科研之友
微信
新浪微博
Facebook
分享链接
摘要
The deposits dominated by pyrite-anhydrite-magnetite (Py-Anh-Mt) ores occur in the Mesozoic continental volcanic basins (e. g, Luzong basin) formed by fault depression in the Middle-Lower Yangtze River Valley. Abundant iron and pyrite mineral deposits are found in volcanic and subvolcanic rocks in Luzong basin, and also distributed in the basin margin. The main volcanic rocks are potassium-rich alkali basalt (shoshonite series) -trachyandesite-trachyte assemblage. In the deep part of the volcanic basin, alkali-gabbro-pyroxene monzonite-syenite rock assemblage occur corresponding to the volcanic rocks, such as, Quekou gabbro, and Yangshan pyroxene syenite. Hydrothermal activities often happened to volcanic rocks and to the deep magmatic rocks. These Py-Anh-Mt deposits are mainly accompanied by two sets of alteration zoning, the inner (deeper) melanocratic alteration and the outer (shallower) leucocratic alteration. The both behave as distinct alteration mineral zones in vertical space. The shallower part; The leucocratic-alteration zone, consists of substantial pyrite and anhydrite ores and silicified rocks, constituting extensive pyrite-anhydrite-quartz rocks that are associated with argillized, sericitized and propylitized ones. The deeper part: The melanocratic-alteration zone, consists of anhydrite and magnetite ores which are associated with alteration minerals such as pyroxene, uralite, apatite, garnet, scapolite, plagioclase, titanite, potassium ::eldspar and phlogopite. In contact zone between monzonite-syenite and volcanic rocks, a strong altered rocks comprising mica and quartz occurred (tourmaline-muscovite-quartz assemblage). Magnetite veins are also found (magnetite-scopolite-sodalite-garnet assemblage) in Quekou gabbro complex rocks. In Yangshan and Makou districts, magnetite ores are present in syenite, in which pyroxene-K-spar-magnetite assemblage, and actinolite-apatite-magnetite assemblage formed. Monzonite-syenite complex rocks are present in the deeper part of the volcanic basin, taking a form of layered intrusion. Investigations indicate that iron ore formations are also related to gabbro-monzonite-syenite rocks. Volcanic rocks and deep magmatic rocks, and ore-formations behave a vertical zoning in the basin. The volcanic rocks and sub-volcanic rocks are present at upper part. In the lower part, gabbro-monzonite-syenite complex rocks occur. In the middle, there is a transition zone, comprising dykes, rock sill. In the upper, shoshonite and trachyandesite occur, and magnetite-pyrite ores are present in the sub-volcanic rocks. In the deeper, iron formation also occur in alkali-gabbro, monzonite-syenite. Measurements of geological age of altered rocks indicate that albite in the altered rocks of Luohe deposit and syenite nearby iron deposit in Makou are almost the same age (110 similar to 119Ma). The facts illustrated that iron ore formation in volcanic and sub-volcanic rocks and the ores in deeper magmatic rocks occurred in nearly simultaneous. The kinetic experiments of syenite-water reactions are carried out at 20 similar to 435 degrees C, 23 similar to 35MPa. The experiments indicate syenite easily dissolves at 400 similar to 435 degrees C. As water reacted with syenite, a metal bearing fluid is forming. The experimental results provide the realistic data that will be useful to understand the deep geophysical survey for volcanic basin.
- 出版日期2010-9
- 单位中国地质科学院
