Abstract:Objectives:The Hongshanzi complex intrusives located in the northeastern part of the Guyuan—Hongshanzi uranium belt, which is composed of early Late Jurassic alkali feldspar granite,biotite granite and early Cretaceous early fine- grained biotite granite and granite porphyry. The composition of the rock is dominated by the alkali- feldspar granite and biotite granite in the early Jurassic. The early Late Jurassic biotite granites include medium—fine- grained biotite granites and porphyritic biotite granites, At present, uranium mineralization has been found in the inner and outer contact zone between the Early—Late Jurassic mid—fine- grained biotite granite and the Late Jurassic volcanic rock in the compound rock body, indicating that this zone is a favorable place for further uranium exploration. However, the geochemical characteristics of the Late Jurassic alkaline feldspar granite and biotite granite that make up the Hongshanzi complex rock mass have not been systematically studied, which restricts the in- depth study of uranium mineralization. Methods:Based on detailed observations of occurrence of Hongshanzi complex rock mass in the field, we have studied the petrology, geochemistry, Sr—Nd—Pb radio isotope and O isotope of these biotite granite to discuss nature of source region and tectonic setting, than, we have discussed the relationship between biotite granite and uranium mineralization. Results:All of biotite granite are characterized by high SiO 2 (75. 2%~76. 6% and 74. 6%~75. 3%, respectively), (K 2O+Na 2O) (8. 19%~8. 96% and 8. 78%~9. 10%, respectively), and K 2O/Na 2O (1. 19~1. 39 and 1. 29~1. 35, respectively), low Al 2O 3 (11. 5%~12. 3% and 12. 5%~12. 7%), CaO (0. 30%~1. 24% and 0. 76%~0. 83%, respectively). It does not contain standard mineral corundum, indicating that the magma source area is magmatic rock; FeOT is 1. 79%~2. 13% and 1. 80%~1. 91%, respectively, both greater than 1. 00%, with iron- rich characteristics of A- type granite; zircon saturation temperatures are 834~869℃ and 819~839℃, greater than 800℃, with the high- temperature characteristics of A- type granite. The contents of Al 2O 3 are 11. 5%~12. 3% and 12. 5%~12. 7%, respectively. A/CNK are 0. 90~0. 97 and 0. 93~0. 96, respectively. Enrichment of large ion lithophile elements Rb, Th, K, etc. and high field strength elements Zr, Hf, Nd, Ta, Y, etc. Loss of large ion lithophile elements Ba, Sr, etc. (Zr+Nb+Ce+Y) are 897×10 -6 ~1236×10 -6 and 513×10 -6 ~643×10 -6 , both of which are greater than 350×10 -6 , and the values of 10 4 *Ga/Al are 6. 28~6. 90 and 3. 28~3. 98, respectively, greater than 2. 6, with trace element characteristics of type A granite, which is the product of the intraplate tensile structure. Their lower n( 87 Sr)n( 86 Sr) i, higher εNd (t) , younger T DM2 , lower n( 206 Pb)n( 204 Pb) i, n( 207 Pb)n( 204 Pb)i, n( 208 Pb)n( 204 Pb) i and lower δ 18 O V-SMOW . Conclusions:The results indicates the magma originated from the partial melting of the young lower crust by type EMⅠ mantle- derived basic magma bottom infiltrating the lower crust, and experienced high- temperature hydrothermal alteration. The U content of medium—fine- grained biotite granite and porphyritic biotite granite is 7. 3×10 -6 ~22. 3×10 -6 (average 14. 6×10 -6 ) and 4. 53×10 -6 ~6. 90×10 -6 (average 6. 01×10 -6 ), especially the uranium mineralization has been found in the inner and outer contact zones of the former and the Late Jurassic volcanic rocks, which is a favorite part for deep exploration of uranium deposits.
