西藏雄村铜金矿区侏罗纪砂岩物源分析：对区域构造背景的制约

发布时间：2018-07-15 14:43

【摘要】：西藏雄村铜金矿区位于冈底斯造山带中段南缘,其南紧邻雅鲁藏布缝合带(IYS)和日喀则弧前盆地,北为谢通门始新世大岩基。目前矿区主要由I、II、III号主矿体及相关矿化体组成,共探获I、II号矿体331+332+333类别铜金量230多万吨、金金属量210多吨、银金属量1000多吨,III号矿体预期铜金属量超过30万吨,且其他矿化体如洞噶金矿等也具有良好的找矿前景。矿床形成于早-中侏罗世,为与新特提斯洋洋壳俯冲作用形成的石英闪长玢岩有关的斑岩型矿床,查明矿床形成的大地构造背景对区域找矿方向具有重要指示意义,同时也为区域构造演化提供参考。本文通过对产于雄村组火山岩沉积岩中的砂岩进行研究,对砂岩采用主量、微量元素分析、锆石U-Pb年代学及镜下鉴定等研究工作,揭示雄村组砂岩的物源属性及物源区的大地构造背景,取得了如下认识:(1)镜下鉴定和A-CN-K图解表明雄村砂岩经历了较强的粘土化作用,但并不影响其对构造背景和物源的判别,碎屑含量大于80%,可见较多火山岩岩屑和长石碎屑,多发生粘土化,部分保留长石晶型假象,为长石岩屑砂岩。局部可见砂岩常具有粒序层理和类似磨拉石堆积特征,为活动的大洋火山岛弧所致。(2)雄村组砂岩中锆石基本为岩浆成因锆石,多具有清晰的振荡环带,且搬运距离不远。两个砂岩样品碎屑锆石年龄组成(205Ma~190Ma)说明雄村组砂岩物源主要为早侏罗世火山-侵入岩。(3)雄村砂岩的主量元素、微量元素及稀土元素特征与大洋岛弧环境相近,结合La-Th-Sc、Th-Sc-Zr/10、Th-Co-Zr/10和La/SC-Ti/Zr图解投图结果,确定雄村砂岩构造环境为大洋岛弧环境。(4)物源判别Co/Th-La/Sc和La/Th-Hf图解表明雄村砂岩物源区为长英质中-酸性火山岩和安山质火山岩,A-CN-K图解同样显示出砂岩成分与安山质、英安质火山岩相同。其次,雄村砂岩主量元素和微量元素特征与该区域火山岩特征相似,指示物源与雄村火山岩-侵入岩有关。所以雄村砂岩物源区为中-酸性安山质、英安质大洋岛弧火山岩,而非陆缘弧的产物。(5)雄村组砂岩形成晚于或近于雄村铜金矿床的成岩成矿年龄,砂岩地球化学特征及矿区内砂岩与成矿岩体的空间关系表明雄村火山岩就是雄村砂岩的物源,所以雄村铜金矿床形成于大洋岛弧环境而非陆缘弧环境,其赋矿围岩是一套产于洋内岛弧背景下的中-酸性火山岩夹火山沉积岩。(6)雄村岛弧型斑岩型矿床的识别对于找矿勘查具有两个重要的指示:一是从斑岩型矿床成群、成带分布的规律来看,在南木林-谢通门雅鲁藏布江北岸分布的大量侏罗纪岩体应该同样具有形成大洋岛弧有关矿床的成矿潜力;二是在雄村矿区的更北部应该存在与新特提斯洋俯冲有关的陆缘火山弧,同样具有形成产于陆缘弧背景下的斑岩型、矽卡岩型矿床。
[Abstract]:Xiongcun copper and gold deposit area in Tibet is located in the southern margin of the Gangdis orogenic belt, adjacent to the Yalu Zangbo suture zone (IYS) and Xigaze forearc basin, and to the north is the large Eocene rock base of Xetongmen. At present, the ore area is mainly composed of the main ore body of Izao II No. III and its related orebodies. A total of more than 2.3 million tons of copper and gold, more than 210 tons of gold and 1000 tons of silver of the No.3 ore body are found to have an expected copper and gold content of more than 300000 tons. Other orebodies, such as Dongga gold deposit, also have good prospecting prospects. The deposit was formed in the early and Middle Jurassic. It is a porphyry type deposit related to the new Tethys oceanic crust subduction. It is found that the tectonic setting of the deposit formation is of great significance to the direction of regional prospecting. It also provides a reference for regional tectonic evolution. In this paper, the sandstone occurring in the volcanic sedimentary rocks of Xiongcun formation is studied, and the main quantity, trace element analysis, zircon U-Pb geochronology and microscopic identification of sandstone are used. By revealing the provenance attribute of Xiongcun formation sandstone and the tectonic background of the source area, the following conclusions have been obtained: (1) the identification and A-CN-K diagram show that Xiongcun sandstone has experienced strong clayization, but it does not affect the discrimination of tectonic background and provenance. The content of clastic rocks is more than 80. More volcanic and feldspar clastic rocks can be seen. Most of them are clay-forming, and some of them retain the false appearance of feldspar crystal type, which is feldspar lithic sandstone. Locally visible sandstone is usually characterized by grain sequence stratification and similar to morlite accumulation, which is caused by active oceanic volcanic island arc. (2) in Xiongcun formation, zircon is basically magmatic zircon, most of them have clear oscillatory ring zone, and the transport distance is not far. The zircon age composition of two sandstone samples (205Ma-190Ma) indicates that the sandstones of Xiongcun formation mainly originated from early Jurassic volcanic-intrusive rocks. (3) the main elements, trace elements and rare earth elements of Xiongcun sandstone are similar to those of the oceanic island arc environment. Combined with La-Th-Sctr Th-Sc-Zr10 / 10 Th-Co-Zr / 10 and La / SC-Ti / Zr diagram, It is determined that the tectonic environment of Xiongcun sandstone is oceanic island arc environment. (4) the source identification of Co-Th-La-Sc and La-Th-Hf shows that the source areas of Xiongcun sandstone are felsic intermediate-acid volcanic rocks and anshanian volcanic rocks. Anglo-volcanic rocks are the same. Secondly, the main elements and trace elements of Xiongcun sandstone are similar to that of volcanic rocks in this area, and the indicator source is related to Xiongcun volcanic rocks and intrusive rocks. Therefore, the source area of Xiongcun sandstone is intermediate-acid anshan, Yingan oceanic island arc volcanic rock, rather than the product of continental margin arc. (5) the sandstone of Xiongcun formation was formed later than or near the diagenetic age of Xiongcun copper-gold deposit. The geochemical characteristics of sandstone and the spatial relationship between sandstone and ore-forming rock mass indicate that Xiongcun volcanic rock is the source of Xiongcun sandstone, so Xiongcun copper-gold deposit was formed in the oceanic island arc environment rather than the continental margin arc environment. The ore-bearing surrounding rock is a set of intermediate-acid volcanic rocks intercalated with volcanic sedimentary rocks under the background of Yu Yang inner island arc. (6) the identification of Xiongcun island arc porphyry deposits has two important indications for prospecting and exploration: first, the formation of porphyry deposits from porphyry deposits. From the rule of zonal distribution, a large number of Jurassic rock bodies distributed in the northern bank of the Nammulin-Xetongmen Yalu Zangbo River should have the same metallogenic potential to form oceanic island arc related deposits. Second, there should be continental margin volcanic arcs related to the new Tethys ocean subduction in the north of Xiongcun mining area, which also has porphyry type and skarn type deposit formed in the background of continental margin arc.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P618.41;P618.51

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