Palladium, iridium, and gold contents of mafic and ultramafic rocks drilled from the Mid-Atlantic Ridge, Leg 37, Deep Sea Drilling Project

1977 ◽  
Vol 14 (4) ◽  
pp. 777-784 ◽  
Author(s):  
James H. Crocket ◽  
Yuko Teruta
Keyword(s):  
Noble Metals ◽  
Sea Water ◽  
Local Heating ◽  
Ultramafic Rocks ◽  
Gold Content ◽  
Secondary Alteration ◽  
Sea Floor ◽  
Mid Atlantic Ridge ◽  
Weak Trend ◽  
Drilling Project

Basalts and ultramafic rocks from holes 332B and 334 of Leg 37, DSDP, were analyzed for palladium, iridium, and gold by neutron activation. Averages obtained for the basalts are: Pd < 0.69 ppb, Ir < 0.025 ppb, and Au = 2.9 ppb. The samples include one representative of each of the main basaltic lithological units except for Unit III, hole 332B, which is represented by a suite of 14 samples. Averages of 43, 0.60, and 16 ppb were obtained for Pd, Ir, and Au respectively in two ultramafic rocks and a gabbro from hole 334.In comparison with basalts from mid-ocean islands such as Hawaii, Leg 37 sea-floor basalts are significantly depleted in Ir and Pd, but are similar in gold content. These differences may be related to differing degrees of alteration sustained by rocks from these differing environments.The depth profiles for Ir and Pd in hole 332B show no significant trends, but a weak trend of increasing gold content with depth is suggested. Variation of Ir and Pd in adjacent lithological units may be as great as a factor of 50. The Pd distribution in 14 samples from Unit III suggests that these differences probably reflect real differences in average metal content rather than sampling effects. Although alteration of Leg 37 basalts is weak, the low Pd and Ir contents and the variability from flow to flow suggest that reaction with sea water has leached Pd and Ir from these rocks. A possible complementary enhancement of some noble metals including Pd has been noted in the sediments immediately overlying mid-ocean rises. Although gold does not seem to be depleted in Leg 37 basalts there is evidence that the metal is easily mobilized by local heating accompanying igneous intrusive rocks.The average Au/Ir ratio of the Leg 37 basalts is four times higher than that of the ultramafic–mafic rocks of hole 334. Although part of this effect is probably due to secondary alteration, it is considered unlikely that the Leg 37 basalts and ultramafic rocks are petrogenetically related.

Distribution and evolution of uranium in the oceanic lithosphere

1979 ◽  
Vol 291 (1381) ◽  
pp. 423-431 ◽  
Keyword(s):  
Sea Water ◽  
Oceanic Lithosphere ◽  
Uranium Content ◽  
Major And Trace Elements ◽  
Ultramafic Rocks ◽  
Layer 2 ◽  
Secondary Enrichment ◽  
Layer 4 ◽  
Mid Atlantic Ridge ◽  
Fractionation Trend

Induced fission track techniques permit us to determine quantitatively the microscopic distribution of uranium in rocks, in their constituent minerals, and in percolating fluids. Both primary magmatic variations and secondary mobilization of uranium can be discerned. Concentrations of uranium in phenocrysts and fresh glasses of oceanic basalts and gabbros are very low (2-80 parts/10 9 ) and are comparable to concentrations in the same minerals of the associated ultramafic rocks. Variations with depth in D.S.D.P. holes show several distinct cyclic variations of uranium, accompanied by parallel trends in some major and trace elements. In Hole 332B (mid-Atlantic ridge, 36 °N), uranium and other elements can be shown to fall into two distinct groupings, each group following its own characteristic fractionation trend, suggesting that two distinct magmas differentiated independently beneath the median valley, the two magmas alternating in their contribution to the formation of oceanic layer 2. Earlier investigations of the uranium distribution in surface pillows and other dredged rocks exposed to sea water had shown that, owing to halmyrolysis, the uranium concentration increases systematically with distance from the axis of a midoceanic ridge. Subsequent investigations on rocks drilled from horizons deeper into oceanic layer 2 indicate that secondary enrichment or redistribution of uranium is confined to specific zones of altered basalt, near fractures, pillow and flow margins, and especially along horizontal planes of breccias and sediments in between massive flow where convective water circulation is thought to occur. Ultramafic rocks from the base of layer 3 and top of layer 4 are also enriched in uranium when hydrated by sea water during the process of serpentinization. A combination of these processes may double the uranium content of an oceanic lithospheric plate between the time of its formation and its eventual subduction.

