关键词: 长江岩体, 绿泥石, 副矿物, 热液蚀变, 铀源矿物

Abstract: Changjiang granite is one of important uranium-ore-bearing granites in the southern Zhuguang granitic composite, northern
Guangdong province. In this paper, we present a systematical on mineralogical characteristics of chlorites and accessory minerals and
their alteration in the Changjiang granite, by using electron-microprobe analysis and scanning electron-microscope analysis. We found
that uranium mineralization was related to the chloritization of biotite by reducing-redox-state hydrothermal fluid in the
pre-mineralization stage. The chloritization of biotite altered the original U-bearing accessory minerals of the granite and formed new
U-bearing minerals such as coffinite near the chlorite. Uranium in the newly formed U-bearing minerals can be easily released into fluid
under circumstance of later hydrothermal fluid being in slightly oxidizing state in the mineralization stage. Accessory minerals in the
Changjiang granite include zircon, apatite, coffinite-thorite, uraninite and monazite. Among these accessory minerals, uraninite,
uranothorite and coffinite are thought of important uranium-source minerals of the Changjiang granite because of their high uraniumcontent that is readily released during later alterations by oxidizing fluids. Monazite has a moderate quantity of uranium that is
potentially able to be liberated when it is altered to synchsite. Such a process only occurs during chloritization of major minerals such as
biotite that enclosed the monazite. Therefore monazite is a potential uranium-source mineral. Zircon is not a uranium-source mineral
because uranium in zircon remains stable and not released even under hydrothermal alteration. Other minerals like allanite and apatite
have little uranium which is even below the detection limit of electron-microprobe, are thus not uranium-source minerals of the
Changjiang granite.

Key words: Changjiang granite, chlorite, accessory minerals, hydrothermal alteration, uranium-source minerals