江西含铜(金钼钨)斑岩体的主要特征

LITHOLOGICAL CHARACTERISTICS OF THE COPPER(GOLD, MOLYBDENUM, TUNGSTEN)-BEARING PORPHYRIES IN JIANGXI PROVINCE

江西含铜(金、钼、钨)斑岩体的K-Ar法及Rb-Sr等时线法同位素年龄在205～80Ma集中在175～130Ma。根据其产出的环境,岩石的主、副矿物组合,微量元素、稀土元素,硫、氧、锶同位素特征以及成岩的温度及压力的估算。它们形成的温度较高(≥800℃),侵位较浅(≤3.7km),物质来源较深(下地壳),并受上陆壳物质混染。

The copper(gold, molybdenum, tungsten)-bearing porphyries are distributed mainly in the north Jiangxi along deep fault zones like a bundle and bead. Their isotopic ages are 80～205Ma(mainly 130～175 Ma). All the rocks are intermediate to acid and dominated by intermediate-acid to weakly acid rocks with the content of SiO_2 being 56～72％ and that of(K_2O+Na_2O)being 5～7.5％. They possess porphyritic texture and massive structure. Clastic texture formed by undelground explossion has been found in some porphyries and flow structure is found in the margin of the porphyries. Plagioclase, orthoclase, quartz, biotite and amphibole dominate the rock-forming minerals with magnetite-apatite-titanite zircon as the accessory mineral assemblage. A water-enriched chamber must exist in the deep part of the intrusive complex. Abundant H_2O^+, Cl and Cu(>100ppm), and more than 50ppm content of copper in minerals are criteria of ore-bearing intrusions. The average content of REE in the rocks is 146.41 ppm. The average ∑Ce/∑Y is 7.19. The average δ Eu is 0.90; δ^(34)S is -2～+6‰; δ^(18)O(SMOW) is +8～+13.16‰. The initial ratio of ^(87)Sr/^(86)Sr is 0.7044～0.70886. The conditions under which the porphyries formed are 800～880℃, at the depth of 2.5～3.7km. This kind of epigene volcanic intrusive complexes differ from that derived either from the mantle or from the crust. They are magmatic rocks of transitional type.