Pyrite trace metal and sulfur isotopic compositions track metalliferous fluid circulation within the Ordovician/Silurian organic-rich black shales in the eastern Sichuan Basin, southwestern China

IF 5.6 2区 工程技术 Q2 ENERGY & FUELS
Shaojie Li , Qilin Xiao , Suyang Cai
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引用次数: 0

Abstract

Depicting metalliferous fluid flows in sedimentary basins has a remarkable implication for understanding the formation and evolution of organic-rich sediments. The Middle-Upper Yangtze region in South China hosts voluminous gaseous hydrocarbons and MVT-type ZnPb deposits. Natural gases are mainly distributed in the Sichuan Basin, yet ZnPb deposits are found in surrounding regions of the basin. Such a unique distribution pattern implies that the interplay between metalliferous fluids and organic-rich sediments may be extensive in the boundary of these two types of deposits. A typical Ordovician/Silurian (Wufeng/Longmaxi formations) organic-rich black shale outcrop occurs in the eastern boundary of the Sichuan Basin. Pyrites are frequently distributed across this section, providing an ideal opportunity to investigate features of metalliferous fluids and their potential impacts on organic-rich sediments. Pyrites associated with high-angle carbonate veinlets are recognized in the studied area, and this group of pyrites (“Group 2”) commonly display planar-laminated morphologies, moderate δ34S values (0.78 ‰–8.86 ‰), and elevated trace metal contents (Ni, Pb, Mn, Mo, Tl, and REE) than those not associated with carbonate veinlets. These features suggest that this group of pyrites may be precipitated via local metalliferous fluid flows. Besides, pyrites with relatively lower trace metal contents can be further divided into two groups, including a group of euhedral/subhedral pyrites with more depleted δ34S values (−18.06 ‰ – -1.15 ‰; “Group 1”) and a group of planar-laminated/cubic pyrites with enriched δ34S values (10.55 ‰–37.62 ‰; “Group 3”). Pyrites of Group 1 and Group 3 may be formed via bacterial sulfate reduction (BSR) and thermochemical sulfate reduction (TSR), respectively. The discovery of fluid-related, trace-metal-enriched pyrites implies that fluid circulation within organic-rich black shales has the potential to remobilize, transport, and re-deposit trace metals. Besides, metalliferous fluid may also promote organic matter maturation within the Sichuan Basin. The outcomes of this study, combined with previous findings of metalliferous fluid flows in the center of the basin and ZnPb mineralization belts surrounding the basin, imply that a widespread Ediacaran-Palaeozoic fluid circulation system may exist in the Middle-Upper Yangtze region.
黄铁矿痕量金属和硫同位素组成追踪中国西南部四川盆地东部奥陶纪/志留纪富含有机质黑色页岩中的冶金流体循环
描绘沉积盆地中的金属流体流对于了解富含有机质沉积物的形成和演化具有重要意义。中国南方的长江中上游地区蕴藏着大量的气态碳氢化合物和 MVT 型锌铅矿床。天然气主要分布在四川盆地,而锌铅矿床则分布在盆地周边地区。这种独特的分布模式意味着,在这两类矿床的边界地区,冶金流体与富含有机质的沉积物之间可能存在着广泛的相互作用。四川盆地东部边界有一个典型的奥陶系/志留系(五峰/龙马溪地层)富含有机质的黑色页岩露头。黄铁矿经常分布在这一地段,为研究金属流体的特征及其对富有机沉积物的潜在影响提供了理想的机会。与高角度碳酸盐细脉相关的黄铁矿在所研究的地区得到了确认,与不与碳酸盐细脉相关的黄铁矿相比,这组黄铁矿("第 2 组")通常显示出平面层状形态、中等的 δ34S 值(0.78 ‰-8.86 ‰)和较高的微量金属含量(镍、铅、锰、钼、钛和稀土元素)。这些特征表明,这类黄铁矿可能是通过当地的金属流体流沉淀而成的。此外,微量金属含量相对较低的黄铁矿可进一步分为两组,包括一组δ34S值较低的八面体/亚面体黄铁矿(-18.06‰--1.15‰;"第1组")和一组δ34S值较高的平面层状/立方体黄铁矿(10.55‰-37.62‰;"第3组")。第 1 组和第 3 组黄铁矿可能分别是通过细菌硫酸盐还原(BSR)和热化学硫酸盐还原(TSR)形成的。与流体有关的痕量金属富集黄铁矿的发现,意味着富含有机质的黑色页岩内部的流体循环有可能使痕量金属再移动、迁移和再沉积。此外,含金属流体还可能促进四川盆地内有机质的成熟。本研究的结果,结合之前在盆地中心金属流体流和盆地周围锌铋成矿带的发现,意味着在长江中上游地区可能存在一个广泛的埃迪卡拉-古生代流体循环系统。
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来源期刊
International Journal of Coal Geology
International Journal of Coal Geology 工程技术-地球科学综合
CiteScore
11.00
自引率
14.30%
发文量
145
审稿时长
38 days
期刊介绍: The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.
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