内蒙古海拉尔盆地东珺铅锌银矿床地球化学特征

Geochemic Features of Dongjun Lead—Zinc—Silver Deposit,Hailar Basin,Inner Mongolia

东珺矿床位于海拉尔侏罗纪火山断陷盆地,具有热液蚀变明显、断裂构造控矿显著、矿体多且规模小等特征,为一产于火山岩中的典型热液型铅锌银矿床。火山岩含碱量较高(K2O+Na2O=5.93%～8.26%),Na2O/K2O平均为1.81,轻稀土相对富集(LaN/YbN=16.72～23.31),具轻微的负Eu异常,大离子亲石元素(LILE)相对高场强元素富集,Nb、Ta、Ti相对于LREE和LILE亏损。矿石硫化物δ34S介于+4.48‰～+6.97‰,具幔源硫特征。矿石硫化物n(206Pb)/n(204Pb)、n(207Pb)/n(204Pb)、n(208Pb)/n(204Pb)分别变化于18.3143～18.4315、15.4934～15.6265、37.9810～38.4236,显示铀铅富集,钍铅微弱亏损。火山岩[n(87Sr)/n(86Sr)]i=0.70506～0.70512,[n(143Nd)/n(147Nd)]i=0.512521～0.512602,εNd(t)值变化于1.4～2.9。矿床地质特征和地球化学特征指示,成矿物质来源于岩浆系统或赋矿围岩,岩浆主要来源于轻稀土富集地幔,可能有少量地壳物质的混染。

The Dongjun deposit,located in the Hailaer Jurassic volcanic fault-depress basin,is a typical hydrothermal lead—zinc—silver deposit generated from volcanic rocks,which is characterized by significant hydrothermal alternation,apparent ore-controlling fault of metallogenic,many orebodies with small scale,etc. Volcanic rocks have high content of Alkali （K2O＋Na2O=5.93%~8.26%）,with the average value of Na2O/K2O at 1.81,relatively rich in light rare earths（LaN/YbN=16.72~23.31）,and with slightly Eu negative abnormality. Also,Large-ion lithophile elements （LILE） are richer than high field strength elements（HFSE）,while Nb、Ta、Ti are relative drawdown,compared to LREE and LILE. The δ34S values of sulfide ores vary from ＋4.48‰ and ＋6.97‰ and are typical of mantle S. In sulfide ores,the n（206Pb）/n（204Pb）,n（207Pb）/ n（204Pb） and n（208Pb）/ n（204Pb） ratios vary in the ranges of 18.3143~18.4315,15.4934~15.6265 and 37.9810~38.4236 respectively,showing that the U-Pb is richer,while Th-Pb is slightly less. Besides,in volcanic rocks,[n（87 Sr） /n（86Sr）]i=0.70506~0.70512,[n（143Nd）/n （147Nd）]i=0.512521~0.512602,εNd（t） values of 1.4~2.9. The geological and geochemical features of ore deposit indicate that the ore-forming matter is from magma system or the host rock,while the magma is mainly from the mantle rich in light rare earths,maybe mixed with a small amount of crustal materials.