Metallogenic Epoch And Its Geodynamic Significance Of The Jinchang Gold Deposit, Heilongjiang Province

The gold deposit of Heilongjiang Province was discovered in the 1990s, which is one of the typical epicontinental super-large hydrothermal ore deposits in Chinese northeastern part. Jinchang gold deposit is located in the edge of embossed belt between Zhang guangcai ridge and Taiping ridge. Quite a few scholars have done a great deal of research about this deposit since 1960s. Until the end of 2009, they have discovered altogether 17 ore bodies and obtained the grand total volume of explored resources amounting to 63406 kg on this area which has tremendous ore-prospecting potential.There are exposing basal rock-series of Huangsong group of neo-proterozoic, medium light Metamorphic Rock, volcanic sedimentary rocks of mesozoic and terrigenous clastic rock of quaternary as well as the intrusive rocks including quartz-diorite, granodiorite, coarse grain bunshox granite, granite and so on, in addition to hypabyssal rocks such as granite-porphyry, dioritic porphyrite,etc in this deposit. Northeasterward Suiyang big fault controls the skeleton of the fault structure which is relatively developed. According to the trend, the fracture can be divided into four groups:①NE-NNE trending compression and scissor fracture and compressive fracture;②NW trending tensional and scissor fracture and tensional fracture;③SN trending compressive fracture and compression and scissor fracture;④EW trending tensional fracture and tensional and scissor fracture. The fold of this area is developed Taiping ridge anticlinorium which is NE trending and stretches throughout the whole area for hundreds of kilometers. The fold has been divided into three parts because of being affected by the fracture of SN and NW trending fracture.There are mainly three mineralization types in Jinchang deposit orebody: hydrothermal breccia type, annular radial fracture filling type and magmatic fornix type. Six oredbodies of hydrothermal breccia type account for 41% of the total resources, about 26 orebodies of relatively large-scale fractrure filling type account for 39%, and 20 orebodies of magmatic fornix account for 20%. The law of space distribution of these orebodies is obvious.According to occurrence of gold orebody, mineralized altered combination and intercalating relationship between each other, the metallogenesis of Jinchang deposit is divided into earlier Yanshanian period, mid-advanced Yanshanian period and surface oxidation period. It is supposed that gold deposit mineralization in earlier Yanshanian period is related to granite-porphyry, and gold mineralization in mid-advanced Yanshanian period is mainly controlled by intrusive activity of dioritic porphyrite. Late mineralization period is composed of surface oxidation and showering and filtering.The research result of major elements, trace elements and rare earth elements in this deposit indicate that the type of granite is S type of granite, and the rock mass belongs to peraluminous, high potassium calcium alkaline and even shoshonite series. The S type of granite has main petrological characteristics of post-orogenic magatism, and is closely related to effect of postorogenic extension.The result of LA-ICP-MS zircon U-Pb dating shows that Qiongbangzi Ditch No.Ⅰore body formed in the Cretaceous period ((109.0±2.4) Ma), and that Gaoli Ditch No.0 ore body formed in the Jurassic period ((192.8±5.8) Ma). It manifests that the emplacement age of quartz is 191.4±6.7Ma in conduit ore-bearing wall rocks of Gaoli Ditch No.0 ore body which belongs to the products of magmatic activity in the earlier Yanshanian period. The granophyre of Qiongbangzi Ditch which belongs to the products of magmatic activity in the mid-advanced Yanshanian period formed in 109.0±2.4Ma. It reflects the multi-phase and multi-stage metallogenic characteristics in Jinchang deposit.According to the summarization of previous studies and the conclusion of this research, the primary understanding on Jinchang metallogenic epoch has been made: there are at least two important metallogenesises in the mining area. The gold metallogenic epoch of Qiongbangzi Ditch No.Ⅰore body is consistent with that of Wulaga, Dongan,Shabaosi gold deposit in the right bank of Heilongjiang Province. The gold metallogenic epoch of Gaoli Ditch No.0 ore body is approximately consistent with that of polymetallic deposit such as Cuihong Hill, Luming, Huoji River, Qianjin East Hill, etc in Xiaoxing'an mountains-Zhangguangcai mountains metallogenic belt. The formation of Qiongbangzi Ditch No.0 ore body is closely relevant to the effect of the Pacific plate subduction. The formation of Qiongbangzi Ditch No.Ⅰore body is possibly related to the tectonic setting characterized by the extension and strike-slip fault in Xiaoxing'an mountains-Zhangguangcai mountains area.