Discovery of the Xileketehalsu porphyry copper deposit on the southern margin of the Altay copper metallogenic belt

Abstract： The Xileketehalasu copper deposit is situated on the southern margin of the Altay copper metallogenic belt, i.e., inside the original Kalaxiangeer porphyry copper belt. The preliminary study and drilling have revealed that copper orebodies are completely controlled by quartz diorite porphyry and granodiorite porphyry. The ores have veinlet and veinlet-disseminated structures. Chalcopyrite and pyrite are dominant metallic minerals with minor magnetite, bornite and specularite. Magnetite formed earlier than chalcopyrite, suggesting relatively highly oxidized magma. Its mineralization and alteration zoning essentially resemble those of typical porphyry copper deposits. K-feldspar, biotite, silicate, and pyrite alteration zones occur within the porphyry, and the quartz-sericite alteration zone is distributed in the contact between the porphyry and its wall rocks, whereas the propylitic zone occurs in the country rocks. The geochemistry of the mineralized porphyry characterizes adakite： high SiO2 (63%-66%) and Al2O3 (15%-17%), enrichment in Sr (378×10-6-447×10-6）, no negative Eu anomalies, depletion in Y（10×10-6-14×10-6）and Yb (1.3×10-6-1.5×10-6, and low initial Sr isotopic value (0.70439), high (εNd)t values (+6.9-+8.2) and low δ18OV-SMOW （<10‰）. The Rb-Sr isochron age for the porphyry is 332.8±8.5 Ma, belonging to Early Carboniferous. Its petrogenesis is related to partial melting of oceanic crust due to southward subduction of the Mongolian ocean plate. Therefore, its metallogenic geological setting is very similar to the famous supergiant porphyry copper deposits in the world. In addition, there are some copper occurrences with similar features in the surrounding areas of the deposit. Therefore the area has good ore prospects and is another potential porphyry copper belt in China.