Bank-derived carbonate sediment transport and dissolution in the Hawaiian Archipelago

This investigation used two approaches to examine the flux of bank-derived carbonate particles and determine the potential influence of benthic carbonate particle dissolution on the carbon chemistry of the waters around the Hawaiian Archipelago. First, the particle flux near several representative carbonate banks in the Hawaiian Archipelago was measured and compared with the flux at a distal site (ALOHA) approximately 100 km north of Oahu, Hawaii. The results of four sediment trap deployments on three carbonate banks in the Hawaiian Archipelago demonstrate that the flux of bank-derived carbonate particles are consistently one to two orders of magnitude higher than the fluxes at the distal station. Furthermore, the mineralogy of the carbonate flux near the banks, which includes very soluble bank-derived aragonite and magnesian calcite particles, is distinctly different from that of the distal fluxes. Second, the chemistry of the waters at each bank station along the archipelago was characterized and compared with the chemistry of the distal waters to determine if differences in the particle flux were reflected in the carbon chemistry. Higher alkalinity and carbonate ion concentrations were observed around all of the banks studied. The saturation state of these waters suggests that the dissolution of some magnesian calcite and aragonite phases could explain the higher alkalinity values. Calculations suggest that the dissolution of benthically-derived aragonite and magnesian calcite may be an important component of the North Pacific alkalinity budget and a potential sink for anthropogenic CO₂.     

桂东北氧化锰矿成矿特征及找矿潜力分析

文章通过介绍桂东北地区锰帽型氧化锰矿的成矿特征,对氧化锰矿床的控矿因素、找矿标志及找矿潜力进行了分析和探讨,认为该区锰矿床的产出受气候、层位、岩性、褶皱及地形等因素的控制,探采前景较好,以供资源开发和管理者参考。     

Petrogenetic modeling of Hawaiian tholeiitic basalts: A geochemical approach

The abundances of 29 elements, including nine REE (La, Ce, Nd, Sm, Eu, Tb, Dy, Yb and Lu), have been determined by instrumental neutron activation analysis in 33 tholeiitic basalts from Mauna Loa, Kohala, Mauna Kea, Lanai and Koolau. These data have been combined with data provided by A. V. Murali et al. on seven basalts from Kilauea for geochemical evaluation.Partial melting models based on the partitioning of the REE and Sc suggest that these basalts can be produced from three distinct source compositions. Thus, the basalts from Mauna Kea, Kohala and Kilauea are generated by 2–10% partial melting of similar source materials in the compositional range 82 ± 4% olivine plus orthopyroxene (ol + opx), 14 ± 3% clinopyroxene (cpx) and 4 ± 1% garnet (gar). Similar amounts of melting of source materials having 74 ± 6% ol + opx, 21 ± 5% cpx and 5 ± 1% gar produce the basalts of Mauna Loa and Lanai. A source material composed of 86 ± 4% ol + opx, 11 ± 2% cpx and 3 ± 1% gar is proposed for the generation of basalts from Koolau.The olivine-crystallization model suggested here requires absolute REE abundances in the preferred Mauna Kea, Kohala and Kilauea source to range from 1.1× (times chondrite) for the LREE (La) to about 1.3× for the HREE; in the Mauna Loa and Lanai source, La is about 1.0× and the HREE are about 1.6×; and in the Koolau source, La is ~0.7× and the HREE are ~0.9×.     

贵州松桃西溪堡锰矿沉积地球化学特征

贵州黔东断裂坳陷带是贵州重要的锰矿成矿带,并发育新元古代大塘坡期的一套完整“黑色岩系”,锰矿主要赋存于该黑色岩系中。本文以松桃西溪堡锰矿床为例,通过岩石学、矿物学、地球化学等研究方法,探讨这类锰矿床的成矿物质来源及成因。研究表明矿石中的矿物组分复杂,结构构造类型多样,富集As、Sb、Ag、Co、Mo、W、Cs和Ba等元素,Fe／Ti、（Fe＋Mn）／Ti、A1／（AI＋Fe＋Mn）、Y／Ho、Nb／Ta比值,以及Cr．zr和Th．u图解均揭示成矿过程中有热水物质参与;V／（V＋Ni）、V／Cr比值表明锰矿形成于缺氧环境;稀土元素分布模式、Ce、Eu异常及La．Ce、La／Yb．EREE图解显示锰矿形成于被动大陆边缘环境,并具有热水沉积特征。因此,古被动大陆边缘是锰矿富集的理想场所,热水（液）活动为其提供了丰富的物质来源。这为锰矿的找矿拓展了新的思路。     

