青海同仁地区Ⅰ型花岗岩带的地球化学特征及成矿意义

Geochemical characteristics of granite and mineralization significance of Ⅰ-type granite in Tongren area,Qinghai

青海同仁地区Ⅰ型花岗岩带SiO2含量变化范围在52.29%～72.25%,平均值为62.58%,A12O3含量变化范围在14.31%～19.15%,平均值为16.73%。低碱(Na2O+K2O变化范围为2.65%～7.57%)、高钾(K2O平均值为3.86%)、轻稀土(Sr、Ba、Ta、Ti)富集,重稀土(Sr、Ta、Zr、Ti)亏损,δEu范围在0.68～0.72,平均值为0.71,具中等的负铕异常,(La/Yb)N范围在8.63～8.85,平均值为8.76,稀土元素配分模型为轻稀土富集的右倾配分模型。主微量元素研究表明,研究区花岗岩为准铝质(A/CNK为0.7～1.1)Ⅰ型花岗岩,形成于中央造山带在地壳加厚作用后岩石圈拆沉作用的地球动力学背景,岩浆在上升侵位过程中受到地壳物质的混染,在成岩过程中存在斜长石、钾长石、黑云母、铜金等矿物的分离结晶作用,岩体与围岩接触带上形成Cu、Pb、Zn、Ag、Mo多金属矿(床)。

The SiO2 range of Ⅰ- type granites is 52.29% -72.25% ,average 62.58% ,A1203 range is 14.31% ~ 19.15% , av-erage 16.73%. Low -alkali （ range of Na2O ＋ K2O is 2.65% - 7.57% ） , potassium （ the average of K2O is 3.86% ） ,It is character with enrichment in LREE （ St, Ba, Ta, Ti ） and depletion in HREE （ Sr, Sr, Ta, Ti ） , range of 8Eu is 0.68～0.72, average 0.71, with moderate negative Eu anomalies,range of （La/Yb）N is 8.63 -8.85, average 8.76 ,The rare earth elements of granite is high,with its rare fractionation performance curve for light rare earth elements is enrichment and heavy rare - earth elements relatively flat but to- wards right type. The research shows of maior elements and trace elements that the granites which have studied （ A/CNK is 0.7 - 1.1 ） is metaluminous Ⅰ - type granites,in the geodynamic background with central orogenic beh of crustal thickening and lithosphefic delami- nation, magma rising in the course of contamination by crustal material,there is in the process of fractional crystallization with diagene-sis plagioclase,potassium feldspar,biotite,copper-gold minerals. The contact zone between the mass and country rock can form poly-metallic ore （deposit）.