北祁连山白山子花岗闪长岩成岩时代

寒山大型金矿是近年来在北祁连山西段发现的与侵人岩有关的构造蚀变岩型金矿。笔者首次利用锆石U-Pb方法测得白山子花岗闪长岩的形成年龄为370±25 Ma，属于华力西期。寒山金矿的成矿主要在213.95~339 Ma间。在多期热液叠加，多期成矿作用中，早期成矿的热液很可能是白山子花岗闪长岩（370±25 Ma) ,寒山辉长岩(347.1±6. 4 Ma）共同提供的。由于该区有较多的中酸性岩体存在，它们可能为金的主要来源，因而，确定这些侵入体的形成年龄，对于在该区寻找蚀变岩型金矿不仅有重要的理论意义，而且有重要的现实意义。

A Preliminay Study of the Petrogenic Age of Granodiorite in Baishanzhi, North Qilian Mountains

The Hanshan gold deposit is a tectonic altered rock type deposit discovered recently in North Qilian Mountains. The formation age of Baishanzhi granodiorite measured by U-Pb method is 370±25 Ma, indicating the Hercynian period. The metallogenic age of the Hanshan gold deposit is 213.95~339 Ma. Among the superimpositions of multi-stage hydrothermal fluids and multi-stage mineralizations, the ore-fornring hydrothermal solution of the early stage was probably provided jointly by Baishanzhi granodiorite (370±25 Ma) and Hanshan diorite (347.1±6.4 Ma). As there exist lots of intermediate-acid rocks, it is obvious that the rocks might serve as the major gold sources. The determination of the formation ages of these intrusives is of great theoretical and practical significance in search for altered rock type gold deposits in this area.