南秦岭柞水—山阳矿集区下官坊含铜岩体矿化特征与岩石地球化学

Mineralization characteristics and petrogeochemistry of copper-bearing rock mass in Xiaguanfang,Zhashui-Shanyang ore concentration area,south Qinling

柞水—山阳矿集区是南秦岭构造—岩浆活动强烈地区,广泛出露白沙沟等浅成—超浅成的花岗岩类侵入体及与之有关的矽卡岩—斑岩型矿床(化)。文章在对柞水—山阳矿集区下官坊岩体矿化地质特征观测的基础上,对该矿集区内的下官坊含矿岩体进行了详细的岩石学、元素地球化学、锆石U-Pb年代学、LuHf同位素及微量元素分析研究,探讨了该岩体的成因、成岩成矿大地构造环境及成矿潜力。下官坊岩体岩性为准铝质高钾钙碱性—钾玄岩系列的花岗闪长斑岩和石英闪长玢岩。LA-ICP-MS锆石U-Pb测年测定表明,下官坊岩体的岩浆侵位年龄为139~144 Ma。Lu-Hf同位素分析结果显示,下官坊岩体的岩浆源区可能为地壳熔融岩浆与地幔重熔岩浆的混合,并且具有较高的混合均一化程度。下官坊岩体显著富集成矿元素Cu,其成岩成矿大地构造环境、矿化地质特征、围岩蚀变类型、岩石矿物组合与国内外矽卡岩型矿床相似,指示该岩体具有形成矽卡岩型铜矿床的成矿潜力。下官坊岩体形成于晚侏罗世—早白垩世之交,造山带应力状态由挤压转向伸展,引发强烈壳幔相互作用和花岗质岩浆活动,并随之形成了含矿岩体及其矽卡岩型矿化。

The Zhashui-Shanyang ore concentrated area is characterized by serious tectomagmatic activity in the South Qinling.It is widely exposed hypabyssal-super hypabyssal granite intrusions such as Baishagou and related skarn-porphyry deposits.Based on the observation of the mineralization geological characteristics of the Xiaguanfang rock in the Zhashui-Shanyang ore district,the detailed petrology,elemental geochemistry,Zircon U-Pb geochronology,Lu-Hf isotope and trace element analysis of the ore-bearing rock are carried out to discuss the origin of the rock mass,diagenesis and ore-forming tectonic environment and metallogenic potential.The Xiaguanfang intrusions comprise granodioritic porphyry and quartz diorite porphyrite and are typical metaluminous high-K calc-alkaline to shoshonite series.The magma emplacement age of the rock mass obtained from zircon LA-ICP-MS U-Pb dataing is 139~144 Ma.The result of Lu-Hf isotope analysis suggests that the magma source of the Xiaguanfang intrusions may be a mixture of crustal melting magma and mantle remelting magma,and they have a high degree of mixed homogenization.The rock mass is significantly enriched with mineralization element Cu.It is similar to skarn deposits at home and abroad in diagenetic ore-forming tectonic environment,mineralization geological characteristics,wall rock alteration type,and rock mineral combination,indicating that the intrusion has the metallogenic potential of forming a skarn type copper deposit.The Xiaguanfang intrusions was formed at the late Jurassic to early Cretaceous.The stress state of the orogenic belt was changed from extrusion to extension,causing strong crust-mantle interaction and granitic magmatism,and ore-bearing rock mass and skarn type mineralization are subsequently formed.