Fe+Mn））指示该硅质岩的沉积环境存在东西差异，南阳盆地以东弧后盆地的规模较大（N(Al)/N（Al+Fe+Mn）=0.30~0.45），沉积环境类似远洋盆地，硅质岩的热液成分比例大，受陆缘物质影响小；而南阳盆地以西弧后盆地的规模较小（N(Al)/N（Al+Fe＋Mn）=0.59），沉积环境为近大陆的边缘海，硅质岩Al含量相对较高，受到陆缘物质影响相对大。地质特征和稀土元素特征（负Eu异常、弱负Ce异常）揭示了二郎坪群硅质岩是弧后盆地型低温热液流体和海水混合形成，这为二郎坪群形成于弧后盆地构造环境的认识提供了新的重要证据。热水沉积硅质岩与铜多金属矿床的共生关系证明研究区铜金属矿床的成因是海底热液喷流沉积作用。     

塔里木盆地下奥陶统白云岩化流体来源的地球化学分析

塔里木盆地是中国重要的含油气盆地,其中奥陶系白云岩是主要储层之一,然而有关白云岩成因的问题众说纷纭,其中的关键是对于白云岩化流体性质的认识不一。元素地球化学和同位素测试分析表明,白云岩的稀土元素来源大部分继承原始灰岩,具有与海水类似的配分特征,只不过稀土元素的含量明显增高了;Sr、Ti含量和Sr/Ba比值较高,且Sr和Mn都具典型的埋藏演化特征;碳、氧同位素分布于正常海相范围内,与典型的埋藏白云岩特征类似;在局部发育一些与断裂相关的铁(锰)白云岩和鞍状白云岩,显示明显的Eu正异常,具相对较高的Fe-Mn-Ba-Si(-Zn-Pb)元素含量及Sr/Ba比值。分析结果说明塔中和塔北下奥陶统的白云岩化流体主要为正常或浓缩了的海水,白云岩形成于准同生和/或埋藏环境,局部发育与断裂相关的热液白云岩,而前人强调的大气淡水或混合水作用对白云岩的形成并不重要。     

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.      

Proximal and distal stratabound ore deposits

Stratiform ore deposits associated with calc-alkaline and tholeiitic volcanism form as chemically precipitated sediments and, like other sediments, display facies variations. An attempt to characterise these vertical and lateral facies variations and to relate them to distance in time and space from the volcanic centre is presented here. With increasing distance in time and space from a volcanic centre, the proportions of volcanics to sediments and intensity of hydrothermal alteration decrease. Footwall alteration pipes, stringer and disseminated ore zones dominated by quartz-, sericite- and Mg-rich assemblages are spatially associated with proximal stratiform base metal deposits whereas slight alteration to quartz-, sericite- and Fe(Mn)-bearing assemblages are present associated with distal stratiform base metal deposits. With increasing distance in time and space from the volcanic centre the Fe, Cu and S content of base metal deposits decreases and the Zn, Pb, Ag, Mn, Ba and F content increases. The trend from copper-dominated to zinc-lead-dominated iron sulphide ores is probably a result of the increasing mixing of seawater with metal-bearing hydrothermal fluid with increasing distance from the volcanic centre.     

内蒙古狼山—渣尔泰山中元古代被动陆缘热水喷流成矿特征

狼山—渣尔泰山中元古代被动陆缘产有东升庙、炭窑口、霍各乞和甲生盘等热水喷流沉积矿床 ,与世界中元古代的SEDEX型矿集区有许多相似之处 :①矿床的产出受华北古陆北缘裂陷槽内三级断陷盆地控制 ;②各大矿床都具有鲜明的层控特征 ,所有矿体总体呈层产在中元古界的白云石大理岩、碳质千枚岩 (或片岩 )中 ;③矿石具有细纹层状、条带状构造 ,喷流沉积成矿特征十分明显 ;④成矿过程中伴有明显的同生断裂活动 ,它在一定程度上控制了矿体的空间分布及其组合 ;但不同矿床同生断裂活动的强度、时限、规模都不同 ,从而导致不同矿床在相同含矿岩组中矿体产出的先后顺序不同和大量层间砾岩与同生角砾状矿石的形成 ;⑤厚大Zn ,Pb ,Cu复合矿体具有明显的分带性 ,自下至上 ,Cu/ (Zn +Pb +Cu)比值由高→低 ;⑥重晶石层发育 ,多与黄铁矿层互层状产出 ,也有与闪锌矿层互层 ,但与世界典型SEDEX型矿床又有重要差别。成矿期间火山活动明显 ,在霍各乞、东升庙、炭窑口矿床惟一容矿的狼山群第二岩组中先后发现了具有变余斑状或聚斑状结构、变余杏仁构造的基性火山岩、钠质“双峰式”火山岩和钾质“双峰式”海相火山岩及凝灰岩夹层。结合①各种硫化物的铅同位素主要分布在地幔和下地壳铅演化曲线附近 ;②部分黄铁矿的Co/Ni值远     

