Rong and 5 co-authors, reported in mid-2020 that REE geochemistry of sandstones and their carbonate cements from the Upper Cretaceous Yaojia Formation in the Qianjiadian uranium deposit, southern Songliao Basin are illustrated in order to reveal effects of basic intrusions on REE mobility of sandstones and their geological significance. Compared with the sandstones far away from the diabase dikes, the sandstones near the diabase dikes are obviously depleted in REEs. PLREE content, PHREE content and PREE content all increase with an increase of the distance away from the diabase dikes.
Carbonate cements in the sandstones comprise of dolomite, siderite, ankerite and calcite, which are successively formed from the early to late stage. In the sandstones near the diabase dikes, the dolomite and siderite are partly dissolved, and the ankerite is accumulated. ΣLREE content and ΣHREE content are both gradually decreasing in turn from the dolomite, to siderite, to ankerite, and to calcite. Dolomite content is positively correlated with PHREE content, siderite content is positively correlated with PLREE content or PHREE content, and ankerite content is inversely correlated with PLREE content. Dissolution of the dolomite and siderite and formation of the ankerite were attacked by intrusion of the diabase dikes, resulting in the sandstones near the diabase dikes being depleted in REEs.
The authors concluded that, in general, high-grade uranium mineralization may be attributed to the diabase dikes, REE depletion of the sandstones can be severe as a new prospecting indicator, and sandstones affected by igneous intrusions should be avoided during sampling for sandstone provenance by REEs. And specifically as follows:
1) Compared with the sandstones far away from the diabase dikes, the sandstones near the diabase dikes are obviously depleted in REEs. PLREE content, PHREE content and REE content are all positively correlated with distance away from the diabase dikes, and they all increase with an increase of the distance away from the diabase dikes.
2) Carbonate cements in the sandstones comprise of dolomite, siderite, ankerite and calcite, which are successively formed from the early to late stage. The dolomite and siderite tend to be partly dissolved in the sandstones near the diabase dikes, the ankerite is mainly accumulated in the sandstones near the diabase dikes, and the calcites are sporadically distributed in the sandstones. ΣLREE and ΣHREE contents are both gradually decreasing in turn from the dolomite, to siderite, to ankerite, and to calcite. The dolomite is characterized by depletion of LREEs and enrichment of HREEs, whereas the siderite, ankerite and calcite are all distinguished by enrichments of LREEs, and flat distribution of HREEs.
3) Dolomite content is rarely correlated with PLREE content, but is positively correlated with PHREE content. Siderite content is positively correlated with PLREE content or PHREE content. Ankerite content is inversely correlated with PLREE content and rarely correlated with PHREE content. Calcite content is inversely correlated with PLREE content or PHREE content. Median grain diameter, standard deviation of grains and content of clay minerals are all rarely correlated with PLREE content or PHREE content.
4) The dissolution of the dolomite and siderite occurred in the early stage of the diagenesis related to the intrusion of diabase dikes, and the ankerite was formed in the late stage of the diagenesis related to the intrusion of diabase dikes. Dissolution of the dolomite and siderite and formation of the ankerite were aroused by intrusion of the diabase dikes, resulting in the sandstones near the diabase dikes being depleted in REEs. High-grade uranium mineralization may be attributed to the diabase dikes, and REE depletion of the sandstones can be severe as a new prospecting indicator. Sandstones affected by igneous intrusions should be avoided during sampling for sandstone provenance by REEs.
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