Mineralogical Characteristics, Formation Mechanism， and Significance of Manganese Dendrites in South Guizhou—West Guangxi Nephrite

Abstract:

The compositions and microstructures of dendrites in south Guizhou-west Guangxi nephrite deposits were investigated by electron microprobe （EPMA）， laser Raman spectroscopy， electron paramagnetic resonance spectroscopy （EPR）， and scanning electron microscope （SEM） equipped with energy disperse spectroscopy （EDS）， and the formation mechanism was discussed as well. The result indicates that the dendrites are （quasi） two-dimensionally or three-dimensionally distributed in various rocks such as nephrite， tremolite marble， talc rock as well as tremolite diopside rock， and have essentially multi-branched fractal structures or patterns formed by rapid growth under non-equilibrium and non-linear conditions. They consist of mainly todorokite and minor birnessite， romanechite， hollandite， meanwhile displaying a microstructure of uniformly scaly to leaf-like crystals disorderly curled into layers or three-dimensional aggregated into balls reminiscent of the desert rose stones. Manganese for the dendrite growth were mainly provided by the Late Paleozoic to Early Mesozoic manganese-bearing sedimentations in the Yunnan-Guizhou-Guangxi Basin. The primary porosity and the induced brittle cracks at a low confining pressure and tectonic stress of nephrite could provide channels and spaces for manganese migration and precipitation. The rocks on both sides of the fracture would heal when pressed or hydrothermal filled.