Pirkko-Liina Elomaa

Suokasvillisuuden ja tupeen käytöstä malminetsinnässä

Elomaa P.-L. Suokasvillisuuden ja tupeen käytöstä malminetsinnässä.

Tiivistelmä

This paper deals with the mineral exploration with the help of mire vegetation, its trophic level (geobotanic) and peat chemistry (biogeochemistry). The study area (Fig. 1) consists of 1. aeroelectrical anomaly zones (6970 ha), where the bedrock potentially contains limestone or skarnrocks with zinc ore, but is without outcrops and covered by peatlands and 2. some granite (1170 ha), quartz diorite (240 ha), gabbro (1210 ha) and amphibolite (270 ha) regions for comparison. The so called calcium influence of differed clearly from others having meso-through the peat. The anomaly region differed clearly from others having meso-and eutrophic mire types 37 % of the area. On amphibolite base there were 15 % and on gabbro base 12 % of rich mire types. Neither granite nor quartz diorite regions had mire types above mesotrophic level, the corresponding percentages being 9 and 4 (table 2). Some properties of peat were measured from 228 surface peat samples, (5—10 cm below the surface, from the first slightly humified peat layer) and from 236 borer samples through the peat horizon (106 points). The correlation analyses (Table 4) and t-tests (Table 3) certified that pH, conductivity, ash and Ca content of peat indicate the trophic level of a mire type and that the type is influenced by the bedrock. Plant species and mire types they form can thus reliably be used as measurement for the nutrient status of mire and peat. The distribution of Ni, Cu, Zn and Pb were studied. The vertical distribution of those heavy metals and Ca resembled more or less the letter c (fig. 2 and 3). The minimum contents were generally in the middle layers, about 150 cm from the bottom of mire, where the correlation (table 4) between the measured properties were also weakest. Ni contents in the surface peat were very significantly positively (+ + +) correlated to the trophic status of mire vegetation. Rich, mire-margin effected types got the greatest values. Ni was the only metal which had a very significant correlation with Ca in the surface and in the bottom layers. The correlation analyses did not show any meaningful relationships between Cu contents and other parameters except for the ash content in 50 cm layer from the bottom and other metals. The highest individual contents in the surface peat were analysed from the samples of meso- and eutrophic types with mire-margin effect. Zn distribution was the most irregular. It has significant correlation only with Cu and Pb. Zn content had sharp variations in peat profiles. The maximum contents were often in the surface peat of oligotrophic types. Pb had a very clear maximum value on the surface peat. In this material, which contains a great amount of samples from the area probably with skarn ore, Pb had a very significant correlation to ash and other heavy metals in the surface. The correlations declined and disappeared in intermediate layers but came out as significant with Ca, Cu and Zn at the bottom. In general the highest contents in surface were often analysed on mire-centre-effected types as with Zn, too. Classifying and mapping vegetation is a useful method before all when locating limestone and skarnrock deposits. It has to be remembered that mire types reflect the bedrock in accordance with the characteristic nutrient situation. The peat of mire-margin effected type might have importance being an accumulator and binder of nutrients and heavy metals coming from the nearest surroundings of the mire. The minerotrophic types with mire-centre effect reflect very locally the mineral soil and bedrock below the mire and are suitable for mineral exploration. When prospecting heavy metals on areas without outcrops of bedrock and covered with peatlands the peat chemical method can be used in connection with other methods like geophysical and -chemical ones. Also then it is relevant to take into account the information given by plants and vegetation units. The results published of the vertical distribution of heavy metals do not always agree and the pnenomenon has to be studied in more detail. One has to consider, also here, the effect of mire characteristic nutrient status (mire-margin and -centre effect). Investigating both vertical and horizontal distributions of heavy metals in peat of different mire types we get, as I understand, important information for mineral exploration. This information would also greatly help to plan a well serving peat sample collecting.

Vastaanotettu 31.10.2017 Julkaistu 1.1.1981

Katselukerrat 1131

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