Sorption of heavy metal cations by low-temperature deposits of Pacific hydrothermal fields

Cation exchange reactions with participation of heavy metals Mn, Co, Ni, Cu, Zn, Cd, Ba, and Pb were studed in oceanic low-temperature hydrothermal deposits of various mineral compositions and in hydrogenic Fe-Mn crusts. Individual minerals and their assemblages differ significantly in absorptive capacity, which increases in the following order: hematite ? Si-protoferrihydrite < protoferrihydrite < geothite < nontronite ? Fe-vernadite + Mn-feroxyhyte < Fe-free vernadite < bernessite + Fe-free vernadite < bernessite; i.e., it successively increases from the mineral with a coordination type of lattice to minerals with a layer-type structure. The exchange complex of all minerals includes Na⁺, K⁺, Ca²⁺, and Mg²⁺, i.e., the main cations of seawater. In Mn minerals, Mn²⁺ is the main exchange component. The contribution of all the mentioned cations to the exchange capacity of minerals is as high as 90–98%. The highest absorptive capacity among the examined low-temperature oceanic deposits is characteristic of hydrothermal Mn minerals. Their capacity exceeds substantially that of hydrothermal oxides, hydroxides, Fe-aluminosilicates, and hydrogenic Fe-Mn minerals. The absorptive capacity of all examined Mn minerals relative to heavy metals increases in the same order: Ni < Zn < Cd < Mn < Co < Pb < Cu.     

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.     

华南海西—印支期成矿地质背景

华南海西—印支成矿期内,成矿序列完整,类型齐全,矿种繁多,为其它成矿期所莫及。沉积矿床需要稳定的地质背景,层控矿床形成的较有利的地质背景是稳中有动。     

Soldiers Cap Group iron‐formations,Mt Isa Inlier,Australia, as windows into the hydrothermal evolution of a base‐metal‐bearing Proterozoic rift basin

The Proterozoic Soldiers Cap Group, a product of two major magmatic rift phases separated by clastic sediment deposition, hosts mineralised (e.g. Pegmont Broken Hill‐type deposit) and barren iron oxide‐rich units at three main stratigraphic levels. Evaluation of detailed geological and geochemical features was carried out for one lens of an apatite‐garnet‐rich, laterally extensive (1.9 km) example, the Weatherly Creek iron‐formation, and it was placed in the context of reconnaissance studies of other similar units in the area. Chemical similarities with iron‐formations associated with Broken Hill‐type Pb–Zn deposit iron‐formations are demonstrated here. Concordant contact relationships, mineralogy, geochemical patterns and pre‐deformational alteration all indicate that the Soldiers Cap Group iron‐formations are mainly hydrothermal chemical sediments. Chondrite normalised REE patterns display positive Eu and negative Ce anomalisms, are consistent with components of both high‐temperature, reduced, hydrothermal fluid (≥250°C) and cool oxidised seawater. Major element data suggest a largely mafic provenance for montmorillonitic clays and other detritus during chemical sedimentation, consistent with westward erosion of Cover Sequence 2 volcanic rocks, rather than local mafic sources. Ni enrichment is most consistent with hydrogenous uptake by Mn‐oxides or carbonates. Temperatures inferred from REE data indicate that although they are not strongly enriched, base metals such as Pb and Zn are likely to have been transported and deposited prior to or following iron‐formation deposition. Most chemical sedimentation pre‐dated emplacement of the major mafic igneous sill complexes present in the upper part of the basin. Heating of deep basinal brines in a regional‐scale aquifer by deep‐seated mafic magma chambers is inferred to have driven development of hydrothermal fluids. Three major episodes of extension exhausted this aquifer, but were succeeded by a final climactic extensional phase, which produced widespread voluminous mafic volcanism. The lateral extent of the iron‐formations requires a depositional setting such as a sea‐floor metalliferous sediment blanket or series of brine pools, with iron‐formation deposition likely confined to much smaller fault‐fed areas surrounded by Fe–Mn–P–anomalous sediments. These relationships indicate that in such settings, major sulfide deposits and their associated chemical sediment marker horizons need not overlie major igneous sequences. Rather, the timing of expulsion of hydrothermal fluid reflects the interplay between deep‐seated heating, extension and magmatism.     

