Influencing Factors Of Heavy Mineral Composition ——Take The Songhua River System As An Example

Songhua River is one of the seven river systems in China,but the factors affecting its heavy mineral composition have not been studied yet.The in-depth study of its sediment composition is helpful to reveal the controlling factors of source area and the law of sediment transport and deposition.Heavy minerals are of great significance in the study of river sediments because of their strong stability and weathering resistance.Heavy minerals contain important information about source rocks and parent rocks,and are important tools for unravelling the process from source to sink and tracing provenance.In order to evaluate the effects of provenance,fluvial processes and chemical weathering on the composition of heavy minerals,32 heavy mineral samples were collected from the banks and river terraces of the main stream and tributaries of the Songhua River system.Heavy mineral analysis of <63 ?m,63?125 ?m and 125?250?m fractions showed that:(1)A total of 29 kinds of heavy minerals were identified in the Songhua River system.Include zircon,apatite,rutile,sphene,leucoxene,moissanite,nativegold,pyrite,anatase,garnet,monazite,tourmaline,pyroxene,epidote,hornblende,ilmenite,limonite,siderite,magnetite,maghemite,magnetite limonite,chromium spinel,fluorite,tremolite,kyanite,spinel,allanite,anthophyllite and weathered detritus and so on.(2)The provenance of heavy minerals was affected by fluvial processes.The source rock information of Songhua River system is well reflected in the tributaries of Nenjiang River,but not in the main stream of Nenjiang River.For example,the heavy mineral information in Nuomin River becomes blurred with the increase of transport distance.(3)Fluvial processes have a significant effect on the composition of heavy minerals.Songhua river drainage heavy mineral content are mainly concentrated in63?125 ?m microns components,the main mineral of hornblende,epidote,ilmenite and titanite;into the same river of different river heavy mineral composition had significant difference(take the Baran River for example),indicates the wide particle size analysis in the process of source-transfer window and the number of samples to acquire enough information source area full of heavy mineral composition.(4)Chemical weathering plays a key role in controlling the heavy mineral composition of river terraces.It is necessary to pay attention to the weathering degree of river terraces when using the heavy mineral composition of river terraces to study the evolution of paleo-drainage system and source-sink tracing.The T2 terrace(weakly weathered)of The Songhua River in Harbin basically retains the characteristics of modern river sand,and the heavy minerals in TI terrace of the Nemoer River with strong weathering degree have been modified to a certain extent.In T3 terrace of Tonghe Songhua River with strong weathering,amphibole and pyroxene have completely disappeared,and the heavy mineral composition has been seriously damaged.(5)The natural process and human factors of heavy mineral composition should be paid close attention to in order to prevent deviation.