大中型豆荚状铬铁矿床地球化学特征研究

Optimal Geochemical Features of Medium and Large-Sized Podiform Chromite Ores

豆荚状铬铁矿作为冶金工业重要材料,具有较高的经济价值。大中型豆荚状铬铁矿常常发育在SSZ(suprasubduction zone,超俯冲带)型蛇绿岩中,但在很多SSZ型蛇绿岩中只发育了小型矿床甚至矿化点。因此,在讨论含铬矿和不含铬矿蛇绿岩体地球化学特征的基础上,对比研究了国内外9个发育不同规模铬铁矿床蛇绿岩体和矿石的地球化学组成特征,发现大中型豆荚状铬矿床具有铬铁矿石Pd/Ir值低(<1.5),其中的造矿铬尖晶石Cr~#值高(>0.6)、Cr/Fe值高(>2.7)和w(TiO_2)低(<0.3%)等地球化学特征,且常常发育在中度亏损的蛇绿岩中,据此认为在其成矿过程中经历了中等程度的部分熔融作用。

Podiform chromite ores, the vital materials for metallurgical industry, are of great economic importance. Medium and large-sized podiform chromite deposits are usually found in SSZ(suprasubduction zone) type ophiolitic complexes, but small and mineralized spots also develop in them. Thus, we study in this paper, based on the discussion of geochemical features of ore-bearing and barren ophiolites, nine chromite ore-bearing ophiolitic complexes by comparing various geochemical composition of the ophiolites and chromitites. The results show that the high Cr#(>0.6), Cr/Fe values(>2.7), low TiO2 content(<0.3%) of the orebody spinels and the low Pd/Ir(<1.5) of the chromitite are the geochemical indicators for medium and large-sized chromite deposits. Moreover, by comparing the REE features and the accessory spinels of these ophiolitic complexes, we can find that medium and large-sized chromite deposits develop in moderately depleted ophiolitic complexes, which indicates this kind of deposit has experienced moderate degree of partial melting.