关键词: 吉瓦, 日贡拉组, 物源分析, 渐新统, 早白垩火山岩, 铜矿

Abstract:

Many detailed field surveys and comprehensive researches have been made to find sandstone copper deposit in Jiwa area, Tibet. Oligocene Rigongla formation sandstoneswere the ore-bearing horizon. The deposit type is strata-bound deposit. Series of provenance analysis technique, for instance, quantitative detrital minerals analysis, elementary geochemical methods and heavy minerals combination analysis,are used to explorethe provenance features and tectonicbackground of Rigongla sandstones. The main lithology is lithic sandstone with a poor sorting and psephicity and low maturation of texture. The detrital compositions hintthe main setting background of provenance is continental island arc, the geochemical characteristics are high value of siliceous, enrich in LREE, relatively depleted in HREE, and negative Eu anomalies. They all show that the provenance is closely related to acid volcanic rocks, the main setting background of Rigongla formation sandstone is continental island arc, the lithic sandstones came from felsic part of upper crust, heavy mineral combinations mainlyarehematite-limonite and magnetite,zircon,tourmaline, garnet,which were related to intermediate-acid magmatic rocks. Sandstone was deposited in dry, restricted shallow water and oxidizing environment. The morphological characteristics of zircons indicate that provenance is close to mother rocks. The correlation analysis of heavy minerals also shows that provenance is closely related to volcanic rocks. Comparingto acid volcanic rocks of the lower stratum and early cretaceous volcanic rocks in this area, trace elements and heavy mineral sreveal that the characteristics of detrital material source area were showed genetic relationship from petrology characteristics, geochemical characteristics and heavy mineral assemblages. The provenance of fragments were closely related to volcanic activities, may come from the acid volcanic rocks of early Cretaceous associated with the southward subduction of the Bangong Co-Nujiang oceanic crust and northward subduction of the Yalung Zangbo oceanic crust. Sandstone copper deposits was found in Rigongla Formation, volcanic rock provides the source of ore-forming materials.

Key words: Jiwa, Rigongla Formation, provenance analysis, Oligocene, Early Cretaceous volcanic rocks, copper deposits