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The widespread clay minerals on Mars have been detected using orbital data using near-infrared spectroscopy, which is limited by its shallow detection depth, low recognition precision and resolution, and can only be qualitative etc. Terrestrial analogues on the Earth provide valuable guidance to further understand the distribution and occurrence of clay minerals on Mars. In this study, seven detrital samples with clay minerals as coatings (Abbreviated as "clay coatings") were collected from four sites in the western Qaidam Basin, a Martian analogue terrain. We identify the mineralogy of the surface coatings to be illite and chlorite, as confirmed by a combination techniques of X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Electron Probe X-ray Microanalysis (EPMA) and Near-infrared spectroscopy (NIR). The NIR results suggested that merely small amounts of clay minerals (~0.5 mg/cm2 and about several micrometers in thickness) masking the surface of sands could lead to well-distinguished characteristic NIR absorption, and their band depth could reach those measured from Martian soil analogues with ~5 wt % to 25 wt % clay minerals at 2.20–2.40 μm. The results of the synthesized samples as coating analogues with clay minerals coated on the surface of quartz grains showed a consistent trend as that of the field samples on the Earth. The further mineralogical analysis indicated that the origin of clay minerals in the coatings of Qaidam Basin is of Aeolian source. Environmental similarities between western Qaidam Basin and Martian surface suggested that various rock coatings potentially exist on Mars and they could affect the mineral detection and the accuracy of mineral identification by remote sensing. • Detrital sand in Qaidam Basin was found coated by Clay minerals of aeolian origin. • NIR band depth of trace clay coating was comparable to that caused by Martian soil. • Clay coatings may also exist on Mars and affect its clay detection and identification. [ABSTRACT FROM AUTHOR]

[Display omitted] • Migration of chalcophile elements and the material source of metallogenesis. • Au and Ag can be leached in an oxidized system, regardless of acidic or alkaline. • Pyrite is the main source of Au, Ag, As in Lower Cambrian black shale. • Highest Au content is up to 0.344 ppm in the black shale of research area. Chalcophile elements hosted by black shales of the Lower Cambrian Niutitang Formation, South China Block, contribute to low-temperature mineralisation in southwest China. To study the mobilisation and migration of ore-forming elements, hydrothermal experiments were performed to simulate leaching of Au, As, Sb and Ag from an Au-rich black shale from the Kaiyang Phosphate Mine (KYPM), China. The experiments were designed to simulate low-temperature mineralisation at 150 °C, with solvent concentrations of ~5%, durations of 15 d and 30 d, and water/rock mass ratios of 13:1 and 26:1. Reagent-grade NaCl, NaHCO 3 and Na 2 S were used to provide the common anions found in hydrothermal systems. The results show that solutions containing Cl− ions in oxidised acidic systems leached Au most effectively. Weakly alkaline systems containing HCO 3 − ions leached Au less effectively. Solutions containing HS− ions did not leach Au effectively, and Au precipitated within the HS−-bearing system. The results for Ag were similar to those for Au, and Ag-leaching was most effective in the oxidised acidic system containing Cl− ions. As-leaching does not occur in the Cl−-bearing system, but As is leached effectively by HS−-bearing and HCO 3 −-bearing solutions. Sb was not leached by our experiments. Oxidised fluids produced by deep-sourced magma during the Indosinian and Yanshanian tectonic events infiltrated black shales affected by extensional deformation through faults, joints and fractures. Fluid–rock interaction leached a range of elements in these structural settings. These experiments provide insights into migration of chalcophile elements, particularly Au and Ag, and the source of large-scale low-temperature mineralisation within the South China Block. [ABSTRACT FROM AUTHOR]