Abstract

The Ordos Basin developed a large depression-type lake basin in the Late Triassic. Here, we report on pyrites from lacustrine hydrothermal sedimentary rocks that were found at the bottom of a black shale layer from the Chang 7-3 sub-member of the Triassic Yanchang Formation in Tongchuan and Yaoqu and Well Z9 sections, on the southern margin of the Ordos Basin. Observations of field outcrops and underground cores were used to identify vein and brecciated pyrites that are distributed within water-explosive dolomite breccias or sandwiched in a textured layer of hydrothermal sedimentary rock. Based on previous work, scanning electron microscopy observations, electronic probe microanalysis, nano-SIMS trace-element mapping and in situ sulfur isotope analyses were completed. The crystal form of pyrites is mainly cubic with surfaces mostly smooth and clean. Pyrites contain trace elements, such as As, Au, Co, Cu, Cr and Zn. The pyrite sulfur isotope values are enriched in ³⁴S (δ³⁴S_V-CDT = 7.31–10.05‰; average 8.49‰) and show that the pyrite is related to hydrothermal deposition. Late Triassic hydrothermal activity at the bottom of the lake provided sulfate for pyrite formation, and hydrothermal sulfide may have also been an important sulfur source.

1. KEY POINTS

2. Pyrites from lacustrine hydrothermal sediments were formed at the bottom of a black shale layer from the Chang 7-3 sub-member of the Triassic Yanchang Formation on the southern margin of the Ordos Basin.

3. The pyrite contains trace elements such as As, Au, Co and Ni.

4. In situ pyrite sulfur isotope values are enriched in ³⁴S and show that the pyrite is related to hydrothermal deposition with sulfur derived from sulfate and hydrothermal sulfide

抽象的

鄂尔多斯盆地在三叠纪晚期形成了一个大型的depression陷型湖盆。在这里，我们报道了湖相热液沉积岩中的黄铁矿，该矿床位于铜川，瑶曲三叠系延长组长7-3分段的长7-3亚段的黑色页岩层的底部，位于南端。鄂尔多斯盆地。野外露头和地下岩心的观察被用来识别分布在水炸白云岩角砾岩中或夹在热液沉积岩带纹理层中的脉状和角状黄铁矿。基于以前的工作，扫描电子显微镜观察，电子探针显微分析，纳米SIMS痕量元素标测和原位硫同位素分析已完成。黄铁矿的晶体形式主要为立方晶，表面大多光滑且清洁。硫铁矿含有微量元素，例如As，Au，Co，Cu，Cr和Zn。黄铁矿硫同位素值在富含³⁴ S（δ ³⁴小号_V-CDT = 7.31-10.05‰;平均8.49‰），并显示该黄铁矿涉及水热沉积。湖底的三叠纪晚期热液活动为形成黄铁矿提供了硫酸盐，而热液硫化物也可能是重要的硫源。

1. 关键点

2. 来自湖泊热液沉积物的硫铁矿形成于鄂尔多斯盆地南缘三叠系延长组的长7-3亚段黑色页岩层的底部。

3. 黄铁矿包含微量元素，例如As，Au，Co和Ni。

4. 在 原位黄铁矿硫同位素值富集³⁴ S和显示，黄铁矿涉及与硫热液沉积选自硫酸和热液硫化物衍生