赤柏松矿田含镍基性岩侵入体的成因矿物学研究

GENESIS-MINERALOGICAL STUDY OF Ni-BEARING BASIC INTRUSIVES IN THE CHIBAISONG OREFIELD

本文从成因矿物学角度对所述岩体中主要造岩矿物橄榄石、辉石与斜长石的颜色、形态、晶胞参数、化学成分、微量元素、稀土及氧、硫、锶稳定同位素等方面进行了研究,从而揭示了岩体的成岩成矿物质来源、形成温度、压力,fo_2,Eh、pH值等物理-化学条件与成岩成矿作用特征。同时,概括出岩体的成矿特点与找矿准则。

Genesis-mineralogical study has shown that δ^(18)O=6.1-7.73‰ for plagioclase, ^(87)Sr/^(88)Sr=0.70321-0.70888 for plagioclase and pyroxene, and δ^(34)S=-0.5-+0.5‰, ^(32)S/^(34)S= 22.218-22.236‰ for the ores. Evidence shows that the rock-and ore-formlng materials were derived from the upper mantle. The crystallization sequece of major rock-forming minerals in the rocks is OL→Py→Pl. The crystallization temperature of the former was estimated at 1412℃ and that of the latter at 1155.81-1206.26℃. The pressure and depth of formation of the intrusive bodies were estimated at 1-5 kb and 3-14 km respectively, belonging to the moderately deep facies intrusions, fo_2= 10^(-4.7)-10^(-2.1) arm, pH=4-7 and Eh=-0.1-0.16 at which the intrusive bodies were formed, indicate that they were formed from acidic mediums under reducing conditions. In the ore-bearing intrusives Fo=77.38-82.90% for olivine, En=65-86% for orthopyroxenes with Ni accounting for 0.124%; Wo=36- 44%, En=50%, and Fs=10% for clinopyroxenes with Ni coming up to 0.53%; olivine and plagioclase contain as much as 0.22% and 0.06%, respectively. The contents of Ni, Cu and Co of the ore-bearing intrusives are two times those in the barren intrusives, and the contents of Cu, Ni and S of the orthopyroxene in the same ore-bearing petrographic facies are 2-4 times those of clinopyroxenes.