Sr-Nd-Pb Isotopic Characteristics and Its Geological Significance of the Jiling Grantic Pluton in the Middle Longshou Mountains

Zhao Yayun; Zhang Shuming; Tang Lin; Yao Hongfu; Yang Chunsi

doi:10.3799/dqkx.2016.084

Abstract：The Early Paleozoic granitic pluton has a closely genetic relationship with the Alkali metasomatism type uranium min-eralization in the middle Longshou Moutains area,which is an important activity zone of Longshoushan granitic magma.How-ever,people do not know more about the cause of Jiling rock mass,properties of magma source area and the relationship between Jiling rock mass and uranium mineralization.The Sr-Nd-Pb isotopic composition characteristics of granitic pluton show that the initial Sr isotope ratios (87 Sr/86 Sr)i of granite in different periods (with first intrusion of gray monzonitic granites in the Early Paleozoic,the pink monzonitic granites of the second intrusion,and pink fine-grained (potassium)granites of the intru-sion in Late Paleozoic )fall in the range of that of the continental crust (from 0.706 to 0.718);at the same time,the average initial Sr isotope ratios (87 Sr/86 Sr)i has a trend of falling after rising (0.707 12→0.710 00→0.707 89),and the average ofεNd(t)shows the trend of rising after falling (- 7.00→ -8.09→ - 4.65).tDM2 average of granites in different periods is 1 735.50 Ma,1 814.66 Ma and 1 737.50 Ma respectively,which is very close to the age of residual crust,indicating that the main material source of the granitic pluton should be the group strata of paleoproterozoic Longshou mountains,with the addition of mantle or young crustal materials.Its Pb Isotope ratios are high:206 Pb/204 Pb range from 18.328 to 19.240,207 Pb/204 Pb range from 15.549 to 15.619,208 Pb/204 Pb range from 38.390 to 39.075,μ values range from 9.37 to 9.43,with an average of 9.40,206 Pb/204 Pb range from 30.209 to 43.529,207 Pb/204 Pb range from 16.097 to 25.076,208 Pb/204 Pb range from 39.107 to 39.42,μ values range from 18.47 to 30.24,with an average of 9.40;206 Pb/204 Pb range from 19.071 to 19.767,207 Pb/204 Pb range from 15.577 to 25.438, 208 Pb/204 Pb range from 38.682 to 42.593,μvalues range from 9.36 to 9.49,with an average of 9.41.All samples show high radioac-tive Pb isotopic characteristics with a mixed source,but the crust is the main source.The comparison of Sr-Nd-Pb Isotope shows that the initial Sr isotope ratios (87 Sr/86 Sr)i andεNd(t)of sodium metasomatic rock (ore)are very similar to those of pink monzonitic gran-ites of the second intrusion in the Early Paleozoic,and the subpoint of (87 Sr/86 Sr)i-εNd (t)diagram is also consistent,which indicates that alkali metasomatism type uranium mineralization of the study area is mainly related to the second invasion in Early Paleozoic.The high uranium background values of granitic pluton in other periods show that it may also provide a source of uranium.