Abstract:

Hematite and goethite are the most stable iron oxides in nature and widely present in different compartments of the global
system. They are responsible for the color origin of many types of sediment. In addition, the formation and preservation of hematite and goethite have been used to track palaeoenvironmental information. There are several approaches to characterizing and distinguishing hematite and goethite, but the quantifying of the concentrations of hematite and goethite in natural samples has been restricted by low concentration, relative poor crystalline and fine-grained as well as the limits of specific analysis methods used. In this paper, the most common quantitative methods of hematite and goethite, including X-ray diffraction (XRD) and diffuse reflectance spectroscopy (DRS), have been introduced. Based on the qualitative analysis of the Cretaceous Oceanic Red Beds (CORBs) samples, we used the K-value method to quantify the hematite contents in the red shale samples from the Chuangde section in Tibet and obtained the hematite contents ranging from 3.81% to 8.11%. Analysis using DRS with multiple linear regression was performed to obtain the absolute contents of iron oxides within Aptian-Albian cyclic oceanic red beds in ODP Hole 1049C 12X Core, North Atlantic. The results reveal that the brown beds contain 0.13~0.82% hematite and 0.22~0.81% goethite. The orange beds contain 0.19~0.46% hematite and 0.29~ 0.67% goethite. The comparison of the calculated results with the test data shows that both methods were feasible for the quantitative analysis of iron oxides in CORBs. In actual practice, the accuracy of qualitative analysis of iron oxides must firstly be improved by the combination of XRD with DRS and then the choosing of quantitative analysis method can be achieved through the comprehensive analysis of both the predicted contents and crystalline of iron oxides.

Key words: iron oxides, quantitative analysis, X-ray diffraction, Diffuse reflectance spectroscopy, Cretaceous Oceanic Red Beds