Age and petrogeochemistry of ore-forming granites, and the metallogenic prospects of U-Nb-Ta-REE in the southern section of the Daxing'anling Mountains for skarn-type iron-tin deposits

Objective The southern segment of the Daxing'anling Range constitutes a significant tin-polymetallic metallogenic belt in northern China. Representative deposits include the Huanggang and Mogutu skarn-type Fe-Sn systems, which exhibit direct spatio-temporal and genetic relationships with highly fractionated alkali-feldspar granites or syenogranites. Further investigation is warranted regarding petrogeochemical characteristics of these granites and their implications for mineral exploration.

Methods This study explores the characteristics of the ore−forming granites and their implications for ore prospecting through zircon U−Pb dating, whole−rock major, trace and rare earth element testing, and mineralogical studies.

Results The weighted average U−Pb ages obtained from zircon dating are 131.8±2.0 Ma(MSWD=1.3) and 137.1±1.3 Ma(MSWD=0.8), indicating that the emplacement of alkali feldspar granite in the Huanggang and Damogotu deposits occurred during the Early Cretaceous. The main elements of the whole rock show that the granite has the characteristics of high silicon (73.97%~79.05%), high alkali (7.83%~8.88%), low calcium, iron, magnesium, titanium and phosphorus, and is a metaluminous to weak peraluminous (A/CNK=0.93~1.09) highly differentiated granite. The trace and rare earth elements in the whole rock show that the granite is characterized by high Rb, Th and Pb, and low Ba, Sr, P and Ti. The rare earth element distribution map is relatively flat (La_N/Yb_N=0.96~12.04), with strong negative Eu anomaly (Eu/Eu^*=0.01~0.03) and weak negative Ce to positive Ce anomaly transition feature (Ce/Ce^*=0.96~1.56), and the trace element distribution map has weak tetrad effect (TE_1,3=0.99~1.14). In the ore−forming granites, elements such as Th, U, Nb, Ta and Yb are enriched with the increase of the degree of differentiation.

Conclusions The metallogenic granites of the Huanggang and Mogutu skarn−type Fe−Sn deposits in the Southern Section of the Daxing'anling Mountains are Early Cretaceous high−silica highly fractionated granites, whose formation process has a significant enrichment effect on ore−forming elements such as U, Sn, Nb and REE. Combined with the research progress of regional geology, geophysical exploration, geochemical exploration and remote sensing, this study of chronology, mineralogy and geochemistry shows that the areas with Late Yanshanian differentiated granites in the Southern Section of the Daxing'anling Mountains not only have metallogenic potential for Sn−Pb−Zn−Ag polymetals, but also have prospecting potential for U−Nb−Ta−REE.