福建省紫金山矿田东南矿段铜钼矿床蚀变与矿化特征

A study on alteration and mineralization characteristics of Cu-Mo orebodies in the Southeast segment of the Zijinshan orefield,Fujian Province, China

紫金山矿田东南矿段铜钼矿床地处紫金山浅成低温热液型铜金矿床和罗卜岭斑岩型铜钼矿床之间。利用近红外光谱技术测试蚀变矿物特征,并结合地质填图、钻孔编录和岩矿鉴定等工作,划分出钾化带、绿泥石绢英岩化带、黄铁绢英岩化带、地开石硅化带、明矾石地开石硅化带等5个蚀变带。钻孔编录和镜下观察发现,金属矿物分为2个期次,生成顺序为磁铁矿-黄铁矿(第1期)→赤铁矿→辉钼矿-黄铜矿-斑铜矿-黄铁矿(第2期)→硫砷铜矿-蓝辉铜矿-铜篮。矿化类型与蚀变分带关系密切:以黄铜矿+斑铜矿+辉钼矿为主的Ⅱ号矿体产出于绿泥石绢英岩化带,与罗卜岭铜钼矿的蚀变矿化特征相似;以蓝辉铜矿+铜蓝交代黄铜矿+斑铜矿为主的Ⅳ号主矿体主要产出于地开石硅化带和明矾石地开石硅化带底部;以蓝辉铜矿+铜蓝+硫砷铜矿为主的Ⅴ号矿体产出于明矾石地开石硅化带,与紫金山铜金矿的蚀变矿化特征相似。明矾石温度分带显示具有罗卜岭斑岩和紫金山火山机构2个高温中心,中、低温混合明矾石化与Ⅳ号主矿体空间上呈显耦合关系。另外,Ⅳ号主矿体的云母矿物Al-OH吸收峰小于2205 nm。初步认为Ⅳ号主矿体是紫金山浅成低温热液叠加罗卜岭斑岩矿床外带所形成。

The Southeast segment of the Zijinshan Cu-Mo-Au orefield is located in the central part between the Zijinshan high-sulfidation epithermal Cu-Au deposit and the Luoboling Porphyry Cu-Mo deposit. Based on the characteristics of alteration minerals which were identified by using the near-infrared spectroscopy, geological mapping, drill core logging,and mineral and lithological microscopic identification, five alteration zones including the potassic zone,chlorite-sericite-quartz zone, pyrite-sericite-quartz zone, dickite-silicification zone, and alunite-dickite-silicification zone have been identified in this deposit. Based on the drill core logging and microscopic observation, it is identified that there are several metal mineral assemblages formed in subsequent order from the early stage of magnetite-pyrite(stage 1), to hematite, to the main stage of molybdenite-chalcopyrite-bornite-pyrite(stage 2), and to the late-stage of enargite-digenite-covelline. There is close relationship between the mineralization type and the alteration zonation. The Ⅱ orebody, which has a metal mineral assemblage consisting mainly of chalcopyrite, bornite, and molybdenite, occurred in the chlorite-sericite-quartz alteration zone, has similar characteristics of alteration and mineralization of the Luoboling Porphyry Cu-Mo deposit. The Ⅳ orebody, which has a metal mineral assemblage consisting mainly of chalcopyrite and bornite partly replaced by digenite and covelline, occurred mainly in the dickite-silicification zone and in the bottom of alunite-dickite-silicification zone. The Ⅴ orebody, which has a metal mineral assemblage consisting mainly of digenite,covelline, and enargite, occurred in the alunite-dickite-silicification zone, has similar characteristics of alteration and mineralization of the Zijinshan high-sulfidation epithermal Cu-Au deposit. The temperature zoning of alunite shows that the Zijinshan volcanic edifice and the Luoboling porphyry are two relatively high temperature centers in this area. There is apparent space coupling relationship between the meso-and epi-thermal alunitization and the Ⅳ orebody. Moreover, the absorption peak for the Al-OH band of mica minerals in the Ⅳ orebody is less than 2205 nm. It is basically believed that the Ⅳ orebody in this deposit was formed by the superimposition of the Zijinshan epithermal mineralization zone and the outer zone of the Luoboling porphyry mineralization.