Geology, geochemistry, and geochronology of the Cuihongshan Fe-polymetallic deposit, Heilongjiang Province, NE China

Abstract

The Cuihongshan deposit is a giant Fe-polymetallic skarn deposit located in the northern zone of the Lesser Xing an-Zhangguangcai Range (LXZR), NE China. It is predominantly hosted in skarn contact zones between marble and alkali-feldspar granites and monzogranites, with minor in fracture zones of granodiorites. Because of dense vegetation cover, complex intrusions, and contact relation between orebodies and rocks, the metallogenesis of the deposit is poorly understood. Here, we present detailed whole-rock geochemistry, zircon U-Pb geochronology of granitoids, and molybdenite Re-Os isotopic dating data. All of the granitoids in the Cuihongshan deposit area are silica and potassium rich, highly fractionated, showing affinities to high-fractionated I-type granites. However, compared with the other granitoids, the Late Triassic alkali-feldspar granites have higher differentiation index, stronger enrichment in F, W, Mo, Pb, Th, U, and volatiles with partial mineralization. The zircon U-Pb dating of the granodiorite, monzogranite, and alkali-feldspar granite yielded weighted average ages of 493 +/- 4, 194 +/- 1, and 204 +/- 1Ma, respectively. The Re-Os dating of molybdenites from the Cuibei and Cuizhong ore sections yielded isochron ages of 205 +/- 2 and 204 +/- 4Ma, respectively, which are consistent with the emplacement age of the alkali-feldspar granite. Combined with the lines of evidence from the contact relationship between the orebodies and alkali-feldspar granite, the disseminated mineralization and the enrichment in ore-forming elements and volatiles in the alkali-feldspar granite, these indicate that the Late Triassic alkali-feldspar granite rather than the monzogranite as previously reported, has a close genetic relationship with the Cuihongshan deposit. In addition, the alkali-feldspar granites occur as apophyses and dikes, but the Late Cambrian and Early Jurassic granitoids occur as batholiths. This indicates that, according to the theory that small intrusions form large deposits, a potential Late Triassic (similar to 204Ma) buried batholith might have provided abundant ore-forming materials. However, the top parts of the Late Cambrian and Early Jurassic granitoids have been denudated, which is unfavourable for significant deposit preservation and mineralization related to the 2 stages of granitoids. This study gives a significant suggestion that exposed, and blind apophyses and dikes should be further considered in the exploration and study of metal deposits in NE China. Three phases of mineralization occurred in the LXZR in the Triassic-Jurassic, namely, porphyry-skarn Cu-Mo polymetallic mineralization (similar to 250-240Ma), skarn Fe-Pb-Zn polymetallic mineralization (similar to 204-190Ma), and porphyry Mo polymetallic mineralization (similar to 180-160Ma). On the basis of regional data, the LXZR experienced subduction and collisional settings during similar to 260-185Ma and similar to 180-160Ma, respectively. Hence, the Early Triassic (similar to 250-240Ma) and Late Triassic-Early Jurassic (similar to 204-190Ma) mineralizations represented by the Baoshan and Cuihongshan deposits, respectively, are related to the early and late subduction of the oceanic plate between the Songliao and Jiamusi massifs beneath the Songliao Massif, respectively. This also indicates a potential mineralization in the LXZR in the Middle Triassic. However, the genesis of the late large-scale porphyry Mo polymetallic deposits (similar to 185-160Ma; e.g. \n \n, Daheishan, Luming, Huojihe, Xinghualong, Xingshan, and Wulugetushan deposits) is constrained by the collision of the Songliao and Jiamusi massifs.