Ferromanganese oxide deposits from the Central Pacific Ocean,I. Encrustations from the Line Islands Archipelago

Chemical and mineralogical analyses of a well-controlled suite of ferromanganese encrustations from the Line Islands Archipelago (Central Pacific) suggest that they represent purely hydrogenous deposits—i.e. they have formed through the slow accumulation of trace metal-enriched oxides directly from the water-column. Mineralogically they consist predominantly of δMnO₂ and amorphous FeOOHxH₂O. Compositionally, they are similar to δMnO₂ nodules from adjoining basinal areas but are enriched in both Mn (mean = 20.4%, max = 29.3%) and Co (mean = 0.55%, max = 1.57%). δMnO₂ is the most important trace metal bearing phase; strong associations are noted between it and Co, Mo, Ni, Zn, and Cd, whilst only Be is associated specifically with FeOOH. V, Sr and Pb are partitioned between the authigenic oxide phases, whilst Ti most probably occurs as TiO₂xH₂O. Cu is contained in both aluminosilicate contaminant phases and Fe oxide phases. These relations are considered to reflect the differing scavenging behaviour of Mn and Fe oxides in the water column.Crusts from ~1–2 km are enriched in Mn and the Mn-related elements and exhibit higher $\text{Mn}\text{Fe}$ ratios than deeper crusts, which are compositionally constant. The higher $\text{Mn}\text{Fe}$ ratios may result from a supply of Mn from continental borderland sediments at these depths, which is transported horizontally by advective-diffusive processes. Since manganophile elements are enriched relative to Mn in the 1–2 km crusts, it is considered that the supply of Mn is scavenged by existing oxides, is oxidised and effectively occludes them. A higher proportion of oxide particles thus exhibit Mn oxide scavenging properties in the 1–2 km depth zone. The increased vertical flux of Mn resulting from the supply at ~1–2 km is not reflected by higher $\text{Mn}\text{Fe}$ ratios in deeper crusts, so that the vertical flux of oxides is not simply related to the standing crop. The $\text{Mn}\text{Fe}$ ratios of the crusts thus reflect the composition of suspended oxides at similar depths.     

Nanhuan manganese deposits within restricted basins of the southeastern Yangtze Platform,China: Constraints from geological and geochemical evidence

The Nanhuan manganese deposits in the southeastern Yangtze Platform occur in the black shale series in the lower part of the Datangpo Formation. In order to constrain the genesis of the deposits, a detailed study was undertaken that involved field observations, major and trace element analyses, organic carbon analyses, and isotope analyses (C, O, S). The major findings are as follows. (1) The ore-bearing rock series, morphology of the ore bodies, and characteristics of ores in several deposits are similar. The ore minerals are rhodochrosite and manganocalcite. The gangue minerals are mainly quartz, feldspar, dolomite, and illite. Minor apatite and bastnaesite occur in the manganese ores. (2) The ores are enriched in Ca and Mg, whereas they are depleted in Si, Al, K, and Ti compared to wall rocks. The ores normalized to average Post-Archean Australian shale (PAAS) are enriched in Co, Mo, and Sr. The chondrite-normalized rare earth element (REE) patterns for ores and wall rocks are between those of typical hydrogenous and hydrothermal type manganese deposits. Additionally, the ores have positive Ce anomalies with an average Ce/Ce* of 1.23 and positive Eu anomalies with an average Eu/Eu* of 1.18 (normalized to PAAS). (3) The average content of organic carbon is 2.21% in the samples, and the average organic carbon isotopic value (δ¹³C_V-PDB) is − 33.44‰. The average inorganic carbon isotopic value (δ¹³C_V-PDB) of carbonates in Gucheng is − 3.07‰, while the values are similar in the other deposits with an average of − 8.36‰. The oxygen isotopic compositions (δ¹⁸O_V-PDB) are similar in different deposits with an average of − 7.72‰. (4) The sulfur isotopic values (δ³⁴S_V-CDT) of pyrite are very high and range from + 37.9‰ to + 62.6‰ (average of 52.7‰), which suggests that the pyrite was formed in restricted basins where sulfate replenishment was limited. The sulfate concentrations in the restricted basins were extremely low and enriched in δ³⁴S, which resulted in the very high δ³⁴S values for the pyrite that formed in the manganese deposits. Therefore, a terrigenous weathering origin for manganese can be excluded; otherwise, the sulfate would have been introduced into the basins together with terrigenous manganese, which would have decreased the δ³⁴S values of pyrites. The manganese, which originated from hydrothermal processes, was enriched in the restricted and anoxic basins, and then, it was oxidized to manganese oxyhydroxide in the overlying oxic waters whereby the products precipitated into the sediments. The manganese oxyhydroxide in the sediment was then reduced to Mn^2 + and released to the pore waters during the process of diagenesis. Some organic carbon was oxidized to CO₃^2 −, which made the depletion of ¹³C in manganese carbonates. Therefore, we suggest that the Nanhuan manganese deposits are hydrothermal–sedimentary/diagenetic type deposits.     

