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

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。

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

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 139~144Ma. 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.