نویسندگان
1 گروه زمینشناسی، دانشکده علوم، دانشگاه ارومیه، ارومیه، ایران
2 گروه مهندسی معدن، دانشگاه صنعتی ارومیه، ارومیه، ایران
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
The Nakhlak lead-zinc deposit is located about 55 km northeast of Anark city, Isfahan Province, Central Iran Zone. This ore deposit is hosted by Upper Cretaceous carbonate rocks. Mineralogical studies show that calcite and dolomite in these carbonate rocks are accompanied by minerals such as quartz, plagioclase, kaolinite, smectite, illite and hematite. Based on the values of CaO/MgO ratio (1.51-18.29), the studied carbonate rocks are composed of dolomitic limestone and calcitic dolomite. The contents of rare earth elements (REE) in the carbonate rocks ranged from 8.67 to 21.30 ppm, which is more than the range of marine carbonates (0.4-14 ppm). The distribution pattern of REE normalized to Post-Archean Australian Shale (PAAS) show depletion of LREE compared to HREE and occurrence of negative Ce anomaly (Ce/Ce* = 0.72-0.89) and negative to positive Eu anomaly (Eu/Eu*= 0.96-1.68) in the studied samples. The detrital origin of lanthanides in the studied carbonate rocks in the Nakhlak can be inferred from positive correlations between LREE with Th, Y and Nb
(r = 0.76-0.86) and positive correlations between HREE with SiO2, Al2O3, TiO2, Ga, Th, Y, Nb, V , and Cu (r = 0.60-0.95) along with negative correlations between CaO with LREE (r = -0.32) and HREE (r = -0.77). Changes in geochemical ratios such as Y/Ho (23.16-47.14) and Er/Nd (0.11-0.28) support this interpretation. Mineralogical evidence and geochemical studies show that the changes of Ce anomaly and the occurrence of positive Eu anomaly are related to the amounts of detrital materials and the presence of plagioclase in the studied carbonate rocks, respectively. The correlation coefficients between REE with P2O5 and Ce/Ce*, Eu/Eu* with Ce/Ce*, Nb, Th, Y, and Zr, also Mn with Sr indicate the lack of influence of post-depositional processes in changing the amounts of lanthanides in the studied carbonate rocks.
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