钦-杭成矿带东段村前含矿斑岩地球化学特征及其构造环境与成矿意义

Geochemistry of the Cunqian ore-bearing porphyry from the eastern Qin-Hang metallogenic belt and its implication for tectonic setting and mineralization

村前铜多金属矿床位于钦杭成矿带东段,为一具有矽卡岩型矿化和斑岩型矿化的铜多金属矿床,含矿岩体为燕山早期花岗闪长斑岩,岩石具有富硅、富铝、富碱的特点,属于偏铝-过铝质钙碱性花岗岩类。岩体具有从深部向浅部蚀变增强,大部分组分活动性不明显,而成矿元素Cu-Mo-Fe-Pb-Zn-Au-Ag含量明显增加,Na2O、Sr含量降低,REE元素除Eu少量丢失外,其余均呈一致的迁入特征。岩体属Ⅰ型花岗质岩石,由具角闪石＋石榴子石残留相的火成岩部分熔融形成的熔浆,混合或混染了地壳重熔型岩浆上侵就位而成。钦杭结合带东段,燕山期中酸性岩浆活动具有从176-150Ma的埃达克岩或具岛弧花岗岩特征的Ⅰ型花岗岩,至150-140Ma的S型花岗岩,向140-110Ma的A型花岗岩演化趋势,显示了地壳由厚减薄的过程,暗示其大地构造背景为岩石圈的伸展减薄环境,而形成于169.3±1.1Ma的村前斑岩体正处于伸展阶段早期。综合岩体成矿特征表明,钦杭成矿带东段及邻近地区,176-160Ma主要形成与Ⅰ型花岗质岩石有关的以Cu为主的多金属矿床;160-150Ma主要形成与Ⅰ型花岗质岩石有关的Cu-Mo矿床与W-Sn矿床;150-140Ma主要形成与S型花岗质岩石有关的以W-Sn-Mo为主的多金属矿床,以及以Ag-Pb-Zn为主的多金属矿床;140-110Ma主要形成与A型花岗质岩石有关的以W-Sn-Mo为主的多金属矿床,少量与Ⅰ型花岗质岩石有关的Pb-Zn矿床。

The Cunqian copper polymetallic deposit in the eastern Qin-Hang metallogenic belt is characterized by skarn type and porphyry type mineralization and granodiorite porphyry of Early Yanshanian is the ore-bearing rock. Geochemical study shows that the granodiorite porphyry is rich in silicon,alkali and,alumina,and belongs to calc-alkaline metaluminous to peraluminous granite. The alteration in the granodiorite porphyry is increased from deep to shallow part of the rock body and the activity of most components is not obvious. The content of ore-forming elements,such as Cu-Mo-Fe-Pb-Zn-Au-Ag,is increased significantly,while the content of Na2 O,Sr decreased. REE elements are characterized by consistent migration except minor loss of Eu. The research is revealed that the granodiorite porphyry belongs to Ⅰ-type granite resulted from emplacement of mixed magma with remelted hornblende ＋ garnet residual phase. Intermediate-acid magmatic rocks of Yanshanian in eastern Qin-Hang metallogenic belt have an evolution tendency from adakites or Ⅰ-type granites with characteristics of island arc rocks in 176 - 150 Ma,to S-type granites in 150 - 140 Ma,to A-type granites in 140- 110 Ma,implying the process from thickness to thinness of the crust and suggesting a tectonic background of lithosphere stretching and thinning. Characteristics of granodiorite porphyry mineralization indicate that copper polymetallic deposits,which are associated with Ⅰ-type granite in eastern Qin-Hang metallogenic belt and its adjacent area,are formed in the period of 176 - 160Ma; Cu-Mo deposits and W-Sn deposits are associated with Ⅰ-type granite and formed in the period of 160 - 150Ma; W-Sn-Mo polymetallic deposit and Ag-Pb-Zn polymetallic deposits are associated with S-type granite and formed in the period of 150 - 140 Ma.