Chlorite and epidote chemistry of the Yandong Cu deposit, NW China: Metallogenic and exploration implications for Paleozoic porphyry Cu systems in the Eastern Tianshan

Three periods and six alteration and mineralization stages were identified at the Yandong Cu deposit, i.e., Porphyry period (including Stage I: Propylitic alteration; II: Quartz-magnetite alteration; Ill: Phyllic alteration); Superimposed period (including Stage IV: Superimposed mineralization and V: Late vein) and Supergene period (Stage VI: Supergene mineralization). Stage IV chlorite contains lower SiO2, MgO, Cr, Ni, Co, B, Ca, Sr, but higher FeO, Al2O3, Sc, Ga, Sn, Ti, Zn and Mn than Stage I chlorite. Stage IV epidote contains lower Zr, Ba and Ti, but higher Sn, Y, Ga, Ag, U, and Sr than Stage I epidote. Concentrations of Ti, Zn, As, V, Sc and Cu are highest near the orebody for both Stage I and IV chlorite. Titanium content of Stage I epidote is highest near the orebody, but V, Sc and Zr are lowest there. Stage I chlorite is geochemically similar to the Batu Hijau porphyry deposit, but Stage IV chlorite contains higher Fe, Al and As, lower Mg and Sn than the latter. Stage I epidote is geochemically similar to the Baguio porphyry and skarn deposits, but Stage IV epidote has higher Sn, Ga and U, but lower Zr, Ti and Ba than the latter.