Description of manganese nodules collected in a metamorphic limestone Cambrian formation near Philipsburg, Montana

In the Philipsburg district, in western Montana a low arch of a Paleozoic limestones has been cut and deformed on the east and a south sides by a small batholith of Tertiary granodiorite. The manganese deposits are confined to an area of about 2 square miles underlain by sedimentary rocks and adjacent to the granodiorite body. The ore, chiefly pyrolusite, was apparently derived from rhodochrosite that was abundant in the veins and had replaced the adjacent limestones. The oxide ore is found chiefly within 600 feet of the surface, though one small body was mined at a depth of 700 feet. Commonly these bodies are aggregates of nodules or spheroids that range in size from that of an egg to that of a coconut or larger. In some places they show an irregular texture somewhat like that of a sponge, and in others the material composing them is loose and friable and apparently structureless. Psilomelane is the principal constituent of many of the nodules, in which it forms layers that alternate with softer oxides.

Tab. 1: Trace-element concentrations in ore samples collected from mercury mines and deposits in southwestern Alaska

A belt of small but numerous mercury deposits extends for about 500 km in the Kuskokwim River region of southwestern Alaska. The southwestern Alaska mercury belt is part of widespread mercury deposits of the circum Pacific region that are similar to other mercury deposits throughout the world because they are epithermal with formation temperatures of about 200 °C, the ore is dominantly cinnabar with Hg-Sb-As±Au geochemistry, and mineralized forms include vein, vein breccias, stockworks, replacements, and disseminations. The southwestern Alaska mercury belt has produced about 1400 t of mercury, which is small on an international scale. However, additional mercury deposits are likely to be discovered because the terrain is topographically low with significant vegetation cover. Anomalous concentrations of gold in cinnabar ore suggest that gold deposits are possible in higher temperature environments below some of the Alaska mercury deposits. We correlate mineralization of the southwestern Alaska mercury deposits with Late Cretaceous and early Tertiary igneous activity. Our 40Ar/39Ar ages of 70 ±3 Ma from hydrothermal sericites in the mercury deposits indicate a temporal association of igneous activity and mineralization. Furthermore, we suggest that our geological ancl geochemical data from the mercury deposits indicate that ore fluids were generated primarily in surrounding sedimentary wall rocks when they were cut by Late Cretaceous and early Tertiary intrusions. In our ore genesis model, igneous activity provided the heat to initiate dehydration reactions and expel fluids from hydrous minerals and formational waters in the surrounding sedimentary wall rocks, causing thermal convection and hydrothermal fluid flow through permeable rocks and along fractures and faults. Our isotopic data from sulfide and alteration minerals of the mercury deposits indicate that ore fluids were derived from multiple sources, with most ore fluids originating from the sedimentary wall rocks.

Contents of rare earth and other chemical elements in Fe-Mn micronodules, nodules, and bottom sediments from the Clarion-Clipperton ore province in the Pacific Ocean

Processes governing the formation of rare earth element (REE) composition are under consideration for ferromanganese deposits (nodules, separate parts of nodules, and micronodules of different size fractions) within the Clarion-Clipperton ore province in the Pacific Ocean. It is shown that ferromanganese oxyhydroxide deposits with different chemical compositions can be produced in sediments under similar sedimentation conditions. In areas with high bioproductivity size of micronodules has positive correlation with Mn content and Mn/Fe and P/Fe ratios and negative correlation with Fe, P, REE, and Ce anomaly. Behavior of REE in micronodules from sediments within bioproductive zones is related to increase of influence of diagenetic processes in sediments as a response to the growth of size of micronodules. Distinctions in chemical composition of micronodules and nodules are related to their interaction with associated sediments. Micronodules grow in sediments using hydrogenous ferromanganese oxyhydroxides. As they grow, micronodules are enriched in labile fraction of sediments reworked during diagenesis. Sources of material of ferromanganese nodules are governed by their formation at the water bottom interface. Their upper part is formed by direct settling of iron oxyhydroxides from bottom water, whereas the lower part is accumulated due to diagenetic processes in sediments. Differences of REE compositions in ferromanganese deposits are caused by the reduction of manganese during diagenesis and its separation from iron. Iron oxyhydroxides form a sorption complex due to sorption of phosphate-ion from bottom and pore waters. Sorption of phosphate-ion results in additional sorption of REE.

