Rock-forming mechanism of Qingshanjiao intrusion in Dongguashan copper(gold) deposit, Tongling area, Anhui province, China

安徽铜陵冬瓜山矿床青山脚岩体的成岩机制（英文）

Dongguashan deposit is a large porphyry-skarn copper（gold） deposit in Tongling ore district. The Qingshanjiao intermediate acid intrusion of Yanshanian had a direct genetic relationship with mineralization. The magma origin, rock-forming dynamic background and rock-forming process were studied, and the rock-forming mechanism of Qingshanjiao intrusion was discussed, based on geological characteristics, detailed observation of petrography and systematic investigation of petrochemistry, trace elements and REE geochemistry characteristics of Qingshanjiao intrusion. The results show that Qingshanjiao rock body belongs to high-K calc-alkaline series with higher LREE elements, Th, Rb and Sr abundance, but depleted in HREE elements, Ba, Nb and Ta. The primary magma originated from the mantle-crust mixtures which were caused by basaltic magma of mantle mixing with syenite magma of partial melting of the lower crust, and the formation environment of Qingshanjiao intrusion was emplaced in the transitional environment from compression to extension. The Harker diagram and hybrid structures of plagioclase and potassium feldspar indicate that the fractional crystallization occurred in the process of magmatic evolution. The petrochemistry, trace elements and REE geochemistry characteristics indicate that the magma was contaminated by crustal material during the rock-forming. These results suggested that the Qingshanjiao intrusion was formed by fractional crystallization and assimilation and hybridization of mantle-crust magma in the transitional environment from compression to extensional.

冬瓜山矿床是铜陵矿集区内一个大型的斑岩-矽卡岩型铜(金)多金属矿床,矿区内的燕山期青山脚中酸性侵入岩体与成矿有直接的成因联系。在对青山脚岩体地质特征研究的基础上,进行了详细的岩相学观察和系统的岩石化学、微量元素和稀土元素地球化学研究。分析了岩浆起源、成岩动力学环境及岩体的成岩作用过程,并对青山脚岩体的成岩机制进行了探讨。结果表明,青山脚岩体为高钾钙碱性岩石,具有富集轻稀土元素、Th、Rb和Sr,亏损重稀土元素、Ba、Nb和Ta的特征。形成成矿岩体的原始岩浆来源于地幔玄武质岩浆和下地壳部分熔融产生的正长岩岩浆的混合,其成岩动力学环境为挤压到伸展的过渡环境。Harker图解和长石的混合结构表明,岩浆在演化过程中发生了自身的分离结晶作用,岩石化学及微量元素、稀土元素特征表明成岩过程中受到了地壳物质的混染。本区岩体是由壳幔混合岩浆在碰撞后的伸展环境中经过自身的分离结晶作用和与地壳的同化混染作用而形成的。