Geology and geochemistry of fault-hosted hydrothermal and sedimentary manganese deposits in the Oakover Basin,east Pilbara,Western Australia

Manganese mineralisation in the Oakover Basin is associated with Mesoproterozoic extension, basin formation and deposition of the Manganese Group. The underlying basement architecture of the Oakover Basin (a local half-graben geometry), inherited from the Neoarchean rifting event, plays an important role on the distribution, style and timing of manganese deposits. Fault-hosted manganese deposits are dominant along the ‘active’ faulted eastern margin, whereas flat-lying sedimentary deposits are dominant along the western ‘passive’ margin reflecting differences in ore-forming processes. The large number of significant manganese deposits in the Oakover Basin, previously thought to reflect a spatial association with Carawine Dolomite, more likely reflects the restricted nature of the Mesoproterozoic basin and development of a large reservoir of Mn²⁺ and Fe²⁺ in an anoxic zone of a stratified basin. Low O₂ conditions in the basin were caused by a paleotopographic high forming a barrier to open ocean circulation. The western margin sedimentary deposits formed later than the fault-hosted hydrothermal deposits along the eastern margin, once a significant reservoir of Mn²⁺ and Fe²⁺ had developed, and when there was sufficient subsidence to allow migration of the redox front onto the shallow shelf, with Mn precipitation on and within the seafloor sediments. The sedimentary manganese deposits are not uniformly distributed along the western edge of the basin; instead they are concentrated into discrete areas (e.g. Mt Cooke–Utah–Mt Rove, Bee Hill, Skull Springs and the Ripon Hills districts), suggesting a degree of structural control on their distribution. Fault-hosted manganese is observed beneath and adjacent to many of the sedimentary deposits. Marked geochemical differences are observed between the Woodie Woodie hydrothermal deposits and the sedimentary deposits. Woodie Woodie deposits display higher Ba, U, Mo, As, Sn, Bi, Pb, S and Cu than the sedimentary deposits, reflecting the composition of the hydrothermal fluids. The Al₂O₃ values of the Ripon Hills and Mt Cooke deposits are much higher than the Woodie Woodie deposits, reflecting the composition of the dominant host rock, as Al₂O₃ is typically <5 wt% in the Carawine Dolomite, but is >10 wt% in basal shale units of the Manganese Group. Highly variable Mn:Fe ratios (?5:1) in the hydrothermal manganese at Woodie Woodie reflects rapid deposition of Mn in and around fault zones. In contrast, slower accumulation of Mn oxides on and within the seafloor to form the large sedimentary deposits results in Mn:Fe ratios closer to 1:1 and elevated Co + Ni and REE values.     

Origin of a carbonate-hosted Fe-Mn-(Ba-As-Pb-Sb-W) deposit of Långban-type in central Sweden

The Sjögruvan deposit is one of the Långban-type Fe-Mn oxide deposits hosted by marble interbeds within Svecofennian metavolcanic rocks in the Bergslagen region, central Sweden. Mineralogical and geochemical studies have been carried out to clarify the premetamorphic origin of this type of deposit, which is set apart from most other Mn mineralizations by a significant enrichment in Ba, As, Sb, Pb, W and Be contained by various oxyminerals. The principal ore types at Sjögruvan are (1) hematite+quartz-magnetite, (2) hausmannite+calcite+tephroite and (3) braunite+celsian+phlogopite. The Mn ores are compositionally akin to modern Mn deposits formed by submarine hydrothermal processes (with a high Mn/Fe ratio and low contents of Co, Ni, Th, U and REE) and likely owe their existence to similar mechanisms of formation. Pb isotope data indicate that the metal source and timing of deposition is similar to the major stratabound base-metal and iron deposits in Bergslagen. All the key elements have been leached from the local felsic volcanic units and were deposited on the sea floor; the excellent Mn-Fe separation occurred in an Eh-pH gradient that essentially corresponded to the mixing zone of hydrothermal solutions and seawater. The braunite ore is chemically distinct from the hausmannite ore, with a high concentration of refractory elements (Al, Ti, Zr) and a positive Ce anomaly, which indicate a detrital/hydrogenetic contribution to its protolith. Carbon isotope ('¹³C) values around 0‰ (relative PDB) suggest that carbonates in the deposit formed directly from seawater.     

