GENESIS AND METALLOGENIC MODEL FOR GUANFANG COPPER DEPOSIT IN SOUTH LANCANGJIANG BELT, WESTERN YUNNAN PROVINCE

The Guanfang copper deposit is a new prospecting ore deposit in the south Lancangjiang magma tectonic belt, Yunxian, Yunnan. In this paper, geological and geochemical characteristics of the ore deposit are studied in detail, and its genesis and material source and metallogenic model are discussed on the basis of trace elements, fluid inclusions and isotopes of the copper ores and ore-bearing rocks. Copper mineralization is closely related to silicification and pyritization. The major oxides of basaltic volcanic rocks of Xiaodingxi Formation belong to high-potassium calc-alkali basalt-shoshonite series. The REE distribution pattern of the ore-bearing rocks is slightly right-oblique in orientation, with an average ∑REE of 173.81×10 -6 and the Eu element being non- or slightly negative-abnormal in terms of abundance, here the pattern is obviously different from that of the ore. In the primary mantle-normalized trace element distribution pattern diagram the ore-bearing rocks show enrichment of K, Rb, Ba, Th and depletion of Ti, Y, Yb, Cr, which is in conformity with the features of arc-volcanic rocks on the continental margin. The orebodies are strictly controlled by the faults that radiate toward the outside and the lithologic characters of the volcanic rocks. The sulfur isotope composition of the main sulfides is within the range of -11.88‰～ -5.67‰ δ 34S V-CDT. Oxygen and hydrogen isotopic analyses and characteristics of inclusions indicate that the ore-forming fluid of the ore deposit is of hybrid type that is composed of magma water and meteoric water. Geological and geochemical characteristics indicate that Guanfang copper deposit is hydrothermal Cu ore deposit that is of genetically low to medium Temperatureeratures and formed in a relatively open system and related to the magma activity of concealed rock bodies, with ore-forming materials being derived from the lower crust and upper mantle.