Mineralogical Characteristics And Genesis Of Changhua “Heijin Stone”

The Changhua stone is one of the four famous seal stones in China,it is facing an exhaustive risk due to excessive exploitation in recent years.“Heijin stone” is a new kind of seal stone discovered recently in Changhua area.Its body color is black,with white and transparent frozen belts interspersed and with golden dots.On the basis of field geological survey,The mineralogical characteristics and color genesis of “Heijin stone” were studied based on the modern test methods such as polarizing microscope,scanning electron microscope,electron probe microanalysis,X-ray powder diffraction,infrared spectroscopy,X ray fluorescence spectroscopy and differential thermal analysis in this paper.And compared with similar seal stones Shoushan “Kengtouhei” in the meantime.Through the determination of H,O isotopic features and Geochemical characteristics of rock,and combined with previous research results and related evidence,the metallogenic temperature,pressure condition and material source of the deposit are summarized.The genetic type of the deposit is determined,and the metallogenic mechanism of the deposit is summarized.The higher the transparency of the "black gold stone",the higher the transparency,the more the content,the reasonable distribution,and the better the quality of the golden material,which is better,and the higher the value.The study shows that the surrounding rock and ore of the “Heijin stone” show the gray and white interference color of first order gray to one level under polarizing microscope,and the surrounding rock particles are coarser and the ore particles are fine,and the microstructure is microscopic.The major mineral composition of “Heijin stone”is dickite,and the secondary mineral composition is pyrite,svanbergite,quartz,rutile,nacrite and rare earth minerals.The higher the transparency,the lighter the color,the higher the degree of order in the different color part,the content of Fe in black part is obviously higher than that in other parts.The black part of the “Heijin stone” is mainly related to the extensive and dense distribution of fine pyrite,and the gray part is related to the fine pulse distribution of the svanbergite,and the white part is pure dickite.Most of the characteristics of Shoushan “Kengtouhei” are consistent with “Heijin stone”,but the content of quartz and pyrite is lesses,and the enrichment and crystal form of svanbergite are better than the “Heijin stone”.The symbiosis of sphalerite,galena and pyrite is only found in the “Kengtouhei”.The variation regularity of the main elements,trace elements and rare earth elements of the "black gold stone" ore and surrounding rock shows that the ore-forming material of the ore comes from the surrounding rock,the rhyolitic glassy chip crumb tuff.The analysis of hydrogen and oxygen isotopic compositions indicates the hydrothermal deposit type,and the meteoric origin of hydrothermal,the temperature of the mineral formation is middle and low temperature.The origin of “Heijin stone” is similar to most of the seal stones,under the pressure of less than 1k Pa,it is formed under the acidic hydrothermal condition at low and medium temperature.The source of the ore-forming material is widely distributed rhyolite and glassy tuff in the mining area,and the hydrothermal solution is derived from meteoric water.S is abundant in the mining area.