辽西南部中生代花岗岩类地球化学特征与成矿关系

GEOCHEMICAL CHARACTERISTICS AND METALLOGENIC SERIES OF MESOZOIC GRANITES FROM THE SOUTHWEST LIAONING

辽西南部中生代花岗岩类呈北东向带状分布,由多期侵入的岩基、岩株和岩脉组成,具有从中性—中酸性—酸性的分异演化系列。固结指数SI=41.02～1.45,分异指数DI=42.84～95.45。随着岩浆分异程度的增高,酸度和碱度明显增高,碱度率AR=1.69～3.95,并由Na_2O>K_2O变为K_2O>Na_2O。同时,岩体中Sc、V、Cr、Co、Ni、Ba、Sr、Th、U、REE及Au、Cu、Pb、Zn等微量元素和成矿元素丰度逐渐降低,而Mo则主要富集在岩浆演化的晚期阶段。随着岩浆由中性—中酸性向酸性演化,相应地形成了Au、Cu→Pb、Zn→Mo矿床(矿化)类型组合,构成一有成因联系的成矿系列。

The distributed area of Mesozoic granites in the southwest Liaoning is about 1200km^2. The granites are distributed northeastly in band. It consists mainly of granitic batholith, stocks and dikes besides a few dioritic bodies. Its evolutional series are intermediate-intermediate acid acid. With the differential index of the rocks increasing (DI=42.84～95.45), the acidity and alkalinity of the rocks increase obviously, and Na_2O>K_2O becomes K_2O>Na_2O, from cale-alkalinity to potastium-rich calc-alkalinity. ANCK(AL/Na+K+2Ca')=0.67～1.25. At the same time, the abundance of transitional elements Sc, V, Ti, Co, Ni alkalibase metal Ba and Sr and others decreases gradually, and the abundance of elements Rb, Th, U increases continuously. The values of ∑ REE, La/Yb(N) and δEu etc. also decrease continuously. The initial ^(87)Sr/^(86)Sr ratios are 0.7031～0.7049, δ^(18)0=7.4～10.3‰. These data show that intermediate acidic magma is formed by deep differentiation of initial magma from the lower crustupper mantle fractional fusion. Granites of mixing type are formed by mixing upper crust of the earth just in the emergence and emplacement process. The abundance of the metallogenic elements Mo, Pb, Zn, Cu, Au etc. in the rocks is higher, showing syntectic type granite's metallogenic features. With the evolution of magma from intermediate-intermediateacid-acid, correspondingly formed Au, Cu, Pb-Zn, Mo deposit, making up a metallogenic series with genetic connection.