Geochemistry on Yangla copper deposit, China

The Yangla copper deposit, situated in the middle section of Jinshajiang tectonic belt between Zhongza-Zhongdian block and Changdu-Simao block, is a representative and giant copper deposit that has been discovered in Jinshajiang-Lancangjiang-Nujiang region in recent years. There are coupled relationship between Yangla granodiorite and copper mineralization in the Yangla copper deposit. Five molybdenite samples yielded a well-constrained 187Re-187Os isochron age of 233.3±3 Ma, the metallogenesis is therefore slightly younger than the crystallization age of the granodiorite. S, Pb isotopic compositions of the Yangla copper deposit indicate that the ore-forming materials were derived from the mixture of upper crust and mantle, also with the magmatic contributions. In the late Early Permian, the Jinshajiang Oceanic plate was subducted to the west, resulting in the formation of a series of gently dipping thrust faults in the Jinshajiang tectonic belt, meanwhile, accompanied magmatic activities. In the early Late Triassic, which was a time of transition from collision-related compression to extension in the Jinshajiang tectonic belt, the thrust faults were tensional; it would have been a favorable environment for forming ore fluids. The ascending magma provided a channel for the ore-forming fluid from the mantle wedge. After the magma arrived at the base of the early-stage Yangla granodiorite, the platy granodiorite at the base of the body would have shielded the late-stage magma from the fluid. The magma would have cooled slowly, and some of the ore-forming fluid in the magma would have entered the gently dipping thrust faults near the Yangla granodiorite, resulting in mineralization.

Speciations of Mn and Fe in Fe-Mn nodules from the western part of the Clarion-Clipperton ore province

Hydrogenic forms of iron and manganese occurrence were studied in samples of ferromanganese nodules sampled within two polygons during Cruise 28 of R/V Dmitry Mendeleeev (1982) in the western part of the Clarion-Clipperton ore province. Contents of labile exchangeable Fe and Mn, amorphous hydroxides and poorly soluble compounds of Fe and Mn were analyzed. In nodules from DM28-2474 Polygon labile exchangeable Fe and Mn and amorphous hydroxides dominated; in nodules from DM28-2483 Polygon poorly soluble compounds dominated. Analysis of contents of labile forms of Fe and Mn occurrence in different morphological types of nodules distinguished predominantly hydrogenous botryoidal nodules, spheroidal and ellipsoidal intergrowth nodules, and hydrogenic-diagenetic discoid nodules.

The formation of a subsurface anticyclonic eddy in the Peru-Chile Undercurrent and its impact on the near-coastal salinity, oxygen and nutrient distributions

The formation of a subsurface anticyclonic eddy in the Peru-Chile Undercurrent (PCUC) in January and February 2013 is investigated using a multi-platform four-dimensional observational approach. Research vessel, multiple glider and mooring-based measurements were conducted in the Peruvian upwelling regime near 12°30'S. The dataset consists of more than 10000 glider profiles and repeated vessel-based hydrography and velocity transects. It allows a detailed description of the eddy formation and its impact on the near-coastal salinity, oxygen and nutrient distributions. In early January, a strong PCUC with maximum poleward velocities of ca. 0.25 m/s at 100 to 200 m depth was observed. Starting on January 20 a subsurface anticyclonic eddy developed in the PCUC downstream of a topographic bend, suggesting flow separation as the eddy formation mechanism. The eddy core waters exhibited oxygen concentrations less than 1mol/kg, an elevated nitrogen-deficit of ca. 17µmol/l and potential vorticity close to zero, which seemed to originate from the bottom boundary layer of the continental slope. The eddy-induced across-shelf velocities resulted in an elevated exchange of water masses between the upper continental slope and the open ocean. Small scale salinity and oxygen structures were formed by along-isopycnal stirring and indications of eddy-driven oxygen ventilation of the upper oxygen minimum zone were observed. It is concluded that mesoscale stirring of solutes and the offshore transport of eddy core properties could provide an important coastal open-ocean exchange mechanism with potentially large implications for nutrient budgets and biogeochemical cycling in the oxygen minimum zone off Peru.

