The Granite In The Baizhangzi,Western Liaoning And The Significance Of Gold Mineralization

The western Liaoning region,located on the North China Craton,is one of significant gold metallogenic areas in China.The magmatic activity in the area is strong and multi-stage.Among them,granite is closely related to the gold mineralization of Baizhangzi.This paper analyzes and studies the petrology,geochemistry and chronology of Baizhangzi granite.And analyses the mineralization period and diagenetic age of the granite,discuss the source area and formation mechanism of granite magma,and analyze the constraints of granitic rocks on gold mineralization.Altered granites are mainly developed K-alteration,silicified,pyritization and sericitization,which are important prospecting marks.The superimposed combination of multiple alterations formed the ore body.When two or more alterations occur simultaneously,the gold grade is higher.The metallogenic stage of Baizhangzi gold deposit can be divided into three periods,from early to late,the gas-liquid metasomatism period(pre-mineralization period),hydrothermal mineralization period(mineralization period),and supergene oxidation period(post-mineralization period).The hydrothermal mineralization period can be subdivided into three stage,including quartz-pyrite(?),quartz-polymetallic sulfides-electrum(?)and carbonate(?).The hydrothermal mineralization period is the main stage of gold formation and precipitation.The Baizhangzi granites have medium-grained unequal-grained texture and massive structure,which are composed of K-feldspar,plagioclase,quartz and biotite.Potassium granite is formed by alteration of biotite granite,all biotite altered to sericite.The Baizhangzi granites enrich in Si,K,and deplete in Ti,Fe,Mg,Ca and P,belong to alkalic rock;All the samples enrich in large ion lithophlie elements(such as Rb,Th,U,K),and deplete in high strength filed element(such as Ta,Nb,Sr,P,Ti),and show strong positive anomalies of Th and U,and strong nagetive anomalies of P and Ti,have the characteristics of crustal origin;The distribution curve of REE presents a right-leaning pattern that is obviously enriched in LREE and depleted in HREE,and the LREE and HREE are clearly differentiated,and shows weakly negative Eu anomalies.The zircon LA-ICP-MS U-Pb age of the Baizhangzi granite is(235?234)Ma,is production of Indosinian magmatism.Combining with the other age data of the Igneous rocks in the area,consider it is formed under the post-collision tectonic environment.The Baizhangzi granite is I-type granite which medium-high differentiation has taken place.Its formation temperature should be slightly lower than 827?.The primary magma is formed in a weakly oxidized environment with high pressure and deep depth,presumably in the thickened lower crust environment;The Baizhangzi granite is formed by partial melting of the lower crustal material,followed by crystallization differentiation evolution;About tectonic environment,the Baizhangzi granite was formed in a post-collision environment;Gold deposits are closely related to the spatial production of granite and the origin of rocks,ore-forming hydrothermal fluid comes from deep source,granite makes a huge contribution to the formation of gold deposits.Through the study of the Baizhangzi granite,it provides a direction for further deep prospecting.