Discovery of spodumene granite−pegmatite dike group in Northern Hongling area, northeastern margin of Qinghai−Xizang Plateau and its prospecting prospect

This paper is the result of geological survey engineering.

Objective The eastern part of Zongwulong tectonic belt is an important Indosinian Li−Be metallogenic belt newly discovered in recent years, and the existing prospecting discoveries and research are limited to the Chakabeishan area. In this study, 52 granite pegmatite dikes were found in Northern Hongling area, 30 km southeast of Li−Be deposit in Chakabeishan, among which 6 dikes have better ore-bearing property, and with lithology of beryl-bearing spodumene granite pegmatite and greisen albite spodumene pegmatite. The highest grade of Li₂O is 3.56%−3.71%, and the grade of BeO is 0.031%−0.048%, which indicate good metallogenic potential. However, the age, source area and origin of these pegmatite veins are still unclear, which further restricts the regional prospecting potential.

Methods The petrology, geochemistry and chronology of the newly discovered beryl−bearing spodumene granite pegmatite in the northern Hongling are systematically studied in this paper.

Results The pegmatite is characterized by high SiO₂(75.4%−84.2%), Al₂O₃(10.23%−16.15%), K₂O (0.32%−3.02%) and Na₂O (0.99%−3.45%),and is peraluminous rock; The total amount of rare earth elements in pegmatite is very low (∑REE=0.15×10⁻⁶−0.85×10⁻⁶), with slight enrichment of LREE (LREE/HREE=2.7−11.4, (La/Yb)_N=3.9−24.7), and δEu is mainly positive anomaly. Characterized by enrichment of Rb, Ta, P, Cs, Pb and loss of Ba, Th, La, Ce, Sr, Nd and Ti. The zircon U−Pb age of pegmatite and columbite−tantalite is (211.2±7)Ma and (223±1)Ma, which indicate the diagenetic and metallogenic age is 223−211Ma. The Hf isotope shows that the εHf(t) value is between −8.61 and −9.43, and the corresponding crustal model age (t_DM2) of Hf isotope is between 1.801 Ga and 1.843 Ga.

Conclusions The beryllite−bearing spodumene granitic pegmatite in the northern Hongling area belongs to LCT pegmatite, which suggest that may be formed by partial melting of metamorphic argillaceous rocks of palaeoproterozoic era based on the geochemical data. The Li−Be deposit was formed in the Indosinian period. The discovery of beryllite−bearing spodumene granite−pegmatite in the northern Hongling area further points out the direction of lithium beryllium ore prospecting in the eastern part of the Zongwulong structural belt, which has good metallogenic potential and is expected to provide a new lithium beryllium ore exploration base for the northeastern edge of the Qinghai−Xizang Plateau.