Contents of metal cations exchange capacity of ore minerals in ferromanganese micronodules from the Atlantic, Indian and Pacific Oceans

Results of experimental studies of ion exchange properties of manganese and iron minerals in micronodules from diverse bioproductive zones of the World Ocean were considered. It was found that sorption behavior of these minerals was similar to that of ore minerals from ferromanganese nodules and low-temperature hydrothermal crusts. The exchange complex of minerals in the micronodules includes the major (Na**+, K**+, Ca**2+, Mg**2+, and Mn**2+) and subordinate (Ni**2+, Cu**2+, Co**2+, Pb**2+, and others) cations. Reactivity of theses cations increases from Pb**2+ and Co**2+ to Na**+ and Ca**2+. Exchange capacity of micronodule minerals increases from alkali to heavy metal cations. Capacity of iron and manganese minerals in oceanic micronodules increases in the following series: goethite < goethite + birnessite < todorokite + asbolane-buserite + birnessite < asbolane-buserite + birnessite < birnessite + asbolane-buserite < birnessite + vernadite ~= Fe-vernadite + Mn-feroxyhyte. Obtained data supplement available information on ion exchange properties of oceanic ferromanganese sediments and refine the role of sorption processes in redistribution of metal cations at the bottom water - sediment interface during micronodule formation and growth.

Composition of sedimentary rocks from the Burun-Tas Formation, Bol'shoi Lyakhov Island (New Siberian Islands)

Graywackes and shales of the Bol'shoi Lyakhov Island originally attributed to Mesozoic were subsequently considered based on microfossils as Late Proterozoic in age. At present, these sediments in the greater part of the island are dated back to Permian based on palynological assemblages. In the examined area of the island, this siliciclastic complex is intensely deformed and tectonically juxtaposed with blocks of oceanic and island-arc rocks exhumed along the South Anyui suture. The complex is largely composed of turbidites with members displaying hummocky cross-stratification. Studied mineral and geochemical charac¬teristics of the rocks defined three provenances of clastic material: volcanic island arc, sedimentary cover and/or basement of an ancient platform, and exotic blocks of oceanic and island-arc rocks such as serpentinites and amphibolites. All rock associations represent elements of an orogenic structure that originated by collision of the New Siberian continental block with the Anyui-Svyatoi Nos island arc. Flyschoid sediments accumu¬lated in a foredeep in front of the latter structure in the course of collision. Late Jurassic volcanics belonging to the Anyui-Svyatoi Nos island arc determine the lower age limit of syncollision siliciclastic rocks. Presence of Late Jurassic zircons in sandstones of the flyschoid sequence in the Bol'shoi Lyakhov Island is confirmed by fission-track dating. The upper age limit is determined by Aptian-Albian postcollision granites and diorites intruding the siliciclastic complex. Consequently, the flyschoid sequence is within stratigraphic range from the terminal Late Jurassic to Neocomian. It appears that Permian age of sediments suggested earlier is based on redeposited organic remains. The same Late Jurassic-Neocomian age and lithology are characteristic of fossiliferous siliciclastic sequences of the Stolbovoi and Malyi Lyakhov islands, the New Siberian Archipelago, and of graywackes in the South Anyui area in the Chukchi Peninsula. All these sediments accumulated in a spacious foredeep that formed in the course the late Cimmerian orogeny along the southern margin of the Arctic conti¬nental block.