The Cretaceous Porphyry Au (Cu) Metallogenic System In The Jinchang Area,Heilongjiang Province,China

The Jinchang Cu-Au ore field in the easternmost portion of the Central Asian Orogenic Belt (CAOB) is one of the major gold ore field in eastern China. The deposit has a metal reserve in excess of 76 tons of Au with an average ore grade of 11.34g/t and 4,683 tons of ton with an average ore grade of 1.44%. Studied on metallogenic dynamics, magmatic evolution and geological of the Jinchang deposits field, this paper presented the Cretaceous porphyry Au (Cu) metallogenic system in the Jinchang area and obtained the following conclusions.1. The mineralization was closely related to the Late Yanshanian porphyritic intrusions in Jinchang area. The sequence of magmatic activity of the Jinchang ore field has went through Late Indosinian and Late Yanshanian. Re-Os isotope age of auriferous pyrite yield a model 1 isochron age of 114+2 Ma, which reveals the direct timing of gold (copper) mineralization shown that the Late Yanshanian porphyritic intrusions closely related to the Early Cretaceous subduction of the Pacific plate (120-110Ma).2. The Late Yanshanian porphyritic intrusions in Jinchang area are the direct prospecting signs. Through studies on trace elements and REE patterns of porphyries from the Jinchang ore field, the author proposes that the Late Yanshanian porphyries were mainly derived from the mantle and are the product of the interaction of crust and mantle. Since the diorite porphyry was formed (118-115Ma) earlier than the granite porphyry (113-109Ma), there are less significant crust characteristics on the patterns of diorite porphyry. The ore-forming materials mainly derived from the crust.3. The Jinchang Cu-Au ore field is a porphyry metallogenic system including granite-porphyry Au-Cu deposits and diorite-porphyry Cu-Au deposits. Trace element patterns and REE patterns of the ores and the pyrite related to the mineralization from the Banjiegou granite porphyry deposit are similar to contemporary granite porphyry indicating their genetic links. This is the same to the Gaoligou diorite porphyry deposit. Also it reveals a cognate magma evolution series. Fluid inclusions in samples from granite porphyry ores have lower homogenization temperature and salinity than that from diorite porphyry ores. That means the ore-forming pressure of the diorite porphyry metallogenic series is higher than the granite porphyry metallogenic series and the ore-forming depth is deeper than the granite porphyry metallogenic series. That indicated that cooper mineralization is more likely formed in a high temperature with alkaline fluid.4. The author proposed a Late Yanshanian porphyry Au (Cu) metallogenic system in the Jinchang area and also conclude that more copper and gold exist in the lower part of porphyry deposits. The system including the breccia pipes orebodies in the shallow and the porphyry orebodies in the depth of the system. All the porphyries belong to the comagmatic evolutionary series with a high exploitation potential. This model also can be used in other porphyry deposits like Jinchang ore feild.