矿床地球化学国家重点实验室知识库

SIMS U-Pb zircon ages for rhyolite porphyries, and geochemical and Nd isotopic data are reported for rhyolite porphyries and the related basalts from the Songjiapo Formation of the Mink copper deposit of Yunnan Province, SW China. The aims are to constrain the origin and petrogenesis of these rocks. The basalts are commonly high in Fe(2)O(3), Al(2)O(3) and Na(2)O contents. In the Harker diagrams, MgO, CaO and P(2)O(5) contents of the basalts decrease with increasing Sit), contents. These rocks with high epsilon(Nd) (t) values (+2. 9 similar to +3. 5), are characterized by relatively low total REE contents (50. 1 x 10(-6) similar to 60. 6 x 10(-6)) with relatively flat REE patterns in the chondrite-normalized diagram and with slightly negative Nb-Ta and positive Sr anomalies in the primitive-normalized spidergram. The parental magma for the basalts exhibits affinity with a sub-alkaline basaltic magma generated by melting of a depleted, plagioclase-rich and garnet-free mantle source in the spinet field. It is suggested that the basalts originated by fractional crystallization of the parental magma plus varying degrees of crustal contamination. Cameca SIMS zircon U-Pb dating indicates that the rhyolite porphyries were emplaced at 234. 8 +/- 2. 4Ma. These rocks have high SiO(2), (Na(2)O + K(2)O) and Al(2)O(3) contents compared with the normal rhyolites, and are enriched in LREE and show relatively flat HREE patterns with slightly negative Eu anomalies in the chondrite-normalized diagram and significantly negative Nb-Ta, Sr, P and Ti anomalies in the primitive mantle-normalized spidergrams. The rhyolite porphyries display geochemical characteristics of I-type granites and exhibit variably initial epsilon(Nd) (t) values ranging from -1. 9 to -0. 51. The parental magma for these rocks exhibits affinity with a mildly alkaline intermediate to felsic magma, which was probably generated by partial melting of the regional Mesoproterozoic to Neoproterozoic mafic to intermediate lower crust and thereafter mixed with small amounts of the Middle Triassic basaltic magmas. The rhyolite porphyries were then formed by extensive crystal fractionation of the mildly alkaline magma. The basalts and the rhyolite porphyries from the Minle copper deposit display the characteristics of arc volcanic rocks, which possibly formed in a late-collisonal to post-collisional environment.