关键词: 矽卡岩型矿床, 锆石U-Pb测年, 地球化学, 白石砬子, 钨矿床, 延边地区

Abstract:

Baishilazi skarn tungesten deposit is located in the eastern part of Jiamusi-Xingmeng terrain. The major ore body occurs along the contact zone between the Early Yanshanian quartz diorite and the marble of the Late Paleozioc Qinglongcun Group. The host rock of the ore deposit is dominated by the garnet skarn. Using the LA-MC-ICP-MS single-zircon U-Pb dating method, the authors determined the ages of zircon grains separated from the intrusion, which are mainly from 195 Ma to 205 Ma with an average value of (198.27±0.80) Ma. Both the quartz diorite and its associated ore deposit were formed at the beginning of the Jurassic period. Major element geochemistry is characterized by low SiO₂ (58.07％-58.98％) and high alkaline (5.96％-6.41％), sodium (3.65％-4.84%) and aluminum (15.82％-17.89％). The quartz diorite belongs to the high-potassium and calcium system.  Based on the features of low REE content (90.06×10^-6-122.05×10^-6), high LREE and LREE/HREE ratios and low positive or negative Eu anomalies, it can be concluded that the quartz diorite was derived from the deep-crust source. As the quartz diorite has high Sr and low Yb content and its Rb/Sr and Rb/Ba ratios are similar to those of the primary mantle, it is inferred that the rockforming materials were derived from the deep part of the subduction plate or the thickened lower crust (＞40 km). In the light of geochronology and geochemistry of the Baishilazi intrusion in combination with regional tectonic evidence, the authors hold that both the intrusion and the associated tungsten deposit were formed during the transforming period between the Paleo-Asian tectonic belt and the Circum-Pacific accretion belt and related to the collision and collage of the terrain group represented by Jiamusi and Songnen massifs in the eastern Central Asian Paleozoic orogenic belt.

Key words: skarn deposit, zircon U-Pb dating, geochemistry, Baishilazi, tungsten deposit, Yanbian area