A comparison of iron oxide-rich joint coatings and rock chips as geochemical sampling media in exploration for disseminated gold deposits

We evaluated the effectiveness of iron oxide-rich fracture coatings as a geochemical sampling medium for disseminated gold deposits, as compared with conventional lithogeochemical methods, for samples from the Pinson mine and Preble prospect in southeastern Humboldt County, Nevada. That disseminated gold mineralization is associated with Hg, As, and Sb is clearly demonstrated in these deposits for both fracture coatings and rock chip samples. However, the relationship is more pronounced for fracture coatings. Fracture coatings at Pinson contain an average of 3.61, 5.13, 14.37, and 3.42 times more Au, As, Sb and Hg, respectively, than adjacent rock samples. At Preble, fracture coatings contain 3.13, 9.72, 9.18, and 1.85 times more Au, As, Sb and Hg, respectively, than do adjacent rock samples. Geochemical anomalies determined from fracture coatings are thus typically more intense than those determined from rock samples for these elements. The sizes of anomalies indicated by fracture coatings are also somewhat larger, but this is less obvious. In both areas, Sb anomalies are more extensive in fracture coatings. At Preble, some Hg and Au anomalies are also more extensive in fracture coatings. In addition to halos formed by the Hg, As and Sb, high values for Au/Ag and Zn/(Fe + Mn) are closely associated with gold mineralization at the Pinson mine. The large enhancement in geochemical response afforded by fracture coatings indicates a definite potential in the search for buried disseminated gold deposits.     

Contributions to the mineralogy of authigenic manganese phases from marine manganese deposits

The formation of authigenic manganese minerals and ores in the pelagic regions of the ocean is related to oxidation of Mn²⁺ extracted from basalts and other rocks with heated seawater. For littoral parts of the ocean and lakes mobilization of Mn²⁺ and Fe²⁺ is admitted finding its way to the bottom sediments (along with the organic substances) from land in the form of Mn⁴⁺. The main manganese mineral of oceanic and continental basins is vernadite. Its deposition is considered a result of the activity of microorganisms.     

浙东脉状铅锌矿地球化学热力学研究

浙东脉状铅锌矿主要赋存于侏罗纪—白垩纪火山碎屑岩中,成矿地质条件相似。本文在对典型矿区主要成矿阶段矿物组合、成矿温度、矿液成分研究的基础上,对成矿的其它物理化学条件,如PH、fo(?)、fs(?)等作了热力学分析与计算,并结合主要矿石矿物的溶解度资料,计算与分析了成矿过程中主要成矿元素的搬运形式及富集机理。     

On the occurrence of a pumice-rich layer in Holocene deposits of western Peloponnesus, Ionian Sea, Greece. A geomorphological and geochemical approach

A single, pumice-rich sandy horizon located in Holocene deposits of western Peloponnesus, Ionian Sea, Greece has been newly detected in a littoral belt 250 m wide and more than 3km long. Pumice fragments are hosted in siliceous-cherty sand that overlies coarser clastic sediments, and occur in varying sizes. The geomorphology of the area and the development of two dune systems played an important role in the entrapment of the pumice fragments. These were transported there by the wind and marine currents, rather than by a tsunami event. The chemistry of the pumice fragments is constistent throughout the deposit. Major and trace element analysis of the pumice suggests an origin in the south Aegean Volcanic Arc, rather than in southern Italy and surroundings. The age of this deposition is thought to be younger than 4,000 years before present.     

