## 2 Geological and Petrographic Overview of Norite
### Origin and Formation of Norite  
The Bushveld Igneous Complex (BIC) is the largest layered igneous intrusion situated in the northern region of South Africa, containing the world's largest known reserves of Platinum Group Metals (PGMs) [10]. The BIC extends for approximately 350 km in an east-west direction, and it is situated in the north-eastern region of the Kaapvaal Craton in Southern Africa [11]. [PERSON] and [PERSON] [12] (2019) added that the BIC intrusion comprises three sill-like mafic to ultramafic lobes or structures, known as the eastern, northern, and western limbs (Figure 1). This review paper focusses on the norite rocks in the eastern region of the eastern limb. Norite is formed through magma intrusion into the earth's crust, crystallizing within layered mafic intrusions at 908 \({}^{\circ}\)C with 5.5-6.0 kbar pressure. The geological setting, temperature, and pressure during its formation play crucial roles in determining its mineral composition. These factors influence chemical reactions, mineral stability, and recrystallization processes, ultimately shaping the final mineral assemblage and rock type [13]. The formation of the BIC evolved through a combination of structural controls, multiple magma sources, and the emplacement of aphyric magmas and crystal-rich magma slurries, potentially originating from deep staging chambers [14]. Norite formation took place over 2.7 billion years ago (2.7 Ga), during a time of higher geothermal gradients. This involves the concurrent formation of Tonalite-T  
Figure 1: A geological map showing the three limbs of the Bushveld Igneous Complex. The boxed area represents the eastern limb [12]. intrusions occurring alongside granulite facies metamorphism and crustal contamination of mantle-derived magma [3]. In addition, [PERSON] [14] (2015) explained that norite is formed through the crystallization of a mafic magma rich in iron and magnesium, which undergoes differentiation over time. The first reference to igneous rocks and minerals in the area now known as the BIC was made by German explorer [PERSON] in the late 1860s when he first identified norite, chromite, and magnetite on a map of the region [15]. The mafic rocks of the BIC, including norite, were deposited in Southern Africa around 2.06 billion years ago and have remained largely unchanged due to isostatic effects on the thickness of the crust [16]. The geological origin of norite primarily includes plagioclase feldspar and pyroxene, which are found in the Lower Zone and Critical Zone of the eastern BIC [17]. Norite is found in various regions around the world, and its distribution is often associated with specific geological settings. Norite is a common rock that can form through normal igneous processes. However, the norite studied here exhibits a number of characteristics, such as its association with PGMs and the high crystallization of pyroxene and plagioclase, which form part of the complex's distinct layering [18]. These norites are found in the Critical Zone, where feldspathic orthopyroxenite is the dominant lithology, characterized by the presence of plagioclase and scattered Cr-spinel magmatism [12]. According to [PERSON] et al. [3] (2020), the hanging wall of UG2 and UG3 in the critical zone is primarily composed of norite, which changes to anorthosite in the Bastard Cyclic Unit (which resembles the Merensky Reef but lacks mineralization). The hanging wall of the UG2 and UG3 is made of norite, which has a thickness of roughly 50 m (Figure 2). Since the key review carried out by [PERSON] [20] in 1996, the understanding of the BIC has evolved from a system governed by basic igneous petrology principles to a state where virtually none of these principles have escaped serious re-evaluation [21]. Despite over a century of mining and research, the BIC in South Africa remains a focus of modernization and re-examination for the purpose of mining activities and safety measures.