The Alteration And Mineralization Characteristics Of Scientific Deep Drilling In Anhui Luzong Basin

Deep drilling program named SinoProbe-03-06 was conducted in Zhuanqiao of Lujiang,Anhui Province.Scientific deep drilling named ZK01 of Zhuanqiao lies in the centre of Luzong Basin,15 km eastof Huangmeijian Pluton.Thorium and uranium anomaly was found in the syenite from the deep drilling,which had reached out off grade in some samples.The drill core from the ZK01 can be divided into 4 parts from the top to bottom:(1)the Quaternary gravels(0?17m)belonging to Lower Cretaceous ZhuanqiaoFormation,clasts mainly composed of trachyandesite,(2)volcanic-sedimentary rocks of Zhuanqiao Formation(17-1488m)mianly including trachyandesite and pyroxene-trachyandesite,(3)syenite(1488-1848m),and(4)monzonite(18482011.95m).Alterations associated with uranium and thorium mineralization are the albitization,tourmalinization,anhydrite and other high-temperature hydrothermal alteration.According to the alteration and mineralization assemblage,mineralization can be divided into five stages,i.e.anhydrite-tourmaline veins at stage?,uranium-thorium mineralization at stage ?,magnetite mineralization at stage ?,sulfidesubordinate quartze at stage IV,and quartz-calcite-sulfide at stage ?.Uranium and thorium mineralization was found at stage ? and ?.This study investigated the thorium and thorium-bearing minerals and summarized the relationship between rock-forming minerals and accessory minerals using microscope and electron microprobe techniques.The results indicated that thorium and uranium have two occurrences in the deposit,including independent thorium minerals,isomorphic form existing in uranium minerals,and micro-isomorphic form lying in accessory minerals.Independent uranium and thorium minerals occur as the euhedral crystal within albite,and often associated with zircon in space,or are dispersed in rutile,apatite,anhydrite and other hydrothermal alteration mineralsas fine particles.Major and trace elements suggest these igneous rocks in ZK01 are characterized by high content of potassium(K2O averaged at 3.7%),rich alkali(K2O+Na2O averaged at 8.4%)and LREE and depleted strong incompatible elements,and belongs to shoshonite series.Trachyandesite(131.29±0.85Ma),syenite(130.95±0.56Ma)and monzonite(130.88±0.41Ma)from ZK01 form almost at the same time.?Hf(t)values of trachyandesite,syenite and monzonite range form-12.9to-7.6,from-10.1 to-6.5,and from-11.1to-3.4,respectively,which suggest that igneous rocks in ZK01 were derived from enriched mantle with heavy contaminated by continental material.Three types of fluid inclusions including liquid-rich(?),gas-rich(?)and daughter mineral-bearing(?)fluid inclusions,respectively,have been observed.The daughter minerals mainly consist of halite and sylvite.The fluid inclusions of stagel are characterized by high temperatures(540?560? at peak)and low to high salinities(65?70%and 0?5%NaCl eq.at peak).The fluid inclusions of stage ? exhibit medium to high temperatures(320?340? at peak)and low salinities(0?5%NaCl eq.at peak).The fluid inclusions of stage? have medium to high temperatures(380?400? at peak)and low salinities(0?5%NaCl eq.at peak).The fluid inclusions of stage? have medium temperatures(240?260? at peak)and low salinities(0?5%NaCl eq.at peak).The fluid inclusions of stageV have low temperatures(160?180? at Peak)and low salinities(0?5%NaCl eq.at peak).A series of features such as the uranium and thorium mineralization,uranium and thorium ratio,mode of occurrence and alteration in deep drilling were quite different from those of uranium deposits(occurrences)nearby.That difference might be a genetic link that uranium and thorium mineralization in deep drilling might reveal a high temperature mineralization style of uranium deposits nearby when it was in the basin deep rock.Fluid properties in deep drilling,are similar to other deposits in Luzong Basin,indicating that ore fluid acts as a part of the fluid in Luzong Basin mineralization system.Boiling are occurred in fluid evolution periodically,which cause the change of physical and chemical state that may be one of the major factors leading to migration and mineral precipitation.