华北南缘老里湾银铅锌矿床矿化特征和岩体地球化学特征:对矿床成因的指示

老里湾银铅锌矿床位于华北克拉通南缘崤山断隆带内，是崤山地区首次发现的大型矿床.其矿体主要赋存于老里湾花岗斑岩体内，同时受断裂构造控制，与区域银铅锌矿床的地质特征明显不同.矿床地质研究表明，老里湾银铅锌成矿作用可分为热液期和表生期，其中热液期又可分为4个成矿阶段:石英-菱铁矿阶段、石英-黄铁矿阶段、石英-多金属硫化物阶段和石英-重晶石-方解石阶段.LA-ICP-MS锆石U-Pb定年结果显示，两件老里湾花岗斑岩样品的成岩年龄分别为129.0±1.7 Ma、129.0±1.1 Ma.岩石地球化学分析表明，该岩体具有高硅、富碱、准铝质-弱过铝质的特点，富集LREE、Rb、Ba、Sr、Pb等大离子亲石元素，亏损HREE、Nb、Ta、Ti、P等高场强元素，具有弱的负Eu异常.综合分析表明，老里湾花岗斑岩体与区域同时期岩体具有相似的地球化学特征，它们的侵位可能与中国东部中生代构造大转折及岩石圈减薄相关.结合矿化特征及区域成岩成矿年代学数据，认为老里湾银铅锌矿床成矿时代应稍晚于花岗斑岩，二者并没有直接的成因联系，但可能为同一深部岩浆房活动的产物.崤山地区断裂带和岩体交汇处是寻找银铅锌矿床的有利部位，这一认识得到了近期老里湾北部中河地区的银铅锌勘查工作的验证.同小秦岭、熊耳山地区相比，崤山地区整体剥蚀较浅，老里湾银铅锌矿体深部还具有寻找斑岩型钼矿床的潜力. 

Mineralization Characteristics of the Laoliwan Ag-Pb-Zn Deposit and Geochemical Features of the Ore-Bearing Granite Porphyry in the Southern North China Craton: Implications for Ore Genesis

The newly discovered Laoliwan large Ag-Pb-Zn deposit is located in the Xiaoshan district, southern margin of North China Craton, which is different from other types of Ag-Pb-Zn deposit in the area since the ore bodies are mainly hosted in the Laoliwan granite porphyry and controlled by the regional faults. The mineralization could be subdivided into two periods:the hydrothermal period and the supergene period. The hydrothermal period consists of four stages:the quartz-siderite stage, the quartz-pyrite stage, the quartz-polymetallic sulfide stage, and the quartz-carbonate stage. LA-ICP-MS zircon U-Pb dating results of two samples from the Laoliwan granite porphyry are 129.0±1.7 Ma and 129.0±1.1 Ma, respectively, indicating the granite porphyry intruded during Early Cretaceous. Based on the rock geochemical analysis, the granite porphyry is characterized by high silicon, high alkali, and weak peraluminous. The REE and trace elements characteristics display enrichment of large ion lithophile elements (LREE, Rb, Ba, Sr, Pb) and depletion of high-field elements (HREE, Nb, Ta, Ti, P) and moderately negative anomaly of Eu. These features are similar with other Early Cretaceous granites in the area, indicating the magmatic activities are probably related to contemporaneous tectonic transition and lithosphere thinning in eastern China. Based on mineralization characteristics and regional geochronological data, it is supposed that the Ag-Pb-Zn mineralization formed later than the granite porphyry and they have no direct genetic relationships. However, they may be the products of activities of the same deep magma chamber. This study of the Laoliwan Ag-Pb-Zn deposit suggests that the superposition of faults and granite rocks could be the prospective places for exploring Ag-Pb-Zn deposits in the Xiaoshan disctrit, which is confirmed by the recent prospecting work at Zhonghe which is in north of Laoliwan. Compared with Xiaoqinling and Xiong'ershan area, the exhumation of the Xiaoshan area is quite shallower. It is potential to find porphyry molybdenum deposit under the Ag-Pb-Zn ore bodies of Laoliwan.