东坪金矿成矿时代研究

东坪金矿是我国在碱性岩中发现的第一个大型金矿,本文在详细野外观察的基础上,用K-Ar法、~(40)Ar/~(39)Ar法测定了成矿期花岗细晶岩脉、主成矿期矿石的同位素年龄,确定东坪金矿成矿时代为燕山期。

The metallogenic epoch of the Dongping gold deposit

Based on detailed field observations, the authors, using K-Ar and 40Ar/39Ar Methods, made a study on metallogenic epoch of the Dongping gold deposit, the first large-sized gold deposit ever discovered in alkaline rocks of China.Located in Chongli County, Hebei Province, the Dongping gold deposit is hosted by the Hercynian Shuiquangou complex 215 km² in area, which consists mainly of monzonite and adamellite a nd has an average gold content of 7.49×10^-9. Orebodies are composed of quartz veins and K-feldspathiztion zones flanking the quartz veins; Wall rock alterationscomprise K-feldspathization and silieification, the 3rd stage K-feldspathization being most intense; the major gold minerals include native gold and calaverite. According to cutting relationships, observations under microscope and Inclusion thermometry, the hydrothermal activities in the ore district might be divided into five stages, in which the 2nd stage(pyrite-gold-quartz veins) and, especially, the 3rd stage (polymetallic sulfides-gold-quartz veins)are major gold mineralization stages. Through thorough and detailed field observation, the authors have found out for the first time the cutting relationships between granite-aplite veins and quartz veins of the ore-forming period in the ore distict: the granite-aplite veins cut the 1st stage quartz veins but are cut by quartz veins of the later stages, indicating that granite-aplite veins were formed at the fairly initial phase of the ore-forming period. Using K-Ar dating and 40Ar/39Ar step-heating dating, the authors determined K-feldspar ages of the granite-aplite veins and the 3rd stage K-feldspathized rocks: K-Ar age of the granite-aplite veins is 191×10⁶a, that of the 3rd stage K-feldspathized rocks is 148.1×10⁶a, and the 40Ar/39Ar plateau age of the 3rd stage K-feldspathized rocks is 156.7×10⁶a. In addition, a late stage heat disturbance took place at 120×10⁶a or so. These data suggest that the Dongping gold deposit was formed in Yanshanian period, consistent with the major gold deposits of East China in metallogenic epoch.