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

In this contribution we discuss a series of porphyry and porphyry-skarn mineral systems, which constitute important metallogenic belts along major lithospheric breaks and/or collision zones that form the margins of the North China craton and the Yangtze craton. We describe a selection of porphyry and porphyry-skarn deposits in the Great Xing’an Range in northeast China, the Yanshan-Liaoning, Xilamulum belts along the northern margin of the North China craton, the Qinling orogen, and the Middle-Lower Yangtze River Valley along the bonudaries between the North China and the Yangtze cratons. The occurrence of platform carbonate successions may have played some role in the evolution of ore fluids that resulted in the formation of porphyry-skarn deposits. The porphyry deposits of eastern China, although sharing some common features with classic porphyry systems that are related to convergent margins, do exhibit unusual features, particularly in terms of ore fluid compositions, the common presence of fluorite, hydrothermal alteration assemblages, which tend to be less hydrous than the porphyry at convergent margins. On the other hand, the porphyry mineral systems of eastern China have some similarities with the Climax-type porphyry. A major tectonothermal event (Yanshanian), which took place in the Jurassic-Cretaceous, affected eastern China and most of the eastern margin of Asia. This Yanshanian event was responsible for the magmatism and associated mineral systems in the region. The granitoid intrusions and accompanying porphyry and porphyry-skarn deposits were developed along orogenic belts and major structural discontinuities mostly along the tectonic boundaries between the North China and Yangtze cratons and between the northern margin of the North China craton and the Mongolia-Siberia plate. The porphyry and porphyry-skarn deposits herein described include: Chalukou in the Great Xing’an Range orogen, Jiguanshan in the Xilamulun metallogenic belt, Xiaojiayingzi, Lanjiagou, Chehugou, Yuanbaoshan in the Yanshan-Liaoning belt, Nanninhu, Yuchiling, Jinduicheng, Lemeingou in the East Qinling orogen, Tongchakoou, Shaxi from the Middle-Lower-Yangtze River Valley. The role of mantle-lithosphere dynamics in eastern China, which led to the formation of these porphyry and porphyry-skarn mineral systems, is discussed and reviewed.

Intracontinental Porphyry and Porphyry-Skarn Mineral Systems in Eastern China: Scrutiny of a Special Case “Made-in-China”

Molybdenum exploration activity in China has accelerated tremendously during the past decade owing to the continuous, increasing demand for Earth resources. China possesses the largest Mo reserves in the world (exceeding 19.6 Mt). The major ore deposits are of porphyry, porphyry–skarn, skarn, vein, and sedimentary types. Porphyry molybdenum deposits contain 77.5% of the Chinese Mo reserves, with lesser amounts in porphyry–skarns (13%), skarns (5.1%), and veins (4.4%). Exploitation of sedimentary-type molybdenum deposits thus far has been uneconomical. The six Mo provinces are in the Northeast China, Yanliao, Qinling–Dabie, middle–lower Yangtze River Valley, South China, and Sanjiang areas. We recognize six ore-forming periods: (1) Precambrian (>541 Ma), (2) Palaeozoic (541–250 Ma), (3) Triassic (250–200 Ma), (4) Jurassic–Early Cretaceous (190–135 Ma), (5) Cretaceous (135–90 Ma), and (6) Cenozoic (55–12 Ma). The abundance of Mo ore deposits in China reflects the occurrence of multiple periods of tectonism,...

Types, characteristics, and time–space distribution of molybdenum deposits in China

Triassic mineralization with Cretaceous overprint in the Dahu Au–Mo deposit, Xiaoqinling gold province: Constraints from SHRIMP monazite U–Th–Pb geochronology

Numerous molybdenum (Mo) ore deposits have been discovered in the East Xingmeng orogenic belt (East Central Asian orogenic belt), over the past 10 years, and this region is becoming one of the world's most important Mo production areas. It contains 6.18 Mt of proven Mo metal reserves, which accounts for 30% of the total proven Chinese Mo reserves. The ore district includes 37 deposits and 15 occurrences, with three major Mo ore types, that is porphyries, skarns, and hydrothermal veins. The latter can be subdivided into quartz- and volcanic hydrothermal-vein types. With the exception of the Ordovician Duobaoshan porphyry Cu–Mo deposit (477 Ma), all the East Xingmeng Mo deposits formed during the Mesozoic. Re–Os dating of molybdenite has documented three episodes of Mo mineralization: Early Triassic (248–242 Ma), Jurassic (178–146 Ma), and Early Cretaceous (142–131 Ma). Early Triassic Mo deposits are distributed along the northern margin fault of the North China Craton (NCC) and include porphyry and quartz ...

