Geochronology, geochemistry, and petrogenesis of the Dongshadegai K-feldspar granite in the northern margin of the North China Craton, China: Implications for Indosinian magmatism and related Au mineralization

As representative examples of alkaline magmatism and related mineralization in the northern margin of the North China Craton, the gold deposits within the Hadamengou Au-enriched region are dominated by K-feldspar-quartz vein-type gold mineralization. In contrast, the Dongshadegai pluton in the northern part of this region mainly consists of K-feldspar granite. In this study, we determined the U-Pb zircon age of the Dongshadegai pluton (236.0 +/- 2.7 Ma), indicating that this pluton was produced by middle Indosinian magmatism. The Dongshadegai pluton are characterized by high concentration of SiO2 (70.4-72.5%), K2O (K2O/Na2O=1.12-1.25) and total alkali (K2O+Na2O, 8.95-9.52%), and relatively low concentration of Al2O3 (13.83-14.8%). They are enriched in light rare earth elements (LREE/HREE, 18.04-21.65) and K, La, Ce, and Hf, and they are depleted in elements of Nb, Ta, P, Ti, and Sr, with weakly negative Eu anomalies (delta Eu=0.61-0.76). Thus, the overall lithogeochemistry of the Dongshadegai pluton resembles that of A-type granite, indicating that the pluton originated from an alkaline-enriched magma. According to the regional tectonic evolutionary history and the geochemical features of the pluton, we conclude that the Dongshadegai pluton formed in an extensional fault setting after a tectonic collision, and its corresponding age is consistent with the formation times of both the Hadamengou gold deposits and the Xishadegai Mo deposits. Based on a comprehensive analysis of the results of recent studies of regional tectonic magmatism and metallogenic processes, we suggest that a large-scale Au-Mo mineralization event occurred in the northern margin of the North China Craton resulted from Indosinian tectono-magmatic event. Compared with regional Late Mesozoic mineralization, the Indosinian mineralization play an important role in study area.