摘要
【目的】滇黔北坳陷不仅是我国南方海相页岩气的重要探区和产地,也是我国重要的伴生有关键金属的大型—超大型密西西比河谷(MVT)型铅锌成矿区。铅锌矿床中不断发现高Pb、Zn含量的沥青或古油藏,探讨研究区黑色页岩干酪根中微量元素分布特征对铅锌找矿选区具有启示意义。【方法】以滇黔北坳陷东部大石板、凉风坳、毛坝地区的黑色页岩露头为研究对象,采用微波消解法对黑色页岩中干酪根进行前处理,并结合岩相学及矿相学观察,对黑色页岩及干酪根中微量元素进行分析测试,通过黑色页岩干酪根中元素地球化学特征研究其成矿的物质贡献以及黑色页岩沉积环境。【结果】Pb、Zn、Cd、Bi、Sb、V、Cr、Ni总体在全岩中含量高于干酪根,Ag、Ge、U、Th在干酪根中含量高于全岩。全岩及干酪根中轻稀土相对富集、重稀土相对亏损。全岩中Eu、部分Ce呈弱负异常;干酪根表现出较强的Ce负异常,Eu弱负异常,总稀土含量均高于全岩。在五峰组—龙马溪组干酪根中三个氧化还原指标(U/Th、Ni/Co、V/Cr)显示五峰组为贫氧—缺氧环境、龙马溪组为富氧—贫氧的环境;研究区利用Co元素计算古水深范围为6.85~54.37 m,Sr/Cu反映的古气候整体为温湿气候,Sr/Ba值均小于0.5,代表了微咸水沉积环境;同时五峰组古生产力大于龙马溪组。【结论】研究区五峰组—龙马溪组总体呈富氧—贫氧的动荡沉积环境,具有温湿气候的微咸水浅水陆棚相沉积特征。黑色页岩干酪根中微量元素可以为区域找矿选区评价提供依据。
[Objective]The Dianqianbei Depression is not only an important exploration and producing area of ma⁃rine shale gas in southern China,but also an important large-super large Mississippi Valley(MVT)type lead-zinc metallogenic area associated with key metals in China.Asphalt or ancient reservoirs with high Pb and Zn contents are constantly found in lead-zinc deposits.It is of great significance to explore the distribution characteristics of trace ele⁃ments in black shale kerogen in the study area for lead-zinc prospecting.[Methods]Taking the black shale outcrops in Dashiban,Liangfengao and Maoba areas in the eastern part of the Dianqianbei Depression as the research object,the kerogen in black shale was pretreated by microwave digestion method,and the trace elements in black shale and kerogen were analyzed and tested in combination with petrographic and mineralographic observation.The material contribution of mineralization and the sedimentary environment of black shale were studied by the geochemical characteristics of elements in black shale kerogen.[Results]The whole rock Pb,Zn,Cd,Bi,Sb,V,Cr,and Ni contents are higher than those in kerogen,and the contents of Ag,Ge,U and Th in kerogen are higher than those in whole rock.The light rare earth is relatively enriched and the heavy rare earth is relatively depleted in the whole rock and kerogen.Eu and part of Ce in the whole rock show weak negative anomalies.The kerogen shows strong Ce and Eu weak negative anomalies,and the total rare earth content is higher than that of the whole rock.Three redox indicators(U/Th,Ni/Co,and V/Cr)in the kerogen of the Wufeng Formation-Longmaxi Formation showed that the Wufeng For⁃mation was oxygen-poor-anoxic,and the Longmaxi Formation was oxygen-rich-oxygen-poor;the ancient water depth calculated by Co element in the study area is 6.85-54.37 m.The paleoclimate reflected by Sr/Cu is warm and humid,and the Sr/Ba value is less than 0.5,representing the sedimentary environment of brackish water.Furthermore,the Wufeng Formation has greater paleoproductivity than the Longmaxi Formation.[Conclusions]Wufeng Formation-Longmaxi Formation in the study area are an oxygen-rich-oxygen-poor turbulent sedimentary environment,with a warm and humid climate of brackish water shallow shelf facies sedimentary characteristics.The trace elements in the black shale kerogen can provide a basis for the evaluation of regional prospecting areas.
作者
裴子璇
胡煜昭
许赛华
张启梦
PEI ZiXuan;HU YuZhao;XU SaiHua;ZHANG QiMeng(Faculty of Land Resource Engineering,Kunming University of Science and Technology,Kunming 650093,China;Sichuan Mineral Resources Exploration Group Co.,Ltd,Chengdu 610057,China)
出处
《沉积学报》
北大核心
2025年第6期2264-2281,共18页
Acta Sedimentologica Sinica
基金
国家自然科学基金项目(41672073)
昆明理工大学2022年研究生拔尖创新人才项目(CA22369M111A)。
关键词
元素地球化学
干酪根
五峰组
龙马溪组
滇黔北坳陷东部
element geochemistry
kerogen
Wufeng Formation
Longmaxi Formation
eastern Dianqianbei Depression
