LUO Xi，YANG Zhi-jun^*，ZHANG Ke^*，WANG Han-yu，DU Heng-heng，HE Wang

(School of Earth Science and Engineering, Sun Yat-sen University, Zhuhai 519080, China)

Abstract: The Danxia Mountain in Guangdong province is the typical representative and named place of the Danxia type landform. The genesis of its distinctive red color is still controversial. In this paper, the polarizing microscope, X-ray Powder Diffraction (XRD) and electron probe microanalysis (EPMA) have been used to carry out a mineralogical study of the red sandstone in the Danxia Mountain. The results show that main minerals of the quartz sandstoneinclude quartz, feldspar, and mica. The red pigment in quartz sandstone is mainly distributed in three states, including clustering, beadlike, and disseminated states, in the cement and matrix of the sandstone. It occurred as a thin film on the surface of minerals, resulting in the appeared red color of the sandstone at macro-scale. Fe is the key factor causing the red color. It could be sourced from non-crystalline iron oxides which belong to the amorphous early state or iron complex state of hematite. The inheritance of parent minerals of ferromagnesian silicates as well as the mechanical penetration of groundwater in debris and clay minerals could provide direct sources of iron for red coloring. The red color of the Danxia Mountain was formed in the reworking process of sediments after sedimentation, as the penetration of groundwater in the sandstone had promoted the dissolution of its feldspar and other minerals, then led to the development of secondary pores and the precipitation of iron-bearing materials. Continuous renewal of the oxygen-containing water environment is conducive to the above dissolution and cementation, which promoted the continuous precipitation of iron released in the rock alteration process or in the mineral dissolution process, then resulted in the deepening of red color, and finally resulted in the formation of widely distributed red beds in the Danxia Mountain. This study on the genesis of red color of the sandstone in the Danxia Mountain is beneficial to provide a new scientific theoretical basis for researches on the genesis of red color and coloration mechanism of the Danxia type landforms represented by the Danxia Mountain.

Keywords: The genesis of red color; mineral composition; iron-bearing materials; the Danxia type landform

ACTA MINERALOGICA SINICA Vol.41, No.6, 2021, page 704-712