Stable Isotope Geochemistry Characteristics Of Da-shui Gold Deposit In Ma Qu Country Of Gan Su Province

Dashui gold deposit,locating in Maqu county, Gansu province, is a rare silica-rock-type gold mine enriched hematite which was found at qingshan area south of Gansu province in 90 s.The gold deposit is not only large, high-grade, shallow- bury, simple mineral composition, easy mining and selection, but also the mineralization characteristics is extremely unique.At present, this type of gold deposit has been studied at a low degree in the world. Lucubrating this type of gold deposit is in favor of further knowing the structure evolution history and mineralization rules of east Qinling Orogenic Belt, evaluating the mineral exploration work in the whole Qinling Orogenic Belt, starting prospecting works of finding gold deposits similar to Dashui gold deposit and researching and deepening the metallogenic theory. Dashui gold deposit locates at the Neopaleozoic- Mesozoic multi-metal mineralization belt of the south qinling in Gansu province. The formers have made a lot of researches and have received important achievements including mineralization structure, mineralization impetus, mineralization age and so on. However, the exact arguments for the source ore-forming fluid and the metallogenic model are still lacking. Plenties of research data shows that Dashui gold deposit with complex causes is closely related to stable isotope in the aspects of time and territory.This paper investigates and surveys the areal geological background, geological feature in mine lot, geological feature of deposit firstly, and then elaborates the stable isotope geochemistry characteristics of Dashui gold deposit. This research, taking calcite, limestone and silicious rock as study objects, measures isotope composition of carbon, oxygen and strontium of calcite and limestone and simulates by the way of calcite liquid-rock theory. The conclusion obtained shows as following:(1)Through carbon, oxygen and strontium geochemistry characteristics of calcite in Dashui gold deposit, the possible source of ore-forming fluid is speculated to come from the deep. Through calcite oxygen isotope geochemistry characteristics, the early liquid is speculated to be related to magmation, and the late liquid is related to meteoric waters.( 2) The composition of Sr isotope has a great function of discuss ore-forming material source, through the Sr isotope geochemistry characteristics, the silicified limestone is speculated to come from crust-mantle mixing areas possibly.(3)CaO and SiO2 of surrounding rock and minerals in Dashui gold deposit has an apparent negative correlation, therefore, the simulation of liquid-rock reaction is practical. And the simulation shows that the soluble carbon of ore-forming fluid in Dashui gold deposit is mainly H2CO3, carbon in early liquid probably comes form the deep and meteoric waters adds into later liquid. The forming temperature of Dashui gold, the medium low temperature thermal liquid ore deposit, is same to that of fluid inclution.By analyzing stable isotope geochemistry, the source of Dashui gold deposit ore-forming fluid is complicated. Several causes may provide the provenance for ore-forming fluid, besides, hydrothermal solution in shallow part is vital to mineralization.