浙赣皖相邻区与德兴、铜陵矿集区燕山期花岗岩类岩石对比研究及其成矿

A comparison of Yanshanian granitoids between the Zhejiang-Jiangxi-Anhui border area and the Dexing and Tongling mineralization-concentated areas, with a discussion on mineralization

浙赣皖相邻区与铜陵、德兴地区岩石系列相似,主要为高钾钙碱性系列;在岩石类型上,浙赣皖相邻区较德兴和铜陵地区两个矿集区的岩体偏酸性,主要岩石类型为二长花岗岩和花岗闪长岩,德兴地区和铜陵地区的主要岩石类型为花岗闪长岩和石英闪长岩。从浙赣皖相邻区→德兴地区→铜陵地区,岩体的里特曼指数逐渐增加,A/CNK逐渐减小,K/(K+Na)逐渐减小。在岩石化学特征上,浙赣皖相邻区较德兴和铜陵矿集区的岩体富Si、K,贫Mg、Fe、Ca等暗色矿物组分及Ti、P等不相容元素组分,从浙赣皖相邻区→德兴地区→铜陵地区岩石明显地向贫Si、K富Mg、Fe方向演化。在岩石成因类型上,浙赣皖相邻区岩石主要为I型花岗岩,个别为S型花岗岩,德兴和铜陵两个矿集区岩石均为Ⅰ型花岗岩,无S型。痕量元素、同位素特征及岩石学特征表明浙赣皖相邻区的物质来源以壳源为主,而德兴地区及铜陵地区为壳幔混合型或有大量幔源物质的参与,其原因可能与3个地区不同的构造背景有关。综合上述对比研究,认为在浙赣皖相邻地区要找到铜陵式的Cu矿和德兴式Cu、Mo矿的可能性较小。

In rock series, Yanshanian intrusive rocks in the Zhejiang-Jiangxi-Anhui border area are similar to those in the Tongling and Dexing areas, being all high-K calc-alkaline series. In rock types, the rocks in the Zhejiang-Jiangxi-Anhui border area are more acid than those in the Tongling and Dexing mineralization-concentrated areas, i.e., the rocks in the former consist mainly of monzonitic granite and granodiorite, whereas those in the latter are granodiorite and quartz diorite. Rittman index gradually increases, A/CNK gradually decreases and K/K ＋ Na gradually decreases from the Zhejiang-Jiangxi-Anhui border area to the Dexing area, and then to the Tongling area. In petrologic chemistry, the intrusions in the Zhejiang-Jiangxi-Anhui border area are richer in Si and K than those in the Dexing and Tongling areas, with the evolution towards the depletion of Si and K from the Zhejiang-Jiangxi-Anhui border area to the Dexing area, and then to the Tongling area. The intrusions in the Zhejiang-Jiangxi-Anhui border area are depleted in Mg, Fe and Ca dark minerals and incompatible elements such as Ti and P. The intrusions evolved towards the depletion of Si, K and enrichment of Mg and Fe from the Zhejiang-Jiangxi-Anhui border area to the Dexing area, and then to the Tongling area. In original petrologic types, the rocks in the Zhejiang-Jiangxi-Anhui border area are mainly I-type monzonitic granite and dioritic granite, with very few samples belonging to S-type granite. There is no S-type granite in the Dexing and Tongling mineralization-concentrated areas. The trace elements, isotope features and petrologic features of the Zhejiang- Jiangxi-Anhui border area indicate that the source was mainly derived from the crust, whereas the source of the intrusions in the Dexing and Tongling areas from crust-mantle mixing, or from the entry of large amounts of mantle materials into magma. The Zhejiang-Jiangxi-Anhui border area is situated on the Jiangnan anticlise; the Dexing mineralization-concentrated area lies on the southeast side of the eastern anticlise, and is close to the Qiantang sag; the Tongling area lies in the lower Yangtze sag area. These backgrounds are likely to be some of the factors which result in the difference in original petrologic types of these areas. In the light of petrologic assemblages, original types, petrochemical features and sources, the authors hold that it is difficult to find the Tongling-type Cu deposits and the Dexing-type Cu, Mo deposits in other areas except for Xiaoyao area.