Silver easily reacts with sulfur and hydrogen sulfide to form black silver sulfide, which is often found on tarnished silver coins or other articles. Silver can react with oxygen at high temperature to produce brown-black silver oxide (it can also react at room temperature, but the speed is very slow).
In the presence of potassium bromide, metallic silver will be eroded by strong oxidants such as potassium permanganate or potassium dichromate; These compounds are used in photography to bleach visible images and convert them into silver halide, which can be removed by sodium thiosulfate and re-developed to enhance the original images.
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The important silver mining areas in China are Guixi Lengshuikeng in Jiangxi, Fankou in Guangdong, Zhushan in Hubei, Fengcheng in Liaoning, Siping in Jilin, Zhashui in Shaanxi, Baiyin in Gansu and Tongbai Silver Mine in Henan.
There are several types of deposits, such as volcanic-sedimentary type, sedimentary type, metamorphic type, intrusive rock type and sedimentary transformation type, among which volcanic-sedimentary type and metamorphic type are the most important.
From the analysis of metallogenic age, there are large and medium-sized silver deposits from Proterozoic to Mesozoic except Archean and Cenozoic silver deposits with industrial significance, among which the most silver deposits were formed in Mesozoic.
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