Types of Pyrophyllite Deposits in Foldbelts

Abstract. Pyrophyllite deposits can be divided into five types on the basis of geology and genesis. The first two types are associated with hydrothermally altered rocks in felsic and intermediate volcanogenic suites. They are characterized by their metasomatites and their subsequent mineralogic transformations under varying volcanic conditions. The third type includes deposits and occurrences of metamorphic-metasomatic genesis, which is caused by transformations of terrigenous-sedimentary interbeds in felsic volcanics under greenschist facies conditions. The fourth type is associated with low and mid-temperature stages of hydrothermal vein formation at the limits of volcanogenic and metamorphic strata. The fifth type comprises pyrophyllite occurrences in weathering crusts on metamorphic strata and metasomatite.
The formation conditions and distribution of raw pyrophyllite deposits were influenced by the geodynamic situations and geochemical conditions, such as character of tectonic dislocations, volcanism and chemical composition of hydrothermal solutions.     

Composition and characteristics of the ferromanganese crusts from the western Arctic Ocean

Layered ferromanganese crusts collected by dredge from a water depth range of 2770 to 2200 m on Mendeleev Ridge, Arctic Ocean, were analyzed for mineralogical and chemical compositions and dated using the excess ²³⁰Th technique. Comparison with crusts from other oceans reveals that Fe-Mn deposits of Mendeleev Ridge have the highest Fe/Mn ratios, are depleted in Mn, Co, and Ni, and enriched in Si and Al as well as some minor elements, Li, Th, Sc, As and V. However, the upper layer of the crusts shows Mn, Co, and Ni contents comparable to crusts from the Atlantic and Indian Oceans. Growth rates vary from 3.03 to 3.97 mm/Myr measured on the uppermost 2 mm. Mn and Fe oxyhydroxides (vernadite, ferroxyhyte, birnessite, todorokite and goethite) and nonmetalliferous detrital minerals characterize the Arctic crusts. Temporal changes in crust composition reflect changes in the depositional environment. Crust formation was dominated by three main processes: precipitation of Fe-Mn oxyhydroxides from ambient ocean water, sorption of metals by those Fe and Mn phases, and fluctuating but large inputs of terrigenous debris.     

Deep-ocean mineral deposits as a source of critical metals for high- and green-technology applications: Comparison with land-based resources

Ferromanganese (Fe–Mn) crusts are strongly enriched relative to the Earth's lithosphere in many rare and critical metals, including Co, Te, Mo, Bi, Pt, W, Zr, Nb, Y, and rare-earth elements (REEs). Fe–Mn nodules are strongly enriched in Ni, Cu, Co, Mo, Zr, Li, Y, and REEs. Compared to Fe–Mn crusts, nodules are more enriched in Ni, Cu, and Li, with subequal amounts of Mo and crusts are more enriched in the other metals. The metal ions and complexes in seawater are sorbed onto the two major host phases, FeO(OH) with a positively charged surface and MnO₂ with a negatively charged surface. Metals are also derived from diagenetically modified sediment pore fluids and incorporated into most nodules. Seafloor massive sulfides (SMS), especially those in arc and back-arc settings, can also be enriched in rare metals and metalloids, such as Cd, Ga, Ge, In, As, Sb, and Se. Metal grades for the elements of economic interest in SMS (Cu, Zn, Au, Ag) are much greater than those in land-based volcanogenic massive sulfides. However, their tonnage throughout the global ocean is poorly known and grade/tonnage comparisons with land-based deposits would be premature.The Clarion–Clipperton Fe–Mn Nodule Zone (CCZ) in the NE Pacific and the prime Fe–Mn crust zone (PCZ) in the central Pacific are the areas of greatest economic interest for nodules and crusts and grades and tonnages for those areas are moderately well known. We compare the grades and tonnages of nodules and crusts in those two areas with the global terrestrial reserves and resources. Nodules in the CCZ have more Tl (6000 times), Mn, Te, Ni, Co, and Y than the entire global terrestrial reserve base for those metals. The CCZ nodules also contain significant amounts of Cu, Mo, W, Li, Nb, and rare earth oxides (REO) compared to the global land-based reserves. Fe–Mn crusts in the PCZ have significantly more Tl (1700 times), Te (10 times more), Co, and Y than the entire terrestrial reserve base. Other metals of significance in the PCZ crusts relative to the total global land-based reserves are Bi, REO, Nb, and W. CCZ nodules and PCZ crusts are also compared with the two largest existing land-based REE mines, Bayan Obo in China and Mountain Pass in the USA. The land-based deposits are higher grade but lower tonnage deposits. Notably, both land-based deposits have < 1% heavy REEs (HREEs), whereas the CCZ has 26% HREEs and the PCZ, 18% HREEs; the HREEs have a much greater economic value. Radioactive Th concentrations are appreciably higher in the land-based deposits than in either type of marine deposit. A discussion of the differences between terrestrial and marine impacts and mine characteristics is also presented, including the potential for rare metals and REEs in marine deposits to be recovered as byproducts of mining the main metals of economic interest in nodules and crusts.