| The Zhongshangou gold deposit is located in the north margin of North China Craton and the south side of Shangyi-Chicheng deep fault.It is one of the typical representatives of the Dongping type gold deposits in Zhangjiakou-Xuanhua area of northwest Hebei Province.At present,the research level of the deposit is relatively low,and there is a lack of systematic analysis and Research on the source of ore-forming materials,characteristics of ore-forming fluid,ore-forming age,ore-forming mechanism,genetic type of the deposit and main ore controlling factors.Therefore,the study of the ore-forming types of the deposit is of great practical significance for regional guidance of ore prospecting,with a view to providing theoretical basis for further exploration of the deposit and the study of the metallogenic law of the gold deposits in Zhangjiakou-Xuanhua area.The ore bodies of the Zhongshangou gold deposit are vein and lenticular in Shuiquangou monzonite complex of Hercynian.The ore bodies are mainly of quartz vein type,potash altered rock type and silicified breccia type.The gold ore is rich in pyrite,galena,sphalerite,chalcopyrite,molybdenite and other sulfides,and the alteration types of potash feldspar,silicification and sericitization are developed.According to the paragenetic association of minerals,ore fabric and vein cutting relationship,the metallogenic stage of the Zhongshangou gold deposit is divided into four metallogenic stages:?I?K-feldspar-pyrite-quartz,?II?opalescent quartz-pyrite,?III?smoky grey quartz-sulfide and?IV?poor sulfide-carbonate.Gold mainly exists in the early milky white quartz in the form of natural gold and in the pyrite fracture in the form of fracture gold in the mineralization period,in which the smoky grey quartz-sulfide stage is the main stage of gold mineralization.The S isotope shows that the average value of?34S of pyrite is-12.03‰,and that of galena is-14.9‰,both of which are negative,and the S isotope is strongly fractionated.Pb isotopes show that most of the projection points of Pb isotopes of ore samples basically fall between the orogenic belt and the upper mantle,indicating that the lead of the Zhongshangou gold deposit may come from crust and mantle source materials.He-Ar isotopes show that the 3He content is 1.58×10-143.07×10-13cm3stp/g,the 4He content is 3.2×10-83.32×10-7 cm3stp/g,the 3He/4He value changes between0.13Ra0.66Ra,the 40Ar/36Ar content is 699.92200.4,and the ore-forming fluid is the crust mantle mixed fluid dominated.The trace elements show that Te,rather than As,replaces s in pyrite in the process of mineralization,which plays an important role in the transport and enrichment of gold.The characteristics of fluid inclusions?including mineralogy,temperature and salinity?show that the ore-forming fluid in stage I belongs to the H2O-NaCl system with medium high temperature?300330??,medium low salinity?4.76.9%?,and gradually evolves to the low temperature?180200??,medium low salinity?4.37.5%?H2O-NaCl system in stage IV along with the mineralization.H-O isotopes show that the early stage of mineralization is mainly magmatic hydrothermal fluid,and the later stage is a mixture of magmatic water and atmospheric precipitation,and the proportion of atmospheric precipitation in the ore-forming fluid increases with the mineralization from early to late.Based on the comparative study of the Dongping gold deposits of the same type in the same area,this paper holds that the mineralization age of the Zhongshangou gold deposit is 140180Ma,which is the product of Yanshanian Mineralization.On the basis of this study,combined with the study of regional metallogenic geological background,it is considered that the ore-forming fluid of the Zhongshangou gold mine should be dominated by atmospheric precipitation,mixed with a small amount of primary rock slurry water.In the long-term geological evolution process,the rock body should be continuously transformed to extract gold from the rock body or the formed ore embryo,so that it can be activated and migrated to form a gold rich ore-bearing fluid.In the later stage,a certain structural activity will occur.During the dynamic period,the contact zone in and out of the alkaline complex was enriched and formed into the Zhongshangou gold deposit. |
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