晚古生代高有机硫煤中硫的同位素地球化学及赋存状态

It is generally believed that almost all the high-sulfur coals were deposited in coastal environments. However, a recent theory suggested that some superhigh-organic-sulfur coals were deposited in a marine-influenced environment, but were subjected to sulfur-rich hydrothermal solutions and igneous intrusion, needing more evidence of sulfur isotopes. Some recent studies also showed that the superhigh-organic-sulfur (>4%) coals showed totally different trends of the sulfur isotope data compared to other coals, indicating that different sulfur origin and/or enrichment mechanism(s) involved in superhigh-sulfur coal formation, which still needs more studies. Some (super)high-organic-sulfur coals of the Late Carboniferous from the northern China and of the Late Permian from the southern China, were collected for the present study. The coal petrology, coal quality, trace element geochemistry, mineralogy, and the sulfur isotope geochemistry of the (super)high-organic-sulfur coals were planned to be investigated, which would be compared with the low and medium sulfur coals. The paleoenvironment is expected to rebuilt, in which of the (super)high-organic-sulfur coals were deposited. A new enrichment model of the sulfur in the (super)high-organic-sulfur coals is expected to be established. A sequential extraction method was planned to be established, which would be used to separate the sulfur forms with different chemical activities in (super)high-organic-sulfur coals, expecting a further understanding of the relationship between organic and pyritic sulfur in the coal.

普遍认为高硫煤的形成与海水有关，但是有新观点认为一些超高硫煤的形成与海底火山喷发、热液活动等有关，然而目前尚缺少硫同位素方面的证据。近期一些研究数据还显示，超高有机硫（>4%）煤的硫同位素特征与低、中硫煤明显不同，这种差异说明超高有机硫煤中硫的来源和/或富集途径具有特殊性，但是仍需要更多的数据来证明和解释。项目拟以我国北方晚石炭世以及南方晚二叠世典型（超）高有机硫煤为主要研究对象，通过与低、中硫煤对比，分析各种形态硫的同位素组成特征及其在典型剖面上的分布模式，综合煤岩学、煤质学、元素地球化学、矿物学等方面的信息，重塑（超）高有机硫煤形成的古环境，建立特定环境下（超）高有机硫煤中硫的富集机制。项目还拟用逐级化学提取法分离煤中不同形态的硫，在“铬还原法”的基础上细化分离方案，将煤中硫分为不同化学活性的硫组分，以期加深对煤中硫的赋存状态以及有机硫与黄铁矿关系的理解。

研究选取了我国典型（特）高有机硫煤分布矿区，包括北方（山西汾西和陕西韩城）石炭-二叠高有机硫煤和沉积于局限碳酸盐台地的南方（广西合山和云南砚山）晚二叠世特高有机硫煤，详细分析了其黄铁矿硫与有机硫的同位素组成。与世界上其他不同含硫量煤的同位素数据进行对比，发现我国南方的特高有机硫煤的硫同位素组成明显偏负。对于砚山、合山晚二叠世特高有机硫煤而言，陆地火山喷发产物并不是其主要硫源；（正常）海水硫酸盐通过微生物还原、歧化等作用可以使硫同位素组成偏负，但是硫含量并不充足，也不能很好地解释“特”高硫煤与普通高硫煤的差异；海底火山喷流，可为特高硫煤提供额外硫源，但是需要叠加微生物作用才可能达到其亏损重同位素的程度；晚二叠世全球硫循环异常，海洋硫酸盐硫同位素组成出现明显的负漂移，与我国南方晚二叠世高硫煤中极高的硫含量和极负硫同位素数值比较吻合，硫循环异常（e.g.硫化海水）很可能是高硫煤形成的直接原因之一。特高有机硫煤中黄铁矿硫含量相对较低，不只是沉积环境“贫铁”造成的，硫同位素数据显示，在某些情况下，黄铁矿硫可以向有机硫转化。