Fj. Nie, RARE-EARTH ELEMENT GEOCHEMISTRY OF THE MOLYBDENUM-BEARING GRANITOIDS IN THE JINDUICHENG-HUANGLONGPU DISTRICT, SHAANXI PROVINCE, NORTHWEST CHINA, Mineralium Deposita, 29(6), 1994, pp. 488-498
Located in the Luonan county, Shaanxi Province, northwest China, Jindu
icheng, Shijiawan and Huanglongpu molybdenum deposits constitute the m
ost important molybdenum mineralized district in China. Among these th
ree deposits, the Jinduicheng and Shijiawan molybdenum deposits are co
nnected spatially and genetically with granitoid porphyry (124 +/- 6 M
a, K-Ar biotite), and consist of disseminated-veinlet ores. Geochemica
l studies of rare earth elements (REE) furnish further evidence for un
derstanding the rock- and ore-forming processes of these two porphyry
molybdenum deposits and their related granitoid rocks. The REE distrib
ution in molybdenum ore, granitoids and their Middle Proterozoic meta-
volcanic wall rocks is discussed. The similarities between the REE sig
natures of the Shijiawan molybdenum-bearing monzogranite porphyry and
the neighbouring Laoneushan monzogranite (130 +/- 5 Ma, K-Ar biotite)
show that they were produced at the same evolutional stage of granitoi
d magma derived mainly from crustal anatexis. The Shijiawan biotite mo
nzogranite porphyry may be an apophysis of the Laoneushan granitoid ba
tholith. Compared to the Shijiawan monzogranite porphyry, the Jinduich
eng molybdenum-bearing granite porphyry is characterized by a high con
tent of HREE, and depletion in LREE. The unique REE patterns indicates
that the molybdenum-bearing granite porphyry was formed by thermograv
itation diffusion of a granitoid magma. The slight depletion of REE ab
undance in the altered granitoid porphyry and meta-volcanic wall rocks
shows that leaching of REE occurred during breakdown of the primary m
ineral assemblage, and crystallization of secondary minerals. The high
REE content of molybdenum ore represented re-deposition of the mobili
zed molybdenum and REE.