云南省大坪金矿区二长花岗岩的 地球化学特征及地质意义

摘 要] 大坪金矿区岩浆活动频繁,矿区出露的二长花岗岩体规模较大,岩性为中粗粒二长花岗岩。在岩石化学组成上,SiO₂含量为67.32%～71.71%、Al₂O₃为14.54%～16.66%,属于过铝质花岗岩类。岩石富集大离子亲石元素(Sr、U、Rb 和Ba)和轻稀土元素(LREE)、相对亏损高场强元素(Ta、Nb和Ti), 且Ta、Nb 和Ti 具“TNT"负异常;啄Eu 值为0. 80～1. 44,负Eu 异常不明显;87 Sr/ 86 Sr 值范围为0.7078～0. 7436,均值0. 7256,高于原始地幔现代值0.7045;¹⁴³Nd/¹⁴⁴Nd 值范围为0. 5119～0. 5122,均值0. 5120,低于原始地幔现代值0. 512638;ε_Nd值范围为-2. 5～-4.2,均值-3.98。表明矿区二长花岗岩源区应来自于“壳-幔混合带"的部分熔融,形成于同碰撞或碰撞晚期的构造环境。二长花岗岩体与大坪金矿成矿流体具有相同源区,岩体为大坪金矿的形成提供了热源和主要成矿流体。

Geochemical Characteristics of Monzonite Granite from the Daping Gold Mining Area, Yunnan Province and Geologic Significance

The Daping gold mining area has underwent active magmatic activities.Granites of large scales outcrop widespread as medium-to coarse-grained monzonite granite in lithology.Contents of SiO2 range from 67.32% to 71.71%,and Al2O3 is between 14.54% and 16.66%,belonging to peraluminous granitoid rocks.The rock is rich in large ion lithiphile elements of Sr,U,Rb,Ba and light rare earth elements(LREE),and is depleted in the high field strength elements(Ta,Nb and Ti).It shows a "TNT" negative anomaly;δEu ranging from 0.80 to 1.44.87Sr/86Sr varies in the range of 0.7078 ～ 0.7436,averaging 0.7256,higher than the contemporary value of primitive mantle 0.7045.The ratio 143Nd/144Nd is in the range of 0.5119～0.5122,averaging 0.5120,lower than the contemporary value of primitive mantle 0.512638.εNd is in the range of-2.5～-4.2,averaging-3.98.All above indicate that the monzonite granite derived from a crust-mantle mixing belt through partial melt and formed in the tectonic regime of syn-or late collisional stage.The source of monzonite granite is identical to the ore-forming fluid,and the rock bodies provided heat and main mineralizing fluid in the Daping gold deposit.