Shapinggou Mo deposit, Jinzhai County, Lu'an, Anhui, Chinai

Regional Level Types
Shapinggou Mo deposit	Deposit
Jinzhai County	County
Lu'an	Prefecture-level City
Anhui	Province
China	Country

Shapinggou porphyry Mo deposit is the largest Climax-type Mo deposit in China and probably also in the world, with total proven Mo reserves of over 2.2 million tonnes at an average grade of 0.17%. It is located in the western Dabie Mountains, along the eastern extension of the East Qinling Mo mineralization belt. Similar to the majority of Mo deposits in the Qinling Mo belt, it is located north of the Triassic suture between the north and south China blocks. The orebody is mainly hosted in Cretaceous high-K granitic porphyry and explosive breccia, with potassic, silicification, and sericite-pyrite alterations. Fluorite is common in Shapinggou, indicating high-F content. The porphyry is closely associated with a large quartz syenite intrusion. Re–Os dating of molybdenite yielded an isochron age of 111.1 ± 1.2 Ma for the mineralization. Zircon U–Pb ages are 111.7 ± 0.8 Ma and 111.9 ± 0.6 Ma for the granitic porphyry and quartz syenite, respectively. Shapinggou is similar to the well-known Climax and Henderson Mo deposits in terms of geochemical characteristics and alterations, etc.

The Shapinggou deposit is located near the intersection of two faults (Shangcheng–Macheng and Xiaotian–Mozitan). It was discovered by the 313 Geologic Team from Anhui Province in 2009 after a lengthy exploration. The orebody is buried and is about 1000 m long, 800 m wide, and over 1000 m thick, with total proven reserves of more than 2.2 million tonnes of Mo metal at an average grade of 0.17 wt.% Mo at a cut-off grade of 0.03 wt.% Mo (1.6 million tonnes at a cut-off grade of 0.06%, some orebodies reaching 0.6%). It is mainly hosted in high-K granitic porphyry. The mineralized porphyry is closely associated with a quartz syenite intrusion, which is also mineralized locally.

Explosive breccias with both angular and round fragments of different sizes occur at shallow depths, hosted mainly in syenite, with potassic, silicification, and sericitepyrite alterations. The outcrop of the breccia is about 500 m2, with a mixture of different rock types, particularly granite, syenite, metavolcanic, and metasedimentary rocks. No outcrops of granite porphyry have been observed to date.

Alterations in the Shapinggou deposit are typical porphyry type, consisting of potassic, pyrite-sericite, silicification, and chloritization. Potassic alteration is widespread. Early potassic alteration is mainly inter-grain alteration within the porphyry. Later potassic alteration during the hydrothermal period is mainly fine veins together with quartz and sulphides. Two generations of silicification alteration are well developed by the granitic porphyry and country rocks. The later silicification event is closely associated with molybdenite mineralization. Pyrite-sericite alteration is mainly distributed in the outer contact zone, which is characterized by replacement of biotite and amphibole by chlorite. Pyrite-sericite veins cut across two phases of silicification and the relation to Mo mineralization is not clear. Fluorite is common in the Shapinggou deposit, including a small fluorite deposit.

There are three main styles of Mo mineralization: quartz-molybdenite veinlets in granitic porphyry, disseminated pyrite molybdenite veinlet stockwork in quartz syenite, and molybdenite in the matrix of the breccia. Molybdenite grains are 300–500 μm in size and occur with pyrite-sericite alteration in the granitic porphyry. In contrast, molybdenite grains in quartz syenite are smaller (100–300 μm) with low-grade mineralization in pyrite veins. Granite porphyry suffered potassic alterations, with some plagioclase crystals having been replaced by K-feldspar. Fine-grained K-feldspar and quartz veins are enriched in large molybdenite grains and other sulphides.