新疆主要金矿床地质和地球化学特征

新疆地处中国西北部,矿产丰富.尤其是近10年来,在金矿地质科研和开采提炼方法的研究有了新的突破,使得新疆成为中国最重要的产金地之一.新疆位于西伯利亚板块和印度板块之间,主要由若干个地块和褶皱造山带组成.迄今为止,已发现岩金矿床40余处.依据主要金矿床的构造背景、矿床地质和地球化学特征,可以得到下列认识:①金矿化作用主要发生于前寒武纪和华力西期;②产于华力西褶皱造山带中的主要金矿床类型有:浊积岩型、火山岩型和韧性剪切带型;③金矿床具备良好的成矿地质条件,金在高背景区通过活化、迁移并富集于适宜的断裂活动带中,形成大而富的金矿床;④金矿床的主要控矿因素是地层、岩浆岩和构造,尤其是韧性剪切带;⑤通过成矿作用物理化学条件研究,金矿化作用是在浅成、中低温、低盐度和强还原环境下进行的;⑥稳定同位素资料显示,金矿床的成矿期在245~359 Ma,并主要集中于270 Ma;⑦围岩蚀变主要有硅化、黄铁绢英岩化、黄铁矿化、钾化、钠化等,其中黄铁矿化、黄铁绢英岩化和玉髓化是良好的找矿标志;⑧根据S、C、Si、Sr、Pb同位素资料,成矿物质主要来源于下地壳和上地幔,并受上地壳混染;⑨依据H、O同位素资料,早期成矿过程中成矿流体以岩浆水和变质水为主,中晚期成矿过程中则以天水为主.     

斑岩型钼矿床的形成机制与地球化学过程

斑岩型钼矿床是世界钼矿床中最重要的种类,其中90%以上的钼矿床都和斑岩有关。斑岩型钼矿床主要分布于环太平洋成矿带和特提斯成矿带上,主要与板块俯冲过程有关,可以分为斑岩铜钼矿床、高氟型斑岩钼矿床和低氟型斑岩钼矿床。我们通过对全球斑岩型钼矿床的时空分布与钼元素地球化学性质分析,认为斑岩型钼矿床的物质来源是钼元素通过表生地球化学作用进行初始富集后形成的富钼沉积物。新元古代晚期(750～542Ma)大气氧再次升高之后,富钼的黑色页岩等才大量出现,因此斑岩型钼矿床主要形成于500Ma之后。富钼黑色页岩等沉积物在板块俯冲过程中脱水,形成富含Mo和Re的变质流体,同时两者发生分异。这种变质流体交代上覆地幔楔使Mo和Re留存在其中。随着俯冲洋壳的部分熔融,形成富Cu(Au)的岩浆,穿过富含Re(Mo)的上覆地幔楔,形成斑岩型铜钼矿床,因此这类矿床的辉钼矿Re含量更高。而随后出现的板块后撤,使软流圈上涌,板片上大量多硅白云母分解,形成了富含F的岩浆,穿过富含Mo的上覆地幔楔,进而形成高氟型斑岩矿床。低氟型钼矿床很可能与俯冲关系较小,富钼沉积物通过造山过程被深埋,在适当的条件下形成低氟型斑岩钼矿床。     

Mineralogy of metamorphosed manganese deposits of the South Urals

A mineralogical investigation of metamorphosed manganese rocks was carried out at ore deposits related to the Devonian volcanic complexes of the Magnitogorsk paleovolcanic belt of the South Urals. The mineralogical appearance of these rocks is determined by three consecutively formed groups of mineral assemblages: (1) assemblages occupying the main volume of orebodies and formed during low-grade regional metamorphism (T = 200−250°C, P = 2–3 kbar); (2) assemblages of segregated and metasomatic veinlets that fill the systems of late tectonic fractures; and (3) assemblages of near-surface supergene minerals. Sixty-one minerals have been identified in orebodies and crosscutting hydrothermal veinlets. The major minerals are quartz, hematite, hausmannite, braunite, tephroite, andradite, epidote, rhodonite, caryopilite, calcite, and rhodochrosite. The mineral assemblages of metamorphosed manganese rocks (metamanganolites) are characterized. Chemical compositions of braunite, epidote-group minerals, piemontite, pyroxenes, rhodonite, pyroxmangite, and winchite are considered. The bibliography on geology and mineralogy of the South Ural manganese deposits is given.     

