四川东北寨金矿床的矿石组构及成因

THE ORE FABRIC AND GENESIS OF THE DONGBEIZHAI GOLD DEPOSIT,SICHUAN PROVINCE

东北寨微细浸染—交代型金矿床赋存于三叠系碳酸盐岩—碎屑岩建造中,容矿岩石为含碳质黑色岩系。典型的矿石组构与含砷黄铁矿—雄黄—低温相毒砂—自然金—辉锑矿—自然砷—石英—方解石为主的矿物组合显示低温浅成的矿石建造特征。同位素研究表明,矿质源于围岩系统,介质来自大气降水。包裹体测试结果说明成矿温度低(均一温度为236—129℃)、矿石就位浅(约1200—1600m)、流体盐度高(5.09％—11.71％,NaCl,wt),具一般地热卤水的特点。矿床成因属渗流(滤)热卤水型。

The Dongbeizhai finely disseminated--replacement gold deposit is hosted in car-bonate and clastic rocks. It is controlled by the steep--dipping fault zone of the largescale N--S--trending thrust--nappe. The westerly dipping of the main fault planecontrols the occurrence and distribution of orebodies. The orebodies are stratoid andthintabular in shape. The mineral assemble is pyrite (As--bearing)--realgar--arsenopyrite(lower-temperature phase)--natural gold--stibnite--natural arsenic--quartz--calcite characteristic of anepithermal deposit. The ore fabric also shows the features of an epithermal deposit. The ore substances are derived from host rocks and hydrothermal fluids consistmainly of meteoric water as indicated by systematic studies of sulfur (sulfidesδ^(34)S= + 6. 3‰--14. 59‰), lead (pyrite and stibnite ^(206)Pb/^(204)Pb= 18. 384--18. 439,^(207)Pb/^(204)Pb == 15. 605--15. 677 and ^(208)Pb/^(204)Pb == 38. 436--38. 670), carbon(calciteδ^(13)G=+ 2. 748‰-- -3. 415‰), hydrogen (fluid inclusions δD_(H_2O)= -66. 566‰-- -75. 490‰)and oxygen (fluid inclusions δ^(18)O_(H_2O)= + 12. 903‰-- + 16. 211‰ ) isotopes. Homogeniza-tion temperature of the fluid inclusions is about 175 + 45℃ and the salinity may beas high as 11.71 equivalent wt％ NaCl. The formation pressure ranges from 3× 10~7to 4 × 10~7 Pa and the formation depth ranges between 1 200 and 1 600m. Gomparison of the deposit with analogous gold deposits suggests that this depositis of infiltration-hot brine origin.