Biogeochemical Selectiveness of Cedars Over Metamorphic Rocks of the Escambray Complex, Sancti Spiritus, Cuba.
Description
Cedars (Thuja L), growing in well-developed alluvium overlying Cretaceous metamorphic rocks from the Escambray Complex, were sampled to determinate whether concentrations of copper and other pathfinder elements in plant tissue were related to ore in the studied sector. These results are compared to those obtained from a soil sampling using the same grid as for the biogeochemical sampling. At each sampling point, leaves, flowers, and the end of young branches were sampled. The main elements concentrated on cedars are lead (65%), silver (24 %), and copper (8%), which are elements directly related to the studied pyrite-copper outcrop. Soil samples chiefly concentrate molybdenum (81%), which is not a pathfinder element for this type of ore. Accordingly, to the results of the degree of contrast of the different anomalies, the best material to be sampled are the ends of young branches. However, also the flowers and the leaves from cedar give better result than the soil sampling. A compound sample of branches, flowers and leaves is also recommended for sampling. Since the biogeochemical sampling is more effective, and it reduces the overall quantity of samples, it is recommended to introduce this method, although more experimental work should be done to improve the quality of the interpretation. These results are also a demonstration of the effectiveness of biogeochemical samplings in tropical environments.
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3. Method 3.1 Sample collection The most frequent type of tree in the area is a variety of cedar. We used a sampling grid of 500 x 100 meters in an area of 1,6 square kilometers, which has a pyrite-copper outcrop near to its center. This grid gives us a total of 32 sampling points. At each of these sampling points, we took a sample from leaves, flowers, and from the end of young branches. A soil sample was also taken, to compare results. 3.2 Sample preparation and analysis The initial weights of the tree's samples were 200 grams. After ignition in an open oven, we obtained near 10 grams of ashes. They were analyzed for Pb, Ag, Mo, Cu, and Zn in an Atomic Absorption Spectrometer. Soil samples were taken at a depth of 0.2 meters, nearly the sampled tree. Each soil sample weighted around 200 grams. After been Sun-dried, they were pulverized and sifted at -200 Mesh, and then analysed for the same set of elements. Sampling took place very early in the morning, and before midday, the samples were sent to the laboratory and processed during the same day. The entire sector was sampled in two days.