325、326矿床钠交代与铀成矿的关系

THE RELATIONSHIP BETWEEN SODA METASOMATISM AND URANIUM MINERALIZATION IN No.325 AND No.326 ORE DEPOSITS

325、326矿床是典型的钠交代型铀矿床。该矿与钠交代有着十分密切的关系,矿体几乎都在钠交代岩内。钠交代增大了花岗岩有效孔隙度,降低了抗压强度,成为同步构造活动的薄弱环节。钠交代形成的“海绵体”为铀的沉淀富集提供了极其有利的空间。钠交代促使原岩中铀的赋存状态发生改变,使铀发生活化转移。钠交代还为铀成矿提供了物质基础。

The No. 325 and No. 326 uranium deposits are typical soda metasomatic ones. Studies show that there exists close relationship between soda metasomatism and uranium mineralization: orebodies almost all occur within soda metasomatite bodies, and the distribution of soda. metasomatite bodies is consistent with that of orebodies. The soda metasomatite bodies are restricted to fracture structures, and lots of large soda metasomatite bodies lie at the intersection between two groups of fault structures. In addition, the development extent of soda metasomatite is governed by characteristics of rocks.Within the ore deposits the soda metasomatite shows the mineralogical character that the original minerals have mostly disappeared as a result of replacement and on their place is now red albite. The red albite can reach over 70% in content and even form pure albitite. Observation under microscope shows that albite exists mainly in two forms: one looks like chessboard and the other (formed rather later) is fine-grained. The soda metasomatite has been strongly crushed and its SiO_2 evidently increases whereas Na_2O and K_2O decrease as compared with the granite. Soda metasomatism led to the growth of effective porosity of granite and reduced its compressive strength. As a result, weak places favorable for structural activities occurred. Soda metasomatism changed the mode of occurrence of uranium and caused its mobilization and transference. During soda metasomatism many uranium-carriers s(?)oh as biotite amphibole were replaced by albite and this also accounts for the mobilization and transference of uranium. The sponge bodies formed as a result of soda metasomatism provided most favorable room for the precipitation of uranium, and soda metasomatism also supplied uranium mineralization with material basis.