Mineralization Of Nephrite Metallogenic Belt In He Tian, Xin Jiang

The Hetian nephrite ore belt deposit in the Tarimu Basin in the southern Xinjiang is the largest nephrite ore belt related to dolomite. The belt contains more than 20 ore deposits and ore occurrences in different scales, and consists mainly of masses of primary (ore) deposits and secondary deposits in the Kara Kashgar River and Yurungkash River. Though more researches have been done on the Hetian nephrite, they mainly focused on ancient jade culture, spectral feature and identifying characteristic without the typical study on actual ore deposit. It is still insufficient in the studies on ore belting, surrounding rock features, source of metallogenic material and mineralogenetic epoch with evolution of ore-forming fluid, and types of ore deposits. In particular, there are few researches on huge amount of dark jades in the Kara Kashgar River. Moreover, the researches need to be further done on mineral composition, features of ore-forming fluid and the source of medium nephrite in the secondary deposit.In this study, deposit type, ore genesis and mineralogenetic epoch are studied taking the primary Alamus deposit and the secondary deposit in the Dark Jade River as the objects of the study. The studies show that the Alamus deposit is a skarn-type one, and emplacement of Alamus granite causes occurrence of nephrite ore. With analysis on geochemical characteristics of Alamus granite and mineralizing constraints of nephrite deposit, the Shrimp zircon age of Alamus deposit is determined as 433.4±4.4Ma. In addition, through the study on the zircon inclusion in gray jade, it is believed that the zircon deposit was formed in the skarn stage which can represent the direct age of the deposit.The secondary deposit in the Kara Kashgar River is also a marble-type nephrite one. The minerals such as essonite, titanite, rutile, diopside, tremolite and chlorite in the mineral assemblages in this nephrite show that this deposit is a typical skarn-type deposit. The color of some dark jade samples is caused by the higher ferric content in its ingredient, and the color of other dark jade samples is related to the inclusion in the dark jade. The homogenization temperature for the inclusion in the dark jade in tremolite was measured as 200℃ to 400℃. Moreover, through the stable isotope in the ore-forming fluid and comparison with other types of nephrite deposits, the hydrogen and oxygen isotope value range for the secondary deposit falls in that of existing marble-type nephrite, but there is a great difference from that of other serpentine-type nephrite deposits. Though mineral composition and color in the Dark Jade River are inconformity with that of most parts of primary ore deposits in the Hetian nephrite ore belt, the dark jade formation in the Kara Kashgar River is also a marble-type nephrite deposit, and formed like the primary nephrite deposit based on study on the mineral composition and fluid source.