Geochemical characteristics of granites and their relationship to gold mineralization in Yangshan gold deposit, Gansu Province, China.
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摘要
Yangshan gold deposit, hosted in the Devonian stratum on the north margin of Bikou Terrane, western Qinling orogenic belt, is a super-large carlin-like gold deposit discovered recently in Gansu Province,China. Many granitic dikes were found in the deposit and had spatially relationhsip to gold ore bodies. But the genetic relationship between them is still controversial. Studies show that the SiO (sub 2) ,K (sub 2) O and Al (sub 2) O (sub 3) of the granites range from 60.64% to 80.77%,2.27% to 4.32% and 11.83% to 23.71% respectively,and the A/CNK varies from 1.24 to 4.29,which indicate the granites are belong to prealuminous,calc-alkaline.The Granites are also enriched in Cs,U,K,Pb , and depleted in Ba,Nb,La,Ce,Sr,Ti. Rare earth elements (REE) content of the granites is between 14.45X10 (super -6) and 143.14X10 (super -6) (average 70.31X10 (super -6) ),with La (sub N) /Yb (sub N) ratios of 1.48- 37.26(average 17.08). Light rare earth elements (LREE) are concentrated evidently and heavy rare earth elements (HREE) are deficient with LREE/HREE ratios of 1.39-19.52(average 10.12).The REE patterns are characterized by slightly negative Eu anomalies,withdelta Eu=0.50-1.21(average 0.77). Combining with the analytical data of the major and trace elements, geochronology and Sm/Nd, Rb/Sr and Pb isotope of Yangshan granites,Bikou group volcanic rock and Devonian Sanhekou section stratum from previous work,it is proposed that the granites were derived from partial melting of deep thickening crust(Bikou group volcanic rock) and mixed with Devonian stratum during ascent.That is to say that the ore-forming material of Yangshan gold deposit directly derived from granitic magma,and the Bikou group volcanic rock and Devonian stratum should be the primary source.