Abstract:

The Chengchao iron deposit is the largest skarn iron deposit in the southeastern Hubei ore cluster, but the genesis of the intrusive rocks is poorly constrained. In this contribution, mineralogy, geochemistry and Sr-Nd-Pb isotope of different type intrusive rocks have been studied. The biotite in the granite, quartzmonzonite porphyry and diorite is high in Mg contents, indicating that they derived from the mixture of mantle and crust material. The oxygen fugacity of the primary biotite in the granite and quartzmonzonite porphyry associated with the iron mineralization is high, indicating that the granite and quartzmonzonite porphyry are more favorable for the iron mineralization. Different types of intrusive rocks dominantly exhibit high K₂O content and metaluminous, and characterized by enrichment in the large iron lithophile elements(e.g. Rb, Ba and K) and light rare earth elements, and depletion in the high field elements(e.g. Nb,Ta and Ti).They have moderately high initial Sr((⁸⁷Sr/⁸⁶Sr)_i=0.705 0-0.709 1) and negtive ε_Nd(ε_Nd(t)=-14.16--6.95), and ratios of ²⁰⁶Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb are 17.636-18.919, 15.451-15.613, 37.833-39.556 respectively. Viewed comprehensively from mineralogical characteristics of minerals in and geochemical and Sr-Nd-Pb isotopic features of intrusive rocks, it can be concluded that the intrusive rocks in the deposit are originated from the partial melting of an enriched mantle source, and then followed by significant contamination of the lower crust material during the evolution of magma. 140 Ma diorite probably contains more mantle components than the granite and quartz monzonite porphyry of 128 Ma. The average zircon saturation temperatures in the granite and quartz monzonite porphyry are 783℃ and 788℃, respectively, similar to that for the diorite(765℃).

Key words: Chengchao skarn iron deposit, mineralogy, geochemistry, Sr-Nd-Pb isotope, southeastern Hubei Province