西秦岭李坝金矿蚀变岩的地质地球化学特征

李坝浊积岩型金矿床赋存于西秦岭北带中泥盆统李坝群浊积岩建造中 ,赋矿围岩蚀变主要为黑云母化、绿泥石化、绢云母化、硅化和碳酸盐化 ,且蚀变分带明显。通过对该矿床各种蚀变岩的常量元素、微量元素及稀土元素的地球化学特征研究 ,探讨了元素在碱交代 K交代及酸交代过程中的地球化学行为。结果表明 ,Si O2 含量 ,Fe2 O3 含量 ,L REE/ HREE,Σ L REE,(L a/ L u) cn,(L a/ Sm) cn,(Tb/ Yb) cn及微量元素的含量等随着 K交代作用强度的增强 ,显示出规律性的变化。最后讨论了 K交代作用及酸交代作用与金矿化之间的关系。

A STUDY OF THE GEOLOGY AND GEOCHEMISTRY OF ALTERED ROCKS FROM LIBA GOLD DEPOSIT IN GANSU

The Liba gold deposit located in the northern zone of west Qinling is situated in the Middle Devonian turbidite formation of the Liba Group. The gold mineralization is strickly controlled by fault and intrusive mass.Alteration from orebodies to unaltered rocks can be grouped into four zones, that is, pyritization silicification sericitization, sericitization, chloritization and biotitization. All gold orebodies lie in the zone of sericitization overlapped pyritization, weak silicification and carbonatitization.K metasomatism belonging to alkaline metasomatism caused significant chemical changes to silt phyllite, which now contains up 4.71% K 2O, 57.83% ~61.66% SiO 2 and 3.12%~3.99% Fe 2O 3. The separation of K, Na which are a pair of incompatible elements took place in the course of biotitization and sericitization. Ti, Al, and HREE remained immobile during the formation of potassic and chlorite alteration, whereas LREE, P, Mg and Au were mobilized. The potassic alteration could provide some ore forming elements leaching from altered rocks.K metasomatism can make the density of altered rocks lower and the porosity increase, and meanwhile provides sufficient room for ore forming fluid which took place pervasive acid alteration to form gold deposits.