The Mo deposits of Northeast China: A powerful indicator of tectonic settings and associated evolutionary trends

Abstract

Northeast (NE) China lies in the eastern sector of the Central Asian Orogenic Belt (CAOB) that connects with the Circum-Pacific Orogenic Belt in the east, and accommodates multistage magmatism, crustal growth and mineralization. In this region 69 Mo-only or Mo-dominated and 9 Cu-Mo deposits have been discovered, including 65 deposits ranking medium-size (>10Kt Mo metal) or larger in tonnage and containing a total resource of 10.5Mt Mo metal. Six giant and seventeen large deposits have total reserves of 6.7 and 3.1Mt Mo, respectively. These deposits occur in the areas surrounding the Songliao Basin, including the northern margin of the North China Craton, the Great Hingan Range and the Ji-Hei Fold Belt, and have been formed during Paleozoic and Mesozoic tectono-magmatic events. All the Mo-only or Mo-dominated deposits were formed in the Mesozoic, postdating the closure of the Paleo-Asia Ocean, and in a series of pulses around 250–200Ma, 200–160Ma, 160–130 and <130Ma (130–100Ma), suggesting that the Paleozoic crust, compared with the Mesozoic crust, was less sialic and unfavorable for Mo mineralization. This is supported by the variation of Re contents in molybdenites from the deposits, i.e., increasing with the Cu/Mo ratios and the ore-forming ages. Mineralization was generally associated with granitic rocks mainly of crust-sourced and high-K calc-alkaline to shoshonite series. The majority of the deposits are porphyry (including breccia pipes) type, followed by the skarn and quartz vein types. The porphyry Mo deposits can be further subdivided into three subtypes, i.e., collision- or Dabie-, rift- or Climax-, and subduction- or Endako-types. The Mo deposits aged 250–200-Ma and 200–160-Ma belong to the collision-type and have been formed in syn- to post-collisional tectonic setting. The 160–130-Ma Mo mineralization mainly occurs in the Great Hingan Range and northern margin of the North China Craton, and includes Endako- and Climax-types of porphyry Mo systems, which resulted from southward subduction of the Mongol-Okhotsk oceanic plate. The 130–100-Ma deposits belong to the Endako-type and are only located in the eastern Ji-Hei Fold Belt, which must be related to the westward subduction of the Paleo-Pacific oceanic plate. Therefore, as shown by the porphyry Mo deposits in NE China, these mineral systems are a powerful indicator of tectonic settings and associated evolutionary trends.