华北克拉通南缘卢氏多金属矿集区硫化物Rb-Sr定年及地质意义

华北克拉通南缘秦岭成矿带发育大量金矿、钼矿及铅锌多金属矿床。卢氏多金属矿集区位于东秦岭成矿带,主要矿床有夜长坪钼钨矿、八宝山铁铜矿、楼房银铜矿、柳关铅锌矿等。其中楼房银铜矿为热液脉状多金属矿床,矿床赋存于太华群角闪斜长片麻岩中,矿体受构造蚀变破碎带控制,矿床中划分出两个成矿阶段:石英-黄铁矿-黄铜矿组合和石英-黄铁矿-方铅矿-闪锌矿-方解石组合,其中前者是铜成矿阶段,后者为铅锌成矿阶段。柳关铅锌矿为矽卡岩矿床,矿体产于官道口群白云岩与花岗斑岩岩体或隐爆角砾岩接触矽卡岩化带内,矿床划分出两个成矿阶段:透辉石-透闪石-阳起石-石榴石-磁铁矿组合和方铅矿-闪锌矿-黄铁矿-绿帘石-蛇纹石-石英-方解石组合,前者为磁铁矿成矿阶段,后者是铅锌成矿阶段。金属硫化物定年结果表明,楼房银铜矿黄铜矿Rb-Sr等时线年龄为127. 8±3. 1Ma(2σ,MSWD=1. 1),初始87Rb/86Sr为0. 710998±0. 000068;柳关铅锌矿黄铁矿Rb-Sr等时线年龄为124. 8±1. 6Ma(2σ,MSWD=1. 4),初始87Rb/86Sr为0. 711074±0. 000064。研究表明卢氏多金属矿集区内热液多金属矿床形成于早白垩世,其形成与区内早白垩世岩浆活动有关。综合区域地质研究,区内多金属矿床形成于早白垩世与克拉通破坏有关的构造环境。

The Rb-Sr isotopic dating of sulfides and geological significance of the Lushi polymetallic ore-concentrated area in southern margin of the North China Craton

There are a lot of Au, Mo and Pb-Zn polymetallic ore deposits developed in Qinling metallogenic belt, southern margin of the North China Craton. The Lushi polymetallic ore-concentrated area is located in eastern part of this belt, which including Yechangping Mo-W deposit, Babaoshan Fe-Cu deposit, Loufang Ag-Cu deposit, Liuguan Pb-Zn deposit, and so on. Loufang Ag-Cu deposit is a hydrothermal lode polymetallic deposit, it occurs within the amphibole plagiogneiss of Taihua Group, and the ore bodies in this deposit are controlled by the structural alteration fracture zones. Two stages of mineralization are identified in Loufang deposit:quartz-pyrite-chalcopyrite and quartz-pyrite-galena-sphalerite-calcite assemblages. The former is the Cu mineralization stage, while the latter is the Pb-Zn mineralization. Liuguan Pb-Zn deposit is a skarn deposit, whose orebodies occur within the skarn belt between dolomite of the Guandaokou Group and granite porphyry or cryptoexplosive breccia. Two stages of mineralization are identified in Liuguan deposit:diopside-tremolite-actinolite-garnet-magnetite and galena-sphalerite-pyrite-epidote-serpentine-quartz-calcite. The former is the magnetite mineralization stage, and the latter is the Pb-Zn mineralization stage. The results of chalcopyrite isochron dating indicate that the Rb-Sr isochron age of the Loufang Ag-Cu deposit is 127.8±3.1Ma (2σ, MSWD=1.1), and the initial ⁸⁷Rb/⁸⁶Sr of which is 0.710998±0.000068; The Rb-Sr isochron age of pyrite in Liuguan Pb-Zn deposit is 124.8±1.6Ma (2σ, MSWD=1.4), and the initial ⁸⁷Rb/⁸⁶Sr of which is 0.711074±0.000064. The age data indicate that the hydrothermal polymetallic deposits in Lushi polymetallic ore-concentrated area were formed in Early Cretaceous, which is associated with Early Cretaceous intrusive magmatism. Combining with regional geological data, it can be concluded that the polymetallic deposits in this area were formed in a tectonic setting related to craton destruction happened in Early Cretaceous.