| Qibaoshan(IOCG) deposit is a large-sized middle-low-temperature hydrothermal cryptoexplosive breccia pipe copper-gold deposits, located in Wulian county of Shandong Province. Considering the geotectonic position, it’s in the middle of Mesozoic basin to the southwest of Jiaolai depression, east of Tan-lu fault belt in Shandong, approach northwest of Jiaonan uplift. This paper discussed the geological characteristics, the source of metallogenic material, the genetic type and the metallogenic model on the basis of previous research in this deposit, and consider Qibaoshan deposit as iron oxide type copper-gold deposit.Geological characteristics minrealography and chronology implited that:(1)Qibaoshan IOCG deposit and other deposits in study area develop breccias pipe, indicating this area may be a large IOCG deposit,(2)the instrusive rocks are mainly dioritic(intermediate) rocks, according to field observation, replace relationship and petrography character, which can be divided into four periods: pyroxene diorite-diorite, pyroxene(hornblende)-andesitic porphyrite, quartz diorite porphyrite-granodioritic porphyry, andesitic porphyrite-dioritic porphyrite,(3) mineralization zones show that the bottom are dominated by k feldspathization, the middle are sericitization, silicification, pyritization, chloritization, while the upper are specularite mineralization, ferritization, sericitization, silicification, pyritization, kaolinization and gypsification,(4) the enriched elements are mainly Cu, Au, Ag, Fe, U, LREE, Bi, Ne, Co, Sb, Sn and F, S, P, As, B, Ba, the ore contain low S,(5)the dominated ore minerals are specularite, magnetite, pyrite, chalcopyrite,native gold, native silver,eletrum,(6)the deposit formed in Cretaceous, the zircon 206Pb/238 U isotopic indicate the formation age is 126±3 Ma, which is accordance with domestic IOCG deposit age 122~125 Ma.Fluid inclusions temperature measurement show that: SL, LV, VL type primary inclusions developed in Ⅰ, Ⅱmineralization stages of Qibaoshan IOCG deposit. Symbiotic LV type inclusions have simliar homogenization temperature range as well as VL type inlcusions, the former homogenize to vapor phase while the latter to liquid phase. SL type inclusion appeared along three different homogenization ways: the daughter minerals firstly dispear, the bubbles firstly dispear, and both of them approach simultaneously dispear. The above indicate that in early mineralization stage, the metallogenic fluid is a high temperature and high salinity boiling system, and the source is probably supercutical fluid exsolved from deep magma chamber. Ⅲmineralization stage only develop LV type inclusions with the homogenization temperature distinctly decrease, suggesting that mineralization inclusion gradually tranfer to intermediate temperature and medium salinity. Ⅳ mineralization stage only develop VL type inclusion as well, but compared with the former stage, the homogenization temperature and salinity obviously decrease, indicating a simple low-temperature and low-salinity Na Cl-H2 O system.Bulk fluid inclusions analysis and H-O, C-O isotope results indicate that the early metallogenetic fluids are mainly magmatic hydrothermal solution while the late fluids mixed with a small amount of precipitation, and the mineralization generated in a higher oxygen fugacity environment. The ore S isotope and Pb isotope results suggest that metallogenetic materials of copper-gold and Pb-Zn mineralization are from deep magmation.Genetic mineralogy indicate that:(1)there are obviously positive correlations for pyrite major elements’ atoms ratio of nS and nFe(nS/nFe=1.985~2.066) as well as δFe and δS diagram, δFe/δS-As diagram,(Fe+S)- As diagram, Co/Ni diagram(Co/Ni=1.2~32), Co-Ni-As diagram, S/Se=668~2641 and Au-As(0.984), Au-Fe(0.902), Bi-Sb(1.000), Bi-Co(0.916), Bi-Se(0.754), Te-Fe(0.789), Te-S(0.664), Te-Zn, Te-Cu(0.660), Ag-S(-0.847) have a negative correlation. The above showing that the pytite was influenced by magmatic hydrothermalism, and the metallogenetic materials have a close relation to magmatism, indicating this deposit derives from hydrothermal origin and was proved to be middle-low-temperature gydrothermal deposit.(2)Ag2O- Ni O(0.775), Ag2O- Fe O(0.537) in specularite have a positive correlation while Au2O- Fe O(-0.791), Ag2O- Sb2O5(-0.598) have a negative correlation, showing that Fe in specularite obstruct the enrichment of Au and lead to a low Au content in a large amount specularite in Ⅰ stage.(3) Au-Ti(0.915), Ag-Ga(0.981), Bi-Ag(0.981), Bi-Fe(0.999), Bi-Zn(0.920) bismuthinite have a positive correlation while Au-Se(-0.918), Au-Zn(-0.797), Ag-S(-0.951), Bi-S(-0.989), Bi-Ti(-0.805) have a negative correlation, showing that Bi is conducive to the enrichment of Ag, and bismuthinite is the principal carrier of Ag.Considering of the impact on the mineralization of strata, fault and intrusive rocks, and summarizing the characteristics of mineralization type, the wall rock alteration and ore-forming fluids, we set up a metallogenic model of Qibaoshan IOCG deposit that mineralization fluids of copper and gold center on dioritic porphyrite and radiate outward. In terms of spatial and temporal distribution, the deposit have a trends of evolution from east to west. |
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