The Mid-Atlantic Ridge Near 45 °N. XVI. Serpentinized Ultramafic Intrusions

1971 ◽  
Vol 8 (6) ◽  
pp. 631-663 ◽  
Author(s):  
F. Aumento ◽  
H. Loubat
Keyword(s):  
Solid State ◽  
Hydrostatic Pressure ◽  
Upper Mantle ◽  
Sea Water ◽  
Mechanical Deformation ◽  
Ultramafic Rocks ◽  
Physical Conditions ◽  
Mid Atlantic Ridge ◽  
Directional Component ◽  
Solid State Recrystallization

Detailed descriptions of the mineralogy, petrography, geochemistry, and physical properties of serpentinized ultramafic rocks dredged from the Mid-Atlantic Ridge at 45° N support an interpretation of the events which affected these rocks after their original crystallization. Crystallization apparently took place in lopoliths emplaced at the Crust/Upper Mantle interface beneath the axis of the ridge under conditions quiet enough to permit gravity crystal differentiation and layering. The rocks were then fractured without hydration under high hydrostatic pressure, with a feeble directional component, possibly under conditions favoring solid-state recrystallization of interstitial minerals. Hydration (amphibolization) began during the last phases of intimate mechanical deformation and the commencement of rodingitic metasomatism. Further hydration resulted in multiple overlapping periods of serpentinization dependent on varying physical conditions. Hydrating fluids may have been derived both from juvenile waters and from sea water.

scholarly journals The Formation and Composition of the Gas Content of Sea Ice

1979 ◽  
Vol 22 (86) ◽  
pp. 67-81 ◽  
Author(s):  
V. L. Tsurikov
Keyword(s):  
Sea Ice ◽  
Sea Water ◽  
Major Effect ◽  
Relative Volume ◽  
Gas Content ◽  
Dominant Factor ◽  
Sea Floor ◽  
Sea Bottom ◽  
Initial Freezing ◽  
Air Pockets

Abstract The different factors contributing to the formation of the gas porosity of sea ice are: (Ia) gases captured during the formation of the initial ice cover, (Ib) gases released from solution during the initial freezing of sea-water, (Ic) the inclusion of gases rising from the sea bottom, (2a) the substitution of gas for brine drained from the ice during times of melting, (2b) the release of gas from the brine within the ice during the course of partial freezing, and (2c) the formation of voids filled with water vapour during the course of internal melting. An analysis is made of each of these processes and it is concluded that processes Ib, 2a, and 2C are important. Process Ic may also be a major effect but it is difficult to evaluate until the rate of gas release from the sea floor is better known. The migration of air pockets into the ice from the overlying snow is shown to be a possible but not a significant effect. Available data on the composition of gas in sea ice are reviewed and it is shown to be significantly different from air. Possible causes for these differences are discussed. The porosity of sea ice, i.e. the total relative volume of its gas plus its brine inclusions, is one of the factors strongly affecting its strength, as has been shown by Tsurikov (1947) and by Weeks and Assur (1968). In seas with high salinities the effect of the presence of brine within the ice will usually be the dominant factor. However on water bodies with low salinities the effect of the gas included within the ice may be greater than the effect of the brine. Despite its significance there have not been any attempts at a quantitative analysis of the entrapment of gas in sea ice. This paper is an attempt at such a study.

