| Tonghua Ermi Cu deposit, Jilin province, is Located at the Sanyuanpu volcanic basinin the eastern area of northern North China Craton, with a long mining history. Theexposed strata of mining areas are Late Jurassic-Cretaceous stratas of terrestrial volcanic-volcaniclastic rocks, with Archean basement and Proterozoic strata partly distributing.Magamtism strongly occurred in this area, Early Cretaceous volcanism can be mainlydivided in three eruption periods (Guosong period, Linzitou period and Sankeyushuperiod), Songdingzi intrusive rocks invaded along the eruption channel; structures ofmining areas are mianly Sanyuanpu composite volcanic edifice mainly includingEast-West trend, South-North trend, and Northeast trend fratures.Ore bodies are mainly distributed within the inner and outside contact zone withvolcanic rocks of southeastern Sondingshan intrusive rocks, and can be divided in toseveral mining areas of Eastern area, Southeastern area, Southern area, Sidaoyangcha area,Sifangdingzi area and Xiaohengdaohezi area, etc. Orebodies output mainly in three forms:(1) vein ore bodies mainly in the tensile fractures the flat dipping tensile fractures, in theinner and outside contact zone within the quartz diorite and granite porphyry; FromNortheast to Southwest, the tendency of these fractures range from Northeast to Southwest;this kind of ore bodies is the main industrial orebodies of Ermi Cu deposit; in addition, theNorthwestern trend steep dipping vein-disseminated ore bodies and East-South trend flatdipping vein-disseminated ore bodies are distributed in the Southern volcanic rocks;(2)disseminated ore boides mainly output within the bodies of quartz diorites and graniteporphyry;(3) the high grade massive ore bides and crystal ore bodies are hosted at the top of granite porphyry. Ore minerals are mainly arsenopyrite, pyrite, pyrrhotite andchalcopyrite, secondly molybdenite, sphalerite, etc; gangue minerals are mainly consistedof quartz, sericite, chlcorite, calcite, etc; wall-rock alteration is mainly silicification,sericitization, tourmalinization, propylitization, carbonation and kaolinization.The mineralization of Ermi Cu deposit had closely connection with Songdingshanintrusive rocks, which are mainly diorites, quartz diorites, quartz monzodiorites,porphyritic quartz diorite, granite porphyries, etc., associated with monzodiorite porphyryand quartz monozodiorite porphyry. The206Pb/238U weight average ages of granodiorite,quartz diorite and porphyritic granodiorite obtained by LA-ICP-MS zircon U-Pb datingare94.2±1.7Ma (N=15, MSWD=0.53),94.3±1.2Ma (N=17, MSWD=0.30) and93.9±1.2Ma (N=19, MSWD=0.22), respectively. Element geochemical characteristicsreflect that they are intermediate-acid intusive rocks, SiO2=56.76~72.69%,Na2O=3.64~6.44%, K2O=1.88~3.87%, CaO=1.86~6.41%, A/CNK=0.86~0.97, A/NK=1.29~2.05, chemically beong to sub-alkaline High K series; they have right-leanedchondrite-normalized rare earth elemt (REE) patterns, light rare earth element(LREE)/heavy rare earth element(HREE)=5.75~9.84,(La/Yb)N=5.27~10.36),δEu=0.71~1.12, and charactered by enrichment of large ion lithophile element(LILEs)(Rb, Ba, Th, U, K, LREE, etc) and depletion of high field strength elements(HFSEs)(Nb, Ta, P, Ti, HREE, etc); the (87Sr/86Sr)I, ratios negative εNd(t) and Nd modelages (TDM) range of0.70765to0.70829,-13.8to-10.8and1.68to2.05Ga, respectively,which are similar to the Sr-Nd isotopic characteristics of Early Creceacous volcanic rocksthis area, indicating their source region is consisted with two end number of Archeanlower crust and underplating basalt, which were derived from the mantle wedge modifiedby oceanic fluid; Combined with previous reasearches, this paper considers the diagenesisand mineralization of Ermi deposits occurred in the Late Cretaceous, formed in theextensional environment under the subduction of Paleo-Pacific plate.The geological characteristics and ore microscopy researches of mineral depositmineralization process include five metallogenic stages: quartz-disseminated pyrite stage,quartz-molybdenite-pyrite-chalcopyrite stage, quatz-chalcopyrite-sulfides stage, quartz-pyrite-chalcopyrite-chlorite stage, quartz-carbonate stage. The study of fluid inclusionshow indicates fluid inclusions have mainly liquid-rich inclusions and daughtermineral-bearing inclusions with a small amount of vapor-rich inclusions; thehomogenization temperature and salinity of fluid inclusion are149.9~450℃and 3.85~52.42wt%, which can be divided into five stages of445~450℃,330.5~419℃,260~328.9℃,204~258.4℃and149.9~180.3℃；the homogenization temperature, salinityand density of liquid-rich inclusion are149.9~450℃,3.85~12.65wt%and0.584~0.970g/cm3, respectively; the homogenization temperature, salinity and desinity of daughtermineral-bearing inlusions are265~419℃,34.72~38.57wt%and1.107~1.110g/cm3；thehomogenization temperature, salinity and desinity of vapor-rich inlusions are358~263℃,3.85~9.65wt%and0.63~0.72g/cm3；Raman spectroscopy analysis of inclusions showsthat the gas components of liquid-rich inclusions are mainly H2O and CH4, which ofdaughter mineral-bearing inclusions is mainly H2O and which of vapor-rich inclusions ismainly CO2and CH4. Bolling and cooling are the main important mineralizationmechanisms of Ermi Cu deposit. |
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