Mesozoic molybdenum deposits in the East Xingmeng orogenic belt, northeast China: characteristics and tectonic setting

The Xilamulun molybdenum metallogenic belt, located in eastern Inner Mongolia, China, has great economic potential as a major producer of molybdenum. Four major types of Mo deposits have been recognized in the Xilamulun molybdenum metallogenic belt: porphyry, quartz vein, volcanic-hosted, and greisen. These Mesozoic Mo deposits are closely related to Si- and K-rich intrusives and are usually hosted by granite plutons or located at the endo- or exo-contact zones of the granite porphyry. SHRIMP zircon U–Pb dating gives the emplacement ages of the intrusions related to Mo mineralization as 245.1 ± 4.4, 152.4 ± 1.6, and 139.1 ± 2.3 Ma. Re–Os analysis of five molybdenite samples from the Chehugou porphyry Mo deposit yields an isochron age of 245 ± 5 Ma (2σ), indicating that the mineralization age of the porphyry Mo deposit is about 245 Ma. Re–Os analyses of six molybdenite samples from the Nianzigou quartz-vein-type Mo deposit yield an isochron age of 154.3 ± 3.6 Ma (2σ), constraining the mineralization age of the quartz-vein Mo deposit to 154 Ma. Our results suggest that the Mo mineralization in the Xilamulun belt formed during at least three stages, i.e., the Triassic, Late Jurassic, and Early Cretaceous, and is coeval with the granitic magmatism. The corresponding geodynamic background covers the syncollision between the North China and Siberian plates during the Early to Middle Triassic, a compression setting related to the subduction of the Paleo-Pacific plate during the Jurassic and lithospheric thinning during the Early Cretaceous in eastern China.

Geology and geochronology of the Xilamulun molybdenum metallogenic belt in eastern Inner Mongolia, China

Lanjiagou is a porphyry Mo deposit in terms of its alteration zonation and mineralization associated with granitic intrusions and predominance of quartz vein-hosted molybdenum mineralization. It is the largest Mo deposit in North China Craton (404,000 t). There is an intimate spatial/temporal association between all stages of mineralization and Early Jurassic granitic intrusions at Lanjiagou. Most of the molybdenum was emplaced during the principal hydrothermal (PH) stage (184.6 ± 1.3 – 185.6 ± 1.4 Ma), contemporaneously with intrusion of fine-grained porphyritic granite (188.9 ± 1.2 Ma) into a granite batholith (193 ± 3 Ma). The PH mineralization stage is mainly hosted by a quartz-dominated stockwork associated with phyllic alteration in the fine-grained porphyritic granite. This stage was followed by the late hydrothermal (LH) activity. Thick Mo-rich quartz veins were emplaced during the LH stage and cut the porphyry ore bodies. A ring breccia zone formed during the last hydrothermal stage and apparentl...

Mineralization, alteration, structure, and Re–Os age of the Lanjiagou porphyry Mo deposit, North China Craton

Geophysical and geological studies attempting to search and explore new mineralisation resources were carried out in the Longtoushan area, Inner Mongolia, northern China. The Longtoushan area is located within a large alteration zone, which is covered by a variety of altered lava, bioclast limestone and Quaternary sediments. In this case study, ground geophysical surveys played an important role in defining the mineralised structures beneath Quaternary sediment cover. The aim of this study was to investigate the subsurface mineralisation in the area using a combination of very low frequency electromagnetic (VLF-EM), Stratagem EH4 and controlled source audiofrequency magnetotelluric (CSAMT) measurements. These successful surveys in the area revealed that the VLF, Stratagem EH4 and CSAMT methods were effective in detecting the unseen mineralised system and results from the different methods confirmed each other. VLF measurements at 2875 stations along 35 lines identified the principal mineralised shear system as two sub-parallel linear conductive belts, tracing the principal mineralised system for a further 650 m of strike length beneath cover loess, in a NW–SE-trending direction. The subsequent Stratagem EH4 soundings along four parallel traverses perpendicular to the mineralised trend indicated that the principal mineralised shear structure, extending for more than 600 m in the dip direction, was almost vertically dipping above the 200 m level but changed to the SSW direction at a steep angle at depth. A CSAMT survey on two lines confirmed that the ore-bearing mineralised zone was a conductive belt and contained a low resistivity anomaly of less than 500 Ωm.

Integrated geophysical exploration for the Longtoushan Ag-Pb-Zn deposit in the southeast of the Da Xing'an Ling mountains, Inner Mongolia, northern China

Weijun Chen

Papers

Geology and geochronology of the Xilamulun molybdenum metallogenic belt in eastern Inner Mongolia, China

Mineralization, alteration, structure, and Re–Os age of the Lanjiagou porphyry Mo deposit, North China Craton

Integrated geophysical exploration for the Longtoushan Ag-Pb-Zn deposit in the southeast of the Da Xing'an Ling mountains, Inner Mongolia, northern China