| Located in 60 km north of Jiagedaqi city,Heilongjiang Province,the newly discovered Guzhonggonglu molybdenum deposit is situated in central-northern Greater Khingan Range,and the east segment of the Central Asian Orogenic Belt.The ore-hosting intrusion is medium-fine grained monzogranite.Based on the regional geology and geological materials of mining area,the conditions of metallogenetic geology,the geological characteristics of deposit and the ore-forming physical-chemical conditions have been defined through field geological investigation,indoor test and comprehensive research.Besides,compared with adjacent typical Mo deposit,the ore genesis and the time of ore-and rock-forming have been determined.Besides the Quaternary,the strata exposed in the mining area is main Lower Devonian-Middle Devonian Niqiuhe Formation.The major structure is Late Caledonian-Hercynian and Late Yanshanian brittle-ductile fractures.The intrusion is complex,and the medium-fine grained monzogranite is temporally,spatially and genetically related to the molybdenum mineralization.The metal minerals in the mainly include molybdenite,pyrite,galena,sphalerite,chalcopyrite,pyrrhotite,scheelite;the non-metal minerals are composed of quartz,K-feldspar,plagioclase,biotite,sericite,chlorite etc.The main textures of the metal minerals are euhedral-hypidiomorphic granular texture,flaky texture and metasomatic texture;the structures mainly include thin film structure,vein structure,disseminated structure,and veinlet structure.The wall-rock alterations include potash feldspathization,silicification,biotitization,chloritization,sericitization and carbonatation.The silicification,potash feldspathization and biotitization are temporally and spatially related with mineralization.Based on the cutting and across relationships of the different vein bodies,the textures and structures of the ore,the mineral assemblages,intergrowth relationships and the characteristics of wall-rock alterations,the metallogenic process can be divided into K-feldspar+quartz,quartz+molybdenite+polymetallic sulfide and quartz+calcite+pyrite stages.The major mineralization stage is quartz+molybdenite+polymetallic sulfide.The preliminary study of fluid inclusions demonstrates that the fluid inclusions in the quartz are mainly gas-liquid two phase inclusions,minor gas-liquid-solid three phase inclusions and CO2-bearing three phase inclusions.The homogenization temperature of all type of inclusions are of 196.3>450?,while the corresponding salinities can be divided into two groups: 0.18%12.62% and 45.33%>53.26%.It therefore can be concluded that the ore-forming fluid belongs to the medium-high temperature,and high salinity NaCl-H2O-CO2 fluid system,and the fluid immiscibility might occur during the ore-forming stage and be the major metallogenic mechanism.The isotopic dating studies indicate that the LA-ICP-MS zircon U-Pb dating of the ore-forming related medium-fine grained monzogranite is?146.3±2.5?Ma;the Re-Os isotope model age of two molybdenite samples are 142.4±2.9Ma and 142.3±2.0Ma,respectively,indicating that the intrusion and the deposit was caused by the Late Jurassic-Early Cretaceous tectonic-magmatic activities.The content of Re in the molybdenite are 11.894×10-6 and 11.584×10-6,respectively,suggesting that the ore-forming materials are mainly derived from the crust.Combined with the characteristics of ore-forming conditions,ore deposit geology and fluid inclusions,the study indicate that the Guzhonggonglu molybdenum deposit is of porphyry type,and formed under the regional extension tectonic settings. |
PDF Full Text Request