沉积岩石氧化-还原性能参数研究及在沉积相分析中的应用

OXIDATION-REDUCTION BEHAVIOUR PARAMETERS OF SEDIMENTARY ROCKS AND THEIR APPLICATIONS TO SEDIMENTARY FACIES ANALYSIS

关键词:  沉积相分析  岩石氧化-还原参数  还原容量  岩石△Eh值  岩石Eh₇值

Key words:  sedimentary facies analysis  oxidation-reduction behaviour parameters  reducting capacity  △Eh value  Eh₇ value

摘要:

在沉积相研究中,对不同沉积环境中所形成的各种岩石进行系统的岩石氧化-还原性能参数的研究,对恢复和判断沉积相有重要的意义。笔者在沉积相的研究中,特别注意沉积岩石氧化-还原性能参数的系统分析,这些研究对阐明沉积环境特征,分析不同氧化-还原岩石带对某些沉积矿产的控制作用等方面起到了重要作用。
沉积岩石氧化-还原性能参数,目前没有公认的标准,参考国内外有关文献,笔者认为对沉积岩石氧化-还原性能起决定作用的是以下一些特征元素及其比值:低价铁(Fe^2-)含量及Fe^3-/Fe^2-比值,还原硫（S²）及S²/Fe^2-比值,有机碳（Cy）及其他变价元素。
在评价沉积岩石的还原容量时,只有当岩石中的全部还原组分都参加进去被测定,这样才可得出岩石还原性能的正确结论。70年代前苏联学者和（1965）使用强氧化剂KMnO₄在碱性条件下（pH=11—13）氧化沉积岩粉末取得岩石ΔEh值,此值是评价沉积岩石还原能力的一个主要参数。
岩石Eh₇值是评价沉积岩石氧化-还原性质的另一个重要参数。前苏联学者（1975）提出将沉积岩粉放入杯中,用蒸馏水调成膏状,然后用插有测量电极的橡皮塞盖住杯口,在密闭条件下测量岩石Eh、pH值的方法。为了采用统一的标准（pH=7）来比较这些数值的大小,作者用公式
Eh₇=K（pH_c—7）+Eh_c（K=59mv）
对所测岩石Eh_c值进行校正。参照地下水氧化-还原划分标准和前述综合参数,本文提出综合的沉积岩石氧化-还原性能参数的划分标准。
作者用中国华南某碳酸盐岩型铀矿床（产于石炭纪地层）和某黄铁矿床（产于泥盆纪地层）为例,详细论述了这两个矿区沉积相分析中用沉积岩石氧化-还原性质研究、判定沉积相（环境）的方法和意义。

Abstract:

The oxidation-reduction behaviour parameters of sedimentary rocks formed in different sedimentary environments have important implications for the restoration and identification of sedimentary facies. The systematic analysis of the parameters plays an important role in elucidating sedimentary environments and the controls of different oxidation-reduction rock zones on some of the sedimentary ore deposits.
Up to date, no generally recognized standards have been established for the oxidation-reduction behaviour parameters of sedimentary rocks. This paper suggests, referenced to the domestic and foreign literatures, that the oxidation-reduction behaviouss depend largely upon:(1)low-valence iron (Fe²⁺) contents and Fe³⁺/Fe²⁺ ratioes; reduced sulfur (S^2-) and S^2-/Fe²⁺ ratioes, organic carbon (Cy) and ether valence-varying elements.
In the evaluation of the reducting capacity of sedimentary rocks, only when all the reduction components are measured can the correct concepts on the reduction bchaviours of the rocks be obtained. In the 1960's, the former Russian scholars and (1965) gained the △Eh values for the oxidized sedimentary rock powder by using strong oxygenant KMnO₄ under alkaline conditions (pH=11-13). The values are considered as primary parameters for evaluating the reducting capacity of sedimentary rocks.
The Eh₇ values are another important parameters for evaluating the oxidation-reduction features of sedimentary rocks. The former Russian scholar (1975) once put forward a method to determine the Eh and pH values of sedimentary rocks by putting sedimentary rock powder into a cup, making the powder paste-like with distilled water, covering the cup with a rubber cork with determining electrodes inserted in it so as to determine Eh and pH values under sealed conditions. In order to compare these values with the unified standard (pH=7), the author proposed the formula
Eh=K(pH-7)+Eh_c (K=59 my)
to correct the determined Eh values of the rocks. In reference to the criteria for distinguishing the oxidation and reduction of ground water and the parameters cited above, new criteria for distinguishing the oxidation and reduction of sedimentary rocks are proposed in this paper.
Taking one carbonate rock-type uranium deposit(in the Carboniferous stata) and one pyrite deposit (in the Devonian strata) in southern China as examples, the present paper deals in detail with the analytical methods and significance of sedimentary facies (environments) with the aid of the study of the oxidation-reduction features of sedimentary rocks in the analysis of sedimentary facies of the two mining districts.