鲁西莱芜三岔河矽卡岩型铁金矿床岩体成因：锆石U-Pb年代学和岩石地球化学证据

【研究目的】莱芜三岔河矿床是鲁西地区首次发现的矽卡岩型铁金矿床（不含铜），以往研究相对薄弱，本文旨在对成矿岩体形成时代、源区性质、岩石成因和构造背景进行讨论。【研究方法】本文开展了LA-ICP-MS锆石U-Pb测年、岩体主微量测试工作。【研究结果】结果显示辉石闪长岩侵位年龄为（138.4±1.2）Ma，属早白垩世。辉石闪长岩里特曼指数σ=2.20～2.54，为钙碱性岩石；辉石闪长岩具高Mg^#、富Na特征，Sc、Cr、Co、Ni含量较高，表明其具有幔源岩浆的属性；富集轻稀土元素（LREE），亏损重稀土元素（HREE），Eu异常不明显，富集大离子亲石元素（Cs、Ba、Sr），亏损高场强元素（Nb、Ta、Zr），暗示有地壳物质的涉入。【研究结论】三岔河辉石闪长岩可能起源于受华北克拉通古老地壳物质改造的富集岩石圈地幔的部分熔融，形成于岩石圈减薄的强烈伸展构造背景，可能与太平洋板块俯冲后撤引起的伸展构造环境有关。

Petrogenesis of the Sanchahe skarn type iron-gold deposit in Laiwu area, western Shandong: Evidences from zircon U-Pb geochronology and geochemistry

This paper is the result of mineral exploration engineering. Objective] Laiwu Sanchahe iron-gold deposit is the first skarn type iron-gold deposit (without copper) discovered in western Shandong. Previous research on the Sanchahe deposit is weak. The purpose of this paper is to discuss the age of ore-forming pluton,magma sources, petrogenesis and tectonic setting. Methods] We carried out LA-ICP-MS zircon U-Pb dating, major and trace elements analysis.Results] Zircon U-Pb age of pyroxene diorite is (138.4 ±1.2) Ma in the Early Cretaceous. Pyroxene diorite is calc-alkalic (Rittmann index σ = 2.20-2.54) and characterized by high Mg^# and high contents of Na₂O, Sc, Cr, Co and Ni, which demonstrates that it has geochemical affinity with mantle-derived magma. It is enriched in LREE and depleted in HREE, with no obvious Eu anomaly, and shows enrichment in Cs, Ba, Sr and depletition in high field strength elements (Nb, Ta, Zr), indicating involvement of some crustal materials. Conclusions] Geochemical features of pyroxene diorite combined with geochronological data imply that it may be generated by partial melting of the enriched lithospheric mantle which had been metasomatized by the ancient crust materials of the North China Craton, and formed in the strong extensional tectonic background of lithospheric thinning, which may be caused by the retreat of the subducting Paleo-Pacific plate.