云南老君山矿集区的晚侏罗世-早白垩世成矿事件

云南省老君山矿集区产出南秧田、花石头、茶叶山等众多钨矿床, 是南岭成矿带西段为数不多的以钨为主的矿集区.由于受到多期构造热事件的影响, 该矿集区的成矿年龄存在较大的争议.为此, 选择白钨矿Sm-Nd同位素体系测定了南秧田钨矿田中长石石英脉型矿体的年龄, 用白云母和黑云母Ar-Ar方法厘定了区域花岗伟晶岩的形成时代及其变质围岩的变质时限.研究表明, 南秧田钨矿田中长石石英脉型白钨矿矿体的形成年龄为159±14 Ma, 明显晚于印支期形成的矽卡岩型矿体; 两花岗伟晶岩及其围岩变质作用的时代分别为144~141 Ma和121~112 Ma, 说明老君山矿集区存在晚侏罗世-早白垩世的构造热事件和成矿作用.综合前人的研究成果, 老君山矿集区受到区域花岗片麻岩和花岗岩产出特征的制约, 成矿时代分布与南岭成矿带一致, 存在晚三叠世、晚侏罗世-早白垩世和晚白垩世3个成矿高峰期.而且, 老君山矿集区的成矿特点与南岭东段的钨矿床有一定的可类比性, 是"东钨西扩"的典型实例, 这可能与老君山矿集区遭受了较高的剥蚀程度有关, 暗示南岭西段的高剥蚀区是寻找晚侏罗世钨矿床的远景区. 

Late Jurassic-Early Cretaceous Mineralization in the Laojunshan Ore Concentration Area,Yunnan Province

The Laojunshan ore concentration area, containing many tungsten deposits of Nanyangtian, Huashitou and Chayeshan, is one of the few tungsten concentration areas in the western Nanling metallogenic belt. But, its regional ore-forming ages are controversial due to multi-stage tectono-thermal events. In this paper, the scheelite Sm-Nd dating method was used to determine the ore-forming age of the feldspar quartz vein type ore bodies in the Nanyangtian ore field, and the muscovite and biotite Ar-Ar dating method were used to determine the crystallization ages of the regional granitic pegmatites and the metamorphic age of their wall rocks respectively. The dating results show that the feldspar quartz veins type ore bodies formed at 159±14 Ma, younger than the skarn type ore bodies, and the pegmatite crystallization ages and the wall rock's metamorphic ages are 144-141 Ma and 121-112 Ma respectively. So the Late Jurassic-Early Cretaceous tectono-thermal event and tungsten mineralization occurred in Laojunshan area. The metallogenic regularity in the Laojunshan areas illustrates that the regional ore deposits or spots are constrained by the regional granite gneiss and granitic intrusion, and the ore-forming period is consistent with the three ore-forming peaks in the Nanling minerallenic belt. Furthermore, the mineralization features in Laojunshan area are similar with that in the eastern Nanling metallogenic belt, which may be due to the high denudation degree. It is concluded that the great denudation area in the western Nanling region has great potential to find tungsten deposit formed in Late Triassic and Indo-Chinese and Late Jurassic-Early Cretaceous.