内蒙古维拉斯托斑岩型锡矿床成岩、成矿时代及其地质意义

维拉斯托Sn矿床为内蒙古中南段地区新发现的大型斑岩型矿床,矿床的形成与石英斑岩有密切的成因联系。该斑岩型Sn矿床的发现与该区已发现的维拉斯托和拜仁达坝大型脉状Cu_Pb_Zn_Ag多金属矿床可能属于同一岩浆_热液成矿体系。虽然前人已对热液脉状Zn_Cu矿床和Ag_Pb_Zn矿床有了较多研究,但对新发现的斑岩型锡矿床开展的研究还十分欠缺。文章首次报道了新发现斑岩型矿床的成岩和成矿年龄。利用LA_ICP_MS方法对石英斑岩中的锆石进行U_Pb同位素定年,获得的年龄为(135.7±0.9)Ma(MSWD=1.4,n=24),表明石英斑岩的侵位时代为早白垩世。对与Sn矿化密切相关的辉钼矿进行了Re_Os同位素定年,结果显示辉钼矿的Re_Os同位素等时线年龄为(125.7±3.8)Ma(MSWD=1.7,n=4),可代表斑岩型矿床中Sn发生矿化的时间。本次获得的年代学数据表明,该斑岩型矿床成矿年龄稍晚于成岩年龄,与国内外众多典型斑岩型矿床具有类似特征。新发现的维拉斯托斑岩型Sn矿床形成于燕山晚期,与该区众多岩浆_热液多金属矿床的形成时代一致,推测矿床的成岩、成矿过程很可能与中生代岩石圈的伸展构造有关。

Geochronological study of Weilasituo porphyry type Sn deposit in Inner Mongolia and its geological significance

The Weilasituo Sn deposit, which is genetically related to a quartz porphyry intrusion, is a large-sized porphyry type deposit discovered in the southern segment of the Da Hinggan Mountains. This deposit, together with the previously discovered Weilasituo Cu-Zn and Bairendaba Ag-Pb-Zn vein deposits in this region, is possibly dominated by one magmatic-hydrothermal system. No detailed research has been conducted to understand this newly-discovered Sn deposit, although numerous studies have been carried out about the local vein type Zn-Cu and Ag-Pb-Zn mineralization. In this study, the authors firstly report the geochronological data of porphyry intrusion and Sn mineralization in Weilasituo. Based on zircon LA-ICP-MS U-Pb dating results, the authors obtained an age of (135.7±0.9) Ma (MSWD=1.4, n=24), indicating that the intrusion of the quartz porphyry took place in the Early Cretaceous. Molybdenite, which shows a close relationship with Sn mineralization, has a Re-Os age of (125.7±3.8) Ma (MSWD=1.7, n=4). The obtained geochronological data of magmatism and mineralization indicate that Sn mineralization was relatively later than porphyry intrusion, comparable with the reported age data from porphyry type deposits in the world. This newly-discovered Weilasituo porphyry type Sn deposit formed in the late Yanshanian period, coincident with the formation time of numerous magmatic-hydrothermal deposits in this region, implying that the local magmatism and its related mineralization were possibly associated with Mesozoic lithospheric extension.