Hongshiquan Leucogranite Type Uranium Deposit Alteration Characteristics And Significance

Hongshiquan pegmatoidal leucogranites type uranium deposit is located in Shandan County, Gansu Province, which is China’s most typical leucogranites type uranium deposit. The main research work in this area was completed in the eighties of the last century and before, the research for alteration mineral closely related to the uranium mineralization is weak. Based on determining Hongshiquan pegmatoidal leucogranites type uranium deposit alteration minerals’ characteristic, we conduct systematic research, explore the formation of the environment, the source material and the relationship between alteration minerals and uranium mineralization.The study found that uranium in this area mainly exists in pegmatoidal leucogranites and in the alteration zone near the juncture of leucogranites and surrounding rock. Uranium mineralization can be categorized into two types, one is black chloritization biotite-rich chlorite blackening ore; the other is red and albitization, hematitization closely related reddening ore. Both superimposed generally present in the center of enriched uranium ore body with the most chloritization, the secondly hematitization, albitization, potash feldspathization, and the least sericitization developed.Compared to normal pegmatoidal leucogranites, in terms of major elements, the altered rocks’ Si, K component reduction, TFe, Mg, Mn, Ti components increase, and Fe valence change. In terms of trace elements, altered rocks’ U, Th, Pb, Mo, Li, Ti are significantly higher, particularly U, Mo increased serveral times; the mean of Th* is 5.84, increased significantly, while the mean of Sr* is 0.83, obvious lower; the whloe trace element spider diagrams is "W" distribution pattern, LILE Rb, Th, U, Pb relatively enrichment and high field strength elements Ti, P, Cr relatively loss is consistent with the normal rock. REE aspects, altered rocks’ ΣREE content(mean of 88.412) increased significantly, especially HREE, altered rocks’ REE distribution patterns tend to be more horizontal, weaker negative δEu(mean of 0.856) abnormal, δCe value is close to 1, showing a weak negative anomaly, which is consistent with the normal lithology. Terms of ore-forming elements, altered rocks’ U content increases significantly, Th change little.Studies show that the hydrothermal alteration zones formed in the low-medium temperature, low oxygen fugacity, low PH value and rich femic constituents environment. On the one hand, alteration can alter the physical properties of rocks, and create favorable conditions for uranium mineralization in space, on the other hand, it can contribute to the activation, transfer and precipitation of uranium. Alteration can be divided into three phases, the first is mainly chloritization-biotite placed in the pegmatoidal leucogranites late diagenesis, part of uraninite precipitate and distribute in alteration minerals edges or fissures, uranium preliminary enrichment; the second phase mainly alkaline metasomatism for specific performance, characterized by sodium feldspathization and potassium feldspathization, uranium further enrichment to depleted uranium ore; in the third stage, with strong acid metasomatism and chloritization alteration, moderate hematitizaton alteration, uranium enrichment to rich ore, which is the main mineralization of Hongshiquan uranium mineralization. The hydrothermal alteration of chloritization, sodium metasomatism and hematitization and so can be used as an important prospecting mark in this area.