科研之友
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摘要
Luzong ore district located at northern margin of Yangtze block is one of important iron-copper polymetallic ore districts in the middle-lower Yangtze river metallogenic belt. The porphyry-type iron and copper deposits are the dominant types in Luzong ore district. Recently, several medium-sized lead-zinc-copper-gold deposits, which are genetically related with regional magmatic intrusive rocks, are discovered in Huangtun area, the northern margin of Luzong Basin, Anhui. Petrological observations, LA-ICP-JVIS zircon U-Pb dating and geochemical analysis were carried out for intrusive rocks in Huangtun area with the aims to determine the temporal framework of magmatic intrusions and to reveal the magmatic evolution process. Huangtun dioritic porphyrite, Yueshan monzonitic and Jiaochong syenitic intrusive rocks form at 135. 0-134. 4, 132. 7-132. 1 and 131. 5-129. 6 Ma, respectively, which belong to the products of intrusive magmatism at the end of Zhuanqiao volcanic cycle in Luzong Basin. The intrusive rocks in Huangtun area are characterized by high SiO2(mean content is 61. 67%), Al2O3(16. 95%), alkaline (10. 25%) and low TiO2(0. 66%), enriched in large ion lithophile elements such as Rb, K as well as light rare earth elements, and depleted in high strength field elements such as Nb and Ta. Geochemical features suggest that the intrusive rocks belong to typical shoshonite series. Combined with Sr-Nd isotopic compositions, the primary magma is probably derived from enriched lithospheric mantle of Yangtze block. Geochemical variations reveal that fractional crystallization controls the evolution process of the magma, during which the fractionation of hornblende dominates the differentiation from diorite to monzonite, and plagioclase dominates the fractional crystallization from monzonite to syenite. ? 2020 Chang'an University.
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