Geology, Geochemistry And Genesis Of Main Gold Deposits In Tulasu Area, Western Tianshan, Xinjiang, China

Although the study on epithermal gold deposits related to volcanic rocks has been continuing for about 100 years, it is still the stage that our cognitions for them have been deepening gradually. Especially from the 1980's on, with a series of this type gold deposits were discovered, the studies on their characters and the cause of formation have being more and more further. So far, researches of this type gold deposit in the different metallogenic provinces have become one of the key fields in modern ore-forming geology.There are many epithermal gold deposits related to subaerial volcanic rocks in Tulasu basin of Yining county, Xinjiang where have Axi, Jingxi and Yelmend represented large and mid-small gold deposits, respectively, which had been researched by many researchers in succession since they were discovered. At present, as for chief problems, the focus of disputation is yet the origin of metallogenic liquid, which brings on bifurcation necessarily for the process and mechanism of mineralization.This study is supported by the subject that is the tenth five-year national plan of tackling science and technology key problems of orientation and forecast of large gold deposits in Tulasu gold belt, and in allusion to those long-standing disputed issues, the much systemic researches on the characteristics, source of metallogenic liquid, process and style of mineralization have been carried out by means of geology, geochemistry and fluid inclusions. So these points of view are put forward thereinafter.1. Combined studying fluid inclusions with geochemistry, the source of fluid and matter of mineralization are made clear in this research. The homogenization temperatures, salinities, pressures, and etc. were mensurated. Moreover, components of these single fluid inclusions in samples were analyzed with a LRM for the first time. And the oxide, trace, REE elements and isotopes of representative rocks and ores in main gold deposits were analyzed. Based on above data, it is considered that the ore-forming fluid is major volcanic-subvolcanic hydrothermal fluid mixed minor meteoric water later. And the material mineralization derives from the intermediate to intermediate-acid volcanic rocks and pyroclastics of the Lower Carboniferous Dahalajunshan Formation.2. By further studying the subvolcanic rocks in mining area, the closerelationship between metallogenism and volcanism is confirmed, that the ore-forming fluid and material were offered by the volcanism, what's more, the heat and dynamics were supplied by it.3. It is defined that Axi, Jingxi and Yelmend gold deposits are the same Au-mineralizing style. By comprehensive analysis the data of the minerals, texture and structure of ores and rocks, the host rocks and the style of mineralization in Axi, Jingxi and Yelmend gold deposits are discussed, and it is suggested that the Lower Carboniferous Dahalajunshan Formation hosted the three gold deposits is advantaged ore-bearing strata and the metallization is related to intense silicification, resulted of forming auriferous secondary quartzite which is one of important ore types of them.4. For the first time, the new idea is put forward that the distribution of ores have the trinity character. Synthesizing the data of field and interior, it is thought that the occurring of metallogeniam lies on strata (the Lower Carboniferous Dahalajunshan Formation), alteration (intense silicification) and structures (calderas, Tianshan structures and anti-Tianshan structures), which will play an important role in guiding exploration and prospecting.Furthermore, there is a quantity of organic compounds such as CH4, C2H4, C6H6, C4H6 and so on in those fluid inclusions. So it is inferred these organic compounds be likely to have a part in ore forming, but the advanced researches have not yet carried out because of limitation in the studying conditions.