河南桐柏老湾金矿床和花岗岩的年龄及其意义

通过老湾金矿床矿石中石英和花岗岩中的 主要造岩矿物石英、钾长石的40Ar/39Ar定 年，获得成矿年龄为91.5±1.0Ma，成岩期高温坪年龄为104.1±1.0Ma～108.9±0.3Ma，等 时线 年龄为102.8±0.1Ma～108.7±0.1Ma，因此认为成岩成矿具同时性。结 合 秦岭-大别造山带的演化历史，提出老湾金矿床和老湾花岗岩均形成于燕山晚期，成矿略晚 于成岩，构造应力环境为挤压向伸展转化的过渡期或以张应力为主的构造体制。

Isochron Age of the Laowan Gold Deposit and Laowan Granite, Tongbai Region, Henan Province and Its Implications

The Laowan gold deposit is a large-sized deposit recen tly discovered in northem slope of the Tongbai Mountains. It occurs in middle Pr oterozoic metamorphic basic volcanic-sedimentary rocks o f the Guishan Formation. The Laowan granite intrue d in the Laowan fault belt. The orebodies are controlled by granite. The ore grade becomes richer where the granite swells. 　　The genesis of Laowan gold deposit is complex. Some scholars considered that it belongs to the shear zone type. In this paper, in order to make sure t he relationship between the deposit and the granite, a prelimina ry study on　40Ar/39Ar dating has been carried out on three representative samples. These samples are: one q u artz sample from the second ore-forming stage of the deposit, one quartz sample from granite, and one potash-feldspar sample from granite.The　40Ar/39Ar analyses were carried out in Beiji ng Institute of Geology, Academia Sinica, by using the RGA-10 mass spectrometer. 　　The　40Ar/39Ar plateau age and isochrone age for corresponding sam ples are: for the quartz from one deposit, 91.5 and 88.9 Ma, respectively; for t he quartz from granite, 104.0 and 102.8 Ma, respectively; for the feldspar f rom granite, 108.9 and 108.7Ma, respectively. These isochrone ages indicate that the granite and the deposit were formed in late Yanshannian and have very close relationship. 　　The analysis on stress condition for mineralization of the Laowan gold deposit a n d petrogenesis of the Laowan granite suggests that they were formed in a transit ion condition f rom compressive stress to tensile stress or in a mainly tensile stress condition . In this stage, large amount of hydrothermal fluids of different origins appears, which is very favorable for ore deposition.