The late Palaeozoic Yong’an–Meizhou depression belt is an important iron (Fe) and polymetallic metallogenic belt in southern China. It has undergone a transformation from Tethys to the circum-Pacific tectonic domain. The Luoyang deposit is one of the typical Fe skarn deposits in the Yong’an–Meizhou depression belt of eastern China. Garnet is a characteristic mineral in the deposit. Two generations of garnets are detected in the deposit based on their textural characteristics and trace-element contents, and are represented by Fe-enriched andradite. The first generation of garnets (Grt1) have two types of garnets (Grt1-A and Grt1-B). Type A garnets of the first generation (Grt1-A) (Adr80-88) replaced by massive diopside-magnetite assemblage exhibit distinct oscillatory zonings and display patterns of enriched light rare earth elements (LREE) to weak heavy rare earth elements (HREE), with weak negative to positive Eu anomalies, and highest U, ΣREE and Sn contents. Type B garnets of the first generation (Grt1-B) are irregular zones (Adr94-96) coexisting with magnetite, in which Grt1-A is generally dissolved, and have obviously LREE-enriched and HREE-depleted patterns, with weak negative to positive Eu anomalies, and moderate U, ΣREE and Zn contents. Garnets of the second generation (Grt2) (Adr96-99) that replaced massive magnetite together with sphalerite show unzoned patterns, with a flat REE pattern and pronounced negative Eu anomalies as well as contents of lowest U and ΣREE, and highest W. The substitution of REEs in garnets occurs as [X2+]VIII –1[REE3+]VIII +1[Si4+]IV –1[Z3+]IV +1in an Al-enriched environment. Luoyang hydrothermal fluids shifted from reducing conditions with relatively high-U and -ΣREE characteristics to oxidizing conditions with relatively low-U and -ΣREE characteristics. The reduced siderophile elements and increased fO2 in fluid during Grt1-B formation caused magnetite mineralization and reduced Zn contents during Grt2 formation, causing the deposition of sphalerite. All garnets formed from magmatic fluid and were controlled by infiltrative metasomatism in an opened system.

The Baimashan granitic complex in central Hunan is a giant multiphase complex pluton within the South China Plate, which contains three phases (the Shuiche, Longtan-Xiaoshajiang, and Longcangwan superunits). It is located in the Jiangnan Orogenic Belt and is of great significance for the study of the regional tectonic magmatic evolution. Herein, we utilized zircon U-Pb dating, major and trace element geochemistry, and zircon Hf isotope geochemistry for three of the Baimashan granitic complexes; data for the Longcangwan superunit were obtained from previous studies. The new zircon U-Pb ages of 418 ± 3.2 Ma and 223 ± 2.6 Ma for the Shuiche and Longtan-Xiaoshajiang superunits, respectively, suggest the existence of Late Silurian and Late Triassic magmatism. Both superunits exhibited weak peraluminosity and high-K calc-alkaline and weak negative Eu anomalies, which are similar to those of I-type granites. The Longcangwan superunit showed strong peraluminosity and high-K calcalkaline and stronger negative Eu anomalies; Hf isotope and mineralogical evidence suggest that it is a fractionated I-type granite. The zircon Hf(t) values and two-stage depleted mantle Hf model ages revealed that the magma of the Baimashan granitic complex originates from the partial melting of metamorphic igneous rocks; the crustmantle differentiation age in the source area was 1.5-1.7 Ga for Longtan-Xiaoshajiang and Longcangwan and 1.7-1.9 Ga for Shuiche. The superunits formed in a post-collisional extensional tectonic setting. In the case of the Shuiche supersuit this is related to the remote effect of the interaction of the South China Plate with the Australian-Indian margin of Eastern Gondwana. The formation of the Longtan-Xiaoshajiang and Longcangwan superunits is linked to the remote effect of the Indosinian and South China Plate collision and the superimposition of the subduction of the Palaeo-Pacific Plate. The weakly fractionated I-type granite that formed during the Caledonian in South China is closely related to scheelite mineralisation.