Active and relict sea-floor hydrothermal mineralization at the TAG hydrothermal field, Mid-Atlantic Ridge

1993 ◽  
Vol 88 (8) ◽  
pp. 1989-2017 ◽  
Author(s):  
Peter A. Rona ◽  
Mark D. Hannington ◽  
C. V. Raman ◽  
Geoffrey Thompson ◽  
Margaret K. Tivey ◽  
...  
Keyword(s):  
Hydrothermal Field ◽  
Sea Floor ◽  
Hydrothermal Mineralization ◽  
Mid Atlantic Ridge ◽  
Tag Hydrothermal Field

Generation of metal deposits on the sea floor

1976 ◽  
Vol 13 (1) ◽  
pp. 126-135 ◽  
Author(s):  
B. J. Fryer ◽  
R. W. Hutchinson
Keyword(s):  
Sea Water ◽  
Metal Sulfide ◽  
Base Metals ◽  
Base Metal Sulfide ◽  
Gold Ores ◽  
Sulfide Deposits ◽  
Sea Floor ◽  
Metalliferous Sediments ◽  
Sea Bottom ◽  
Metal Abundances

Recent studies of volcanogenic base metal sulfide deposits and of metalliferous sediments in the Red Sea indicate precipitation of iron and base metals under conditions varying from reducing to oxidizing, at or near sites of fumarolic brine emission onto the sea floor. Differing lithofacies of iron-rich sediments were apparently deposited penecontemporaneously, mainly in response to changing chemical, biological, and sedimentary lithofacies conditions.Iron-rich sediments associated with the cupriferous pyrite bodies of Cyprus have been studied to determine the behavior of Fe, Mn, Cu, Zn, Pb, Ni, Co, Cr, Sn, Mo, Ag, and Au, when these fumarolic brines enter the sea bottom environment. Variations in metal abundances and ratios indicate that rapidly changing Eh is a major factor controlling metal deposition on the sea floor. The Fe/Mn ratio in these sediments is a useful indicator of the amount of interaction of these fumarolic brines and normal oxygenated sea water. Results suggest that zinc, copper, and gold are concentrated in the high Fe/Mn ratio proximal sediments; nickel is concentrated in the low Fe/Mn ratio distal sediments; and lead, silver, tin, and molybdenum are relatively unaffected by oxidation of the fumarolic brine solution by normal sea water.These concepts of sea floor deposition controlling the distribution of metals may also be applicable to other types of stratabound metalliferous deposits, like certain skarn, greisen, and gold ores, heretofore considered to be of epigenetic origin.

MIDDLE DEVONIAN SALT FORMATIONS AND THEIR BROMIDE CONTENT, ELK POINT AREA, ALBERTA

1966 ◽  
Vol 3 (3) ◽  
pp. 263-275 ◽  
Author(s):  
N. C. Wardlaw ◽  
D. W. Watson
Keyword(s):  
Fresh Water ◽  
Surface Runoff ◽  
Middle Devonian ◽  
Sea Water ◽  
Weight Percent ◽  
Downward Movement ◽  
Sea Floor ◽  
Surface Evaporation ◽  
Crystallization Solution ◽  
Cold Lake

The Prairie Evaporite formation, or First Salt, of the Elk Point area contains three types of halite: chevron, clear, and brown. The chevron halite is thought to be primary and to have grown upwards from the Devonian sea floor. The origin of the clear and brown varieties is not known. Where these types occur together, the clear halite has a tendency to contain more bromide than either chevron halite or brown halite. The total range for bromide in halite from the Prairie Evaporite is from 0.004 to 0.02 weight percent (wt.%).The Cold Lake and Lotsberg formations, the lower two salts, consist of clear halite which is so low in bromide (0.0004 wt.%) that it could not have crystallized from sea water, neither could this halite have crystallized from sea water previously saturated by dissolving halite. It is probable that the lower two salts resulted from solution of halite in fresh water, with subsequent crystallization. Solution may have occurred during discharge of meteoric groundwater, while the basin was structurally low, subsequent surface evaporation having promoted crystallization. In this way, salt could have been recycled without removal from the area. Alternatively, surface runoff, and downward movement of surface runoff, may have been important in the recycling of halite.Groundwater in Devonian formations of central Alberta, and spring waters from Devonian formations in Manitoba, are saline and relatively high in bromide (0.001–0.10 wt.% Br). The bromide content cannot be explained simply by solution of halite in meteoric waters. Either these brines are modified remnants of seawater, or else there is some undefined source of bromine causing enrichment.

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