Exudative metallogeny of the Hadatu sandstone-type uranium deposit in the Erlian Basin, Inner Mongolia

This paper is the result of mineral exploration engineering.

Objective The Hadatu uranium deposit is a giant uranium deposit that occurs in the upper part of the early Cretaceous Saihan Formation in the Erlian Basin.Unlike traditional sandstone-type uranium deposits, the Hadatu uranium orebody exhibits stratiform and tabular shape, and the ore-controlling grey sandstone body is surrounded by red mottled oxidized sandstone.It is difficult to explain the genesis of the Hadatu uranium deposit with the traditional infiltration (phreatic and interlayer oxidization-reduction) metallogenic theory of sandstone-type uranium deposits.Therefore, identification of the ore genesis and ore-controlling factors of the Hadatu uranium deposit becomes very significant to the innovations of metallogenic theory for sandstone-type uranium deposits and to uranium prospecting in red mottled sandstone.

Methods Both fieldwork and lab analysis were conducted, and macro-and micro-observations were made.Adopted methods include field observations, regional geology, tectonics, sedimentology, petrology, mineralogy, geochemistry (i.e.element, organic and isotopic analysis), seismic interpretation and uranium metallogenic studies, etc.

Results The signatures of the orebody, ore-controlling grey sandstone body and the metallogenic characteristics of the Hadatu uranium deposit are clarified.It is evidenced that the upper part of the red mottled Saihan Formation, Erlian Formation and the Irdin Manha Formation are of the primary oxidization origin, whereas the ore-controlling grey sandstone body in the ore-bearing Saihan Formation is of epigenetic origin, resulted from secondary reduction through deep-seated reducing fluids that are mainly controlled by the fault structures and pertinent river channels or unconformities.Based on the analysis of the ore-forming uranium source, fluids deriving from the depth and their transportation and precipitation of the uranium, this paper demonstrates a new exudative uranium metallogeny.The authors propose that Hadatu sandstone-type uranium deposit occurs predominantly by exudative uranium metallogeny and correspondingly establishes the exudative uranium metallogenic model.

Conclusions  The exudative uranium metallogeny, as a new kind of uranium metallogeny in red mottled sandstone-type uranium deposits, has been established.The new methods to identify uranium mineralization in red mottled sandstone have been concluded, i.e. "combining the information of the upper red and lower black sedimentary formation, connecting pathways of the upper red formation with lower black one, finding grey sandstone body in red mottled formation and uranium in the grey sandstone body".The perspective of sandstone-type uranium deposits in red mottled sedimentary formation has been pointed out and new prospecting area from margins to the center of the basin and from near surface to deeper strata have been expanded.