Most of the diamond deposits in China are in the North China Craton. In addition to gem diamonds in kimberlite, a large number of microdiamonds have also been discovered in alkaline dolerites. These microdiamonds show very different characteristics from those recovered in kimberlite. Here, we report the morphology, colour, nitrogen contents, and carbon isotopic compositions of the diamonds recovered from the alkalic dolerites in eastern China. The microdiamonds are mainly cube and rhombic dodecahedron with diameters of 0.2 to 0.6 mm. Infrared spectrum analysis shows that these microdiamonds are mostly type Ib with a small amount of type Ia. The Y centre is obvious in type Ib diamond. Modelling mantle residence times for the IaAB diamonds is about 550 Ma. Nitrogen contents of the diamonds range from 4.5–503 ppm, with a median value of 173 ppm. The total δ¹³C range of the microdiamonds varies between −18.6 and −21.1‰ and are similar to those of ophiolite diamond.

The Shiquanhe–Laguoco–Yongzhu–Jiali ophiolite mélange belt in Tibet includes the Laguoco Tso ophiolite as part of its western segment. Researchers studying the evolution of the Tibetan Plateau and the Tethys have taken a keen interest in the debated relationship between this ophiolite belt and the Bangong–Nujiang ophiolite belt. However, there is little research in this field. This study reports the rock geochemistry, SIMS (the secondary ion mass spectrometry) zircon U-Pb ages, and O isotope compositions of gabbro from the Laguoco ophiolite. Gabbro has substantial depletion in HFSEs (the high field strength elements) such as Th, Nb, Zr, and Hf, as well as exhibits comparatively high Mg^# (80.6 on average), and low K, N, P, and Ti contents. Therefore, it was possibly formed in an intra oceanic subduction island arc environment originating from ~30% partial melting of the depleted spinel lherzolite. The SIMS zircon U-Pb ages of the gabbro samples are 187 ± 1.2 Ma and 189 ± 2.1 Ma, and the weighted averages of δ¹⁸O are 5.24‰ ± 0.12‰ and 5.34‰ ± 0.13‰, which are close to mantle-derived zircon δ¹⁸O (5.3‰ ± 0.3‰). These results suggest that during the Early Jurassic, the Laguoco ophiolite recorded the intra oceanic subduction of the northern branch of the Neo-Tethys.

Striking differences in potentiality of diamond mineralization are shown in the three kimberlite belts of Changmazhuang, Xiyu and Poli in Mengyin, Shandong Province. Previous studies of diamonds have focused on the Changmazhuang belt; however, genesis of diamonds from the other two belts, as well as comparative studies on diamonds from the three belts, are relatively scarce. In this paper, the morphological and spectral features of 44 diamonds ranging from 0.03 mg to 16.46 mg in weight from the three belts are investigated systematically by microscopic observation, Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. The results show that the formation temperature is 1118–1251 °C for Changmazhuang diamonds, 1091–1167 °C for Xiyu diamonds, and 1132–1172 °C for Poli diamonds. Diamonds in the three belts exhibit uniform pre–kimberlite surface features of multiple serrate, triangular laminae and small trigons, suggesting a similar condition of diamond destructive metasomatism caused by carbonatitic and silicate-carbonatitic melts. However, Poli diamonds probably suffered from a silicate component-enriched carbonatitic melt in the deep mantle. Nitrogen contents (0–539 ppm) of diamonds from the three belts have a slight impact on their morphological features.

