长江中下游地区若干Cu(Au)、Cu-Fe(Au)和Fe矿床中钙质夕卡岩的稀土元素地球化学

本区夕卡岩的稀土元素（ＲＥＥ）分布模式表现为富集轻稀土元素（ＬＲＥＥ）的直线型和以Ｃｅ、Ｐｒ或Ｎｄ为峰值的折线型。夕卡岩全岩中ＲＥＥ分布模式基本上受石榴子石中ＲＥＥ的分配行为控制。石榴子石富集ＬＲＥＥ可能是承袭形成它们的初始物中ＲＥＥ丰度和分配行为的反映。石榴子石中ＲＥＥ（尤其是Ｌａ）分布的不均匀性、石榴子石微裂隙及包裹体中ＲＥＥ的丰度可能是导致直线型和过渡型ＲＥＥ分布模式的主要原因。石榴子石中折线型ＲＥＥ分布模式可能受石榴子石晶体化学和晶体结构的控制。具有这种ＲＥＥ分布模式的钙铁－钙铝榴石可能代表相对平衡条件下岩浆结晶分异产物。

REE geochemical studies of whole rock and rock-forming mineralsin skarns from Cu (Au), Cu-Fe (Au) and Fe ore depositsdistributed along middle-lower reaches of Yangtze River, China

The REE distribution patterns of skarns from middle-lower reaches of Yangtze River,China are characterized by straight-line type and kick-down-line type with Ce, Pr or Nd peaks,and both of them are enriched in LREE. The REE patterns in whole rocks of skams are basi-cally controlled by REE partition behavior in the garnets. LREE enrichment in the garnets isprobably inherited from the REE abundances and REE partition behavior in starting materialsfrom which garnets were formed. The inhomogeneity of the REE (especially La)distribution,the REE abundances in microfractures and inclusions of the garnets are probably the mainreasons resulting in the straight-line type and the transition type. The REE patterns ofkick-down-line type are perhaps controlled by crystal chemistry and crystal structure of thegarnet. Andrite-grossular-bearing skarns with such REE pattern are probably the products ofmagmatic crystallization-differentiation in the relative equilibrium condition.