Advances of Researches on the Evolution of Ore-forming Fluids and the Vapor Transport of Metals in Magmatic—Hydrothermal Systems
LENG Chengbiao1, 2), ZHANG Xingchun1),WANG Shouxu1, 3),QIN Chaojian1),WU Kongwen1, 2),REN Tao1, 2)1) State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang, 550002;2) Graduate School of Chinese Academy of Sciences,Beijing, 100049;3)Shandong Gold Group Co., LTD., Jinan, 260014
Based on the researches on volcanic degassing, characteristics of ore forming fluids in magmatic hydrothermal ore deposits and experiments on the metal dissolving in vapor and the partition of metals between vapor phase and brine phase, this paper has briefly decribed the advance of researches on the vapor transport of metals and the role of CO2 in metallogentic process of the magmatic—hydrothermal system. The high concentration of Cu, Zn, Pb, As, Ag and Au in volcanic degassing sublimates and the presence of sulfides in low density phase (vapor) of fluid inclusions of the porphyry-type deposits could indicate that those above metals were transported in vapor phase. The experiment of metal dissolving into vapor phase indicates that metals are dissolved into vapor phase in form of hydrate species such as MeXm (H2O)n, with their solubility increasing sharply due to the increase of water fugacity and HCl fugacity of the vapor phase. The experiment of melt—fluid partition coefficient of metals shows that there is phase separation between vapor and brine in the NaCl—H2O system, Au and As are normally in favor to be dissolved into the vapor phase in form of HS-complex in the S-bearing system, whereas Fe, Zn, Pb, Mn, Cs are dissolved in favor into the brine phase in form of chloride complex. Cu is favorablely partitioned into the vapor phase in the sulfur-rich systems, but favorablely partitioned into the brine phase in the chlorine-rich sulfur-free system. This suggests that Cu could be transported in form of chloride complex or HS-complex in magmatic fluids. CO2 could have played important role in the processes of transport and precipitation of Au, Cu and other metals. Firstly, the CO2 could cause phase separation between magma and magmatic fluids and between the CO2-rich vapor phase and the brine phase of the mgmatic fluids due to the increase of T—P range of immiscibilities among them. Secondly, it could cause the enrichment of HS-complex into vapor phase. Thirdly, the acidity of ore-forming fluids also could be changed due to the existence of CO2. The mineralization process for Porphyry Cu—Au deposit could be roughly divided into three stages. Firstly, a small amount of magmatic fluids derived from the emplaced porphyry could result in wide proplytic alteration and partly potassic alteration with weak mineralization in the porphyry. Secondly, the critical magmatic fluids derived from early stage of magma degassing in deep magma chamber could strengthen the alteration of the porphyry and form the main stage Cu—Au mineralization in forms of dissemination and quartz—sulfide networking veinlets overlapped on the early potassic altered porphyry, and could result in advanced argillic alteration with the epithermal Cu—Au mineralization in the high-level of the porphyry. Thirdly, the magmatic fluid derived from late stage of degassing in deep magma chamber could result in the phyllic alteration and quartz—(calcite)—sulfide vein type mineralization in top part or above the porphyry body.
【CateGory Index】： P595
【CateGory Index】： P595