Microbial iron reduction in the formation of iron ore caves

传统上，人们认为洞穴只能通过地下水溶解岩石而形成;然而，硫酸洞穴的不寻常化学表明微生物也可能在洞穴形成中发挥重要作用。 通过研究这种生物地球化学，研究人员发现洞穴可以通过硫化氢气体的微生物氧化形成，这占全球洞穴形成的25%。 他们假设了微生物驱动洞穴形成的一种新的潜在机制，基于富铁岩石（称为带状铁地层; BIF）中铁（III）矿物的微生物呼吸。 在BIF洞穴形成过程的识别是重要的，因为它大大扩展了洞穴形成的环境，为许多稀有和濒危动物物种提供了重要的地下栖息地。 这些BIF洞穴的位置与具有全球经济意义的铁矿石的存在之间也有很强的相关性，为钢铁生产提供了原材料。 这种相关性表明，洞穴形成过程可能与这些重要铁矿床的形成有关。 通过更好地了解形成洞穴的微生物过程，有可能选择性地识别导致矿石形成的过程。 这可能有助于更准确地有针对性地识别和开采铁矿床，限制勘探此类矿石往往产生的环境影响。研究人员的初步研究表明，BIF洞穴内存在活性Fe（III）还原微生物群落，孔隙流体中存在丰富的溶解Fe（II），以及Fe（III）相还原溶解的纹理证据。总之，这些观察结果表明，微生物Fe（III）的减少可能是负责驱动质量分离，而地下水流可能是负责Fe（II）的去除，以创建洞穴空隙。 因此，研究人员将测试这一假设，即Fe（III）还原微生物的活动是铁矿石洞穴形成的原因。 为了验证这一假设，他们将使用一种方法，整合了地球化学，环境微生物学，实验室微观，Fe（III）生物还原的动力学研究，以及现场规模的经验数据。 模型的Fe（III）还原率和Fe（II）运输将被用来整合这一经验数据与潜在的洞穴形成过程在一个范围内的规模，从微观到区域。 这些数据将使他们能够限制铁洞形成的机制和速率，并确定微生物在铁洞洞穴形成中的作用。

Traditionally, it was thought that caves formed only through the dissolution of rock by groundwater; however, the unusual chemistry of sulfuric acid caves suggested that microorganisms could also play an important role in cave formation. By studying this biogeochemistry, researchers discovered that caves could form through microbial oxidation of hydrogen sulfide gas, which accounted for as much as 25% of cave formation worldwide. They have hypothesized a new potential mechanism for microbially-driven cave formation, based on microbial respiration of iron(III) minerals in iron-rich rocks (known as banded iron formations; BIF). The identification of cave forming processes in BIF is significant as it dramatically expands the environments in which caves can form, which provide critical subterranean habitats for many rare and endangered animal species. There is also a strong correlation between the location of these BIF caves and the presence of iron ores of global economic significance, providing the source material for the production of steel. This correlation suggests that the cave forming processes may be linked to the creation of these important iron ore deposits. By gaining a better understanding of the microbial processes that form caves, it may be possible to selectively identify the processes that lead to ore formation. This may allow for more precisely targeted identification and mining of iron ore deposits, limiting the environmental impact that prospecting for such ores often generates. Investigators' preliminary research has demonstrated the presence of active Fe(III) reducing microbial communities within BIF caves, abundant dissolved Fe(II) in pore fluids, and textural evidence of reductive dissolution of Fe(III) phases. Together, these observations suggest that microbial Fe(III) reduction may be responsible for driving mass separation, while groundwater flow may be responsible for Fe(II) removal to create the cave voids. Investigators will therefore test the hypothesis that the activities of Fe(III) reducing microorganisms are responsible for the formation of iron ore caves. To test this hypothesis they will use an approach that integrates biogeochemistry, environmental microbiology, laboratory microcosms, kinetic studies of Fe(III) bioreduction, and field-scale empirical data. Models of Fe(III) reduction rates and Fe(II) transport will be used to integrate this empirical data with potential cave forming processes across a range of scales, from microscopic to regional. Together these data should allow them to constrain the mechanisms and rates of iron cave formation and determine the role that microbes play in iron cave speleogenesis.