The Penglai sapphires are mainly hosted in alkaline basalts and derived in alluvial sediments. Previous studies have investigated the formation of the Penglai sapphires; however, the genesis of color zoning remains ambiguous. In this paper, we report spectral and chemical composition data of sapphires using ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), and laser-ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS). The results show that the Penglai sapphire has a magmatic origin, mostly showing various shapes of incomplete girdles, barrels, and flakes. The content of Ti in rims is higher than in cores of color-banded sapphire, which results from ubiquitous Ti-bearing inclusions within grown bands. The main chromophore of the deep-blue core is Fe²⁺-Ti⁴⁺, which pairs with Fe³⁺-Fe³⁺, Cr^3+, and V³⁺ in the core, likely producing purple-hued blue in an oxidizing environment. The yellowish-brown rim is due to Fe³⁺ and Cr³⁺ in a reduced environment. Compared with the basaltic sapphires worldwide, the Fe content is moderately higher than those of most Asian sapphires but obviously lower than those of Changle sapphires in Shandong, China, and overlaps with those of African sapphires.

The Yarlung Zangbo suture zone (YZSZ) separates Indian plate and its northern passive margin units to the south from Eurasian plate and its active continental margin units of Xigaze forearc basin and Gangdese batholith to the north (Xu et al., 2015; Yang et al., 2015). The western YZSZ in southern Tibet is divided by the Zhongba terrane into the northern belt (NB) and southern belt (SB). Ophiolites in the NB are dismembered as ophiolitic mélanges. Peridotite, cumulated gabbro, ocean plate stratigraphy (OPS) of seamount remnants and pelagic‐hemipelagic sequence as blocks in serpentinite matrix are mainly observed, from west to east, in Dajiweng, Baer, Kazhan, Cuobuzha, Zhalai, Gongzhu. Ophiolites in the SB are absent ophiolitic units of sheeted dikes and MORB‐like pillow lavas, occur as much larger peridotite massifs (i.e., Dongbo, 400 km²; Purang, 650 km²; Xiugugabu, 700 km²; Dangqiong, 300 km²) which are intruded by mafic dike swarms and overlain by volcanic sedimentary OPS (Liu et al., 2018). We propose that the SB mafic–ultramafic rocks and volcanic sedimentary OPS represent fragments of an early Cretaceous continental margin ophiolite whose magmatic evolution was influenced by 140–137 Ma plume magmatism (Liu et al., 2015; Zheng et al., 2019). Relics of Late Paleocene to very Early Eocene deep‐marine basin were developed in Saga and Gyirong (Ding, 2003; Li et al., 2018). In contract, the NB ophiolitic mélanges report a travel log of an oceanic plate ranging from Middle Triassic to Early Cretaceous.

A total of 48 natural alluvial diamonds from the Yangtze Craton, China, also called Hunan diamonds, were studied using morphology and IR spectroscopy. These diamond samples, collected downstream of the Yuan River, Hunan Province, with unknown host-rock source(s), were observed by scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FTIR). Most Hunan diamonds are monocrystal forms of octahedra, tetrahexahedra (THH) and dodecahedra; octahedral–rhom-dodecahedral transitional behaviors and irregular forms are also visible. Trigons and tetragons, terraces and shield-shaped laminae are surface features that frequently indicate dissolution and reabsorption; green and brown spots, network patterns, and other mechanical abrasion marks are typical evidence of long-time deposition and transportation of Hunan diamonds. The main types of Hunan diamonds are type IaAB and type Ⅱa. Diamond samples have a wide range of total nitrogen content (N_tot) from 196–1094 ppm. Two populations are distinguished by two-peak distribution models of N_A (A-center concentrations) and %B (proportion of aggregated nitrogen). Hunan diamonds are low in structure hydrogen (0.03–4.67 cm⁻¹, mostly below 1 cm⁻¹) and platelets (0.23–17 cm⁻¹, mostly below 2 cm⁻¹). Moreover, there is a significant positive correlation between the hydrogen correlation peak and N_tot, which is similar to Argyle diamonds. The temperature conditions of the diamond formation have been estimated at 1075–1180 °C, mainly conforming to the kimberlite diamond range. Besides, some samples with slightly higher temperatures are close to the ultramafic-related Juina diamonds. Therefore, the FTIR characteristics analysis and comparison indicate the multiple sources of Hunan diamonds.