Study On Buried Granite And Its Contact Metamorphism In Yangjiazhangzi,Western Liaoning Province

Magnetotelluric sounding,earthquake and borehole verification are carried out in order to determine the occurrence of concealed granite and its contacting metamorphism below the lower part of the Yangjiazhangzi syncline,supported by the project of the filed test and demonstration of key instrument and equipment base of the deep probe.Our result indicates that concealed granite was found at 1727 meters depth for the Shangfuergou borehole JK-1,1514.79 meters depth for the Nangou borehole JK-2,and 1159.92 meters depth for the Xiquegou borehole JK-5,respectively.Data of earthquake and magnetotelluric sounding also show that concealed granite occurred at depth between 1160 to 1750 meters below the lower part of the Yangjiazhangzi syncline,and connected with the Hongluoshan batholith.Taking Xiquegou borehole JK-5 as an example,when drilling down to 379.02 meters,thermal contact metamorphism begins to develop.Tremolite-bearing microcrystalline marble begins to appear,which was metamorphosed albite-epidote hornfel facies.Acicular tremolite occasionally appears.It is called the contact metamorphic zone of tremolite-bearing microcrystalline marble.It is diopside-marble zone when drilling down to 558.41 meters,marble with metamorphic minerals which contain diopside,grossularite et al.,begins to appear,which was metamorphosed at hornblende-hornfel facies.Diopside-bearing marble is begin to appear.When drilling down to 700 meters,hydrothermal metasomatic minerals were produced,silty mudstone begins into hornstone lithification,skarnization occurs in carbonate rocks.Rocks are characterized by grossularite diopsidite,diopsidite,flogopite diopsidite,cordierite hornfels,and andalusite-cordierite hornfels.It is called hornfel-skarn zone,which was metamorphosed at pyroxene-hornfel facies,and accompanied by molybdenite mineralization.Concealed granite was found at 1159.92 meters.The inner part of contact metamorphic zone which is ~500 meters thick,the middle part of contact metamorphic zone which is ~100 meters thick,and the outer part of contact metamorphic zone which is ~180 meters thick,begin to appear successively from the granite body upward.The rocks over 180 meters are unmetamorphic limestone.The distance of thermal contact metamorphism of concealed granite is about 780 meters.Furthermore,the petrochemical type of the concealed granite below the lower part of the Yangjiazhangzi syncline is monzonitic granite,which belongs to weak peraluminous and high potassium calc-alkaline series rocks.The formation period was 183.7~186.1 Ma,it is same with the outer Hongluoshan batholith.It indicates that concealed granite below the lower part of the Yangjiazhangzi syncline,and connected with the Hongluoshan batholith.In addition,borehole verification is also fully proved the existence of thermal contact metamorphic zone caused by the encroachment of the early Jurassic magma and molybdenite mineralization.The thickness from the rock mass contact zone to the appearance of the skarn molybdenite mineralization is ~500 meters.There is still the molybdenite mineralization when drilled into the granite more than 100 meters.It indicates that the main ore bodies of the Yangjiazhangzi molybdenum deposit are produced in skarn and porphyritic granite in the contact zone of limestone and granite,which are skarn-porphyry type molybdenum deposit.It shows that the Yangjiazhangzi molybdenum deposit structure still has great prospecting potential.The results of this study provide new scientific basis for further prospecting works in the area.