Geochemical Characteristics Of Trace Element Of Calcite Vein In Dashui Gold Deposit, Gansu Province

Dashui Gold Deposit in Maqu located in the region of Xiqing Mountain, Southern Gansu Province, which is a extra big gold deposit with unique ore-fo rming characteristics all over the world found in recent decades. Dashui Gold Deposit is large in size, which is noted for its high grade ores, shallow burial depth and simple ore composition. Its wall rock alteration is mainly intense h ematitization and silicification and the deposit is sulfur-deficient compared to ot her gold deposit. The gold mlneralization in Dashui Gold Deposit mainly occur red in the T2m.Calcite is one of most important gangue minerals closely relate d to ore-forming process. Calcite veins formed throughout the ore-forming proc ess. According to field observation and laboratory analysis, the formation of ca lcite vein can be divided into 3 phases:before of metallogenic period, ore-for ming period and the later of metallogenic period. Study on geochemical charact eristics of trace element of calcite vein can provides important information for deposit genesis.Based on the calcite geology and geochemistry characteristics of different ore-forming stages, analysising of trace elements in different stages, characteri zation parameter and ree distribution pattern of calcite, discussing the source a nd evolution of calcite fluid, even relationship between mineralization and calci te, we get the following conclusions:1. It suggests that trace element of Dashui Gold Deposit has little changes in trend during 3 phases, the trace element contents of Dashui Gold Deposit ncreased during ore-forming process. The source of the fluid of calcite is extre mely complex, belonging to middle low temprature range. The formation of cal cite vein ore-forming period is closely related with gold mineralization in time and space. Trace element content variation might depend on element migration between surrounding rock and calcite. The enrichment of trace element of ca lcite such as Pb、Hf、Rb、Zr、Mo、Sn、Li、Nb、Ba、Th is bound up with mineralization tightly, while the enrichment of trace element of calcite like Sr, Cd, Cr, Ni has nothing to do with mineralization.2. REE geochemistry of calcite of Dashui Gold Deposit suggesting a sligh tly right-inclined LREE enrichment type, REE distribution pattern and characteri stics of REE showed largely similar and discontinuous changes, REE also prese nted that slightly negative Eu anomaly and intense negative Ce anomaly. The d eposit generation of calcite in hydrothermal system tended to LREE enrichment, which suggests that fluid with LREE enrichment involved in formation of cal cite. In the process of calcite formation, there are continuously REE moving in to it, there is highest content of REE during later of metallogenic period, whic h reduced the level of negative Eu anomaly that means the process of formati on of calcite might add reducing matter or it belonged to reducing environment. Through comparing, REE geochemistry characteristics of calcite of Dashui Gol d Deposit is close to the primitive mantle, which suggests that the source of fl uid of formation of calcite might be related to mantle fluid with better crystall ization differentiation.