The Ore-forming Fluid And Mineralization Mechanism In Super Giant Jinding Lead-zinc Deposit

Jinding in Yunnan provience which is the largest lead-zinc deposit in chinaattracts much attention, because it has ultra large scale and complex geologicalcharacteristics. As hydrothermal deposits, for that ore-forming fluid is the carrier ofmineral transport and unloading, the research of the fluid characteristics andmechanism of metal mineralization are indispensable in deposit study, and it also havebe done on Jinding deposit in this work. Research on Jinding metallogenic fluids havebeen done much, but there are some problem on the choice of inclusion, and it’s lackon the mechanism of mineralization and geochemical studies of hydrothermalminerals. Therefore, there are still a lot of controversy on the ore-forming fluidcharacteristics and origin. In addition, there are less researches about the characteristicof ore-forming fluid and mineralization in Tuzishan ore block, which lay on about9Km northeast of Jinding deposit.The main object of this study is the fluid inclusion and hydrothermal minerals inJinding open pit, Paomaping ore block and Tuzishan ore block. First, through datacollection, field geological mapping and microscopy identification, ascertain thegeological features of deposits and the characteristics of hydrothermal mineralsformed. Based on this, make analysis and comparison of ore-fluid characteristics,origin and evolution in three ore block to explain the fluid mineralization mechanismby fluid inclusion study, minerals composition analysis, calcite C-O isotope andsulfates and metal sulfides S isotope research.Researches show that, three lithology systems are present in the Jinding open pit,referred to “autochthonous system”,“allochthonous system” and “cream salt (sand)diaper lithology system”. The native mineralization located in the cream salt (sand)diaper lithology system which is make up by variety of breccias and cream, sand etc..According to wall rock, the ore can be divided into sandstone-type, containinglimestone breccias sandstone and limestone breccias three types. In Jinding open pitand paomaping ore block metal sulfide minerals are mainly galena, sphalerite, pyrite,marcasite etc., gangue minerals are calcite, celestite, barite, gypsum etc., and asphalt distribute commonly. In Tuzishan ore block, mineralization appears in Sanhedongdolomitic limestone in veined by calcite, quartz, galena, sphalerite and pyrite.The liquid-vapor (L-V) two-phase inclusion and ore-bearing inclusion whichoften contain CO2and CH4in gas mainly developed in Jinding open pit andPaomaping ore block. Aqueous fluid inclusions hosted by hydrothermal calcite showthe homogenization temperature is between145~<245℃, suggesting that ore-formingfluid is low temperature and magmatic fluid has no contribution to the ore-formingfluid; the salinity concentrated in14.0~16.0wt%NaCl eq. in Jinding open pit, butthere are two salinity range for20.5~20.8wt%NaCl eq. and4.7~5.9wt%NaCl eq. inPaomaping. Tuzishan ore block mainly develop liquid-vapor (L-V) two-phaseinclusion, showing the fluid temperature are170.0~258.0℃and salinity are22.7~23.1wt%NaCl.. In the three blocks, the hydrothermal calcite is rich in18O between16‰~24‰，showing the ore-forming fluid come from crust. These features suggestthat there are basin brine (low temperature and high salinity) migrating metal and oilrich fluid from the ancient reservoirs in Jinding open pit and Paomaping ore blokc,but only basin brine in Tuzishan ore block. Mixture or not and different conditions ofmixture are probably the reason why fluid inclusions have different homogenizationtemperature and salinities in different ore blocks.The mineralization marcasite in Jinding open pit showing the ore-forming fluidhave polysulfides and slightly lower pH characteristic. In Jinding open pit andPaomaping ore block, sphalerite grow ring by Cd element change greatly, whichreflect the fluid is unstable in physical and chemical conditions during mineralization.From Tuzishan ore block to Jinding open pit and Paomaping ore block, thehydrothermal calcite decreases in Mg content and increases in Mn content, showingore-froming fluid have reaction with wall rock. In addition, the content of Fe and Cdin sphalerite in Jinding and Paomaping have the feature of MVT mineralization.In Jinding and Paomaping, δ~13C of plateau calcite cement in mineralizaedsandstone, ore/barren calcite cement in limestone breccias and ore calcite vein varyin between-26.2‰and-9‰, reflecting organic carbon add into during mineralization.Of them, sandstone plateau calcite cement is riched in13C than other kinds of hydrothermal calcite, indicating the latter have possibility in organic addingcontinuously during mineralization, while the former is lack of that. In these twoblocks the δ~34S value of sulfide precipitating early between-28‰~-8.3‰and sulfideassociated with late phase of sulfate precipitating later between-5.4‰~+0.5‰,considering the sulfur isotopic composition of gypsum in mine, reflect the interactionbetween metal-rich fluids and H2S produced by biological sulfate reduction (BSR)lead to sulfide precipitation in early stage and the interaction between metal-rich fluidand H2S produced by organic thermal sulfate reduction (TSR) lead to sulfideprecipitation in late stage. Different form Jinding and Paomaping, the δ~13C ofTuzishan vary between-3.8‰~+1.6‰, S isotope in galena is-1.6‰, showing there islack of organic matter during mineralization and the metal sulfide precipitation maybe caused by temperature fell and other non-fluid mixing factors.