Widespread in West Qinling are intermediate-acid intrusive rocks, which cover 85% of the total area and involve five geological periods: (1) Caledonian (457---408 m.y.), (2)Variscan (367--278m.y.), (3) Indosinian (231...Widespread in West Qinling are intermediate-acid intrusive rocks, which cover 85% of the total area and involve five geological periods: (1) Caledonian (457---408 m.y.), (2)Variscan (367--278m.y.), (3) Indosinian (231--190m.y.), (4) Yenshanian (186--107m.y.), and (5) Himalayan, with Indosinian and Yenshanian granitic rocks being dominant. The bulk petrochemical composition of these intermediateacid rocks is: SiO2 64.91,TiO2 0.5, Fe2O5 1.19, FeO 3.07, Mn 0.08, MgO 2.38, CaO 3.52, Na2O 3.40, K2O 3.38 and P2O5 0.16, similar to that of granodiorite in China. According to M. A. Peacock's classlfication, the intermediate-acid rocks in this region, for the most part, belong to the calci-alkalic series and only a part of them (e.g. Yenshanian) to the alkali-lime series. As for these rocks, two genetic types can be distinguished: remelting-metasomatic granitic rocks (Rb/Sr 0.73---4.2, K/Rb 104--207, K/St 146---463; the principal components including W, Sn, Ta, Pb, Zn, U, Th, Zr, Y, Yb, Nb, La, Rb, etc. ) and upper mantle remelting-magmatic granitic rocks consisting mainly of granodiorite and quartz diorite (Rb/Sr 0.05--0.6, K/Rb 200--726 (the maximum 1000.7), K/St 10--120 (the maximum 152); Cu, As, Mo, Fe, Cr, Ni, Co, Mn, Ti, etc. as the major components).展开更多
The most productive chromite ore deposits are formed by crystallizing from chromite-ore magmas under definite physico-chemical conditions. The formation of chromite ore is controlled mainly by the degree of differenti...The most productive chromite ore deposits are formed by crystallizing from chromite-ore magmas under definite physico-chemical conditions. The formation of chromite ore is controlled mainly by the degree of differentiation of ultrabasic magma. How to diagnose uitrabasic magmatie differentiation is key to the understanding of the mechanism of formation of chromite ore. It is considered that chromite ore is derived from ulttabasic rocks. The rock-forming minerals include olivine, pyroxene and spinel. The minerals are well homomorphous minerals. The contents of major chemical elements in these minerals show little variation. On the contrary in those ultrubasie rocks which show no association with chromite ore deposits the contents of the elements vary over a wide range. Abundant data available.indicate that chromite ore deposits arc derived from chrore.ire-ore magmas resulting from the transport and accumulation of chromic elements. Since the transport and accumulation of chromic elements follows the statistical law,we must study the mechanism of formation of ehromite ore from the statistical point of view. If chromite ore is formed from spinel under the action of gravitation o.r other dynamic actions, we must elucidate the mechanism of formation of chromite ore from the dynamic viewpoint.展开更多
文摘Widespread in West Qinling are intermediate-acid intrusive rocks, which cover 85% of the total area and involve five geological periods: (1) Caledonian (457---408 m.y.), (2)Variscan (367--278m.y.), (3) Indosinian (231--190m.y.), (4) Yenshanian (186--107m.y.), and (5) Himalayan, with Indosinian and Yenshanian granitic rocks being dominant. The bulk petrochemical composition of these intermediateacid rocks is: SiO2 64.91,TiO2 0.5, Fe2O5 1.19, FeO 3.07, Mn 0.08, MgO 2.38, CaO 3.52, Na2O 3.40, K2O 3.38 and P2O5 0.16, similar to that of granodiorite in China. According to M. A. Peacock's classlfication, the intermediate-acid rocks in this region, for the most part, belong to the calci-alkalic series and only a part of them (e.g. Yenshanian) to the alkali-lime series. As for these rocks, two genetic types can be distinguished: remelting-metasomatic granitic rocks (Rb/Sr 0.73---4.2, K/Rb 104--207, K/St 146---463; the principal components including W, Sn, Ta, Pb, Zn, U, Th, Zr, Y, Yb, Nb, La, Rb, etc. ) and upper mantle remelting-magmatic granitic rocks consisting mainly of granodiorite and quartz diorite (Rb/Sr 0.05--0.6, K/Rb 200--726 (the maximum 1000.7), K/St 10--120 (the maximum 152); Cu, As, Mo, Fe, Cr, Ni, Co, Mn, Ti, etc. as the major components).
文摘The most productive chromite ore deposits are formed by crystallizing from chromite-ore magmas under definite physico-chemical conditions. The formation of chromite ore is controlled mainly by the degree of differentiation of ultrabasic magma. How to diagnose uitrabasic magmatie differentiation is key to the understanding of the mechanism of formation of chromite ore. It is considered that chromite ore is derived from ulttabasic rocks. The rock-forming minerals include olivine, pyroxene and spinel. The minerals are well homomorphous minerals. The contents of major chemical elements in these minerals show little variation. On the contrary in those ultrubasie rocks which show no association with chromite ore deposits the contents of the elements vary over a wide range. Abundant data available.indicate that chromite ore deposits arc derived from chrore.ire-ore magmas resulting from the transport and accumulation of chromic elements. Since the transport and accumulation of chromic elements follows the statistical law,we must study the mechanism of formation of ehromite ore from the statistical point of view. If chromite ore is formed from spinel under the action of gravitation o.r other dynamic actions, we must elucidate the mechanism of formation of chromite ore from the dynamic viewpoint.
