闽北上房钨矿床锆石U-Pb和辉钼矿Re-Os定年及其地质意义

Zircon U-Pb and Molybdenite Re-Os dating of the Shangfang Tungsten Deposit in Northern Fujian Province: Implications for Regional Mineralization

上房钨矿床是武夷山成矿带新近发现的大型白钨矿矿床,也是福建省发现的钨矿新类型.矿床产于上房似斑状黑云母正长花岗岩体的外接触带上,赋矿围岩主要为古元古代大金山岩组斜长角闪岩和黑云斜长变粒岩,矿体产状与围岩的片理一致,矿石类型为石英细脉型和浸染型,金属矿物主要为白钨矿和辉钼矿,其次为少量磁黄铁矿、黄铁矿和黄铜矿等.野外地质观察和矿化特征研究表明,上房钨矿的矿床类型为接触交代型.采用LA-ICP-MS锆石U-Pb和辉钼矿Re-Os测年技术,对与成矿有关的上房似斑状黑云母正长花岗岩和与白钨矿共生的辉钼矿进行成岩成矿年代测定,获得上房似斑状正长花岗岩体的成岩年龄为158.8±1.6Ma(1σ),辉钼矿Re-Os模式年龄为159.40±0.86～149.92±1.39Ma(n=5),模式年龄的加权平均值为156.5±4.0Ma,等时线年龄为158.1±5.4Ma(2σ).同位素定年结果表明,上房钨矿床与矿区似斑状黑云母正长花岗岩关系密切,二者均形成于晚侏罗世,与华南地区中生代大规模钨多金属矿床的成矿时代一致.传统观点认为,华南地区晚侏罗世(160～150Ma)钨多金属矿床大规模成矿作用集中于南岭成矿带中东段的湘南、粤北和赣南地区,而本文的研究结果则说明这一区域成矿作用向北东延伸进入到武夷山成矿带的闽西和闽北地区.因此,华南钨多金属矿床的空间分布不是传统认为的近东西向,而是具有北东向或北东东向展布的特点,是滨太平洋构造-岩浆-成矿域的重要组成部分.

The newly discovered large-scale Shangfang tungsten deposit represents a new type of tungsten mineralization in Fujian Prov- ince, offering new pespectives for exploration of tungsten deposits in the province. The ore bodies are mostly hosted in amphibolite and biotite leptynite of the Paleoproterozoic Dajinshan Formation proximal to the Shangfang syenogranite imrusion and, less significantly, in the contact zone between the intrusion and the metamorphic rocks. Tungsten mineralization consists of quartz-scheelite veins and disseminated scheelite in alteration assemblages, with scheelite and molybdenite as the main ore minerals coexisting with minor pyrrhotite, pyrite, and chalcopyrite. Field relations and petrographic characterization indicate that the Shangfang deposit is typified by skarn mineralization. Zircons from the Shangfang syenogranite intrusion have LA-ICP-MS U-Pb age of 158. 8±1.6 Ma （lσ）, whereas five molyb denite separates yield model ages ranging from 159. 40±0. 86 to 149. 92±1. 39 Ma with a weighted mean of 156. 5 ± 4. 0 Ma, which is consistent with an isochrone age of 158. 1±5. 4 Ma （2σ）. The geochronological data thus demonstrate that the Shangfang tungsten deposit formed in the Late Jurassic and is genetically related to the syenogranite intrusion in the mine. The data also indicate that the Shangfang deposit resulted from the pervasive Late Mesozoic tunsgten mineralization in South China. It has long been considered that the Late Jurassic tungsten metallogenic belt in South China is restricted in the middle-eastern portion of the Nanling Range coveting areas of southern Hunan, northern Guangdong, and southern Jiangxi Province. The discovery of the Shangfang deposit, however, allows this metallogenic belt to extend into western and northern Fujian Province, which is an integral part of the Wuyishan metallogenic belt. As such, the South China polymetallic belt is distributed along a northeast strike, rather than an east-west extension as previously thought, and can be regarded as an important part of the giant Circle-Pacific tectono-magmtic-metallogenic domain.