Petrogenetic Constraints of Early Cenozoic Mafic Rocks in the Southwest Songliao Basin, NE China: Implications for the Genesis of Sandstone-Hosted Qianjiadian Uranium Deposits

Abstract

The tectonic inversion of the Songliao Basin during the Cenozoic may have played an important role in controlling the development of sandstone-type uranium deposits. The widely distributed mafic intrusions in the host sandstones of the Qianjiadian U ore deposits provided new insights to constrain the regional tectonic evolution and the genesis of the U mineralization. In this study, zircon U-Pb dating, whole-rock geochemistry, Sr-Nd-Pb isotope analysis, and mineral chemical compositions were presented for the mafic rocks from the Qianjiadian area. The mafic rocks display low SiO2 (44.91–52.05 wt.%), high TFe2O3 contents (9.97–16.46 wt.%), variable MgO (4.59–15.87 wt.%), and moderate K2O + Na2O (3.19–6.52 wt.%), and can be subdivided into AB group (including basanites and alkali olivine basaltic rocks) and TB group (mainly tholeiitic basaltic rocks). They are characterized by homogenous isotopic compositions (εNd (t) = 3.47–5.89 and 87Sr/86Sr = 0.7032–0.7042) and relatively high radiogenic 206Pb/204Pb (18.13–18.34) and Nb/U ratios (23.0–45.6), similar to the nearby Shuangliao basalts, suggesting a common asthenospheric origin enriched with slab-derived components prior to melting. Zircon U-Pb and previous Ar-Ar dating show that the AB group formed earlier (51–47 Ma) than the TB group (42–40 Ma). Compared to the TB group, the AB group has higher TiO2, Na2O, K2O, P2O5, Ce, and HREE contents and Ta/Yb and Sr/Yb ratios, which may have resulted from variable depth of partial melting in association with lithospheric thinning. Combined with previous research, the Songliao Basin experienced: (1) Eocene (~50–40 Ma) lithospheric thinning and crustal extension during which mafic rocks intruded into the host sandstones of the Qianjiadian deposit, (2) a tectonic inversion from extension to tectonic uplift attributed to the subduction of the Pacific Plate occurring at ~40 Ma, and (3) Oligo–Miocene (~40–10 Ma) tectonic uplift, which is temporally associated with U mineralization. Finally, the close spatial relation between mafic intrusions and the U mineralization, dike-related secondary reduction, and secondary oxidation of the mafic rocks in the Qianjiadian area suggest that Eocene mafic rocks and their alteration halo in the Songliao Basin may have played a role as a reducing barrier for the U mineralization.

Mineralogical and Geochemical Evidence for the Origin of the DL Uranium Deposit in the Songliao Basin, Northeast China

“…However, diabase dikes intruded in the southwestern Songliao Basin, and some orebodies of the Qianjiadian, Baixingtu, and DL deposits locally developed along the contact between diabase dikes and sandstones of the Yaojia Formation. The emplacement ages (53.0 ± 2.3 to 40 ± 1 Ma) [55,56] of the diabase dikes are similar to the U mineralization ages of these deposits (89-20 Ma) [13][14][15]44]. Therefore, it cannot be excluded that the minor sulfur of the pyrites might be derived from the diabase magma.…”

“…Additionally, some diabase dikes develop within these deposits which are green in color and ophitic in texture. Whether the diabase dikes were altered or not is rarely reported, but sandstones occurring around these dikes often have a green alteration which includes chlorite, epidote, and carbonate [13,16]. Many researchers have extensively investigated these deposits, but debate remains as to whether U mineralization is associated with BSR.…”

Genetic Mechanism of Tabular-Shaped Orebody of the Hailijin Sandstone-Type Uranium Deposit in the Songliao Basin: Constraints on the Clay Mineralogy of Ore-Bearing Sandstone

“…In recent years, a series of remarkable achievements regarding uranium exploration have occurred in the southwestern Songliao Basin, and a large number of large or supersized sandstone-type uranium deposits (such as Qianjiadian uranium deposit, Baolongshan uranium deposit, HLJ uranium deposit, and Dalin uranium deposit) have been newly discovered [1][2][3][4][5]. The uranium orebody is a multi-stratiform and tabular-shaped orebody [6][7][8],…”

Geochemical Characteristics, Palaeoenvironment and Provenance of Uranium-Bearing Sandstone in the Sifangtai Formation, Northern Songliao Basin, Northeast China

“…From east to west, these deposits form the southern region of the Songliao, Erlian, Ordos, and Yili Basins. These basins comprise the Yaojia, Saihan, Zhiluo, and Xishangyao uranium-bearing groups [6][7][8][9][10][11]. In recent years, two medium-sized deposits have been discovered in the southern region of the basin.…”