西秦岭寒武系硅岩建造中金矿床成矿物质来源研究

ORE FORMING MATERIAL SOURCES OF GOLD DEPOSITS IN THE CAMBRIAN SILICALITE FORMATION, WEST QINLING

西秦岭寒武系硅岩建造中的金矿床，是我国境内发现的一种具有独特地质特征的层控金矿床。通过对寒武系硅岩建造以及金矿石中金的浸出率、微量元素及其特征元素比值、稀土配分型式以及硫、铅、碳、氧、氢、硅等同位素组成等方面的系统研究表明，在后期成矿过程中，金及其它伴生元素主要来自寒武系硅岩建造；成矿溶液主要来自大气降水。地下热液在环流过程中，促使硅岩建造中的成矿物质发生活化、迁移和再聚集，并最终导致矿床的形成。

Gold deposits occurring in the southern subzone of western Qinling include Laerma and Qiongmo ore deposits and Yaxiang ore occurrence.They are a new type of stratabound bold deposits closely associated with submarine exhalative sedimentation and showing many distinctive features.Existing in the Cambrian silicalite formation composed of black shert and slate,the gold deposits are so clearly controlled by strata,host rock types and structures that their stratabound character is agreed by many geologists. The abundances of gold and other elements are relatively high in hte Camerian silicalite formation.According to the results of gold absorbing and releasing experiments of organic matters and clay minerals and the results of gold leaching rate,the authors conclude that the activated gold is so ight that it can be easily remobilized to take part in the ore forming process.Co/Ni and S/Se ratios of hydrothermal pyrite vary in the range of 0 0736～0 3263 and 1137～656138 respectively.It is reasonably assumed that the gold deposits have affinity with exhalative sedimentary silicalite formation.The REE patterns of gold ores are similar to those of the host rocks,with negative Ce and Eu anomalies. The hydrothermal minerals and ores in the gold deposits have δ 34 S values -32 2‰～ +46 9‰ (sulfides)and +2 4‰～+33 3‰(sulfates), δ 13 C values -10 3‰～-30 5‰(organic carbon), δ 30 Si values -0 2‰～+0 7‰(quartz)and +0 4‰～+1 3‰(cherts),ore lead isotopic values 206 Pb/ 204 Pb=16 532～37 266, 207 Pb/ 204 Pb=15 257～16 879 and 208 Pb / 204 Pb =36 703～39 555,rock lead isotopic values 206 Pb/ 204 Pb=18 635～36 697,and 207 Pb/ 204 Pb =15 586～17 821 and 208 Pb/ 204 Pb=36 644～39 638.Hydrothermal fluids have δ 18 O values -11 06‰～+15 34‰(figured out from isotope fractionation equation of quartz water and barite witer), δ D values -58‰～-122‰(fluid inclusions).The above described isotopic study shows that the ore forming solution was mainly derived from the ancient meteoric water,sulfur in the fluids from the reduced sulfur in the country rocks,carbon from organic carbon in the black layer,and silica from the silicalite formation.Lead isotopic composition shows that the ore lead has genetic relation with the leaching process in the silication formation. Obviously,the silicalite formation was the main source of the metallogenic materials.During the ore forming process of hot circulating groundwater(meteoric water),the ore forming materials in the silicalite formation were remobilized and reconcentreted after migration,resulting in the formation of the present ore deposits.