安徽宣城茶亭铜金矿区岩浆岩特征及成因

发布时间：2018-07-24 21:41

【摘要】：安徽宣城茶亭地区近年来新发现规模可望达到大型-超大型的斑岩型铜金矿床。本文在系统收集前人研究资料并综合矿区最新勘探成果的基础上,通过区域地质调查和矿区钻孔岩芯编录,结合室内岩相学、锆石U-Pb同位素地质年代学以及主微量元素、稀土元素、锆石Hf同位素及全岩和斜长石单矿物Sr-Nd-Pb同位素等研究工作,初步确定了茶亭铜金矿区岩浆岩的地质和地球化学特征,探讨了矿区岩浆岩成岩物质来源和成岩作用机制。取得的主要认识和成果如下:1、宣城茶亭铜金矿区火山岩大部分被第四系地表沉积物覆盖,岩石类型主要有晶岩屑凝灰岩和角闪安山岩,它们表现出低碱低钠富钾低钛等特征,为高钾钙碱性系列岩石;矿区岩浆岩侵位于区域火山岩地层之下,岩石类型以中酸性石英闪长玢岩为主,是茶亭铜金矿床的主要赋矿岩石,闪长玢岩、闪斜煌斑岩呈岩脉状穿切。侵入岩岩石化学成分表现出富碱富钠低钛的特征,为准铝质高钾钙碱性系列岩石。2、宣城茶亭矿区侵入岩的LA-ICP MS锆石U-Pb年龄分别为:石英闪长玢岩137.8±1.3Ma、闪长玢岩135.9±1.2Ma、闪斜煌斑岩138.0±1.3Ma,指示侵入岩成岩时代为早白垩世;矿区晶岩屑凝灰岩和角闪安山岩U-Pb年龄分别为130.2±1.2Ma和132.2±1.6Ma,显示矿区火山岩为同一期岩浆喷发作用的产物,矿区火山岩成岩时代为早白垩世。3、宣城茶亭矿区赋矿石英闪长玢岩富集轻稀土元素和大离子亲石元素,亏损高场强元素,岩石显示出强烈富集La、Sr、K等及Nb、Ta、Ce和Ti强亏损等特征。锆石Hf同位素组成和全岩及斜长石单矿物Sr-Nd-Pb同位素组成均介于下地壳与富集地幔端元之间,显示出茶亭矿区岩浆岩具有壳幔混源特征。对比发现,上述一系列地球化学特征类似于铜陵矿集区等断隆区侵入岩,而与宁芜、庐枞等断凹区侵入岩存在一定的差异。4、通过与长江中下游构造-岩浆-成矿带中的其它地区岩浆岩对比发现,矿区赋矿石英闪长玢岩不仅在成岩时代上,而且在成岩机制及成岩构造背景上与铜陵矿集区侵入岩一致,即矿区中酸性侵入岩岩浆起源于富集岩石圈地幔熔融和上涌并引起下地壳物质部分熔融,岩浆作用发生于区域构造应力由挤压向伸展过渡的构造背景之下。另外,对比矿区火山岩与宁芜庐枞等地区发育的火山岩可以发现,其成岩年龄基本一致,均为130Ma左右,且它们的地球化学特征类似。因此,茶亭铜金矿区发育的侵入岩与铜陵矿集区侵入岩一致,而火山岩地质地球化学特征与宁芜、庐枞等矿集区发育的火山岩相一致,且均未见矿化。矿区赋矿石英闪长玢岩与铜陵矿集区内侵入岩一致的地质地球化学特征及成因机制,也指示其成矿专属性的相似性。
[Abstract]:In recent years, the newly discovered scale of Chating area in Xuancheng, Anhui Province, is expected to be large-super-porphyry copper-gold deposit. On the basis of systematically collecting the previous research data and synthesizing the latest exploration results in the mining area, this paper combines the indoor petrography, zircon U-Pb isotopic geochronology and main trace elements through the regional geological survey and the cataloguing of the borehole cores in the mining area. The geological and geochemical characteristics of magmatic rocks in the Chating copper and gold deposit area have been preliminarily determined by the studies of rare earth elements, zircon HF isotopes and Sr-Nd-Pb isotopes of whole rocks and plagioclase monomorphic minerals. The source of diagenetic material and diagenesis mechanism of magmatic rocks in mining area are discussed. The main knowledge and results obtained are as follows: 1. The volcanic rocks in the Chating copper and gold deposit area of Xuancheng are mostly covered by Quaternary surface sediments. The main rock types are crystalline lithic tuff and hornblende andesite, which show the characteristics of low alkali, low sodium, rich potassium and low titanium, etc. The magmatic intrusions are located under the regional volcanic strata, and the main rock types are intermediate-acid quartz diorite porphyrite, which is the main ore-bearing rock and diorite-porphyrite in the copper deposit of Chatiing. The diorite lamprophyre is cut in the form of veins. The chemical composition of intrusive rocks shows the characteristics of rich alkali, rich sodium and low titanium. The LA-ICP MS zircon U-Pb age of the intrusive rocks in the Xuancheng Chatiing area is 137.8 卤1.3 Ma for quartz diorite porphyrite, 135.9 卤1.2 Mafor for diorite porphyrite and 138.0 卤1.3 Mafor for dioric lamprophyre, indicating that the intrusive rocks were diagenetic in early Cretaceous. The U-Pb ages of crystalline tuff and hornblende andesite are 130.2 卤1.2Ma and 132.2 卤1.6 Ma, respectively, indicating that the volcanic rocks are the product of magmatic eruption in the same period. The diagenetic age of volcanic rocks in the area is early Cretaceous. 3. The ore-bearing diorite porphyrite in Xuancheng Chatiing mine is rich in light rare earth elements and large ion lithophile elements, and is depleted of high field strength elements. The zircon HF isotopic composition and the Sr-Nd-Pb isotopic composition of the whole rock and plagioclase are between the lower crust and the enriched mantle, indicating that the magmatic rocks in the Chatiing mining area have the characteristics of crust-mantle mixing. It is found by comparison that the geochemical characteristics mentioned above are similar to those of intrusive rocks in faulted uplift areas such as Tongling ore concentration area, and are similar to those in Ningwu area. There are some differences in intrusive rocks in Luzong and other fault-depression areas. By comparing with other magmatic rocks in the tectonic-magma metallogenic belt of the middle and lower reaches of the Yangtze River, it is found that the ore-bearing diorite porphyrite was not only in the diagenetic epoch. Moreover, the diagenetic mechanism and diagenetic structure background are consistent with the intrusive rocks in Tongling ore concentration area, that is, the intermediate-acid intrusive magma of the ore area originated from the melting and upwelling of the enriched lithospheric mantle and caused partial melting of the lower crust material. Magmatism occurred in the tectonic setting of regional tectonic stress transition from compression to extension. In addition, the volcanic rocks developed in comparison with those developed in Ningwu, Luzong and other areas can be found to be basically the same diagenetic age, all of which are about 130Ma, and their geochemical characteristics are similar. Therefore, the intrusive rocks developed in the Chating copper-gold deposit area are consistent with the intrusive rocks in Tongling ore concentration area, while the geological and geochemical characteristics of volcanic rocks are consistent with those developed in Ningwu and Luzong ore concentration areas, and no mineralization has been observed. The geological and geochemical characteristics and genetic mechanism of the ore-bearing diorite porphyrite are consistent with the intrusive rocks in Tongling ore concentration area, which also indicate the similarity of metallogenic specificity.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P618.41;P618.51

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