Genesis And Deep Prospecting Of Altered Granite Type Orebody In Baizhangzi Gold Deposit,Liaoning Province

Liaoning Baizhangzi gold deposit is one of the large scare gold deposits in the Eastern Hebei-Western Liaoning gold district.There are two types of ore bodies in Baizhangzi including gold-bearing quartz vein type and altered granite type and the latter one has been mainly exploited in recent years.Therefore,this paper takes altered granite type ore bodies as the research object and methods such as genetic mineralogy,chronology,short-wave infrared analysis are used to systematically study the metallogenic regularity and establish metallogenic models for providing guidance to deep prospecting.There are mainly two types of granitic intrusions in this deposit.Biotite monzonite is scattered and mainly located in the depth.Quartz monzonite is widely distributed and closely related to ore bodies in space.Quartz monzonite is the most important ore-bearing rock in this deposit and with molybdenum mineralization at the top of quartz monzonite.The ages of biotite monzonite and quartz monzonite were 236±1.5 Ma and 233±1.9 Ma respectively,both of which were products of the late Triassic extensional tectonic background.The thermoelectricity coefficient of pyrites from different levels ranges from-330.5 ?V / ? to 344.3 ?V / ?.Among them,the proportion of N-type pyrites is 90.1% and 9.9% for P-type pyrites.The ore body erosion rate is between 58.7% and 85.0%,indicating that the current ore bodies have reached the middle to lower part,and there is still prospecting potential in the deeper part.The formation temperature of pyrites is mainly between 270? to 350 ?,indicating that the deposit is a medium temperature deposit.The temperature decreases from the deeper SW end to the upper NE end,indirectly indicating the migration of ore-forming fluids from the deeper SW end to the upper NE end.The known orebodies are inclined to the NE end in the deep part of the deposit.The high-value areas of P-type pyrite occurrence rate corresponds to the position of the known orebodies,and there is still high-value areas in the deeper part of the NE end,indicating that the deeper part of NE end has great potential for ore exploration.A total of 19 kinds of altered minerals were measured with short-wave infrared spectrometer,and illite—muscovite—kaolinite—montmorillonite—sheridanite were successively developed from the ore bodies outward,correspond to phyllic zone,muddy zone and chloritization zone respectively.The high-value areas of illite and muscovite contents,which are closely related to the ore bodies space,are taken as indicator for prospecting.In combination with the known orebody distribution rules,it is speculated that new orebodies may appear in the depth of line 112,line 103~107 and line 123.The H-O,S and Pb isotopes show that the ore-forming fluids and ore-forming materials of the Baizhangzi gold deposit were mainly come from magma,and the fluid inclusions were also characterized by magmatic hydrothermal fluids.Combined with the rock-and ore-forming ages,it is speculated that there were multistage magmatisms in this deposit.The late Triassic magmatism formed the granitic intrusions and molybdenum mineralization at the top of the granitic intrusions.The gold mineralization occurred at 128 Ma,so it is speculated that there may be one stage of Cretaceous magmatism which produced the altered rock-type gold ore bodies and gold-bearing quartz vein ore bodies.