Surficial rocks

Meybeck M (1987) Global chemical weathering of surficial rocks estimated from river dissolved loads. Am J Sci 287 401 —428... 

Element Surficial rock concentration (mg g 1) Soil concentration (mg g 1) Particulate concentration (mg g 1) Dissolved concentration (mg L-1) Particulate load (106 tons y-1) Dissolved load (106 tons y-1) River particulate/ rock Particulate/ (particulate+ dissolved)... 

Table 3 A comparison of the concentration of major elements in average riverine particulate material and surficial rocks...

In Fig. 16.5, the suspended matter composition of the Amazon major tributaries is compared with mean trace element concentration for the varzea (Konhauser et al. 1994), and with the average composition of the surficial rocks exposed to weathering, computed by Martin and Meybeck (1979). Among the major tributaries of the Amazon River, the Rio Solimoes presents the highest concentrations for all the elements studied, with few exceptions POC, Zn, Fe, and Pb concentrations are more elevated in the Rio Negro, Co and Ni are in the same range in... 

Figure 16. 5 Comparison of the trace element suspended matter composition of the Amazon tributaries with the composition of varzea sediments (Konhauser et al. 1994) and average composition of the surficial rocks (Martin and Meybeck 1979)-...

Compared to average composition of surficial rocks, the SPM composition of the Amazon basin rivers shows in a first approximation two types of elements ... 

Heat flow data are not very sensitive to small-scale horizontal variations of heat production and integrate the heat production in the entire crustal column, and hence alleviate many of the sampling problems encountered when using only geochemical data. They are sensitive to heat production in the whole crustal column, including surficial rocks, which may have been affected by late-stage leaching and alteration processes, as well as deeper material which has remained untouched. Eurther, they are sensitive to the deepest crustal levels, which can seldom be sampled. 

Meybeck, M. (1987), Global Chemical Weathering of Surficial Rocks Estimated from River Dissolved Loads, Am. J. Sci. 287, 401-428. 

From numerous reviews (Jackson et al, [1952], Jackson and Sherman [1953], Fieldes and SwiNDALE [1954], Arnold [1960], Keller [1964]), the conclusion can be drawn that— except in soils developed under extreme climatical conditions—a close correlation exists between mica contents of soils and their corresponding parent material. This relation is not only reflected by total mica concentrations or by the lack of micas in soils developed from mica-free rocks, but also by the corresponding particle size distribution of micas in soils and their parent rocks (Lentschig and Fiedler [1967]). In soils developed from parent material free of mica, the concentration and size distribution of micas permit even conclusions concerning the admixture of aeolic or glacial increments. Thus, micaceous minerals in soils on basalt have been related to loess by Schwertmann and Niederbudde [1969]. The mica content of soils on nephelinite and diabase was found to be due to increments of loess from weathered mica schists, being the surficial rock in adjoining areas. This confirms the view that soil micas are mainly detrital in nature. 

V-Surficial, weakly coherent, alluvial deposits readily eroded by water. (Vj-<3 percent slope V2-<12 percent slope). I-Incompetent, or weakly coherent, bedrock such as shales and tuffs readily eroded by water and (or) prone to mass movement on steep slopes (li-<12 percent slope l2->12 percent slope). C-Competent, or strongly coherent, bedrock such as layered lava flow rocks and igneous intrusives not readily eroded by water, nor generally prone to mass movement except for rockslides and rockfalls from very steep slopes and cliffs (Ci-<12 percent slope). 

Bedrock and surficial Geology At Shiko Lake (Fig. 1) a Jurassic complex composed of diorite, monzonite, and syenite intrudes basalt and volcaniclastic rocks. Chalcopyrite, bornite, and gold occur disseminated and in veins mainly within the syenite (Fig. 2). 

From MW17, the ground water flows initially SE beneath the NATA but due to rock outcrops veers N to combine with surface water in the RA. The sediment in this area has been contaminated with As from the surficial runoff from the ARS as well as earlier mining operations. The As in the surface water is then attenuated by ferric (Fe(lll)) oxyhydroxides (HFO) so that by the time it reaches Snow Lake level of As are significantly reduced to <0.005 mg/L. 

In many places on earth, mining companies have already discovered (mostly in the last 50 years) the majority of mineral deposits exposed at the surface. As a result, mineral deposits that have not been discovered are typically buried by some form of surficial material, such as gravel, till or volcanic ash. This exotic cover makes exploration for most buried mineral deposits expensive and difficult, because the chemistry of this overlying material is different from that in the mineral deposits or its host rocks. 

Fyffe, L.R. Pronk, A.G. 1985. Bedrock and surficial geology, rock and till geochemistry in the Trousers Lake area, Victoria County, New Brunswick. New Brunswick Department of Natural Resources Report of Investigation, 20, 74 p. 

Dissimilatory Reduction in Surficial Sediments. Porewater profiles from a number of sites throughout Little Rock Lake show that sulfate is always depleted below the sediment-water interface (Figure 3). Sulfate depletion in porewaters occurs not onlyin the soft gyttja but also in sandy, littoral sites with organic contents < 10%. The observed depletion of sulfate and the occurrence of H2S indicate that the sediments are anoxic immediately below the sediment-water interface and that sulfate reduction occurs in surficial sediments. 

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