## 2 Geological Setting  
The chromite-bearing ophiolite belt in Tibet is mainly located in the Yarlung Zangbo deep fault [8; 30; 31]. The Lhasa block is located in Yarlung Zangbo ophiolite belt in the eastern part of the Tethys-Himalayan tectonic belt and is regionally controlled by the Indus-Yarlung Zangbo suture zone, bordered by the Gangdese-Nyaingentanglha tectonic belt to the north and the Himalayan tectonic belt to the south [32; 33] (Figure 1a,b). Due to the superimposition of the Himalayan orogen and a series of fault structures, the ophiolites have been modified by late tectonic activity, and the massits on both sides of the north-south axis are limited by faults [30; 34]. The massits form a south-dipping wall-shaped complex, with the northern part composed of Paleogene-Neogene conglomerate and the new Cenozoic Gangdese granite, and the southern part composed of late Triassic metamorphic slate, sandstone, and phyllite (Figure 1c) [34; 35].  
The Lhasa massits extend nearly east-west and have a planar shape that is an inverted \"S\" shape [36; 37]. The chromitite orebodies are grouped into three clusters, designated from west to east, the Lubbusa, Xiangkashan, and Kangjinla districts [1; 6; 38]. The ophiolitic section forms a tectonic slab, made up primarily of mantle peridotites with minor crustal cumulates and mafic dikes. The mantle rocks constitute \(\sim\)93% of the exposure section and include harkapurgite and less dunite. Both the drill core and surface samples indicate that the periodtites consist chiefly of harkapurgite. Most of the harkapurgites, both in the outcrop and drill core, are fresh, dark green, and massive. The rocks mostly have coarse-grained, granular textures and consist chiefly of olivine (68-85 modal%) and orthopyroxene (14-30%) with minor clinopyroxene, magnesiochromite, and magnetite [1]. The cumulate rocks consist of wehrlite, Iberzolite, pyroxenite, and gabbro [1; 34; 35; 39].  
Figure 1: **(a)** The study area is located in China’s geographical location; (b) tectonics in the study area, adapted from Ref. [40]; (c) a geological map of the study area is shown on the right, which was derived from an initial geological map at 1:50,000. The geological map is not shown strictly in accordance with the criteria, but in other bright and easily distinguishable colors to more clearly show the spatial distribution and boundaries of litho-units. The extent defined by corner points (1) 29\({}^{\circ}\)14\({}^{\prime}\)40\({}^{\prime\prime}\) N, 92\({}^{\circ}\)10\({}^{\prime}\)35\({}^{\prime\prime}\) E; (2) 29\({}^{\circ}\)12\({}^{\prime}\)24\({}^{\prime\prime}\) N, 92\({}^{\circ}\)931\({}^{\prime\prime}\) E; (3) 29\({}^{\circ}\)11\({}^{\prime}\)47\({}^{\prime\prime}\) N, 92\({}^{\circ}\)19\({}^{\prime}\)41\({}^{\prime\prime}\) E; (4) 29\({}^{\circ}\)92\({}^{\prime\prime}\) N, 92\({}^{\circ}\)18\({}^{\prime}\)47\({}^{\prime\prime}\) E.  
Chromic deposits are mainly hosted in mantle peridotite and appear in groups and belts, which is typical of alpine-type chromitite deposits [6]. Most of the orebodies lie near the top of the mantle section [41]. The structure of chromite ore includes blocky, beauty, banded, and impregnated shapes (Figure 2). The main characteristic of the ore is that it is rich in Cr\({}_{2}\)O\({}_{3}\) and associated with platinum group elements, mainly osmium and ruthenium, which can be comprehensively utilized [2]. Mantle peridotite is an exclusive rock for podiform chromite deposits, and chromite is closely associated with the mantle peridotite belt, so the chromium needed for chromite may mainly come from mantle peridotite itself [4; 38; 42]. Furthermore, previous studies have shown that the chromium content in the mantle and in chondrite meteorites is much higher than that in the crust, and ultra-high-pressure minerals from the deep mantle, such as diamonds, have been found in the Luobusa chromite deposits, providing important information on the deep-seated genesis of chromite [1; 5; 6; 35; 43; 44; 45].