A geochemical model for evaluating theories on the genesis of Florida''s sedimentary phosphate deposits

Present ionic concentrations of Ca ⁺⁺,HCO ₃ ^- ,and HPO ₄ ⁼ in surface and groundwater runoff in Florida indicate that phosphorus is being concentrated in rock through dissolution and reprecipitation, with calcium phosphate increasing at the expense of calcium carbonate. Analog computer simulation of a systems model of this process suggests that significant enrichment can occur in 20 million years. The degree of enrichment depends on the supply of new phosphorus to Florida through rain and oceanic exchange processes. If the calcium phosphate content of original rock is 0.5 to 1.0 percent (0.52 to 1.05 percent P ₂ O ₅),a formation with 10 to 20 percent calcium phosphate (CaPO ₄ or 10.5 to 21.0 percent P ₂ O ₅)as in the Hawthorn Formation (Miocene)may result. Nutrient upwelling along the continental slope coupled with transport to the estuaries by lateral eddy diffusion can supply an additional 400 mg P|m ² |yr which, if deposited, would result in a sediment with a 4.3 percent CaPO ₄ (4.5 percent P ₂ O ₅)content. If this is enriched later by resolution, 40 percent CaPO ₄ (42 percent P ₂ O ₅)results. Through geologic time, the ocean may be considered as a source of phosphorus to the land through rain or estuarine sediment.     

Glacigenic deposits of the Central Deep: a key to the Late Quaternary evolution of the eastern Barents Sea

Sparker and shallow drilling data indicate that the Quaternary deposits in the Central Deep of the Barents Sea are mainly composed of glacigenic sediments. They comprise basal till and proximal and distal glaciomarine sediments deposited during the last glacial cycle. Apparent glaciotectonic features imply strong glacial erosion of Mesozoic bedrock. The general ice movement is assumed to have been from off Novaya Zemlya and it is concluded that the whole eastern Barents Sea was covered by the Late Weichselian ice-sheet.     

A structural interpretation of magnetometer and seismic profiler records in the Bismarck Sea,Melanesian Archipelago

During a marine geophysical survey of the Bismarck Sea by the Australian Bureau of Mineral Resources in 1970, magnetic, gravity, and seismic reflection recordings were made along north‐south traverses with a spacing of 30 to 40 km. The magnetic data have been interpreted, first by visual inspection of magnetic and topographic trends and then by two‐dimensional computer modelling along typical profiles. The interpretation indicates that the Bismarck Sea is divided into two main tectonic provinces separated by a boundary which roughly coincides with a line joining Manus Island and the Willaumez Peninsula of New Britain. An area of apparently nonmagnetic basement about 10 km wide coincides with a well defined band of shallow earthquakes which runs east‐west across the centre of the Sea. A major boundary is present at the eastern end of the Sea along the west coast of the Gazelle Peninsula of New Britain; it continues along an offset in the band of earthquakes to New Hanover.     

石英脉型钼矿地质和地球化学特征研究现状综述

石英脉型钼矿床作为钼矿资源的一种主要工业类型,对于钼资源的开发具有重要意义,因此,其地质、地球化学特征及其成矿机制也引起了国内外学者的广泛关注。本文通过整理和分析国内主要石英脉型钼矿的矿床地质、矿区花岗岩的地球化学特征,以及相关成矿地球化学资料,发现石英脉型钼矿床具有如下地质和地球化学特征：产于断裂构造发育的地区,断裂为主要的控矿空间;矿区常发育花岗岩体,与成矿具有密切的空间和时间关系;矿体呈脉状,由石英脉和其两侧的蚀变围岩组成,其中主要矿物组合为辉钼矿、黄铁矿、黄铜矿、钾长石和石英;与成矿有关的花岗岩地球化学特征显示矿床主要形成于后碰撞伸展构造环境,岩浆源区为下地壳,并且有少量幔源物质的加入;流体包裹体数据显示,成矿流体具有中低温（160 ℃～375 ℃）、中低盐度（4%～28%）的特点;成矿流体的δ18O值为-7.3‰～4.8‰、δD值为-129‰～-50‰,表现为岩浆水和大气降水混合成因;成矿热液的总δ34S值为1.1‰～8.8‰,指示成矿体系中的硫来源于岩浆,并受地层硫的不同程度影响。     

Crustal structure of the Hawaiian Archipelago, northern Melanesia, and the Central Pacific Basin by seismic refraction methods

The crustal structure of the Hawaiian Archipelago, northern Melanesia, and parts of the Central Pacific Basin have been studied by seismic refraction methods. The systematic variation found in crustal thickness in the Hawaiian Islands is explainable by a hypothesis of differential subsidence. The crustal structure of northern Melanesia points to tensional forces in an east-west direction and compressional forces in a north-south direction. In the Central Pacific Basin, a 7.4 km/sec layer in the lower crust seems to be present over a wide area.