C-horizon Soils Research Articles

Distribution and behaviour of platinum in soils, sediments and waters of the Tulameen ultramafic complex, southern British Columbia, Canada

This paper reports Pt content of surficial media associated with Pt-rich chromitites in the dunite core of the Tulameen ultramafic complex. Platinum content of the −212 μm fraction of soils and sediments was determined by fire assay-inductively coupled plasma spectroscopy. C-horizon soils on dunite colluvium (mean: 24.2% MgO), locally-derived dunitic till (16.5% MgO) and exotic non-dunitic till (5.7% MgO) have median Pt concentrations of 88 ppb, 36 ppb and 8 ppb, respectively. Corresponding medians in ashed LFH horizons are 65 ppb, 13 ppb and 7 ppb Pt. Platinum values of 8–91 ppb are found in sediments from the small stream that drains the area. Stream and bog waters contain less than 1 ppt to a maximum of 2.45 ppt Pt. Geochemical patterns for Pt indicate that glacial transport and mass wasting are the dominant processes that control distribution of Pt in soils on Grasshopper Mountain. There is also some (slight) evidence for very limited hydromorphic mobility of Pt and its accumulation in bogs. During routine exploration geochemical programmes the considerable local variability in soil parent materials and related variations in background concentrations of Pt need to be taken into account in evaluating the significance of Pt values. This requires careful identification of soil parent materials. Soil MgO content provides a useful index of their dunite content for this purpose.

Sorption and mineral equilibria controls on moisture chemistry in a C-horizon soil

A study was made of the chemistry of soil moisture collected over a period of 12 months from sandy loam soils in central Pennsylvania. Samples were taken at depths of from 1 to 9 m by means of suction lysimeters. The prevalent chemical character of soil moisture was generally Ca 2+ > Na + > Mg 2+ ≈ K +, with HCO − 3 > Cl − > SO 2− 4 ≈ NO − 3 on both a mole and weight basis. Soil-moisture pH ranged from 5.20 to 6.74. Dissolved silica averaged 54 mg/l (as SiO 2) and was as high as 117 mg/l. The specific conductance ranged from 20 to 400 μS/cm. Total dissolved solids (TDS) in the water increased with decreasing atmospheric precipitation and increasing temperature. This was due to evapotranspiration, which increased TDS directly, and also indirectly by reducing soil relative permeabilities and increasing the contact time between soil minerals and water. A secondary cause was greater precipitation acidity during the warmer months and during periods of lower precipitation. Soil colloids are predominantly Fe- and Mn-oxyhydroxides, with usually smaller amounts of illite and kaolinite. Total cation exchange capacity is 2–3 meq./100 g. Regression analysis of dissolved-ion activities showed that the aquo-cations are strongly buffered by Donnan equilibrium and selective adsorption with selectivities in the order K + > H + > Mg 2+ > Ca 2+. Calculation of the degree of saturation of the soil moisture with respect to soil minerals showed that the soil moisture is undersaturated with respect to calcite, dolomite, amorphous silica and illite, and super-saturated with respect to quartz and probably also kaolinite. Sorption equilibria controlled major-cation concentrations at all depths in the soil, whereas solution-mineral equilibria did not limit concentrations of these cations.

EFFECTS OF SOIL PREPARATION ON DTPA-EXTRACTABLE ELEMENTS IN SOILS OF THE NORTHERN GREAT PLAINS

Regulatory guidelines in several western states require that diethylenetriamine pentaacetic acid (DTPA) be used as an extracting agent for estimating the availability of several elements in natural soils, reclaimed mine soils, and strip mine overburden. Because different sample preparation methods may result in conflicting analytical results, the effects of different methods of sample preparation are compared for DTPA extraction of cadmium, cobalt, copper, iron, manganese, nickel, lead, and zinc from soil. Samples of A- and C-horizon soils, with known diverse chemical properties, were collected at 21 localities in unglaciated portions of the Northern Great Plains. Each sample was split into three parts. One part was disaggregated to <10 mesh; the second was disaggregated and ground to <100 mesh; and the third was disaggregated and sieved, the <100 mesh portion being retained. The concentration of elements in the DTPA extracts of the samples prepared in these three ways varied by element and by method of preparation. Consistently, for all methods of sample preparation and in both soil horizons, the effect of sample preparation was not significant for nickel; was significant for iron and manganese; and, for cadmium and cobalt, analytical imprecision invalidated the results. Inconsistent results were obtained for copper, lead, and zinc either between methods of preparation or between soil horizons. Significant linear equations relating the various methods were obtained for copper, iron, manganese, nickel, lead and zinc, but, because of poor analytical precision, not for cadmium and cobalt.