摘要
硅岩建造是西秦岭拉尔玛—邛莫层控金矿床的含矿岩系。含矿层状硅岩呈块状、条带状、层纹状、多孔状和同生角砾状等,单层厚度一般为30m~200m。主要成分SiO2平均含量高达95.30%,其余为FeO、Fe2O3和有机炭等。硅岩的Al/(Al+Fe+Mn)比值低于0.35(平均0.153)。硅岩中微量元素十分丰富,不仅含具基性、超基性特征的元素群(如Cu、Cr、Pt、Pd、Os等),而且含具酸性特征的元素群(如W、Mo、U等)。硅岩中稀土以总量低(32.9×10-6~100×10-6)、δCe亏损为特征。经北美页岩标准化后,稀土含量随原子序数的增大而增大。硅岩的δ18O值为17.60‰~23.24‰,其形成温度约为70℃~118℃。硅岩的δ30Si值主要在+0.4‰~+0.8‰之间。硅岩的上述特点均显示其与喷流沉积作用有关。喷流沉积作用不仅形成了特殊的硅岩建造,而且也使金等元素在硅岩建造中发生了明显的聚集。
The Cambrian silicalite formation,composed of bedded chert and slate ,is the host rock of Laerma and Qiongmo gold deposits in western Qinling The presence of the typical chert offers an important evidence to evaluate the possible submarine exhalative system and its controls over the formation of gold deposits The ore bearing chert is characterized by massive ,banded ,laminated ,porous, spherulitic and pseudobrecciated structures which changes regularly in space The thickness of a chert bed generally varies from 30 to 200 meters It contains principally SiO 2 (95 30% on average),with FeO,Fe 2 O 3 and organic carbon greater than 1 0% .The ratios of Al/(Al+Fe+Mn)in all chert samples are lower than 0 3 (0 153 on average) The chert is enriched in most trace elements, which is characterized by not only the basic and ultrabasic elements group(e g Ag, Pt,Pd,Cu, Cr) but also the acid elements group (e g W,Mo,U).Rare earth are characterized by a low total contents (ranging between 3 29×10 -6 and 100×10 -6 ),negative Ce anormaly and a gradually increasing NASC—normalized value with increasing atomic number δ 18 O Values of chert mainly vary from 17 60‰ to 23 24‰ (19 17 on average),suggesting that the tempreature for deposition was from 70℃ to 118℃ δ 30 Si values of the chert in the area range mainly from +0 4‰ to +0 8‰ All the geological and geochemical characteristics show that the chert is a product of submarine exhalative sedimentation. During the submarine exhalative sedimentary period ,the silicalite formation and mineralization of some elements were all formed
出处
《高校地质学报》
CAS
CSCD
1998年第1期20-33,共14页
Geological Journal of China Universities
基金
中国-澳地利国际合作项目
国家自然科学基金
中国博士后科学基金
关键词
硅岩建造
喷流沉积
矿质聚集
西秦岭
硅质岩
silicalite formation, exhalative sedimentation, mineralization,western Qinling.