祁连山木里三露天天然气水合物伴生矿物特征及其指示意义

发布时间：2018-05-01 12:07

  本文选题：祁连山木里三露天 + 天然气水合物　； 参考：《中国地质大学(北京)》2016年硕士论文

【摘要】：祁连山木里三露天天然气水合物与碳酸盐相伴产出是一种常见现象。为了探讨碳酸盐、黄铁矿的形成与天然气水合物的关系,本文对研究区31件碳酸盐样品、25件黄铁矿样品进行了矿物学、微量元素、稀土元素、碳酸盐碳氧同位素、黄铁矿硫同位素的分析测试。根据对伴生碳酸盐和黄铁矿的野外观察及镜下鉴定,碳酸盐可以分为4种类型:(1)薄层状碳酸盐,厚2-4cm,主要分布于天然气水合物层段的泥岩中;(2)薄壳状碳酸盐,厚度小于1mm,一般分布于天然气水合物层段的泥岩微裂隙中;(3)菱形晶簇状碳酸盐,晶形较好,主要分布于天然气水合物附近的泥岩、粉-细砂岩中;(4)微细浸染状碳酸盐,主要分布于黑色泥岩和炭质泥岩中。黄铁矿分为3种类型:(1)薄膜状,厚度小于1mm,一般分布于天然气水合物附近的粉-细砂岩裂隙中;(2)条带状,长度3-5cm,主要分布于灰黑色泥岩中;(3)结核状,直径不超过1cm,主要分布于黑色泥岩中。分析结果显示,不同类型碳酸盐、黄铁矿的矿物学、地球化学特征具有明显区别。菱形晶簇状碳酸盐具有清楚的晶形,其微量元素含量较低、稀土元素含量较高,Ni/Co7,相比其它三类碳酸盐,认为菱形晶簇状碳酸盐形成于相对还原的环境。并且,不同类型碳酸盐的碳同位素有着明显区别。薄层状和薄壳状碳酸盐碳同位素相对偏正,平均为2.5‰和3.5‰,浸染状碳酸盐碳同位素平均-0.13‰,而菱形晶簇状碳酸盐相对偏负,最低达-6.4‰,平均为-2.41‰。综合认为,菱形晶簇状碳酸盐可能与天然气水合物的分解有关,其碳源部分来自于天然气水合物分解释放的甲烷。薄膜状黄铁矿中则观察到一种新的晶体形态——八角截面体,具有典型的自生特征。条带状黄铁矿和结核状黄铁矿在镜下不能观察到好的晶形,并且显示被其它矿物所充填,反应了较老的形成时间。与其它两类黄铁矿相比,薄膜状黄铁矿具有相对较低的硫同位素值,δ34SV-CDT值为-20.9‰~17‰,平均为1.25‰,其形态与薄片状天然气水合物相似,且与天然气水合物共生或分布在天然气水合物产出位置附近,其可能是天然气水合物分解释放的甲烷与硫酸盐还原的结果。通过研究得出,菱形晶簇状碳酸盐和薄膜状黄铁矿形成都跟天然气水合物分解有关,这两种自生矿物可能记录了天然气水合物层曾经的顶底界,可以作为祁连山冻土区乃至其它冻土区天然气水合物勘查的示踪性性矿物。
[Abstract]:The concomitant production of natural gas hydrate and carbonate in Muli three open air in Qilian Mountain is a common phenomenon. In order to study the relationship between the formation of carbonate, pyrite and natural gas hydrate, the mineralogy, trace elements, rare earth elements, carbonate carbon and oxygen isotopes of 31 carbonate samples and 25 pyrite samples were studied in this paper. Analysis and test of sulfur isotopes in pyrite. According to the field observation and microscopic identification of associated carbonate and pyrite, carbonates can be divided into four types: 1) thin layer carbonate, 2-4 cm thick carbonate, mainly distributed in mudstone of gas hydrate formation and (2) thin shell carbonate. The mudstone with thickness less than 1 mm, which is generally distributed in the microfracture of natural gas hydrate formation, is a rhombic cluster carbonate with good crystal shape. It mainly distributes in mudstone near natural gas hydrate and in silt-fine sandstone. Mainly distributed in black mudstone and carbonaceous mudstone. Pyrite is divided into three types: 1) thin film, less than 1 mm thick, generally distributed in the siltstone / fine sandstone fissure near natural gas hydrate with a length of 3 to 5 cm, and mainly distributed in the gray and black mudstone. Not more than 1 cm in diameter, mainly distributed in black mudstone. The results show that the mineralogical and geochemical characteristics of different types of carbonate and pyrite are obviously different. The rhombohedral cluster carbonate has a clear crystal shape, its trace element content is low, and its rare earth element content is higher than that of other three kinds of carbonate, it is considered that the rhombic cluster carbonate was formed in the environment of relative reduction. Moreover, the carbon isotopes of different types of carbonates are obviously different. The carbon isotopes of thin layer carbonate and thin shell carbonate are relatively positive, with average values of 2.5 鈥，

本文编号：1829270