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| 滇西茅草坪脉状铜矿床脉体构造与成矿时代研究 | |
| 引用本文： | 程杨,宋玉财,薛传东,黄世强.滇西茅草坪脉状铜矿床脉体构造与成矿时代研究[J].地质学报,2015,89(3):583-598. |
| 作者姓名： | 程杨 宋玉财 薛传东 黄世强 |
| 作者单位： | 1. 中国地质科学院地质研究所,北京,100037;中国地质大学(北京),北京,100083 2. 中国地质科学院地质研究所,北京,100037 3. 昆明理工大学,昆明,650000 |
| 基金项目： | 国家自然科学基金、中国地质调查局地质调查项目 |
| 摘 要： | 西南三江造山带兰坪盆地西缘发育一条重要的脉状铜矿带,通常认为其成矿与盆地演化有关,而忽略了同处于盆地西缘的崇山剪切带和成矿的关系。茅草坪是近来在该带南段新发现的一例脉状铜矿床,本文通过详细野外工作厘定矿床地质特征,重点开展露头及镜下尺度的含矿脉体构造观察,在此基础上,分选成矿期热液白云母开展40 Ar/39 Ar定年,进而探讨成矿与剪切变形的关系。研究表明,矿床热液矿物以3种形式出现:热液蚀变晕、平行剪切面理的热液脉(A1脉)、横切剪切面理的热液脉(A2脉)。以上不同脉体中的矿物不仅有连续生长的特点,而且存在一定的交切关系,反映它们大致同期形成,但矿物沉淀顺序由早到晚变化。蚀变晕形成于早期,主要由电气石和石英组成,矿物呈强定向排列,长轴平行于剪切面理,为将挤压剪切应变下形成;A1脉形成略晚于蚀变晕,主要由电气石、石英、方解石、白云石、白云母、黄铜矿等组成,矿物弱定向排列,长轴近平行于剪切面理,为弱挤压剪切应变下形成;A2脉形成最晚,脉内矿物与A1脉相似,矿物无定向性、张性充填,反映形成时剪切变形已停止,可能为变形后应力松弛阶段形成的张性脉。因此,茅草坪矿床矿化形成在剪切作用由强变弱、直至停止的过程中,为剪切作用末期的产物。A1脉体中的白云母40 Ar/39 Ar坪年龄为20.34±0.19 Ma,可以代表矿床形成年龄,表明茅草坪地区的剪切作用结束于20Ma。综上表明,茅草坪矿床形成在崇山剪切带区域剪切走滑期间(末期),矿化受与剪切变形末期相关构造控制,是一个与崇山剪切带演化有关的脉状Cu矿床。因此,兰坪盆地西缘脉状铜矿带矿床成因应充分考虑与崇山剪切带演化的关系。 |
| 关 键 词： | 白云母40Ar/39Ar定年 脉状铜矿床 茅草坪 兰坪盆地 崇山剪切带 |
| 收稿时间： | 2014/12/8 0:00:00 |
| 修稿时间： | 2015/1/21 0:00:00 |
A Synthetic Study of Veins Structure and Mineralogenetic Epoch of Maocaoping Vein-Type Cu Deposit Western Yunnan |
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| CHENG Yang,SONG Yucai,XUE Chuandong and HUANG Shiqiang.A Synthetic Study of Veins Structure and Mineralogenetic Epoch of Maocaoping Vein-Type Cu Deposit Western Yunnan[J].Acta Geologica Sinica,2015,89(3):583-598. | |
| Authors: | CHENG Yang SONG Yucai XUE Chuandong and HUANG Shiqiang |
| Institution: | CHENG Yang;SONG Yucai;XUE Chuandong;HUANG Shiqiang;Institute of Geology,Chinese Academy of Geological Sciences;China University of Geosciences(Beijing);Department of Earth Sciences,Kunming University of Science and Technology; |
| Abstract: | An important vein-type copper metallogenic belt developed in western Yunnan, SW China. Previous researches mainly linked the Cu mineralization to the evolution of Lanping Basin, ignoring the shearing process of the Chongshan shear zone, however. Maocaoping vein-type Cu deposit, discovered recently, is located in the south of the the copper metallogenic belt, belonging to Chongshan shear zone. Geological features were determined during detailed field work, and the structural characteristic of the veins was confirmed by microscopic observation, as well. This paper gives the hydrothermal muscovite Ar-Ar age of the metallogenic period, and discuss the relationship between Cu mineralization and regional shear deformation in Maocaoping vein-type Cu deposit based on these work. Hydrothermal minerals in Maocaoping are presented as alteration halos, ore-bearing veins parallel to shear foliation of host rocks (named as A1 vein), and ore-bearing vein crosscutting shear foliation (named as A2 vein). Minerals of the alteration halos, A1 veins, and A2 veins have the characters of transitional growth, and crosscut each other in part. This phenomenon indicates that the minerals in them were generally formed in the same mineralization event, but precipitated during different stages. The alteration halos are mainly composed of tourmaline and quartz formed in earlier stage. The minerals are well orientated, parallel to shear foliation of host rocks in the halos, implying vein formation under stronger shear stress. Subsequently, A1 veins were formed, which mainly composed of tourmaline, quartz, calcite, dolomite, muscovite and chalcopyrite. The minerals are weaker orientated, approximately parallel to or oblique to shear foliation in the veins, suggesting the vein formation during waning stage of shear stress. A2 veins were finally formed and had similar minerals to the A1 veins. The minerals were non-orientated or grew with comb texture in the veins as the result of extensional filling, suggesting that the veins were formed immediately after shearing and possibly generated by nearly horizontal compressive stress. In summary, the mineralization is a result of the final stage of the shearing action which experienced a waning process.40Ar/39Ar dating of muscovite from the A1 veins determines a plateau age of 20.34±0.19 Ma, representing the mineralization age of the Maocaoping Cu deposit. This age also suggests that the shear deformation in the Maocaoping area ceased at about 20 Ma, apparently prior to the cessation timing (~14 Ma) in other areas in Chongshan shear zone. In conclusion, the Maocaoping vein-type Cu deposit was formed during the shearing of the Chongshan shear zone (late stage), and mineralization was controlled by tectonics related to the final-stage shearing deformation, which means that it is related to the evolution of the Chongshan shear zone. This study suggests that the origin of the vein-type Cu deposit in the west of Lanping Basin has a close relationship with the evolution of the Chongshan shear zone. |
| Keywords: | 40Ar/39Ar dating of muscovite vein type copper deposit Maocaoping Lanping Basin Chonghan Shear Zone |
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