我国南方早古生代聚煤过程中硫的生物地球化学行为及成矿效应

Biogeochemical Characteristic and Mineralization Process of Sulfur during the Coal Accumulation Process in Early Paleozoic of Southern China

我国早古生代煤主要蕴藏在煤炭资源贫乏的南方各省,因坚硬似岩石又称之为石煤,储量极为丰富,仅浙江至广西就分布有长约1 600 km的石煤矿,石煤中含有或富集了多种金属元素,目前已发现的伴生元素达60多种,如钒、钼、磷、钡、镍、铀、金、银等,局部可形成工业矿床而作为某种矿物资源单独开采,是我国有待系统开发的潜在的多矿产资源。研究表明:石煤形成于以菌藻类为主的生物堆积和浅表海或古陆边缘的海相还原环境,含有大量的菌藻类(如蓝绿藻和褐藻)、古孢子、海绵骨针及一些分类尚不明确的原始动、植物等生物化石,具有低碳、高灰、高硫的特点,海相沉积环境和藻类对硫的机械富集与捕集是造成含石煤岩系中硫含量高的主要因素。石煤中富集的金属元素绝大多数是亲硫元素,早期聚煤作用过程是石煤中伴生元素富集的重要阶段,多金属硫化物是石煤中金属元素最重要的赋存形式,主要有硫磺、黄铁矿、黄铜矿、闪锌矿、方硫镍矿、辉镍矿、辉砷镍矿、针镍矿、含镍黄铁矿和硫钼矿等,大量实验及同位素研究资料揭示了细菌还原硫酸盐作用是导致大规模金属硫化物矿化最可能的生物营力,也是石煤和金属硫化物矿床主要的成煤和成矿机制,硫的生物地球化学行为直接影响了金属元素的富集与赋存状态,但早期聚煤过程中硫的生物地球化学转化过程和金属元素超常富集的关系等基础地质地球化学问题仍未得到完善解决。因此,深入研究早古生代聚煤过程中硫的生物地球化学行为,不仅可以揭示我国南方含石煤岩系与多金属硫化物的共生机理和成矿效应,为我国含煤岩系中硫的形成机理及金属微量元素的富集效应研究提供科学依据,而且可以为提炼石煤中的稀有金属提供理论支持,为我国国民经济建设提供更多急需的稀散、贵重金属材料。

The early Paleozoic coals were well-developed in southern provinces of China poor in coal resources.It was also known as ＂stone coal＂ due to being hard like rock.Stone coal was widely spread throughout southern China.Though the stone coal bed is discontinuous,the horizon can be recognized in a band of transitional shelf zone sediments stretching 1 600 km only across southern China from Zhejiang Province to Guangxi Province.There contains and sometimes enriches a variety of metal elements in stone coal.It has been found that as many as 60 species of associated elements such as vanadium,molybdenum,phosphorus,barium,nickel,uranium,gold,silver,etc.in stone coal up to now.Because some elements of the special enrichment can form industrial deposits in some areas,stone coal can be used as a single extraction of mineral resources and will have a great development potential to be multi-mineral resources.Researches show that stone coal formed in the marine reducing environment with abundant bacteria and algae bioaccumulation.A large number of fossils,such as bacteria and algae（e.g.Cyanobacteria and brown algae）,acritarchs,the paleospore,the sponge spicules and a number of primitive fauna and flora whose categories are not clear contained in stone coal.Low carbon,high ash and high sulfur contents were the main characteristics of stone coal.The high sulfur quantity could be commonly interpreted as the marine sedimentary environment and the mechanical concentration and sequestration of algae.Most of the enrichment metal elements in stone coal are chalcophile.The early coal accumulation process is an important stage with enrichment of associated elements in stone coal.Polymetallic sulfides（e.g.sulfur,pyrite,chalcopyrite,sphalerite,vaesite,polydymite,dobschauite,millerite,blucite and jordisite,etc.） are the main occurrences of metal elements in stone coal.A large number of experiments and isotope data reveal that the bacterial sulfate reduction is the most likely biological agent,and it not only leads to the large-scale mineralization of metal sulphide,but also is the major coal and ore-forming mechanism of the stone coal and metal sulphide deposits,and apparently the biogeochemical behavior of sulfur directly impacts the occurrence and enrichment of the metal elements.But the conversion of sulfur biogeochemical processes and the relationship between the abnormal enrichment of metals and other basic geological and geochemical issues are not yet to be improved to solve during the early coal accumulation process.Therefore,further study of biogeochemical behavior of sulfur in the early Palaeozoic coal accumulation process,not only helps revealing the symbiotic mechanism and ore-forming effect of stone-coal bearing formation and polymetallic sulfide in South China,but also helps providing scientific basis for the formation mechanism of sulfur and the enrichment effect of metal trace elements in China′s stone-coal bearing formation.In addition,those researches could help providing the theoretical support for the extraction of rare metals in the stone coal,and also help providing scattered and precious metal materials in urgent need for the construction of China＇s national economy.