الگوی پراکنش فلزهای سنگین در رسوبات آبراهه‌ای خاور و جنوب‌خاور معدن انگوران، باختر زنجان

به‌منظور ارزیابی آلودگی‌های زیست‌محیطی فلزهای سنگین در آبراهه‌های خاور و جنوب‌خاور معدن روی سرب انگوران، نمونه‌برداری از رسوبات آبراهه‌ای در 77 ایستگاه انجام شد. نتایج تجزیه‌وتحلیل نمونه‌های یادشده نشان دادند مقدار میانگین محتوای آرسنیک، آنتیموان، کادمیوم، سرب و روی در این نمونه‌ها به‌ترتیب برابر با 89.81، 6.67، 10.46، 659.83 و 1189.32 گرم در تن و در اکثر ایستگاه‌ها بیشتر از میانگین پوستۀ قاره‌ای بالایی است و غلظت کبالت با مقدار میانگین 18.69 گرم در تن در بیشتر ایستگاه‌ها کمتر از میانگین پوستۀ قاره‌ای بالایی است. بررسی همبستگی عناصر مطالعه‌شده نشان داد همبستگی مثبت متوسط تا بسیار قوی بین عناصر سرب، روی، کادمیوم، آنتیموان و آرسنیک وجود دارد و کبالت با عناصر دیگر همبستگی ندارد. بررسی نقشه‌های پراکنش عناصر، شاخص غنی‌شدگی و شاخص زمین‌انباشت نشان داد بیشترین غنی‌شدگی و آلودگی در محدودۀ مطالعه‌شده به عناصر سرب، روی، آرسنیک، آنتیموان و کادمیوم مربوط و به‌ویژه در بخش‌های شمالی و شمال‌خاور (حوضۀ آبریز الله‌لوچای) متمرکز است. داده‌های به‌دست‌آمده نشان دادند بی‌هنجاری‌های عناصر سرب، روی، کادمیوم، آرسنیک و آنتیموان هم‌پوشانی بسیار زیادی باهم دارند. تحلیل داده‌ها و بررسی ارتباط آنها با زمین‌شناسی منطقه گویای اینست که بخشی از منشا عناصر مطالعه‌شده، طبیعی (زمین‌زاد) و درارتباط‌با کانی‌سازی‌ها، دگرسانی‌ها و واحدهای سنگی منطقه است، ولی وجود فعالیت‌های استخراجی در معدن روی سرب انگوران سبب افزایش غلظت فلزهای سنگین و ورود آنها به آب‌های سطحی منطقه و گسترش تمرکز عناصر یادشده در شمال‌خاور منطقه و حوضۀ آبریز الله‌لوچای شده است.

Distribution Pattern of the Heavy Metals in Stream Sediments at the East and Southeast of Angouran Mine, West of Zanjan

Abstract In order to assess the concentrations of heavy metals in stream sediments of eastern and southeastern drainages of the Angouran ZnPb mine, stream sediment samples were selected from 77 stations. Results of samples analysis demonstrate that concentrations of As, Sb, Cd, Pb and Zn are higher and Co is less than the averages of upper continental crust in most stations. The elements correlation analysis indicates that there are intermediate to very strong positive correlations between Pb, Zn, Cd, Sb and As, and Co has no correlation with other elements. Investigation of distribution maps, enrichment factor and geoaccumulation index demonstrate that the highest enrichment and pollution in the study area related to Pb, Zn, Cd, Sb and As which are concentrated at the northern and northeastern parts of the study area (AllahlouChay catchment). Investigation of the relationship between the obtained data and geology of the study area demonstrates that the origin of these elements concentrations are geogenic and related to mineralizations and alterations. Exploitation activities at the Angouran ZnPb mine caused increasing the concentration of heavy metals and their entry into the surface waters which with the result of expansion of mentioned elements to northeast of study area and AllahlouChay catchment.    Keywords: Stream sediment, Heavy metals, Spatial distribution, Geoaccumulation index, Angouran.   Introduction Heavy metals are one of the most important soil contaminants which are naturally present in the soil, but large amounts of these metals are the result of human activities like mining, transportation, disposal of industrial wastewater, improper disposal of wastes and use of chemical fertilizers and pesticides (Rahimpour and Abbaspour 2014; Zare Khosh Eghbal et al. 2012). Seasonal rivers during heavy rains transfer contaminated sediments and mineral waste from adjacent mines to downstream areas and cause heavy metal dispersion. As such, studying stream sediments is one of the best ways to assess pollution. Angouran ZnPb mine is one of the mines that due to a large volume of extraction and mineral production has produced a lot of waste around the mine. These wastes, in turn, can cause many problems for the environment around the mine. In this study, an attempt was made to evaluate the role of mining in the environment by investigation of heavy metal concentrations in the stream sediment samples of the rivers at the east and southeast of the Angouran ZnPb mine (AllahlouChay and Kakaroud catchments).   Materials and Methods In order to evaluate the environmental contamination of heavy metals at the eastern and southeastern catchments of Angouran ZnPb mine, 77 samples were selected from intended stations. In this stage, about 500 gr of stream sediments from a depth of 515 cm was selected from each station. After crushing and milling the samples, the obtained powders were dissolved by the four acid solutions and were analyzed by the ICPOES at laboratories of Geological Survey of Iran. The studied elements in this research include As, Sb, Cd, Pb, Zn and Co. After receiving the analytical results from the laboratory, the data were processed statistically. For this purpose, statistical parameters such as the mean, median, mode, standard deviation, skewness, Kurtosis, range, minimum and maximum were analyzed for the 6 mentioned elements using SPSS 22 software. Furthermore, KolmogorovSmirnov test was used to examine the distribution of the normality of data. In the absence of normal data, the logarithm transformation method was used to normalize the data. In order to determine the level of stream sediments contamination to heavy metals in the study area, the enrichment factor and the geoaccumulation index were used. To survey elements distribution maps, interpolation of reverse weight weighting and pixel estimation were employed.   Discussion of Results & Conclusions Evaluation of normality of data indicates that except for the cobalt, the other elements do not have a normal distribution. The results of sample analysis demonstrate that concentrations of As, Sb, Cd, Pb and Zn are higher and Co is less than the average of upper continental crust in most stations.  The results of correlation between the elements indicate that Co has no correlation with other elements while others show moderate to strong positive correlations with each other. The element distribution maps in the study area demonstrate that the elements anomalies mainly locat in the northern and northeastern parts. Furthermore, these maps show that anomalies of Pb, Zn, Cd, As and Sb have an overlap with each other. The enrichment factor investigations indicate that the highest enrichment is related to Pb, Zn, Cd, As and Sb located on northeastern and eastern parts of the study area (AllahlouChay catchment). Moreover, in terms of geoaccumulation index, Cd, As, Sb, Pb and Zn caused the pollution of most parts of the study area especially the northeastern and eastern parts (AllahlouChay catchment). In general, the analysis of the result of samples from stream sediments of the study area demonstrates that the origin of investigated elements is partly natural (geogenic) and related to mineralizations and alterations. But, exploitation activities in Angouran ZnPb mine, weathering of ores and leaching of soils and waste damps led to increasing the heavy metals concentrations and their entrance into the current waters. This led, in turn, to expansion of heavy metal concentrations to other parts of the study area far from the mineralized region (northeastern part and AllahlouChay catchment). These data are in agreement with the  results of Ghadimi and Nabatian (2014) showing that the water of catchments in upper levels of Angouran ZnPb mine show no pollution for Pb, Zn, As and Cd, while by crossing the mining site they become polluted because of these elements.