A new fossil vent biota in the Ballynoe barite deposit, Silvermines, Ireland: Evidence for intracratonic sea-floor hydrothermal activity about 352 Ma
A new fossil vent biota in the Ballynoe barite deposit, Silvermines, Ireland: Evidence for intracratonic sea-floor hydrothermal activity about 352 Ma
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DOI：
10.2113/98.3.649
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发表时间：
2003-05-01
期刊：
影响因子：
--
通讯作者：
Russell, MJ
中科院分区：
文献类型：
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作者：
Boyce, AJ;Little, CTS;Russell, MJ
关于密西西比期碳酸盐岩中重要的爱尔兰型Zn + Ph +/- Ba +/- Ag矿床的形成时间存在相当大的争议。银矿矿床被定义为这种类型的端元，因为它们被解释为显示海底沉积的纹理指示。支持这一解释的最有力论据之一是关于热液喷口区的报告，包括巴利诺露天重晶石存款中的黄铁矿烟囱。本文通过描述来自同一喷口区的热液喷口动物群来补充这一证据，该动物群包括由块状黄铁矿和明显源自微生物的赤铁矿化丝状物组成的精细黄铁矿化蠕虫管。蠕虫管是非常相似的化石蠕虫管从现代和古代火山岩托管块状硫化物矿床，和丝状微化石有相似之处，现代铁氧化细菌。我们没有发现蠕虫管和正常的密西西比化石之间的相关性，如海百合，在直接下伏的巴利诺下盘被黄铁矿取代破坏了原始形态。蠕虫管和寄主黄铁矿的硫同位素组成基本上与喷口田黄铁矿和银矿硫化物的主硫化矿阶段的硫同位素组成相同，均具有约-20 ‰的平均值，表明开放系统细菌成因硫化物源。这些发现为银矿部分矿体的喷流性质提供了额外的证据，并意味着爱尔兰矿田在图尔奈阶晚期（类似于352 Ma）就开始矿化。
Considerable controversy exists as to the timing of the important Mississippian carbonate-hosted Irish-type Zn + Ph +/- Ba +/- Ag deposits. The Silvermines deposits have been defined as an end member of this style in that they have been interpreted to display textures indicative of sea-floor deposition. One of the strongest arguments in favor of this interpretation was the report of a hydrothermal vent field, including pyritic chimneys in the Ballynoe open-pit barite deposit. This paper adds to that body of evidence by describing a hydrothermal vent fauna from the same vent field, consisting of a delicately pyritized worm tube hosted by massive pyrite and hematized filaments of apparent microbial origin. The worm tube is remarkably similar to fossil worm tubes from modern and ancient volcanic-hosted massive sulfide deposits, and the filamentous microfossils have similarities to modern Fe-oxidizing bacteria. We have found no correlation between the worm tube and normal Mississippian fossils such as crinoids, whose replacement by pyrite in the immediately underlying Ballynoe footwall destroys original morphology. The sulfur isotope composition of the worm tube and host pyrite is essentially identical to that of the vent field pyrite and the main sulfide ore stage of Silvermines sulfides, all having a mean value about -20 per mil, indicating an open-system bacteriogenic sulfide source. These discoveries provide additional evidence for the exhalative nature of parts of the Silvermines orebodies, and imply that mineralization had begun in the Irish ore field by the late Tournaisian (similar to352 Ma).